Method 625.1 – Base/Neutrals and Acids by 

GC/MS

December 2014
U.S. Environmental Protection Agency

Office of Water

Office of Science and Technology

Engineering and Analysis Division (4303T)

1200 Pennsylvania Avenue, NW

Washington, DC 20460

EPA-821-R-14-015

Method 625.1 i December 2014
METHOD 625.1 – BASE/NEUTRALS AND ACIDS BY GC/MS

1. Scope and Application

1.1 This method is for determination of semivolatile organic pollutants in industrial discharges and 

other environmental samples by gas chromatography combined with mass spectrometry (GC/MS), 

as provided under 40 CFR 136.1. This revision is based on a previous protocol (Reference 1), on 

the basic revision promulgated October 26, 1984 (49 FR 43234), and on an interlaboratory method 

validation study (Reference 2). Although this method was validated through an interlaboratory 

study conducted more than 29 years ago, the fundamental chemistry principles used in this method 

remain sound and continue to apply. 

1.2 The analytes that may be qualitatively and quantitatively determined using this method and their 

CAS Registry numbers are listed in Tables 1 and 2. The method may be extended to determine the 

analytes listed in Table 3; however, extraction or gas chromatography of some of these analytes 

may make quantitative determination difficult. For examples, benzidine is subject to oxidative 

losses during solvent concentration. Under the alkaline conditions of the extraction, alpha-BHC, 

gamma-BHC, endosulfan I and II, and endrin are subject to decomposition. Hexachlorocyclopentadiene is subject to thermal decomposition in the inlet of the gas chromatograph, chemical 

reaction in acetone solution, and photochemical decomposition. N-nitrosodiphenylamine and other 

nitrosoamines may decompose in the gas chromatographic inlet. EPA has provided other methods 

(e.g., Method 607 – Nitrosamines) for determination of some of these analytes.

1.3 The large number of analytes in Tables 1 - 3 of this method makes testing difficult if all analytes are 

determined simultaneously. Therefore, it is necessary to determine and perform quality control 

(QC) tests for the “analytes of interest” only. Analytes of interest are those required to be 

determined by a regulatory/control authority or in a permit, or by a client. If a list of analytes is not 

specified, the analytes in Tables 1 and 2 must be determined, at a minimum, and QC testing must be 

performed for these analytes. The analytes in Tables 1 and 2, and some of the analytes in Table 3 

have been identified as Toxic Pollutants (40 CFR 401.15), expanded to a list of Priority Pollutants 

(40 CFR 423, Appendix A). 

1.4 In this revision to Method 625, the pesticides and polychlorinated biphenyls (PCBs) have been 

moved from Table 1 to Table 3 (Additional Analytes) to distinguish these analytes from the 

analytes required in quality control tests (Tables 1 and 2). QC acceptance criteria for pesticides and 

PCBs have been retained in Table 6 and may continue to be applied if desired, or if requested or 

required by a regulatory/control authority or in a permit. Method 608 should be used for 

determination of pesticides and PCBs. Method 1668C may be useful for determination of PCBs as 

individual chlorinated biphenyl congeners, and Method 1699B may be useful for determination of 

pesticides. At the time of writing of this revision, Methods 1668C and 1699B had not been 

approved for use at 40 CFR part 136. The screening procedure for 2,3,7,8-tetrachlorodibenzo-pdioxin (2,3,7,8-TCDD) contained in the version of Method 625 promulgated October 26, 1984 (49 

FR 43234) has been replaced with procedures for selected ion monitoring (SIM), and 2,3,7,8-

TCDD may be determined using the SIM procedures. However, EPA Method 613 or 1613B should 

be used for analyte-specific determination of 2,3,7,8-TCDD because of the focus of these methods 

on this compound. Methods 613 and 1613B are approved for use at 40 CFR part 136. 

1.5 Method detection limits (MDLs; Reference 3) for the analytes in Tables 1, 2, and 3 are listed in 

those tables. These MDLs were determined in reagent water (Reference 4). Advances in analytical 

technology, particularly the use of capillary (open-tubular) columns, allowed laboratories to 

routinely achieve MDLs for the analytes in this method that are 2 - 10 times lower than those in the 

Method 625.1 1 December 2014
version promulgated in 1984 (40 FR 43234). The MDL for an analyte in a specific wastewater may 

differ from those listed, depending upon the nature of interferences in the sample matrix.

1.5.1 EPA has promulgated this method at 40 CFR Part 136 for use in wastewater compliance 

monitoring under the National Pollutant Discharge Elimination System (NPDES). The data 

reporting practices described in Section 15.2 are focused on such monitoring needs and 

may not be relevant to other uses of the method. 

1.5.2 This method includes “reporting limits” based on EPA’s “minimum level” (ML) concept 

(see the glossary in Section 22). Tables 1, 2, and 3 contain MDL values and ML values for 

many of the analytes. The MDL for an analyte in a specific wastewater may differ from 

those listed in Tables 1, 2, and 3, depending upon the nature of interferences in the sample 

matrix.

1.6 This method is performance-based. It may be modified to improve performance (e.g., to overcome 

interferences or improve the accuracy of results) provided all performance requirements are met.

1.6.1 Examples of allowed method modifications are described at 40 CFR 136.6. Other 

examples of allowed modifications specific to this method are described in Section 8.1.2. 

1.6.2 Any modification beyond those expressly permitted at 40 CFR 136.6 or in Section 8.1.2 of 

this method shall be considered a major modification subject to application and approval of 

an alternate test procedure under 40 CFR 136.4 and 136.5. 

1.6.3 For regulatory compliance, any modification must be demonstrated to produce results 

equivalent or superior to results produced by this method when applied to relevant 

wastewaters (Section 8.3).

1.7 This method is restricted to use by or under the supervision of analysts experienced in the use of a 

gas chromatograph/mass spectrometer and in the interpretation of mass spectra. Each laboratory 

that uses this method must demonstrate the ability to generate acceptable results using the 

procedure in Section 8.2. 

1.8 Terms and units of measure used in this method are given in the glossary at the end of the method. 

2. Summary of Method

2.1 A measured volume of sample, sufficient to meet an MDL or reporting limit, is serially extracted 

with methylene chloride at pH 11 - 13 and again at a pH less than 2 using a separatory funnel or 

continuous liquid/liquid extractor. 

2.2 The extract is concentrated to a volume necessary to meet the required compliance or detection 

limit, and analyzed by GC/MS. Qualitative identification of an analyte in the extract is performed 

using the retention time and the relative abundance of two or more characteristic masses (m/z’s). 

Quantitative analysis is performed using the internal standard technique with a single characteristic 

m/z. 

Method 625.1 2 December 2014
3. Contamination and Interferences

3.1 Solvents, reagents, glassware, and other sample processing labware may yield artifacts, elevated 

baselines, or matrix interferences causing misinterpretation of chromatograms and mass spectra. 

All materials used in the analysis must be demonstrated to be free from contamination and 

interferences by analyzing blanks initially and with each extraction batch (samples started through 

the extraction process in a given 12-hour period, to a maximum of 20 samples - see Glossary for 

detailed definition), as described in Section 8.5. Specific selection of reagents and purification of 

solvents by distillation in all-glass systems may be required. Where possible, labware is cleaned by 

extraction or solvent rinse, or baking in a kiln or oven. 

3.2 Glassware must be scrupulously cleaned (Reference 5). Clean all glassware as soon as possible 

after use by rinsing with the last solvent used in it. Solvent rinsing should be followed by detergent 

washing with hot water, and rinses with tap water and reagent water. The glassware should then be 

drained dry, and heated at 400 °C for 15 - 30 minutes. Some thermally stable materials, such as 

PCBs, may require higher temperatures and longer baking times for removal. Solvent rinses with 

pesticide quality acetone, hexane, or other solvents may be substituted for heating. Volumetric 

labware should not be heated above 90 °C. After drying and cooling, glassware should be sealed 

and stored in a clean environment to prevent any accumulation of dust or other contaminants. Store 

inverted or capped with solvent-rinsed or baked aluminum foil. 

3.3 Matrix interferences may be caused by contaminants co-extracted from the sample. The extent of 

matrix interferences will vary considerably from source to source, depending upon the nature and 

diversity of the industrial complex or municipality being sampled. Interferences extracted from 

samples high in total organic carbon (TOC) may result in elevated baselines, or by enhancing or 

suppressing a signal at or near the retention time of an analyte of interest. Analyses of the matrix 

spike and duplicate (Section 8.3) may be useful in identifying matrix interferences, and gel 

permeation chromatography (GPC; Section 11.1) and sulfur removal (Section 11.2) may aid in 

eliminating these interferences. EPA has provided guidance that may aid in overcoming matrix 

interferences (Reference 6).

3.4 In samples that contain an inordinate number of interferences, the use of chemical ionization (CI) 

mass spectrometry may make identification easier. Tables 4 and 5 give characteristic CI m/z’s for 

many of the analytes covered by this method. The use of CI mass spectrometry to support electron 

ionization (EI) mass spectrometry is encouraged, but not required. 

4. Safety

4.1 Hazards associated with each reagent used in this method have not been precisely defined; 

however, each chemical compound should be treated as a potential health hazard. From this 

viewpoint, exposure to these chemicals must be reduced to the lowest possible level by whatever 

means available. The laboratory is responsible for maintaining a current awareness file of OSHA 

regulations regarding the safe handling of the chemicals specified in this method. A reference file 

of safety data sheets (SDSs, OSHA, 29 CFR 1910.1200[g]) should also be made available to all 

personnel involved in sample handling and chemical analysis. Additional references to laboratory 

safety are available and have been identified (References 7 - 9) for the information of the analyst.

4.2 The following analytes covered by this method have been tentatively classified as known or 

suspected human or mammalian carcinogens: benzo(a)anthracene, benzidine, 3,3’-dichlorobenzidine, benzo(a)pyrene, alpha-BHC, beta-BHC, delta-BHC, gamma-BHC, Dibenz(a,h)-

anthracene, N-nitrosodimethylamine, 4,4’-DDT, and PCBs. Other compounds in Table 3 may also 

Method 625.1 3 December 2014
be toxic. Primary standards of toxic compounds should be prepared in a chemical fume hood, and a 

NIOSH/MESA approved toxic gas respirator should be worn when handling high concentrations of 

these compounds. 

4.3 This method allows the use of hydrogen as a carrier gas in place of helium (Section 5.6.1.2). The 

laboratory should take the necessary precautions in dealing with hydrogen, and should limit 

hydrogen flow at the source to prevent buildup of an explosive mixture of hydrogen in air. 

5. Apparatus and Materials

Note: Brand names, suppliers, and part numbers are for illustration purposes only. No 

endorsement is implied. Equivalent performance may be achieved using equipment and 

materials other than those specified here. Demonstrating that the equipment and supplies 

used in the laboratory achieves the required performance is the responsibility of the 

laboratory. Suppliers for equipment and materials in this method may be found through an 

on-line search. Please do not contact EPA for supplier information. 

5.1 Sampling equipment, for discrete or composite sampling. 

5.1.1 Grab sample bottle – amber glass bottle large enough to contain the necessary sample 

volume, fitted with a fluoropolymer-lined screw cap. Foil may be substituted for 

fluoropolymer if the sample is not corrosive. If amber bottles are not available, protect 

samples from light. Unless pre-cleaned, the bottle and cap liner must be washed, rinsed 

with acetone or methylene chloride, and dried before use to minimize contamination.

5.1.2 Automatic sampler (optional) – the sampler must incorporate a pre-cleaned glass sample 

container. Samples must be kept refrigerated at <6 °C and protected from light during 

compositing. If the sampler uses a peristaltic pump, a minimum length of compressible 

silicone rubber tubing may be used. Before use, however, the compressible tubing should 

be thoroughly rinsed with methanol, followed by repeated rinsings with reagent water to 

minimize the potential for contamination of the sample. An integrating flow meter is 

required to collect flow-proportioned composites. 

5.2 Glassware

5.2.1 Separatory funnel – Size appropriate to hold sample volume and extraction solvent volume, 

and equipped with fluoropolymer stopcock. 

5.2.2 Drying column – Chromatographic column, approximately 400 mm long by 19 mm ID, 

with coarse frit, or equivalent, sufficient to hold 15 g of anhydrous sodium sulfate. 

5.2.3 Concentrator tube, Kuderna-Danish – 10 mL, graduated (Kontes 570050-1025 or 

equivalent). Calibration must be checked at the volumes employed in the test. A ground 

glass stopper is used to prevent evaporation of extracts. 

5.2.4 Evaporative flask, Kuderna-Danish – 500 mL (Kontes 57001-0500 or equivalent). Attach 

to concentrator tube with springs.

Note: Use of a solvent recovery system with the K-D or other solvent evaporation 

apparatus is strongly recommended. 

Method 625.1 4 December 2014
5.2.5 Snyder column, Kuderna-Danish – Three ball macro (Kontes 503000-0121 or equivalent).

5.2.6 Snyder column, Kuderna-Danish – Two-ball micro (Kontes 569001-0219 or equivalent).

5.2.7 Vials – 10-15 mL, amber glass, with Teflon-lined screw cap.

5.2.8 Continuous liquid-liquid extractor – Equipped with fluoropolymer or glass connecting 

joints and stopcocks requiring no lubrication. (Hershberg-Wolf Extractor, Ace Glass 

Company, Vineland, N.J., P/N 6848-20, or equivalent.) 

5.2.9 In addition to the glassware listed above, the laboratory should be equipped with all 

necessary pipets, volumetric flasks, beakers, and other glassware listed in this method and 

necessary to perform analyses successfully.

5.3 Boiling chips – Approximately 10/40 mesh, glass, silicon carbide, or equivalent. Heat to 400 °C for 

30 minutes, or solvent rinse or Soxhlet extract with methylene chloride.

5.4 Water bath – Heated, with concentric ring cover, capable of temperature control (±2 °C). The bath 

should be used in a hood. 

5.5 Balances

5.5.1 Analytical, capable of accurately weighing 0.1 mg 

5.5.2 Top loading, capable of accurately weighing 10 mg 

5.6 GC/MS system

5.6.1 Gas chromatograph (GC) – An analytical system complete with a temperature 

programmable gas chromatograph and all required accessories, including syringes and 

analytical columns.

5.6.1.1 Injection port – Can be split, splitless, temperature programmable split/splitless 

(PTV), solvent-purge, large-volume, on-column, backflushed, or other. An 

autosampler is highly recommended because it injects volumes more precisely 

than volumes injected manually. 

5.6.1.2 Carrier gas – Helium or hydrogen. Data in the tables in this method were 

obtained using helium carrier gas. If hydrogen is used, analytical conditions may 

need to be adjusted for optimum performance, and calibration and all QC tests 

must be performed with hydrogen carrier gas. See Section 4.3 for precautions 

regarding the use of hydrogen as a carrier gas.

5.6.2 GC column – See the footnotes to Tables 4 and 5. Other columns or column systems may 

be used provided all requirements in this method are met. 

5.6.3 Mass spectrometer – Capable of repetitively scanning from 35-450 Daltons (amu) every 

two seconds or less, utilizing a 70 eV (nominal) electron energy in the electron impact 

ionization mode, and producing a mass spectrum which meets all the criteria in Table 9A or 

9B when 50 ng or less of decafluorotriphenyl phosphine (DFTPP; CAS 5074-71-5; 

bis(pentafluorophenyl) phenyl phosphine) is injected into the GC. 

Method 625.1 5 December 2014
5.6.4 GC/MS interface – Any GC to MS interface that meets all performance requirements in this 

method may be used. 

5.6.5 Data system – A computer system must be interfaced to the mass spectrometer that allows 

the continuous acquisition and storage of mass spectra acquired throughout the 

chromatographic program. The computer must have software that allows searching any 

GC/MS data file for specific m/z’s (masses) and plotting m/z abundances versus time or 

scan number. This type of plot is defined as an extracted ion current profile (EICP). 

Software must also be available that allows integrating the abundance at any EICP between 

specified time or scan number limits.

5.7 Automated gel permeation chromatograph (GPC)

5.7.1 GPC column – 150 - 700 mm long x 21 - 25 mm ID, packed with 70 g of SX-3 Biobeads; 

Bio-Rad Labs, or equivalent 

5.7.2 Pump, injection valve, UV detector, and other apparatus necessary to meet the requirements 

in this method.

5.8 Nitrogen evaporation device – Equipped with a water bath than can be maintained at 30 - 45 °C; 

N-Evap, Organomation Associates, or equivalent. 

6. Reagents

6.1 Reagent water – Reagent water is defined as water in which the analytes of interest and interfering 

compounds are not detected at the MDLs of the analytes of interest.

6.2 Sodium hydroxide solution (10 N) – Dissolve 40 g of NaOH (ACS) in reagent water and dilute to 

100 mL. 

6.3 Sodium thiosulfate – (ACS) granular.

6.4 Sulfuric acid (1+1) – Slowly add 50 mL of H2SO4 (ACS, sp. gr. 1.84) to 50 mL of reagent water. 

6.5 Acetone, methanol, methylene chloride, 2-propanol – High purity pesticide quality, or equivalent, 

demonstrated to be free of the analytes of interest and interferences (Section 3). Purification of 

solvents by distillation in all-glass systems may be required.

6.6 Sodium sulfate – (ACS) granular, anhydrous, rinsed or Soxhlet extracted with methylene chloride 

(20 mL/g), baked at in a shallow tray at 450°C for one hour minimum, cooled in a desiccator, and 

stored in a pre-cleaned glass bottle with screw cap that prevents moisture from entering. 

6.7 Stock standard solutions (1.00 μg/μL) – Stock standard solutions may be prepared from pure 

materials, or purchased as certified solutions. Traceability must be to the National Institute of 

Standards and Technology (NIST) or other national standard, when available. Stock solution 

concentrations alternate to those below may be used. Because of the toxicity of some of the 

compounds, primary dilutions should be prepared in a hood, and a NIOSH/MESA approved toxic 

gas respirator should be worn when high concentrations of neat materials are handled. The 

following procedure may be used to prepare standards from neat materials.

Method 625.1 6 December 2014
6.7.1 Prepare stock standard solutions by accurately weighing about 0.0100 g of pure material. 

Dissolve the material in pesticide quality methanol or other suitable solvent and dilute to 

volume in a 10 mL volumetric flask. Larger volumes may be used at the convenience of 

the laboratory. When compound purity is assayed to be 96% or greater, the weight may be 

used without correction to calculate the concentration of the stock standard. Commercially 

prepared stock standards may be used at any concentration if they are certified by the 

manufacturer or by an independent source. 

6.7.2 Transfer the stock standard solutions to fluoropolymer-sealed screw-cap bottles. Store at 

<6 °C and protect from light. Stock standard solutions should be checked frequently for 

signs of degradation or evaporation, especially just prior to preparing calibration standards 

from them.

6.7.3 Replace purchased certified stock standard solutions per the expiration date. Replace stock 

standard solutions prepared by the laboratory or mixed with purchased solutions after one 

year, or sooner if comparison with QC check samples indicates a problem.

6.8 Surrogate standard spiking solution 

6.8.1 Select a minimum of three surrogate compounds from Table 8 that most closely match the 

recovery of the analytes of interest. For example, if all analytes tested are considered acids, 

use surrogates that have similar chemical attributes. Other compounds may be used as 

surrogates so long as they do not interfere in the analysis. The deuterium and carbon-13 

labeled compounds in Method 1625 are particularly useful because Method 1625 contains 

QC acceptance criteria for recovery of these compounds. If only one or two analytes are 

determined, one or two surrogates may be used. 

6.8.2 Prepare a solution containing each selected surrogate such that the concentration in the 

sample would match the concentration in the mid-point calibration standard. For example, 

if the midpoint of the calibration is 100 μg/L, prepare the spiking solution at a 

concentration of 100 μg/mL in methanol. Addition of 1.00 mL of this solution to 1000 mL 

of sample will produce a concentration of 100 μg/L of the surrogate. Alternate volumes 

and concentrations appropriate to the response of the GC/MS instrument or for selective ion 

monitoring (SIM) may be used, if desired. 

6.8.3 Store the spiking solution at ≤ 6°C in a fluoropolymer-sealed glass container. The solution 

should be checked frequently for stability. The solution must be replaced after one year, or 

sooner if comparison with quality control check standards indicates a problem. 

6.9 Internal standard spiking solution 

6.9.1 Select three or more internal standards similar in chromatographic behavior to the analytes 

of interest. Internal standards are listed in Table 8. Suggested internal standards are: 

1,4-dichlorobenzene-d4; naphthalene-d8; acenaphthene-d10; phenanthrene-d10; chrysene-d12; 

and perylene-d12. The laboratory must demonstrate that measurement of the internal 

standards is not affected by method or matrix interferences (see also Section 7.3.4). 

6.9.2 Prepare the internal standards at a concentration of 10 mg/mL in methylene chloride or 

other suitable solvent. When 10 μL of this solution is spiked into a 1-mL extract, the 

concentration of the internal standards will be 100 μg/mL. A lower concentration 

appropriate to the response of the GC/MS instrument or for SIM may be used, if desired.

Method 625.1 7 December 2014
6.9.3 To assure accurate analyte identification, particularly when SIM is used, it may be 

advantageous to include more internal standards than those suggested in Section 6.9.1. An 

analyte will be located most accurately if its retention time relative to an internal standard is 

in the range of 0.8 to 1.2. 

6.10 DFTPP standard – Prepare a solution of DFTPP in methanol or other suitable solvent such that 50 

ng or less will be injected (see Section 13.2). An alternate concentration may be used to 

compensate for specific injection volumes or to assure that the operating range of the instrument is 

not exceeded, so long as the total injected is 50 ng or less. Include benzidine and pentachlorophenol in this solution such that ≤100 ng of benzidine and ≤50 ng of pentachlorophenol will be 

injected.

6.11 Quality control check sample concentrate – See Section 8.2.1. 

6.12 GPC calibration solution

6.12.1 Prepare a methylene chloride solution to contain corn oil, bis(2-ethylhexyl) phthalate 

(BEHP), perylene, and sulfur at the concentrations in Section 6.12.2, or at concentrations 

appropriate to the response of the detector. 

Note: Sulfur does not readily dissolve in methylene chloride, but is soluble in warm corn oil. 

The following procedure is suggested for preparation of the solution:

6.12.2 Weigh 8 mg sulfur and 2.5 g corn oil into a 100-mL volumetric flask and warm to dissolve 

the sulfur. Separately weigh 100 mg BEHP and 2 mg perylene and add to flask. Bring to 

volume with methylene chloride and mix thoroughly.

6.12.3 Store the solution in an amber glass bottle with a fluoropolymer-lined screw cap at 0 - 6 oC. 

Protect from light. Refrigeration may cause the corn oil to precipitate. Before use, allow the 

solution to stand at room temperature until the corn oil dissolves, or warm slightly to aid in 

dissolution. Replace the solution every year, or more frequently if the response of a 

component changes.

6.13 Sulfur removal – Copper foil or powder (bright, non-oxidized), or tetrabutylammonium sulfite (TBA 

sulfite).

6.13.1 Copper foil, or powder – Fisher, Alfa Aesar 42455-18, 625 mesh, or equivalent. Cut 

copper foil into approximately 1-cm squares. Copper must be activated on each day it will 

be used, as follows: 

6.13.1.1 Place the quantity of copper needed for sulfur removal (Section 11.2.1.3) in a 

ground-glass-stoppered Erlenmeyer flask or bottle. Cover the foil or powder 

with methanol.

6.13.1.2 Add HCl dropwise (0.5 - 1.0 mL) while swirling, until the copper brightens. 

6.13.1.3 Pour off the methanol/HCl and rinse 3 times with reagent water to remove all 

traces of acid, then 3 times with acetone, then 3 times with hexane.

6.13.1.4 For copper foil, cover with hexane after the final rinse. Store in a stoppered flask 

under nitrogen until used. For the powder, dry on a rotary evaporator or under a 

stream of nitrogen. Store in a stoppered flask under nitrogen until used. 

Method 625.1 8 December 2014
6.13.2 Tetrabutylammonium sodium sulfite (TBA sodium sulfite) 

6.13.2.1 Tetrabutylammonium hydrogen sulfate, [CH3(CH2)3]4NHSO4

6.13.2.2 Sodium sulfite, Na2SO3

6.13.2.3 Dissolve approximately 3 g tetrabutylammonium hydrogen sulfate in 100 mL of 

reagent water in an amber bottle with fluoropolymer-lined screw cap. Extract 

with three 20-mL portions of hexane and discard the hexane extracts.

6.13.2.4 Add 25 g sodium sulfite to produce a saturated solution. Store at room 

temperature. Replace after 1 month. 

7. Calibration

7.1 Establish operating conditions equivalent to those in the footnote to Table 4 or 5 for the 

base/neutral or acid fraction, respectively. If a combined base/neutral/acid fraction will be 

analyzed, use the conditions in the footnote to Table 4. Alternative temperature program and flow 

rate conditions may be used. It is necessary to calibrate the GC/MS for the analytes of interest 

(Section 1.3) only. 

7.2 Internal standard calibration

7.2.1 Prepare calibration standards for the analytes of interest and surrogates at a minimum of 

five concentration levels by adding appropriate volumes of one or more stock standards to 

volumetric flasks. One of the calibration standards should be at a concentration near the 

ML for the analyte in Table 1, 2, or 3. The ML value may be rounded to a whole number 

that is more convenient for preparing the standard, but must not exceed the ML values

listed in Table 1, 2, or 3 for those analytes which list ML values. Alternatively, the 

laboratory may establish the ML for each analyte based on the concentration of the lowest 

calibration standard in a series of standards obtained from a commercial vendor, again, 

provided that the ML values do not exceed the MLs in Tables 1, 2, or 3, and provided that 

the resulting calibration meets the acceptance criteria in Section 7.2.3, based on the RSD, 

RSE, or R2

. 

The other concentrations should correspond to the expected range of concentrations found 

in real samples or should define the working range of the GC/MS system for full-scan 

and/or SIM operation, as appropriate. A minimum of six concentration levels is required 

for a second order, non-linear (e.g., quadratic; ax2 + bx + c) calibration. Calibrations higher 

than second order are not allowed. To each calibration standard or standard mixture, add a 

known constant volume of the internal standard solution (Section 6.9), and dilute to volume 

with methylene chloride.

Note: The large number of analytes in Tables 1 through 3 may not be soluble or stable in 

a single solution; multiple solutions may be required if a large number of analytes 

are to be determined simultaneously.

7.2.1.1 Prior to analysis of the calibration standards, inject the DFTPP standard (Section 

6.10) and adjust the scan rate of the mass spectrometer to produce a minimum of 

5 mass spectra across the DFTPP GC peak. Adjust instrument conditions until 

Method 625.1 9 December 2014
the DFTPP criteria in Table 9A or 9B are met. Calculate peak tailing factors for 

benzidine and pentachlorophenol. Calculation of the tailing factor is illustrated 

in Figure 1. The tailing factor for benzidine and pentachlorophenol must be <2; 

otherwise, adjust instrument conditions and either replace the column or break 

off a short section of the front end of the column, and repeat the test. 

Note: The DFTPP spectrum may be evaluated by summing the intensities of the 

m/z’s across the GC peak, subtracting the background at each m/z in a 

region of the chromatogram within 20 scans of but not including any part 

of, the DFTPP peak. The DFTPP spectrum may also be evaluated by 

fitting a Gaussian to each m/z and using the intensity at the maximum for 

each Gaussian or by integrating the area at each m/z and using the 

integrated areas. Other means may be used for evaluation of the DFTPP 

spectrum so long as the spectrum is not distorted to meet the criteria in 

Table 9A or 9B. 

7.2.1.2 Analyze the mid-point combined base/neutral and acid calibration standard and 

enter or review the retention time, relative retention time, mass spectrum, and 

quantitation m/z in the data system for each analyte of interest, surrogate, and 

internal standard. If additional analytes (Table 3) are to be quantified, include 

these analytes in the standard. The mass spectrum for each analyte must be 

comprised of a minimum of 2 m/z’s (Tables 4 and 5); 3 to 5 m/z’s assure more 

reliable analyte identification. Suggested quantitation m/z’s are shown in Tables 

4 and 5 as the primary m/z. If an interference occurs at the primary m/z, use one 

of the secondary m/z’s or an alternate m/z. A single m/z only is required for 

quantitation. 

7.2.1.3 For SIM operation, determine the analytes in each descriptor, the quantitation 

and qualifier m/z’s for each analyte (the m/z’s can be the same as for full-scan 

operation; Section 7.2.1.2), the dwell time on each m/z for each analyte, and the 

beginning and ending retention time for each descriptor. Analyze the verification 

standard in scan mode to verify m/z’s and establish the retention times for the 

analytes. There must be a minimum of two m/z’s for each analyte to assure 

analyte identification. To maintain sensitivity and capture enough scans (≥5) 

across each chromatographic peak, there should be no more than 10 m/z’s in a 

descriptor. For example, for a descriptor with 10 m/z’s and a chromatographic 

peak width of 5 sec, a dwell time of 100 ms at each m/z would result in a scan 

time of 1 second and provide 5 scans across the GC peak. The quantitation m/z

will usually be the most intense peak in the mass spectrum. The quantitation m/z

and dwell time may be optimized for each analyte. However, if a GC peak spans 

two (or more) descriptors, the dwell time and cycle time (scans/sec) should be set 

to the same value in both segments in order to maintain equivalent response. The 

acquisition table used for SIM must take into account the mass defect (usually 

less than 0.2 Daltons) that can occur at each m/z being monitored. 

7.2.1.4 For combined scan and SIM operation, set up the scan segments and descriptors 

to meet requirements in Sections 7.2.1.1 - 7.2.1.3. 

7.2.2 Analyze each calibration standard according to Section 12 and tabulate the area at the 

quantitation m/z against concentration for each analyte of interest, surrogate, and internal 

standard. If an interference is encountered, use a secondary m/z (Table 4 or 5) for 

Method 625.1 10 December 2014
quantitation. Calculate a response factor (RF) for each analyte of interest at each 

concentration using Equation 1. 

Equation 1 

(A

RF = sxCis)

(AisxCs)

where:

As = Area of the characteristic m/z for the analyte of interest or surrogate.

Ais = Area of the characteristic m/z for the internal standard.

Cis = Concentration of the internal standard (μg/mL).

Cs = Concentration of the analyte of interest or surrogate (μg/mL).

7.2.3 Calculate the mean (average) and relative standard deviation (RSD) of the responses 

factors. If the RSD is less than 35%, the RF can be assumed to be invariant and the average 

RF can be used for calculations. Alternatively, the results can be used to fit a linear or 

quadratic regression of response ratios, As/Ais, vs. concentration ratios Cs/Cis. If used, the 

regression must be weighted inversely proportional to concentration. The coefficient of 

determination (R2 ; Reference 10) of the weighted regression must be greater than 0.920. 

Alternatively, the relative standard error (Reference 11) may be used as an acceptance 

criterion. As with the RSD, the RSE must be less than 35%. If an RSE less than 35% 

cannot be achieved for a quadratic regression, system performance is unacceptable and the 

system must be adjusted and re-calibrated.

Note: Using capillary columns and current instrumentation, it is quite likely that a laboratory can 

calibrate the target analytes in this method and achieve a linearity metric (either RSD or 

RSE) well below 35%. Therefore, laboratories are permitted to use more stringent 

acceptance criteria for calibration than described here, for example, to harmonize their 

application of this method with those from other sources.

7.3 Calibration verification – The RF or calibration curve must be verified immediately after calibration 

and at the beginning of each 12-hour shift, by analysis of a mid-point calibration standard (Section 

7.2.1). The standard(s) must be obtained from a second manufacturer or a manufacturer’s batch 

prepared independently from the batch used for calibration. Traceability must be to a national 

standard, when available. The concentration of the standard should be near the mid-point of the 

calibration. Include the surrogates (Section 6.8) in this solution. It is necessary to verify calibration 

for the analytes of interest (Section 1.3) only. 

Note: The 12-hour shift begins after the DFTPP (Section 13.1) and DDT/endrin tests (if DDT and 

endrin are to be determined), and after analysis of the calibration verification standard. 

The 12-hour shift ends 12 hours later. The DFTPP and DDT/endrin tests are outside of the 

12-hour shift.

7.3.1 Analyze the calibration verification standard(s) beginning in Section 12. Calculate the 

percent recovery of each analyte. Compare the recoveries for the analytes of interest 

against the acceptance criteria for recovery (Q) in Table 6, and the recoveries for the 

surrogates against the acceptance criteria in Table 8. If recovery of the analytes of interest 

and surrogates meet acceptance criteria, system performance is acceptable and analysis of 

samples may continue. If any individual recovery is outside its limit, system performance 

is unacceptable for that analyte.

Method 625.1 11 December 2014
Note: The large number of analytes in Tables 6 and 8 present a substantial probability 

that one or more will fail acceptance criteria when all analytes are tested 

simultaneously.

7.3.2 When one or more analytes fail acceptance criteria, analyze a second aliquot of the 

calibration verification standard and compare only those analytes that failed the first test 

(Section 7.3.1) with their respective acceptance criteria. If these analytes now pass, system 

performance is acceptable and analysis of samples may continue. A repeat failure of any 

analyte that failed the first test, however, will confirm a general problem with the 

measurement system. If this occurs, repair the system (Section 7.2.1.1) and repeat the test 

(Section 7.3.1), or prepare a fresh calibration standard and repeat the test. If calibration 

cannot be verified after maintenance or injection of the fresh calibration standard, recalibrate the instrument. 

Note: If it is necessary to perform a repeat verification test frequently; i.e., perform two 

tests in order to pass, it may be prudent to perform two injections in succession and 

review the results, rather than perform one injection, review the results, then 

perform the second injection if results from the first injection fail. To maintain the 

validity of the test and re-test, system maintenance and/or adjustment is not 

permitted between the injections.

7.3.3 Many of the analytes in Table 3 do not have QC acceptance criteria in Table 6, and some of 

the surrogates in Table 8 do not have acceptance criteria. If calibration is to be verified and 

other QC tests are to be performed for these analytes, acceptance criteria must be developed 

and applied. EPA has provided guidance for development of QC acceptance criteria 

(References 12 and 13).

7.3.4 Internal standard responses – Verify that detector sensitivity has not changed by comparing 

the response of each internal standard in the calibration verification standard (Section 7.3) 

to the response of the respective internal standard in the midpoint calibration standard 

(Section 7.2.1). The peak areas or heights of the internal standards in the calibration 

verification standard must be within 50% to 200% (1/2 to 2x) of their respective peak areas 

or heights in the mid-point calibration standard. If not, repeat the calibration verification 

test using a fresh calibration verification standard (7.3), or perform and document system 

repair. Subsequent to repair, repeat the calibration verification test (Section 7.3.1). If the 

responses are still not within 50% to 200%, re-calibrate the instrument (Section 7.2.2) and 

repeat the calibration verification test.

8. Quality Control

8.1 Each laboratory that uses this method is required to operate a formal quality assurance program. 

The minimum requirements of this program consist of an initial demonstration of laboratory 

capability and ongoing analysis of spiked samples and blanks to evaluate and document data quality 

(40 CFR 136.7). The laboratory must maintain records to document the quality of data generated. 

Results of ongoing performance tests are compared with established QC acceptance criteria to 

determine if the results of analyses meet performance requirements of this method. When results of 

spiked samples do not meet the QC acceptance criteria in this method, a quality control check 

sample (laboratory control sample; LCS) must be analyzed to confirm that the measurements were 

performed in an in-control mode of operation. A laboratory may develop its own performance 

criteria (as QC acceptance criteria), provided such criteria are as or more restrictive than the criteria 

in this method.

Method 625.1 12 December 2014
8.1.1 The laboratory must make an initial demonstration of capability (DOC) to generate 

acceptable precision and recovery with this method. This demonstration is detailed in 

Section 8.2. 

8.1.2 In recognition of advances that are occurring in analytical technology, and to overcome 

matrix interferences, the laboratory is permitted certain options (Section 1.6 and 40 CFR 

136.6(b)) to improve separations or lower the costs of measurements. These options may 

include alternate extraction, concentration, and cleanup procedures (e.g., solid-phase 

extraction; rotary-evaporator concentration; column chromatography cleanup), changes in 

column and type of mass spectrometer (40 CFR 136.6(b)(4)(xvi)). Alternate determinative 

techniques, such as substitution of spectroscopic or immunoassay techniques, and changes 

that degrade method performance, are not allowed. If an analytical technique other than 

GC/MS is used, that technique must have a specificity equal to or greater than the specificity 

of GC/MS for the analytes of interest. The laboratory is also encouraged to participate in 

inter-comparison and performance evaluation studies (see Section 8.10). 

8.1.2.1 Each time a modification is made to this method, the laboratory is required to 

repeat the procedure in Section 8.2. If the detection limit of the method will be 

affected by the change, the laboratory must demonstrate that the MDLs (40 CFR 

Part 136, Appendix B) are lower than one-third the regulatory compliance limit or 

the MDLs in this method, whichever are greater. If calibration will be affected by 

the change, the instrument must be recalibrated per Section 7. Once the 

modification is demonstrated to produce results equivalent or superior to results 

produced by this method, that modification may be used routinely thereafter, so 

long as the other requirements in this method are met (e.g., matrix spike/matrix 

spike duplicate recovery and relative percent difference).

8.1.2.1.1 If SPE, or another allowed method modification, is to be applied to a 

specific discharge, the laboratory must prepare and analyze matrix 

spike/matrix spike duplicate (MS/MSD) samples (Section 8.3) and 

LCS samples (Section 8.4). The laboratory must include surrogates 

(Section 8.7) in each of the samples. The MS/MSD and LCS 

samples must be fortified with the analytes of interest (Section 1.3). 

If the modification is for nationwide use, MS/MSD samples must be 

prepared from a minimum of nine different discharges (See Section 

8.1.2.1.2), and all QC acceptance criteria in this method must be 

met. This evaluation only needs to be performed once other than for 

the routine QC required by this method (for example it could be 

performed by the vendor of the SPE materials) but any laboratory 

using that specific SPE material must have the results of the study 

available. This includes a full data package with the raw data that 

will allow an independent reviewer to verify each determination and 

calculation performed by the laboratory (see Section 8.1.2.2.5, items 

a-q). 

8.1.2.1.2 Sample matrices on which MS/MSD tests must be performed for 

nationwide use of an allowed modification: 

(a) Effluent from a POTW

(b) ASTM D5905 Standard Specification for Substitute Wastewater

(c) Sewage sludge, if sewage sludge will be in the permit

(d) ASTM D1141 Standard Specification for Substitute Ocean 

Water, if ocean water will be in the permit

Method 625.1 13 December 2014
(e) Untreated and treated wastewaters up to a total of nine matrix 

types (see 

http:water.epa.gov/scitech/wastetech/guide/industry.cfm) for a 

list of industrial categories with existing effluent guidelines).

At least one of the above wastewater matrix types must have at 

least one of the following characteristics:

(i) Total suspended solids greater than 40 mg/L 

(ii) Total dissolved solids greater than 100 mg/L 

(iii) Oil and grease greater than 20 mg/L

(iv) NaCl greater than 120 mg/L

(v) CaCO3 greater than 140 mg/L 

The interim acceptance criteria for MS, MSD recoveries that do not 

have recovery limits specified in Table 6, and recoveries for 

surrogates that do not have recovery limits specified in Table 8, must 

be no wider than 60 -140 %, and the relative percent difference 

(RPD) of the concentrations in the MS and MSD that do not have 

RPD limits specified in Table 6 must be less than 30%. 

Alternatively, the laboratory may use the laboratory’s in-house limits 

if they are tighter.

(f) A proficiency testing (PT) sample from a recognized provider, in 

addition to tests of the nine matrices (Section 8.1.2.1.1). 

8.1.2.2 The laboratory is required to maintain records of modifications made to this 

method. These records include the following, at a minimum:

8.1.2.2.1 The names, titles, street addresses, telephone numbers, and e-mail

addresses of the analyst(s) that performed the analyses and 

modification, and of the quality control officer that witnessed and will 

verify the analyses and modifications.

8.1.2.2.2 A list of analytes, by name and CAS Registry Number.

8.1.2.2.3 A narrative stating reason(s) for the modifications.

8.1.2.2.4 Results from all quality control (QC) tests comparing the modified 

method to this method, including:

a) Calibration (Section 7).

b) Calibration verification (Section 7).

c) Initial demonstration of capability (Section 8.2).

d) Analysis of blanks (Section 8.5).

e) Matrix spike/matrix spike duplicate analysis (Section 8.3).

f) Laboratory control sample analysis (Section 8.4).

Method 625.1 14 December 2014
8.1.2.2.5 Data that will allow an independent reviewer to validate each 

determination by tracing the instrument output (peak height, area, or 

other signal) to the final result. These data are to include:

a) Sample numbers and other identifiers.

b) Extraction dates.

c) Analysis dates and times.

d) Analysis sequence/run chronology.

e) Sample weight or volume (Section 10).

f) Extract volume prior to each cleanup step (Sections 10 and 11).

g) Extract volume after each cleanup step (Section 11).

h) Final extract volume prior to injection (Sections 10 and 12).

i) Injection volume (Section 12.2.3).

j) Sample or extract dilution (Section 12.2.3.2).

k) Instrument and operating conditions.

l) Column (dimensions, material, etc).

m) Operating conditions (temperature program, flow rate, etc).

n) Detector (type, operating conditions, etc).

o) Chromatograms, mass spectra, and other recordings of raw data.

p) Quantitation reports, data system outputs, and other data to link 

the raw data to the results reported.

(q) A written Standard Operating Procedure (SOP)

8.1.2.2.6 Each individual laboratory wishing to use a given modification must 

perform the start-up tests in Section 8.1.2 (e.g., DOC, MDL), with 

the modification as an integral part of this method prior to applying 

the modification to specific discharges. Results of the DOC must 

meet the QC acceptance criteria in Table 6 for the analytes of interest 

(Section 1.3), and the MDLs must be equal to or lower than the 

MDLs in Tables 4 and 5 for the analytes of interest.

8.1.3 Before analyzing samples, the laboratory must analyze a blank to demonstrate that 

interferences from the analytical system, labware, and reagents, are under control. Each 

time a batch of samples is extracted or reagents are changed, a blank must be extracted and 

analyzed as a safeguard against laboratory contamination. Requirements for the blank are 

given in Section 8.5. 

8.1.4 The laboratory must, on an ongoing basis, spike and analyze a minimum of one sample, in 

duplicate, with the samples in an extraction batch (Section 3.1). The laboratory must also 

spike and analyze, in duplicate, a minimum of 5% of all samples from a given site or 

discharge to monitor and evaluate method and laboratory performance on the sample 

matrix. The batch and site/discharge samples may be the same. The procedure for spiking 

and analysis is given in Section 8.3. 

8.1.5 The laboratory must, on an ongoing basis, demonstrate through analysis of a quality control 

check sample (laboratory control sample, LCS; on-going precision and recovery sample, 

OPR) that the measurement system is in control. This procedure is given in Section 8.4. 

8.1.6 The laboratory should maintain performance records to document the quality of data that is 

generated. This procedure is given in Section 8.9. 

Method 625.1 15 December 2014
8.1.7 The large number of analytes tested in performance tests in this method present a 

substantial probability that one or more will fail acceptance criteria when many analytes are 

tested simultaneously, and a re-test is allowed if this situation should occur. If, however, 

continued re-testing results in further repeated failures, the laboratory should document the 

failures (e.g., as qualifiers on results) and either avoid reporting results for analytes that 

failed or report the problem and failures with the data. Failure to report does not relieve a 

discharger or permittee of reporting timely results.

8.2 Initial demonstration of capability (DOC) – To establish the ability to generate acceptable recovery 

and precision, the laboratory must perform the DOC in Sections 8.2.1 through 8.2.6 for the analytes 

of interest. The laboratory must also establish MDLs for the analytes of interest using the MDL 

procedure at 40 CFR 136, Appendix B. The laboratory’s MDLs must be equal to or lower than 

those listed in Tables 1, 2, or 3 or lower than one third the regulatory compliance limit, whichever 

is greater. For MDLs not listed in Tables 4 and 5, the laboratory must determine the MDLs using 

the MDL procedure at 40 CFR 136, Appendix B under the same conditions used to determine the 

MDLs for the analytes listed in Tables 1, 2, and 3. All procedures used in the analysis, including 

cleanup procedures, must be included in the DOC. 

8.2.1 For the DOC, a QC check sample concentrate containing each analyte of interest (Section 

1.3) is prepared in a water-miscible solvent. The QC check sample concentrate must be 

prepared independently from those used for calibration, but may be from the same source 

as the second-source standard used for calibration verification (Section 7.3). The 

concentrate should produce concentrations of the analytes of interest in water at the midpoint of the calibration range, and may be at the same concentration as the LCS (Section 

8.4). Multiple solutions may be required. 

Note: QC check sample concentrates are no longer available from EPA.

8.2.2 Using a pipet or micro-syringe, prepare four LCSs by adding an appropriate volume of the 

concentrate to each of four 1-L aliquots of reagent water, and mix well. The volume of 

reagent water must be the same as the volume that will be used for the sample, blank 

(Section 8.5), and MS/MSD (Section 8.3). A concentration of 100 μg/L was used to 

develop the QC acceptance criteria in Table 6. Also add an aliquot of the surrogate spiking 

solution (Section 6.8). Also add an aliquot of the surrogate spiking solution (Section 6.8) 

to the reagent-water aliquots. 

8.2.3 Extract and analyze the four LCSs according to the method beginning in Section 10. 

8.2.4 Calculate the average percent recovery ( X ) and the standard deviation of the percent 

recovery (s) for each analyte using the four results.

8.2.5 For each analyte, compare s and ( X ) with the corresponding acceptance criteria for 

precision and recovery in Table 6. For analytes in Table 3 not listed in Table 6, DOC QC 

acceptance criteria must be developed by the laboratory. EPA has provided guidance for 

development of QC acceptance criteria (References 12 and 13). If s and ( X ) for all 

analytes of interest meet the acceptance criteria, system performance is acceptable and 

analysis of blanks and samples may begin. If any individual s exceeds the precision limit 

or any individual ( X ) falls outside the range for recovery, system performance is 

unacceptable for that analyte.

Note: The large number of analytes in Tables 1 - 3 present a substantial probability that 

one or more will fail at least one of the acceptance criteria when many or all 

Method 625.1 16 December 2014
analytes are determined simultaneously. Therefore, the analyst is permitted to 

conduct a “re-test” as described in Sec. 8.2.6.

8.2.6 When one or more of the analytes tested fail at least one of the acceptance criteria, repeat 

the test for only the analytes that failed. If results for these analytes pass, system 

performance is acceptable and analysis of samples and blanks may proceed. If one or more 

of the analytes again fail, system performance is unacceptable for the analytes that failed 

the acceptance criteria. Correct the problem and repeat the test (Section 8.2). See Section 

8.1.7 for disposition of repeated failures. 

Note: To maintain the validity of the test and re-test, system maintenance and/or 

adjustment is not permitted between this pair of tests.

8.3 Matrix spike and matrix spike duplicate (MS/MSD) – The laboratory must, on an ongoing basis, 

spike at least 5% of the samples from each sample site being monitored in duplicate to assess 

accuracy (recovery and precision). The data user should identify the sample and the analytes of 

interest (Section 1.3) to be spiked. If direction cannot be obtained, the laboratory must spike at 

least one sample per extraction batch of up to 20 samples with the analytes in Tables 1 and 2. 

Spiked sample results should be reported only to the data user whose sample was spiked, or as 

requested or required by a regulatory/control authority.

8.3.1 If, as in compliance monitoring, the concentration of a specific analyte will be checked 

against a regulatory concentration limit, the concentration of the spike should be at that 

limit; otherwise, the concentration of the spike should be one to five times higher than the 

background concentration determined in Section 8.3.2, at or near the midpoint of the 

calibration range, or at the concentration in the LCS (Section 8.4) whichever concentration 

would be larger.

8.3.2 Analyze one sample aliquot to determine the background concentration (B) of the each 

analyte of interest. If necessary, prepare a new check sample concentrate (Section 8.2.1) 

appropriate for the background concentration. Spike and analyze two additional sample 

aliquots, and determine the concentration after spiking (A1 and A2) of each analyte. 

Calculate the percent recoveries (P1 and P2) as 100 (A1 - B) / T and 100 (A2 - B) / T, where 

T is the known true value of the spike. Also calculate the relative percent difference (RPD) 

between the concentrations (A1 and A2) as 200 |A1 - A2| / (A1 + A2). If necessary, adjust the 

concentrations used to calculate the RPD to account for differences in the volumes of the 

spiked aliquots. 

8.3.3 Compare the percent recoveries (P1 and P2) and the RPD for each analyte in the MS/MSD 

aliquots with the corresponding QC acceptance criteria in Table 6. A laboratory may 

develop and apply QC acceptance criteria more restrictive than the criteria in Table 6, if 

desired.

8.3.3.1 If any individual P falls outside the designated range for recovery in either 

aliquot, or the RPD limit is exceeded, the result for the analyte in the unspiked 

sample is suspect and may not be reported or used for permitting or regulatory 

compliance purposes.. See Section 8.1.7 for disposition of failures. 

8.3.3.2 The acceptance criteria in Table 6 were calculated to include an allowance for 

error in measurement of both the background and spike concentrations, assuming 

a spike to background ratio of 5:1. This error will be accounted for to the extent 

that the spike to background ratio approaches 5:1 (Reference 14). If spiking is 

Method 625.1 17 December 2014
performed at a concentration lower than 100 μg/L, the laboratory must use either 

the QC acceptance criteria in Table 6, or optional QC acceptance criteria 

calculated for the specific spike concentration. To use the optional acceptance 

criteria: (1) Calculate recovery (X’) using the equation in Table 7, substituting 

the spike concentration (T) for C; (2) Calculate overall precision (S') using the 

equation in Table 7, substituting X' for X ; (3) Calculate the range for recovery at 

the spike concentration as (100 X’/T) ± 2.44(100 S'/T)% (Reference 14). For 

analytes in Table 3 not listed in Table 6, QC acceptance criteria must be 

developed by the laboratory. EPA has provided guidance for development of QC 

acceptance criteria (References 12 and 13).

8.3.4 After analysis of a minimum of 20 MS/MSD samples for each target analyte and surrogate, 

the laboratory must calculate and apply in-house QC limits for recovery and RPD of future 

MS/MSD samples (Section 8.3). The QC limits for recovery are calculated as the mean 

observed recovery ± 3 standard deviations, and the upper QC limit for RPD is calculated as 

the mean RPD plus 3 standard deviations of the RPDs. The in-house QC limits must be 

updated at least every two years and re-established after any major change in the analytical 

instrumentation or process. At least 80% of the analytes tested in the MS/MSD must have 

in-house QC acceptance criteria that are tighter than those in Table 6. If an in-house QC 

limit for the RPD is greater than the limit in Table 6, then the limit in Table 6 must be used. 

Similarly, if an in-house lower limit for recovery is below the lower limit in Table 6, then 

the lower limit in Table 6 must be used, and if an in-house upper limit for recovery is above 

the upper limit in Table 6, then the upper limit in Table 6 must be used. The laboratory 

must evaluate surrogate recovery data in each sample against its in-house surrogate 

recovery limits. The laboratory may use 60 -140% as interim acceptance criteria for 

surrogate recoveries until in-house limits are developed. 

8.4 Laboratory control sample (LCS) – A QC check sample (laboratory control sample, LCS; on-going 

precision and recovery sample, OPR) containing each analyte of interest (Section 1.3) and surrogate 

must be prepared and analyzed with each extraction batch of up to 20 samples to demonstrate 

acceptable recovery of the analytes of interest from a clean sample matrix.

8.4.1 Prepare the LCS by adding QC check sample concentrate (Section 8.2.1) to reagent water. 

Include all analytes of interest (Section 1.3) in the LCS. The LCS may be the same sample 

prepared for the DOC (Section 8.2.1). The volume of reagent water must be the same as 

the volume used for the sample, blank (Section 8.5), and MS/MSD (Section 8.3). Also add 

an aliquot of the surrogate spiking solution (Section 6.8). The concentration of the analytes 

in reagent water should be the same as the concentration in the DOC (Section 8.2.2). 

8.4.2 Analyze the LCS prior to analysis of field samples in the extraction batch. Determine the 

concentration (A) of each analyte. Calculate the percent recovery (PS) as 100 (A/T)%, 

where T is the true value of the concentration in the LCS.

8.4.3 Compare the percent recovery (PS) for each analyte with its corresponding QC acceptance 

criterion in Table 6. For analytes of interest in Table 3 not listed in Table 6, use the QC 

acceptance criteria developed for the MS/MSD (Section 8.3.3.2). If the recoveries for all 

analytes of interest fall within their respective QC acceptance criteria, analysis of blanks 

and field samples may proceed. If any individual PS falls outside the range, proceed 

according to Section 8.4.4. 

Note: The large number of analytes in Tables 1 - 3 present a substantial probability that 

one or more will fail the acceptance criteria when all analytes are tested 

Method 625.1 18 December 2014
simultaneously. Because a re-test is allowed in event of failure (Sections 8.1.7 and 

8.4.3), it may be prudent to extract and analyze two LCSs together and evaluate 

results of the second analysis against the QC acceptance criteria only if an analyte 

fails the first test.

8.4.4 Repeat the test only for those analytes that failed to meet the acceptance criteria (PS). If 

these analytes now pass, system performance is acceptable and analysis of blanks and 

samples may proceed. Repeated failure, however, will confirm a general problem with the 

measurement system. If this occurs, repeat the test using a fresh LCS (Section 8.2.2) or an 

LCS prepared with a fresh QC check sample concentrate (Section 8.2.1), or perform and 

document system repair. Subsequent to repair, repeat the LCS test (Section 8.4). If failure 

of the LCS indicates a systemic problem with samples in the batch, re-extract and reanalyze the samples in the batch. See Section 8.1.7 for disposition of repeated failures. 

Note: To maintain the validity of the test and re-test, system maintenance and/or 

adjustment is not permitted between the pair of tests.

8.4.5 After analysis of 20 LCS samples, the laboratory must calculate and apply in-house QC 

limits for recovery to future LCS samples (Section 8.4). Limits for recovery in the LCS are 

calculated as the mean recovery ±3 standard deviations. A minimum of 80% of the 

analytes tested for in the LCS must have QC acceptance criteria tighter than those in Table 

6. Many of the analytes and surrogates may not contain recommended acceptance criteria. 

The laboratory should use 60 -140% as interim acceptance criteria for recoveries of spiked 

analytes and surrogates that do not have recovery limits specified in Table 8, until in-house 

LCS and surrogate limits are developed. If an in-house lower limit for recovery is lower 

than the lower limit in Table 6, the lower limit in Table 6 must be used, and if an in-house 

upper limit for recovery is higher than the upper limit in Table 6, the upper limit in Table 6 

must be used.

8.5 Blank – A blank must be extracted and analyzed with each extraction batch to demonstrate that the 

reagents and equipment used for preparation and analysis are free from contamination. 

8.5.1 Spike the surrogates into the blank. Extract and concentrate the blank using the same 

procedures and reagents used for the samples, LCS, and MS/MSD in the batch. Analyze 

the blank immediately after analysis of the LCS (Section 8.4) and prior to analysis of the 

MS/MSD and samples to demonstrate freedom from contamination. 

8.5.2 If any analyte of interest is found in the blank: 1) at a concentration greater than the MDL 

for the analyte, 2) at a concentration greater than one-third the regulatory compliance limit, 

or 3) at a concentration greater than one-tenth the concentration in a sample in the 

extraction batch, whichever is greater, analysis of samples must be halted and samples 

affected by the blank must be re-extracted and the extracts re-analyzed. Samples must be 

associated with an uncontaminated blank before they may be reported or used for 

permitting or regulatory compliance purposes.

8.6 Internal standards responses

8.6.1 Calibration verification – The responses (GC peak heights or areas) of the internal 

standards in the calibration verification must be within 50% to 200% (1/2 to 2x) of their 

respective responses in the mid-point calibration standard. If they are not, repeat the 

calibration verification (Section 7.4) test or perform and document system repair. 

Subsequent to repair, repeat the calibration verification. If the responses are still not within 

Method 625.1 19 December 2014
50% to 200%, re-calibrate the instrument (Section 7) and repeat the calibration 

verification/LCS test.

8.6.2 Samples, blanks, LCSs, and MS/MSDs – The responses (GC peak heights or areas) of the 

internal standards in each sample, blank, and MS/MSD must be within 50% to 200% (1/2 

to 2x) of its respective response in the most recent LCS. If, as a group, all internal 

standards are not within this range, perform and document system repair, repeat the 

calibration verification/LCS test (Section 8.4), and re-analyze the affected samples. If a 

single internal standard is not within the 50% to 200% range, use an alternate internal 

standard for quantitation of the analyte referenced to the affected internal standard.

8.7 Surrogate recoveries – Spike the surrogates into all samples, blanks, LCSs, and MS/MSDs. 

Compare surrogate recoveries against the QC acceptance criteria in Table 8 and/or those developed 

in Section 7.3.3. If any recovery fails its criteria, attempt to find and correct the cause of the 

failure. Surrogate recoveries from the blank and LCS may be used as pass/fail criteria by the 

laboratory or as required by a regulatory authority, or may be used to diagnose problems with the 

analytical system.

8.8 DDT and endrin decomposition (breakdown) – If DDT and/or endrin are to be analyzed using this 

method, a DDT/endrin decomposition test must be performed to reliably quantify these two 

pesticides. The DDT/endrin decomposition test to be used is in EPA Method 608A or 1656. 

8.9 As part of the QC program for the laboratory, control charts or statements of accuracy for 

wastewater samples must be assessed and records maintained (40 CFR 136.7(c)(1)(viii)). After 

analysis of five or more spiked wastewater samples as in Section 8.3, calculate the average percent 

recovery ( X ) and the standard deviation of the percent recovery (sp). Express the accuracy 

assessment as a percent interval from X -2sp to X +2sp. For example, if X = 90% and sp = 10%, 

the accuracy interval is expressed as 70 - 110%. Update the accuracy assessment for each analyte 

on a regular basis (e.g., after each 5 - 10 new accuracy measurements).

8.10 It is recommended that the laboratory adopt additional quality assurance practices for use with this 

method. The specific practices that are most productive depend upon the needs of the laboratory 

and the nature of the samples. Field duplicates may be analyzed to assess the precision of 

environmental measurements. Whenever possible, the laboratory should analyze standard reference 

materials and participate in relevant performance evaluation studies.

9. Sample Collection, Preservation, and Handling

9.1 Collect samples as grab samples in glass bottles or in refrigerated bottles using automatic sampling 

equipment. Collect 1-L of ambient waters, effluents, and other aqueous samples. If the sensitivity of 

the analytical system is sufficient, a smaller volume (e.g., 250 mL), but no less than 100 mL, may be 

used. Conventional sampling practices (Reference 15) should be followed, except that the bottle 

must not be pre-rinsed with sample before collection. Automatic sampling equipment must be as 

free as possible of polyvinyl chloride or other tubing or other potential sources of contamination. If 

needed, collect additional sample(s) for the MS/MSD (Section 8.3).

9.2 Ice or refrigerate samples at ≤6 °C from the time of collection until extraction, but do not freeze. If 

residual chlorine is present, add 80 mg of sodium thiosulfate per liter of sample and mix well. Any 

method suitable for field use may be employed to test for residual chlorine (Reference 16). Do not 

add excess sodium thiosulfate. If sodium thiosulfate interferes in the determination of the analytes, 

an alternate preservative (e.g., ascorbic acid or sodium sulfite) may be used.

Method 625.1 20 December 2014
9.3 All samples must be extracted within 7 days of collection and sample extracts must be analyzed 

within 40 days of extraction.

10. Extraction 

10.1 This section contains procedures for separatory funnel liquid-liquid extraction (SFLLE) and 

continuous liquid-liquid extraction (CLLE). SFLLE is faster, but may not be as effective as CLLE 

for recovery of polar analytes such as phenol. SFLLE is labor intensive and may result in 

formation of emulsions that are difficult to break. CLLE is less labor intensive, avoids emulsion 

formation, but requires more time (18-24 hours) and more hood space, and may require more 

solvent. The procedures assume base-neutral extraction followed by acid extraction. For some 

matrices and analytes of interest, improved results may be obtained by acid-neutral extraction 

followed by base extraction. A single acid or base extraction may also be performed. If an 

extraction scheme alternate to base-neutral followed by acid extraction is used, all QC tests must be 

performed and all QC acceptance criteria must be met with that extraction scheme as an integral 

part of this method. 

10.2 Separatory funnel liquid-liquid extraction (SFLLE) and extract concentration

10.2.1 The SFLLE procedure below assumes a sample volume of 1 L. When a different sample 

volume is extracted, adjust the volume of methylene chloride accordingly. 

10.2.2 Mark the water meniscus on the side of the sample bottle for later determination of sample 

volume. Pour the entire sample into the separatory funnel. Pipet the surrogate standard 

spiking solution (Section 6.8) into the separatory funnel. If the sample will be used for the 

LCS or MS or MSD, pipet the appropriate check sample concentrate (Section 8.2.1 or 

8.3.2) into the separatory funnel. Mix well. Check the pH of the sample with wide-range 

pH paper and adjust to pH 11 - 13 with sodium hydroxide solution. 

10.2.3 Add 60 mL of methylene chloride to the sample bottle, seal, and shake for approximately 

30 seconds to rinse the inner surface. Transfer the solvent to the separatory funnel and 

extract the sample by shaking the funnel for two minutes with periodic venting to release 

excess pressure. Allow the organic layer to separate from the water phase for a minimum 

of 10 minutes. If the emulsion interface between layers is more than one-third the volume 

of the solvent layer, the analyst must employ mechanical techniques to complete the phase 

separation. The optimum technique depends upon the sample, but may include stirring, 

filtration of the emulsion through glass wool, centrifugation, or other physical methods. 

Collect the methylene chloride extract in a flask. If the emulsion cannot be broken 

(recovery of <80% of the methylene chloride), transfer the sample, solvent, and emulsion 

into a continuous extractor and proceed as described in Section 10.3. 

10.2.4 Add a second 60-mL volume of methylene chloride to the sample bottle and repeat the 

extraction procedure a second time, combining the extracts in the Erlenmeyer flask. 

Perform a third extraction in the same manner.

10.2.5 Adjust the pH of the aqueous phase to less than 2 using sulfuric acid. Serially extract the 

acidified aqueous phase three times with 60 mL aliquots of methylene chloride. Collect 

and combine the extracts in a flask in the same manner as the base/neutral extracts.

Note: Base/neutral and acid extracts may be combined for concentration and analysis 

provided all QC tests are performed and all QC acceptance criteria met for the 

Method 625.1 21 December 2014
analytes of interest with the combined extract as an integral part of this method, and 

provided that the analytes of interest are as reliably identified and quantified as 

when the extracts are analyzed separately. If doubt exists as to whether 

identification and quantitation will be affected by use of a combined extract, the 

fractions must be analyzed separately.

10.2.6 For each fraction or the combined fractions, assemble a Kuderna-Danish (K-D) 

concentrator by attaching a 10-mL concentrator tube to a 500-mL evaporative flask. Other 

concentration devices or techniques may be used in place of the K-D concentrator so long 

as the requirements in Section 8.2 are met.

10.2.7 For each fraction or the combined fractions, pour the extract through a solvent-rinsed 

drying column containing about 10 cm of anhydrous sodium sulfate, and collect the extract 

in the K-D concentrator. Rinse the Erlenmeyer flask and column with 20-30 mL of 

methylene chloride to complete the quantitative transfer.

10.2.8 Add one or two clean boiling chips and attach a three-ball Snyder column to the 

evaporative flask for each fraction (Section 10.2.7). Pre-wet the Snyder column by adding 

about 1 mL of methylene chloride to the top. Place the K-D apparatus on a hot water bath 

(60-65°C) so that the concentrator tube is partially immersed in the hot water, and the entire 

lower rounded surface of the flask is bathed with hot vapor. Adjust the vertical position of 

the apparatus and the water temperature as required to complete the concentration in 15-20 

minutes. At the proper rate of distillation, the balls of the column will actively chatter but 

the chambers will not flood with condensed solvent. When the apparent volume of liquid 

reaches 1 mL or other determined amount, remove the K-D apparatus from the water bath 

and allow to drain and cool for at least 10 minutes. Remove the Snyder column and rinse 

the flask and its lower joint into the concentrator tube with 1 - 2 mL of methylene chloride. 

A 5-mL syringe is recommended for this operation. If the sample will be cleaned up, 

reserve the K-D apparatus for concentration of the cleaned up extract. Adjust the volume 

to 5 mL with methylene chloride and proceed to Section 11 for cleanup; otherwise, further 

concentrate the extract for GC/MS analysis per Section 10.2.9 or 10.2.10. 

10.2.9 Micro Kuderna-Danish concentration – add another one or two clean boiling chips to the 

concentrator tube for each fraction and attach a two-ball micro-Snyder column. Pre-wet the 

Snyder column by adding about 0.5 mL of methylene chloride to the top. Place the K-D 

apparatus on a hot water bath (60-65°C) so that the concentrator tube is partially immersed 

in hot water. Adjust the vertical position of the apparatus and the water temperature as 

required to complete the concentration in 5-10 minutes. At the proper rate of distillation 

the balls of the column will actively chatter but the chambers will not flood with condensed 

solvent. When the apparent volume of liquid reaches about 1 mL or other determined 

amount, remove the K-D apparatus from the water bath and allow it to drain and cool for at 

least 10 minutes. Remove the Snyder column and rinse the flask and its lower joint into the 

concentrator tube with approximately 0.2 mL of or methylene chloride. Adjust the final 

volume to 1.0 mL or a volume appropriate to the sensitivity desired (e.g., to meet lower 

MDLs or for selected ion monitoring). Record the volume, stopper the concentrator tube 

and store refrigerated if further processing will not be performed immediately. If the 

extracts will be stored longer than two days, they should be transferred to fluoropolymerlined screw-cap vials and labeled base/neutral or acid fraction as appropriate. Mark the 

level of the extract on the vial so that solvent loss can be detected.

10.2.10 Nitrogen evaporation and solvent exchange – Extracts may be concentrated for analysis 

using nitrogen evaporation in place of micro K-D concentration (Section 10.2.9). Extracts 

Method 625.1 22 December 2014
that have been cleaned up using sulfur removal (Section 12.2) and are ready for analysis are 

exchanged into methylene chloride.

10.2.10.1 Transfer the vial containing the sample extract to the nitrogen evaporation 

(blowdown) device (Section 5.8). Lower the vial into the water bath and begin 

concentrating. If the more volatile analytes (Section 1.2) are to be concentrated, 

use room temperature for concentration; otherwise, a slightly elevated (e.g., 30 - 

45 °C) may be used. During the solvent evaporation process, keep the solvent 

level below the water level of the bath and do not allow the extract to become 

dry. Adjust the flow of nitrogen so that the surface of the solvent is just visibly 

disturbed. A large vortex in the solvent may cause analyte loss.

10.2.10.2 Extracts to be solvent exchanged – When the volume of the liquid is 

approximately 200 μL, add 2 to 3 mL of methylene chloride and continue 

concentrating to approximately 100 μL. Repeat the addition of solvent and 

concentrate once more. Adjust the final extract volume to be consistent with the 

volume extracted and the sensitivity desired. 

10.2.10.3 For extracts that have been cleaned up by GPC and that are to be concentrated to 

a nominal volume of 1 mL, adjust the final volume to compensate the GPC loss. 

For a 50% GPC loss, concentrate the extract to 1/2000 of the volume extracted. 

For example, if the volume extracted is 950 mL, adjust the final volume to 0.48 

mL. For extracts that have not been cleaned up by GPC and are to be 

concentrated to a nominal volume of 1.0 mL, adjust the final extract volume to 

1/1000 of the volume extracted. For example, if the volume extracted is 950 mL, 

adjust the final extract volume to 0.95 mL. 

Note: The difference in the volume fraction for an extract cleaned up by GPC 

accounts for the loss in GPC cleanup. Also, by preserving the ratio 

between the volume extracted and the final extract volume, the 

concentrations and detection limits do not need to be adjusted for 

differences in the volume extracted and the extract volume.

10.2.11 Transfer the concentrated extract to a vial with fluoropolymer-lined cap. Seal the vial and 

label with the sample number. Store in the dark at room temperature until ready for GC 

analysis. If GC analysis will not be performed on the same day, store the vial in the dark at 

≤6 °C. Analyze the extract by GC/MS per the procedure in Section 12. 

10.2.12 Determine the original sample volume by refilling the sample bottle to the mark and 

transferring the liquid to an appropriately sized graduated cylinder. For sample volumes on 

the order of 1000 mL, record the sample volume to the nearest 10 mL; for sample volumes 

on the order of 100 mL, record the volume to the nearest 1 mL. Sample volumes may also 

be determined by weighing the container before and after filling to the mark with water. 

10.3 Continuous liquid/liquid extraction (CLLE)

Note: With CLLE, phenol, 2,4-dimethyl phenol, and some other analytes may be preferentially 

extracted into the base-neutral fraction. Determine an analyte in the fraction in which it is 

identified and quantified most reliably. Also, the short-chain phthalate esters (e.g., 

dimethyl phthalate, diethyl phthalate) and some other compounds may hydrolyze during 

prolonged exposure to basic conditions required for continuous extraction, resulting in low 

Method 625.1 23 December 2014
recovery of these analytes. When these analytes are of interest, their recovery may be 

improved by performing the acid extraction first.

10.3.1 Use CLLE when experience with a sample from a given source indicates an emulsion 

problem, or when an emulsion is encountered during SFLLE. CLLE may be used for all 

samples, if desired. 

10.3.2 Mark the water meniscus on the side of the sample bottle for later determination of sample 

volume. Check the pH of the sample with wide-range pH paper and adjust to pH 11-13 

with sodium hydroxide solution. Transfer the sample to the continuous extractor. Pipet 

surrogate standard spiking solution (Section 6.8) into the sample. If the sample will be 

used for the LCS or MS or MSD, pipet the appropriate check sample concentrate (Section 

8.2.1 or 8.3.2) into the extractor. Mix well. Add 60 mL of methylene chloride to the 

sample bottle, seal, and shake for 30 seconds to rinse the inner surface. Transfer the 

solvent to the extractor.

10.3.3 Repeat the sample bottle rinse with an additional 50-100 mL portion of methylene chloride 

and add the rinse to the extractor.

10.3.4 Add a suitable volume of methylene chloride to the distilling flask (generally 200 - 500 

mL), add sufficient reagent water to ensure proper operation, and extract for 18 - 24 hours. 

A shorter or longer extraction time may be used if all QC acceptance criteria are met. Test 

and, if necessary, adjust the pH of the water during the second or third hour of the 

extraction. After extraction, allow the apparatus to cool, then detach the distilling flask. 

Dry, concentrate, and seal the extract per Sections 10.2.6 through 10.2.11. See the note at 

Section 10.2.5 regarding combining extracts of the base/neutral and acid fractions. 

10.3.5 Charge the distilling flask with methylene chloride and attach it to the continuous extractor. 

Carefully, while stirring, adjust the pH of the aqueous phase to less than 2 using sulfuric 

acid. Extract for 18 - 24 hours. A shorter or longer extraction time may be used if all QC 

acceptance criteria are met. Test and, if necessary, adjust the pH of the water during the 

second or third hour of the extraction. After extraction, allow the apparatus to cool, then 

detach the distilling flask. Dry, concentrate, and seal the extract per Sections 10.2.6 

through 10.2.11. Determine the sample volume per Section 10.2.12. 

11. Extract Cleanup

Note Cleanup may not be necessary for relatively clean samples (e.g., treated effluents, 

groundwater, drinking water). If particular circumstances require the use of a cleanup 

procedure, the laboratory may use any or all of the procedures below or any other 

appropriate procedure. Before using a cleanup procedure, the laboratory must demonstrate 

that the requirements of Section 8.1.2 can be met using the cleanup procedure as an integral 

part of this method.

11.1 Gel permeation chromatography (GPC) 

11.1.1 Calibration

11.1.1.1 Load the calibration solution (Section 6.12) into the sample loop 

Method 625.1 24 December 2014
11.1.1.2 Inject the calibration solution and record the signal from the detector. The 

elution pattern will be corn oil, bis(2-ethylhexyl) phthalate, pentachlorophenol, 

perylene, and sulfur.

11.1.1.3 Set the “dump time” to allow >85% removal of the corn oil and >85% collection 

of the phthalate.

11.1.1.4 Set the “collect time” to the peak minimum between perylene and sulfur. 

11.1.1.5 Verify calibration with the calibration solution after every 20 or fewer extracts. 

Calibration is verified if the recovery of the pentachlorophenol is greater than 

85%. If calibration is not verified, recalibrate using the calibration solution, and 

re-extract and clean up the preceding extracts using the calibrated GPC system.

11.1.2 Extract cleanup – GPC requires that the column not be overloaded. The column specified 

in this method is designed to handle a maximum of 0.5 g of high molecular weight material 

in a 5-mL extract. If the extract is known or expected to contain more than 0.5 g, the 

extract is split into fractions for GPC and the fractions are combined after elution from the 

column. The solids content of the extract may be obtained gravimetrically by evaporating 

the solvent from a 50-μL aliquot.

11.1.2.1 Filter the extract or load through the filter holder to remove particulates. Load 

the extract into the sample loop. The maximum capacity of the column is 0.5 - 

1.0 g. If necessary, split the extract into multiple aliquots to prevent column 

overload. 

11.1.2.2 Elute the extract using the calibration data determined in Section 11.1.1. Collect 

the eluate in the K-D apparatus reserved in Section 10.2.8. 

11.1.3 Concentrate the cleaned up extract per Sections 10.2.8 and 10.2.9 or 10.2.10. 

11.1.4 Rinse the sample loading tube thoroughly with methylene chloride between extracts to 

prepare for the next sample.

11.1.5 If a particularly dirty extract is encountered, run a methylene chloride blank through the 

system to check for carry-over.

11.2 Sulfur removal

Note: Separate procedures using copper or TBA sulfite are provided in this section for sulfur 

removal. They may be used separately or in combination, if desired.

11.2.1 Removal with copper (Reference 17) 

Note: If (1) an additional compound (Table 3) is to be determined; (2) sulfur is to be 

removed; (3) copper will be used for sulfur removal; and (4) a sulfur matrix is 

known or suspected to be present, the laboratory must demonstrate that the 

additional compound can be successfully extracted and treated with copper in the 

sulfur matrix. Some of the additional compounds (Table 3) are known not to be 

amenable to sulfur removal with copper (e.g. Atrazine and Diazinon).

Method 625.1 25 December 2014
11.2.1.1 Quantitatively transfer the extract from Section 10.2.8 to a 40- to 50-mL flask or 

bottle. If there is evidence of water in the concentrator tube after the transfer, 

rinse the tube with small portions of hexane:acetone (40:60) and add to the flask 

or bottle. Mark and set aside the concentrator tube for use in re-concentrating the 

extract.

11.2.1.2 Add 10 - 20 g of granular anhydrous sodium sulfate to the flask. Swirl to dry the 

extract.

11.2.1.3 Add activated copper (Section 6.13.1.4) and allow to stand for 30 - 60 minutes, 

swirling occasionally. If the copper does not remain bright, add more and swirl 

occasionally for another 30 - 60 minutes.

11.2.1.4 After drying and sulfur removal, quantitatively transfer the extract to a nitrogenevaporation vial or tube and proceed to Section 10.2.10 for nitrogen evaporation 

and solvent exchange, taking care to leave the sodium sulfate and copper in the 

flask.

11.2.2 Removal with TBA sulfite

11.2.2.1 Using small volumes of hexane, quantitatively transfer the extract to a 40- to 50-

mL centrifuge tube with fluoropolymer-lined screw cap.

11.2.2.2 Add 1 - 2 mL of TBA sulfite reagent (Section 6.13.2.4), 2 - 3 mL of 2-propanol, 

and approximately 0.7 g of sodium sulfite (Section 6.13.2.2) crystals to the tube. 

Cap and shake for 1 - 2 minutes. If the sample is colorless or if the initial color is 

unchanged, and if clear crystals (precipitated sodium sulfite) are observed, 

sufficient sodium sulfite is present. If the precipitated sodium sulfite disappears, 

add more crystalline sodium sulfite in approximately 0.5 g portions until a solid 

residue remains after repeated shaking.

11.2.2.3 Add 5 - 10 mL of reagent water and shake for 1 - 2 minutes. Centrifuge to settle 

the solids. 

11.2.2.4 Quantitatively transfer the hexane (top) layer through a small funnel containing a 

few grams of granular anhydrous sodium sulfate to a nitrogen-evaporation vial or 

tube and proceed to Section 10.2.10 for nitrogen evaporation and solvent 

exchange.

12. Gas Chromatography/Mass Spectrometry

12.1 Establish the operating conditions in Table 4 or 5 for analysis of a base/neutral or acid extract, 

respectively. For analysis of a combined extract (Section 10.2.5, note), use the operating conditions 

in Table 4. Included in these tables are retention times and MDLs that can be achieved under these 

conditions. Examples of the separations achieved are shown in Figure 2 for the combined extract. 

Alternative columns or chromatographic conditions may be used if the requirements of Section 8.2 

are met. Verify system performance per Section 13.

Method 625.1 26 December 2014
12.2 Analysis of a standard or extract 

12.2.1 Bring the standard or concentrated extract (Section 10.2.9 or 10.2.11) to room temperature 

and verify that any precipitate has redissolved. Verify the level on the extract and bring to 

the mark with solvent if required.

12.2.2 Add the internal standard solution (Section 6.9) to the extract. Mix thoroughly. 

12.2.3 Inject an appropriate volume of the sample extract or standard solution using split, splitless, 

solvent purge, large-volume, or on-column injection. If the sample is injected manually the 

solvent-flush technique should be used. The injection volume depends upon the technique 

used and the ability to meet MDLs or reporting limits for regulatory compliance. Injected 

volumes must be the same for standards and sample extracts. Record the volume injected 

to two significant figures.

12.2.3.1 Start the GC column oven program upon injection. Start MS data collection after 

the solvent peak elutes. Stop data collection after benzo(ghi)perylene elutes for 

the base/neutral or combined fractions, or after pentachlorophenol elutes for the 

acid fraction. Return the column to the initial temperature for analysis of the 

next standard solution or extract.

12.2.3.2 If the concentration of any analyte of interest exceeds the calibration range, either 

extract and analyze a smaller sample volume, or dilute and analyze the diluted 

extract after bringing the concentrations of the internal standards to the levels in 

the undiluted extract. 

12.2.4 Perform all qualitative and quantitative measurements as described in Sections 14 and 15. 

When standards and extracts are not being used for analyses, store them refrigerated at 

≤6°C protected from light in screw-cap vials equipped with un-pierced fluoropolymer-lined 

septa.

13. Performance tests

13.1 At the beginning of each 12-hour shift during which standards or extracts will be analyzed, perform 

the tests in Sections 13.2 - 13.7 to verify system performance. If DDT and/or endrin are to be 

determined, perform the decomposition test in Section 13.8. If an extract is concentrated for greater 

sensitivity (e.g., by SIM), all tests must be performed at levels consistent with the reduced extract 

volume. 

13.2 DFTPP – Inject the DFTPP standard (Section 6.10) and verify that the criteria for DFTPP in 

Section 7.2.1.1 and Table 9A (Reference 18) for a quadrupole MS, or Table 9B (Reference 19) for a 

time-of-flight MS, are met. It is not necessary to meet DFTPP criteria for SIM operation. 

13.3 GC resolution – There must be a valley between benzo(b)fluoranthene and benzo(k)fluoranthene at 

m/z 252, and the height of the valley must not exceed 25 percent of the shorter of the two peaks. 

13.4 Calibration verification – Verify calibration per Sections 7.3 and Table 6. 

13.5 Peak tailing – Verify the tailing factor specifications are met per Section 7.2.1.1. 

Method 625.1 27 December 2014
13.6 Laboratory control sample and blank – Analyze the extracts of the LCS and blank at the beginning 

of analyses of samples in the extraction batch (Section 3.1). The LCS must meet the requirements 

in Section 8.4, and the blank must meet the requirements in Section 8.5 before sample extracts may 

be analyzed. 

13.7 Matrix spike/matrix spike duplicate – Analyze the background sample for the MS/MSD and the MS 

and MSD after the blank (Section 8.3.2). Results for the MS/MSD must meet the requirements in 

Section 8.3 before a result for an analyte in any unspiked sample in the batch may be reported or 

used for permitting or regulatory compliance purposes. 

13.8 DDT/endrin decomposition test – If DDT and/or endrin analytes of interest, the DDT/endrin test 

(Section 8.8) must be performed and the QC acceptance criteria must be met before analyzing 

samples for DDT and/or endrin. 

14. Qualitative Identification

14.1 Identification is accomplished by comparison of data from analysis of a sample or blank with data 

stored in the GC/MS data system (Sections 5.6.5 and 7.2.1.2, and Tables 4 and 5). Identification of 

an analyte is confirmed per Sections 14.1.1 through 14.1.4.

14.1.1 The signals for all characteristic m/z’s stored in the data system for each analyte of interest 

must be present and must maximize within the same two consecutive scans.

14.1.2 Based on the relative retention time (RRT), the RRT for the analyte must be within ± 0.06 

of the RRT of the analyte in the calibration verification run at the beginning of the shift 

(Section 7.3 or 13.4). Relative retention time is used to establish the identification window 

because it compensates for small changes in the GC temperature program whereas the 

absolute retention time does not (see Section 6.9.3). 

Note: RRT is a unitless quantity (see Sec. 20.2), although some procedures refer to “RRT 

units” in providing the specification for the agreement between the RRT values in the 

sample and the calibration verification or other standard. 

14.1.3 Either (1) the background corrected EICP areas, or (2) the corrected relative intensities of 

the mass spectral peaks at the GC peak maximum, must agree within 50% to 200% (1/2 to 

2 times) for all m/z’s in the reference mass spectrum stored in the data system (Section 

7.2.1.2), or from a reference library. For example, if a peak has an intensity of 20% relative 

to the base peak, the analyte is identified if the intensity of the peak in the sample is in the 

range of 10% to 40% of the base peak.

14.1.4 The m/z’s present in the acquired mass spectrum for the sample that are not present in the 

reference mass spectrum must be accounted for by contaminant or background m/z’s. A 

reference library may be helpful to identify and account for background or contaminant 

m/z’s. If the acquired mass spectrum is contaminated, or if identification is ambiguous, an 

experienced spectrometrist (Section 1.7) must determine the presence or absence of the 

compound. 

14.2 Structural isomers that have very similar mass spectra can be identified only if the resolution 

between authentic isomers in a standard mix is acceptable. Acceptable resolution is achieved if the 

baseline to valley height between the isomers is less than 50% of the height of the shorter of the two 

peaks. Otherwise, structural isomers are identified as isomeric pairs.

Method 625.1 28 December 2014
15. Calculations 

15.1 When an analyte has been identified, quantitation of that analyte is based on the integrated 

abundance from the EICP of the primary characteristic m/z in Table 4 or 5. Calculate the 

concentration in the extract using the response factor (RF) determined in Section 7.2.2 and 

Equation 2. If the concentration of an analyte exceeds the calibration range, dilute the extract by 

the minimum amount to bring the concentration into the calibration range, and re-analyze the 

extract. Determine a dilution factor (DF) from the amount of the dilution. For example, if the 

extract is diluted by a factor of 2, DF = 2. 

Equation 2 

A

Cex (μg/mL)= s x Iis

Ais x RF

where:

Cex = Concentration of the analyte in the extract, in μg/mL, and the other terms are as defined in 

Equation 1 

Calculate the concentration of the analyte in the sample using the concentration in the extract, the 

extract volume, the sample volume, and the dilution factor, per Equation 3: 

Equation 3 

Cex x V 

Cs (μg/L) = ex x DF

Vs

where:

Cs = Concentration of the analyte in the sample

Cex = Concentration of the analyte in the extract, in μg/mL

Vex = Volume of extract (mL) 

Vs = Volume of sample (L) 

DF = Dilution factor

15.2 Reporting of results

As noted in Section 1.4.1, EPA has promulgated this method at 40 CFR Part 136 for use in 

wastewater compliance monitoring under the National Pollutant Discharge Elimination System 

(NPDES). The data reporting practices described here are focused on such monitoring needs and 

may not be relevant to other uses of the method. 

15.2.1 Report results for wastewater samples in μg/L without correction for recovery. (Other units 

may be used if required by in a permit.) Report all QC data with the sample results.

15.2.2 Reporting level

Unless otherwise specified in by a regulatory authority or in a discharge permit, results for 

analytes that meet the identification criteria are reported down to the concentration of the 

ML established by the laboratory through calibration of the instrument (see Section 7.3.2 

and the glossary for the derivation of the ML). EPA considers the terms “reporting limit,” 

“quantitation limit,” and “minimum level” to be synonymous. 

15.2.2.1 Report a result for each analyte in each sample, blank, or standard at or above the 

ML to 3 significant figures. Report a result for each analyte found in each 

Method 625.1 29 December 2014
sample below the ML as “<ML,” or as required by the regulatory authority or 

permit.. Results are reported without blank subtraction unless requested or 

required by a regulatory authority or in a permit. In this case, both the sample 

result and the blank results must be reported together.

15.2.2.2 In addition to reporting results for samples and blanks separately, the 

concentration of each analyte in a blank associated with the sample may be 

subtracted from the result for that sample, but only if requested or required by a 

regulatory authority or in a permit. In this case, both the sample result and the 

blank results must be reported together.

15.2.2.3 Report a result for an analyte found in a sample or extract that has been diluted at 

the least dilute level at which the area at the quantitation m/z is within the 

calibration range(i.e., above the ML for the analyte) and the MS/MSD recovery 

and RPD are within their respective QC acceptance criteria (Table 6). This may 

require reporting results for some analytes from different analyses.

15.2.3 Results from tests performed with an analytical system that is not in control (i.e., that does 

not meet acceptance criteria for all of QC tests in this method) must not be reported or 

otherwise used for permitting or regulatory compliance purposes, but do not relieve a 

discharger or permittee of reporting timely results. If the holding time would be exceeded 

for a re-analysis of the sample, the regulatory/control authority should be consulted for 

disposition. 

16. Method Performance

16.1 The basic version of this method was tested by 15 laboratories using reagent water, drinking water, 

surface water, and industrial wastewaters spiked at six concentrations over the range 5-1300 μg/L 

(Reference 2). Single operator precision, overall precision, and method accuracy were found to be 

directly related to the concentration of the analyte and essentially independent of the sample matrix. 

Linear equations to describe these relationships are presented in Table 7.

16.2 As noted in Sec. 1.1, this method was validated through an interlaboratory study conducted more 

than 29 years ago. However, the fundamental chemistry principles used in this method remain 

sound and continue to apply. 

16.3 A chromatogram of the combined acid/base/neutral calibration standard is shown in Figure 2. 

17. Pollution Prevention

17.1 Pollution prevention encompasses any technique that reduces or eliminates the quantity or toxicity 

of waste at the point of generation. Many opportunities for pollution prevention exist in laboratory 

operations. EPA has established a preferred hierarchy of environmental management techniques 

that places pollution prevention as the management option of first choice. Whenever feasible, the 

laboratory should use pollution prevention techniques to address waste generation. When wastes 

cannot be reduced at the source, the Agency recommends recycling as the next best option.

17.2 The analytes in this method are used in extremely small amounts and pose little threat to the 

environment when managed properly. Standards should be prepared in volumes consistent with 

laboratory use to minimize the disposal of excess volumes of expired standards. This method 

Method 625.1 30 December 2014
utilizes significant quantities of methylene chloride. Laboratories are encouraged to recover and 

recycle this and other solvents during extract concentration. 

17.3 For information about pollution prevention that may be applied to laboratories and research 

institutions, consult Less is Better: Laboratory Chemical Management for Waste Reduction, 

available from the American Chemical Society’s Department of Governmental Relations and 

Science Policy, 1155 16th Street NW, Washington DC 20036, 202/872-4477. 

18. Waste Management 

18.1 The laboratory is responsible for complying with all Federal, State, and local regulations governing 

waste management, particularly the hazardous waste identification rules and land disposal 

restrictions, and to protect the air, water, and land by minimizing and controlling all releases from 

fume hoods and bench operations. Compliance is also required with any sewage discharge permits 

and regulations. An overview of requirements can be found in Environmental Management Guide 

for Small Laboratories (EPA 233-B-98-001). 

18.2 Samples at pH <2, or pH >12 are hazardous and must be neutralized before being poured down a 

drain, or must be handled and disposed of as hazardous waste.

18.3 Many analytes in this method decompose above 500 oC. Low-level waste such as absorbent paper, 

tissues, and plastic gloves may be burned in an appropriate incinerator. Gross quantities of neat or 

highly concentrated solutions of toxic or hazardous chemicals should be packaged securely and 

disposed of through commercial or governmental channels that are capable of handling these types 

of wastes.

18.4 For further information on waste management, consult The Waste Management Manual for 

Laboratory Personnel and Less is Better-Laboratory Chemical Management for Waste Reduction, 

available from the American Chemical Society’s Department of Government Relations and Science 

Policy, 1155 16th Street NW, Washington, DC 20036, 202/872-4477. 

19. References

1. “Sampling and Analysis Procedures for Screening of Industrial Effluents for Priority Pollutants,” 

U.S. Environmental Protection Agency, Environmental Monitoring and Support Laboratory, 

Cincinnati, Ohio 45268, March 1977, Revised April 1977. 

2. “EPA Method Study 30, Method 625, Base/Neutrals, Acids, and Pesticides,” EPA 600/4-84-053, 

National Technical Information Service, PB84-206572, Springfield, Virginia 22161, June 1984.

3. 40 Code of Federal Regulations 136, appendix B. 

4. Olynyk, P., Budde, W.L. and Eichelberger, J.W. “Method Detection Limit for Methods 624 and 

625,” Unpublished report, May 14, 1980. 

5. Annual Book of ASTM Standards, Volume 11.02, D3694-96, “Standard Practices for Preparation 

of Sample Containers and for Preservation of Organic Constituents,” American Society for Testing 

and Materials, Philadelphia.

Method 625.1 31 December 2014
6. Solutions to Analytical Chemistry Problems with Clean Water Act Methods, EPA 821-R-07-002, 

March 2007. 

7. “Carcinogens-Working With Carcinogens,” Department of Health, Education, and Welfare, Public 

Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, 

Publication No. 77-206, August 1977. 

8. “OSHA Safety and Health Standards, General Industry,” (29 CFR Part 1910), Occupational Safety 

and Health Administration, OSHA 2206 (Revised, January 1976). 

9. “Safety in Academic Chemistry Laboratories,” American Chemical Society Publication, Committee 

on Chemical Safety, 7th Edition, 2003. 

10. http://en.wikipedia.org/wiki/Coefficient_of_determination (accessed on 09/10/2013) 

11. 40 Code of Federal Regulations 136.6(b)(4)(x) 

12. 40 Code of Federal Regulations 136.6(b)(2)(i) 

13. Protocol for EPA Approval of New Methods for Organic and Inorganic Analytes in Wastewater and 

Drinking Water (EPA-821-B-98-003) March 1999 

14. Provost, L.P. and Elder, R.S. “Interpretation of Percent Recovery Data,” American Laboratory, 15, 

58-63 (1983). (The value 2.44 used in the equation in Section 8.3.3 is two times the value 1.22 

derived in this report.) 

15. ASTM Annual Book of Standards, Part 31, D3370-76. “Standard Practices for Sampling Water,” 

American Society for Testing and Materials, Philadelphia.

16. 40 Code of Federal Regulations 136.3(a), Table IB, Chlorine – Total Residual

17. “Manual of Analytical Methods for the Analysis of Pesticides in Human and Environmental 

Samples,” EPA-600/8-80-038, U.S. Environmental Protection Agency, Health Effects Research 

Laboratory, Research Triangle Park, North Carolina.

18. Eichelberger, J.W., Harris, L.E., and Budde, W.L. “Reference Compound to Calibrate Ion 

Abundance Measurement in Gas Chromatography-Mass Spectrometry,” Analytical Chemistry, 47, 

995 (1975). 

19. Letter of approval of acceptance criteria for DFTPP for time-of-flight mass spectrometers from 

William A. Telliard and Herb Brass of EPA to Jack Cochran of LECO Corporation, February 9, 

2005. 

Method 625.1 32 December 2014
20. Tables

Table 1 – 1 Non Pesticide/PCB Base/Neutral Extractables

Analyte CAS Registry MDL4 ML5

Acenaphthene 83-32-9 1.9 5.7

Acenaphthylene 208-96-8 3.5 10.5

Anthracene 120-12-7 1.9 5.7

Benzidine 2 92-87-5 44 132

Benzo(a)anthracene 56-55-3 7.8 23.4

Benzo(a)pyrene 50-32-8 2.5 7.5

Benzo(b)fluoranthene 205-99-2 4.8 14.4

Benzo(k)fluoranthene 207-08-9 2.5 7.5

Benzo(ghi)perylene 191-24-2 4.1 12.3

Benzyl butyl phthalate 85-68-7 2.5 7.5

bis(2-Chloroethoxy)methane 111-91-1 5.3 15.9

bis(2-Ethylhexyl)phthalate 117-81-7 2.5 7.5

bis(2-Chloroisopropyl) ether (2,2’-Oxybis(1-chloropropane)) 108-60-1 5.7 17.1

4-Bromophenyl phenyl ether 101-55-3 1.9 5.7

2-Chloronaphthalene 91-58-7 1.9 5.7

4-Chlorophenyl phenyl ether 7005-72-3 4.2 12.6

Chrysene 218-01-9 2.5 7.5

Dibenz(a,h)anthracene 53-70-3 2.5 7.5

Di-n-butylphthalate 84-74-2 2.5 7.5

3,3’-Dichlorobenzidine 91-94-1 16.5 49.5

Diethyl phthalate 84-66-2 1.9 5.7

Dimethyl phthalate 131-11-3 1.6 4.8

2,4-Dinitrotoluene 121-14-2 5.7 17.1

2,6-Dinitrotoluene 606-20-2 1.9 5.7

Di-n-octylphthalate 117-84-0 2.5 7.5

Fluoranthene 206-44-0 2.2 6.6

Fluorene 86-73-7 1.9 5.7

Hexachlorobenzene 118-74-1 1.9 5.7

Hexachlorobutadiene 87-68-3 0.9 2.7

Hexachloroethane 67-72-1 1.6 4.8

Indeno(1,2,3-cd)pyrene 193-39-5 3.7 11.1

Isophorone 78-59-1 2.2 6.6

Naphthalene 91-20-3 1.6 4.8

Nitrobenzene 98-95-3 1.9 5.7

N-Nitrosodi-n-propylamine 3 621-64-7 -- --

Phenanthrene 85-01-8 5.4 16.2

Pyrene 129-00-0 1.9 5.7

1,2,4-Trichlorobenzene 120-82-1 1.9 5.7

1 All analytes in this table are Priority Pollutants (40 CFR 423, Appendix A) 2 Included for tailing factor testing

3 See Section 1.2

4 MDL values from the 1984 promulgated version of Method 624 5 ML = Minimum Level – see Glossary for definition and derivation

Method 625.1 33 December 2014
Table 2--Acid Extractables1

Analyte CAS Registry MDL3 ML4

4-Chloro-3-methylphenol 59-50-7 3.0 9.0

2-Chlorophenol 95-57-8 3.3 9.9

2,4-Dichlorophenol 120-83-2 2.7 8.1

2,4-Dimethylphenol 105-67-9 2.7 8.1

2,4-Dinitrophenol 51-28-5 42 126

2-Methyl-4,6-dinitrophenol 534-52-1 24 72

2-Nitrophenol 88-75-5 3.6 10.8

4-Nitrophenol 100-02-7 2.4 7.2

Pentachlorophenol 2 87-86-5 3.6 10.8

Phenol 108-95-2 1.5 4.5

2,4,6-Trichlorophenol 88-06-2 2.7 8.1

1 All analytes in this table are Priority Pollutants (40 CFR 423, Appendix A) 2 See Section 1.2; included for tailing factor testing 3 MDL values from the 1984 promulgated version of Method 624 4 ML = Minimum Level – see Glossary for definition and derivation

Method 625.1 34 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Acetophenone 98-86-2

2-Acetylaminofluorene 53-96-3

1-Acetyl-2-thiourea 591-08-2

Alachlor 15972-60-8

Aldrin 3 309-00-2 1.9 5.7

Ametryn 834-12-8

2-Aminoanthraquinone 117-79-3

Aminoazobenzene 60-09-3

4-Aminobiphenyl 92-67-1

3-Amino-9-ethylcarbazole 132-32-1

Anilazine 101-05-3

Aniline 62-53-3

o-Anisidine 90-04-0

Aramite 140-57-8

Atraton 1610-17-9

Atrazine 1912-24-9

Azinphos-methyl 86-50-0

Barban 101-27-9

Benzanthrone 82-05-3

Benzenethiol 108-98-5

Benzidine 3,4 92-87-5 44 132

Benzoic acid 65-85-0

2,3-Benzofluorene 243-17-4

p-Benzoquinone 106-51-4

Benzyl alcohol 100-51-6

alpha-BHC3,4 319-84-6

beta-BHC 3 319-85-7 3.1 9.3

gamma-BHC (Lindane) 3,4 58-89-8 4.2 12.6

delta-BHC 3 319-86-8

Biphenyl 92-52-4

Bromacil 314-40-9

2-Bromochlorobenzene 694-80-4

3-Bromochlorobenzene 108-39-2

Bromoxynil 1689-84-5

Butachlor 2318-4669

Butylate 2008-41-5

n-C10 (n-decane) 124-18-5

n-C12 (n-undecane) 112-40-2

n-C14 (n-tetradecane) 629-59-4

n-C16 (n-hexadecane) 544-76-3

n-C18 (n-octadecane) 593-45-3

n-C20 (n-eicosane) 112-95-8

n-C22 (n-docosane) 629-97-0

n-C24 (n-tetracosane) 646-31-1

n-C26 (n-hexacosane) 630-01-3

n-C28 (n-octacosane) 630-02-4

n-C30 (n-triacontane) 638-68-6

Captafol 2425-06-1

Method 625.1 35 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Captan 133-06-2

Carbaryl 63-25-2

Carbazole 86-74-8

Carbofuran 1563-66-2

Carboxin 5234-68-4

Carbophenothion 786-19-6

Chlordane 3,5 57-74-9

bis(2-Chloroethyl) ether 3,4 111-44-4 5.7 17.1

Chloroneb 2675-77-6

4-Chloroaniline 106-47-8

Chlorobenzilate 510-15-6

Chlorfenvinphos 470-90-6

4-Chloro-2-methylaniline 95-69-2

3-(Chloromethyl)pyridine hydrochloride 6959-48-4

4-Chloro-2-nitroaniline 89-63-4

Chlorpropham 101-21-3

Chlorothalonil 1897-45-6

1-Chloronaphthalene 90-13-1

3-Chloronitribenzene 121-73-3

4-Chloro-1,2-phenylenediamine 95-83-0

4-Chloro-1,3-phenylenediamine 5131-60-2

2-Chlorobiphenyl 2051-60-7

Chlorpyrifos 2921-88-2

Coumaphos 56-72-4

m+p-Cresol 65794-96-9

o-Cresol 95-48-7

p-Cresidine 120-71-8

Crotoxyphos 7700-17-6

2-Cyclohexyl-4,6-dinitro-phenol 131-89-5

Cyanazine 21725-46-2

Cycloate 1134-23-2

p-Cymene 99-87-6

Dacthal (DCPA) 1861-32-1

4,4’-DDD 3 72-54-8 2.8 8.4

4,4’-DDE 3 72-55-9 5.6 16.8

4,4’-DDT 3 50-29-3 4.7 14.1

Demeton-O 298-03-3

Demeton-S 126-75-0

Diallate (cis or trans) 2303-16-4

2,4-Diaminotoluene 95-80-7

Diazinon 333-41-5

Dibenz(a,j)acridine 224-42-0

Dibenzofuran 132-64-9

Dibenzo(a,e)pyrene 192-65-4

Dibenzothiophene 132-65-0

1,2-Dibromo-3-chloropropane 96-12-8

3,5-Dibromo-4-hydroxybenzonitrile 1689-84-5

2,6-Di-tert-butyl-p-benzoquinone 719-22-2

Method 625.1 36 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Dichlone 117-80-6

2,3-Dichloroaniline 608-27-5

2,3-Dichlorobiphenyl 16605-91-7

2,6-Dichloro-4-nitroaniline 99-30-9

2,3-Dichloronitrobenzene 3209-22-1

1,3-Dichloro-2-propanol 96-23-1

2,6-Dichlorophenol 120-83-2

Dichlorvos 62-73-7

Dicrotophos 141-66-2

Dieldrin 3 60-57-1 2.5 7.5

1,2:3,4-Diepoxybutane 1464-53-5

Di(2-ethylhexyl) adipate 103-23-1

Diethylstilbestrol 56-53-1

Diethyl sulfate 64-67-5

Dilantin (5,5-Diphenylhydantoin) 57-41-0

Dimethoate 60-51-5

3,3’-Dimethoxybenzidine 119-90-4

Dimethylaminoazobenzene 60-11-7

7,12-Dimethylbenz(a)anthracene 57-97-6

3,3’-Dimethylbenzidine 119-93-7

N,N-Dimethylformamide 68-12-2

3,6-Dimethylphenathrene 1576-67-6

alpha, alpha-Dimethylphenethylamine 122-09-8

Dimethyl sulfone 67-71-0

1,2-Dinitrobenzene 528-29-0

1,3-Dinitrobenzene 99-65-0

1,4-Dinitrobenzene 100-25-4

Dinocap 39300-45-3

Dinoseb 88-85-7

Diphenylamine 122-39-4

Diphenyl ether 101-84-8

1,2-Diphenylhydrazine 122-66-7

Diphenamid 957-51-7

Diphenyldisulfide 882-33-7

Disulfoton 298-04-4

Disulfoton sulfoxide 2497-07-6

Disulfoton sulfone 2497-06-5

Endosulfan I 3,4 959-98-8

Endosulfan II 3,4 33213-65-9

Endosulfan sulfate 3 1031-07-8 5.6 16.8

Endrin 3,4 72-20-8

Endrin aldehyde 3,4 7421-93-4

Endrin ketone 3,4 53494-70-5

EPN 2104-64-5

EPTC 759-94-4

Ethion 563-12-2

Ethoprop 13194-48-4

Ethyl carbamate 51-79-6

Method 625.1 37 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Ethyl methanesulfonate 65-50-0

Ethylenethiourea 96-45-7

Etridiazole 2593-15-9

Ethynylestradiol-3-methyl ether 72-33-3

Famphur 52-85-7

Fenamiphos 22224-92-6

Fenarimol 60168-88-9

Fensulfothion 115-90-2

Fenthion 55-38-9

Fluchloralin 33245-39-5

Fluridone 59756-60-4

Heptachlor 3 76-44-8 1.9 5.7

Heptachlor epoxide 3 1024-57-3 2.2 6.6

2,2’,3,3’,4,4’,6-Heptachlorobiphenyl 52663-71-5

2,2’,4,4’,5’,6-Hexachlorobiphenyl 60145-22-4

Hexachlorocyclopentadiene 3,4 77-47-4

Hexachlorophene 70-30-4

Hexachloropropene 1888-71-7

Hexamethylphosphoramide 680-31-9

Hexanoic acid 142-62-1

Hexazinone 51235-04-2

Hydroquinone 123-31-9

Isodrin 465-73-6

2-Isopropylnapthalene 2027-17-0

Isosafrole 120-58-1

Kepone 143-50-0

Leptophos 21609-90-5

Longifolene 475-20-7

Malachite green 569-64-2

Malathion 121-75-5

Maleic anhydride 108-31-6

Merphos 150-50-5

Mestranol 72-33-3

Methapyrilene 91-80-5

Methoxychlor 72-43-5

2-Methylbenzothioazole 120-75-2

3-Methylcholanthrene 56-49-5

4,4’-Methylenebis(2-chloroaniline) 101-14-4

4,4’-Methylenebis(N,N-dimethylaniline) 101-61-1

4,5-Methylenephenanthrene 203-64-5

1-Methylfluorene 1730-37-6

Methyl methanesulfonate 66-27-3

2-Methylnaphthalene 91-57-6

Methylparaoxon 950-35-6

Methyl parathion 298-00-0

1-Methylphenanthrene 832-69-9

2-(Methylthio)benzothiazole 615-22-5

Metolachlor 5218-45-2

Method 625.1 38 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Metribuzin 21087-64-9

Mevinphos 7786-34-7

Mexacarbate 315-18-4

MGK 264 113-48-4

Mirex 2385-85-5

Molinate 2212-67-1

Monocrotophos 6923-22-4

Naled 300-76-5

Napropamide 15299-99-7

1,4-Naphthoquinone 130-15-4

1-Naphthylamine 134-32-7

2-Naphthylamine 91-59-8

1,5-Naphthalenediamine 2243-62-1

Nicotine 54-11-5

5-Nitroacenaphthene 602-87-9

2-Nitroaniline 88-74-4

3-Nitroaniline 99-09-2

4-Nitroaniline 100-01-6

5-Nitro-o-anisidine 99-59-2

4-Nitrobiphenyl 92-93-3

Nitrofen 1836-75-5

5-Nitro-o-toluidine 99-55-8

Nitroquinoline-1-oxide 56-57-5

N-Nitrosodi-n-butylamine 4 924-16-3

N-Nitrosodiethylamine 4 55-18-5

N-Nitrosodimethylamine 3,4 62-75-9

N-Nitrosodiphenylamine 3,4 86-30-6

N-Nitrosomethylethylamine 4 10595-95-6

N-Nitrosomethylphenylamine 4 614-00-6

N-Nitrosomorpholine 4 59-89-2

N-Nitrosopiperidine 4 100-75-5

N-Nitrosopyrrolidine 4 930-55-2

trans-Nonachlor 39765-80-5

Norflurazon 27314-13-2

2,2’,3,3’,4,5’,6,6’-Octachlorobiphenyl 40186-71-8

Octamethyl pyrophosphoramide 152-16-9

4,4’-Oxydianiline 101-80-4

Parathion 56-38-2

PCB-1016 3,5 12674-11-2

PCB-1221 3,5 11104-28-2 30 90

PCB-1232 3,5 11141-16-5

PCB-1242 3,5 53469-21-9

PCB-1248 3,5 12672-29-6

PCB-1254 3,5 11097-69-1 36 108

PCB-1260 3,5 11098-82-5

PCB-1268 3,5 11100-14-4

Pebulate 1114-71-2

Pentachlorobenzene 608-93-5

Method 625.1 39 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Pentachloronitrobenzene 82-68-8

2,2’,3,4’,6-Pentachlorobiphenyl 68194-05-8

Pentachloroethane 76-01-7

Pentamethylbenzene 700-12-9

Perylene 198-55-0

Phenacetin 62-44-2

cis-Permethrin 61949-76-6

trans-Permethrin 61949-77-7

Phenobarbital 50-06-6

Phenothiazene 92-84-2

1,4-Phenylenediamine 624-18-0

1-Phenylnaphthalene 605-02-7

2-Phenylnaphthalene 612-94-2

Phorate 298-02-2

Phosalone 2310-18-0

Phosmet 732-11-6

Phosphamidon 13171-21-6

Phthalic anhydride 85-44-9

alpha-Picoline (2-Methylpyridine) 109-06-8

Piperonyl sulfoxide 120-62-7

Prometon 1610-18-0

Prometryn 7287-19-6

Pronamide 23950-58-5

Propachlor 1918-16-7

Propazine 139-40-2

Propylthiouracil 51-52-5

Pyridine 110-86-1

Resorcinol (1,3-Benzenediol) 108-46-3

Safrole 94-59-7

Simazine 122-34-9

Simetryn 1014-70-6

Squalene 7683-64-9

Stirofos 22248-79-9

Strychnine 57-24-9

Styrene 100-42-5

Sulfallate 95-06-7

Tebuthiuron 34014-18-1

Terbacil 5902-51-2

Terbufos 13071-79-9

Terbutryn 886-50-0

alpha-Terpineol 98-55-5

1,2,4,5-Tetrachlorobenzene 95-94-3

2,2’,4,4’-Tetrachlorobiphenyl 2437-79-8

2,3,7,8-Tetrachlorodibenzo-p-dioxin 1746-01-6

2,3,4,6-Tetrachlorophenol 58-90-2

Tetrachlorvinphos 22248-79-9

Tetraethyl dithiopyrophosphate 3689-24-5

Tetraethyl pyrophosphate 107-49-3

Method 625.1 40 December 2014
Table 3 – Additional Extractable Analytes1, 2

Analyte CAS Registry MDL6 ML7

Thianaphthene (2,3-Benzothiophene) 95-15-8

Thioacetamide 62-55-5

Thionazin 297-97-2

Thiophenol (Benzenethiol) 108-98-5

Thioxanthone 492-22-8

Toluene-1,3-diisocyanate 26471-62-5

Toluene-2,4-diisocyanate 584-84-9

o-Toluidine 95-53-4

Toxaphene 3,5 8001-35-2

Triadimefon 43121-43-3

1,2,3-Trichlorobenzene 87-61-6

2,4,5-Trichlorobiphenyl 15862-07-4

2,3,6-Trichlorophenol 933-75-5

2,4,5-Trichlorophenol 95-95-4

Tricyclazole 41814-78-2

Trifluralin 1582-09-8

1,2,3-Trimethoxybenzene 634-36-6

2,4,5-Trimethylaniline 137-17-7

Trimethyl phosphate 512-56-1

Triphenylene 217-59-4

Tripropyleneglycolmethyl ether 20324-33-8

1,3,5-Trinitrobenzene 99-35-4

Tris(2,3-dibromopropyl) phosphate 126-72-7

Tri-p-tolyl phosphate 78-32-0

O,O,O-Triethyl phosphorothioate 126-68-1

Trithiane 291-29-4

Vernolate 1929-77-7

1 Compounds that have been demonstrated amenable to extraction and gas chromatography 2 Determine each analyte in the fraction that gives the most accurate result 3 Priority Pollutant (40 CFR 423, Appendix A) 4 See Section 1.2 5 These compounds are mixtures of various isomers 6 MDL values from the 1984 promulgated version of Method 624 7 ML = Minimum Level – see Glossary for definition and derivation

Method 625.1 41 December 2014
Table 4 – Chromatographic Conditions and Characteristic m/z’s for Base/Neutral Extractables

Analyte

Retention 

Time 

(sec) 1 

Characteristic m/z’s

Electron impact ionization Chemical ionization

Primary Second Second Methane

N-Nitrosodimethylamine 385 42 74 44 ... ... ...

bis(2-Chloroethyl) ether 704 93 63 95 63 107 109

bis(2-Chloroisopropyl) ether 799 45 77 79 77 135 137

Hexachloroethane 823 117 201 199 199 201 203

N-Nitrosodi-n-propylamine 830 130 42 101 ... ... ...

Nitrobenzene 849 77 123 65 124 152 164

Isophorone 889 82 95 138 139 167 178

bis(2-Chloroethoxy) methane 939 93 95 123 65 107 137

1,2,4-Trichlorobenzene 958 180 182 145 181 183 209

Naphthalene 967 128 129 127 129 157 169

Hexachlorobutadiene 1006 225 223 227 223 225 227

Hexachlorocyclopentadiene 1142 237 235 272 235 237 239

2-Chloronaphthalene 1200 162 164 127 163 191 203

Acenaphthylene 1247 152 151 153 152 153 181

Dimethyl phthalate 1273 163 194 164 151 163 164

2,6-Dinitrotoluene 1300 165 89 121 183 211 223

Acenaphthene 1304 154 153 152 154 155 183

2,4-Dinitrotoluene 1364 165 63 182 183 211 223

Fluorene 1401 166 165 167 166 167 195

4-Chlorophenyl phenyl ether 1409 204 206 141 ... ... ...

Diethyl phthalate 1414 149 177 150 177 223 251

N-Nitrosodiphenylamine 1464 169 168 167 169 170 198

4-Bromophenyl phenyl ether 1498 248 250 141 249 251 277

alpha-BHC 1514 183 181 109 ... ... ...

Hexachlorobenzene 1522 284 142 249 284 286 288

beta-BHC 1544 183 181 109 ... ... ...

gamma-BHC 1557 181 183 109 ... ... ...

Phenanthrene 1583 178 179 176 178 179 207

Anthracene 1592 178 179 176 178 179 207

delta-BHC 1599 183 109 181 ... ... ...

Heptachlor 1683 100 272 274 ... ... ...

Di-n-butyl phthalate 1723 149 150 104 149 205 279

Aldrin 1753 66 263 220

Fluoranthene 1817 202 101 100 203 231 243

Heptachlor epoxide 1820 353 355 351 ... ... ...

gamma-Chlordane 1834 373 375 377 ... ... ...

Pyrene 1852 202 101 100 203 231 243

Benzidine 2 1853 184 92 185 185 213 225

alpha-Chlordane 1854 373 375 377 ... ... ...

Endosulfan I 1855 237 339 341 ... ... ...

4,4’-DDE 1892 246 248 176 ... ... ...

Dieldrin 1907 79 263 279 ... ... ...

Endrin 1935 81 263 82 ... ... ...

Endosulfan II 2014 237 339 341 ... ... ...

4,4’-DDD 2019 235 237 165 ... ... ...

Endrin aldehyde 2031 67 345 250 ... ... ...

Method 625.1 42 December 2014
Table 4 – Chromatographic Conditions and Characteristic m/z’s for Base/Neutral Extractables

Analyte

Retention 

Time 

(sec) 1 

Characteristic m/z’s

Electron impact ionization Chemical ionization

Primary Second Second Methane

Butyl benzyl phthalate 2060 149 91 206 149 299 327

Endosulfan sulfate 2068 272 387 422 ... ... ...

4,4’-DDT 2073 235 237 165 ... ... ...

Chrysene 2083 228 226 229 228 229 257

3,3’-Dichlorobenzidine 2086 252 254 126 ... ... ...

Benzo(a)anthracene 2090 228 229 226 228 229 257

bis(2-Ethylhexyl) phthalate 2124 149 167 279 149 ... ...

Di-n-octyl phthalate 2240 149 43 57 ... ... ...

Benzo(b)fluoranthene 2286 252 253 125 252 253 281

Benzo(k)fluoranthene 2293 252 253 125 252 253 281

Benzo(a)pyrene 2350 252 253 125 252 253 281

Indeno(1,2,3-cd) pyrene 2650 276 138 277 276 277 305

Dibenz(a,h)anthracene 2660 278 139 279 278 279 307

Benzo(ghi)perylene 2750 276 138 277 276 277 305

Toxaphene ... 159 231 233 ... ... ...

PCB 1016 ... 224 260 294 ... ... ...

PCB 1221 ... 190 224 260 ... ... ...

PCB 1232 ... 190 224 260 ... ... ...

PCB 1242 ... 224 260 294 ... ... ...

PCB 1248 ... 294 330 262 ... ... ...

PCB 1254 ... 294 330 362 ... ... ...

PCB 1260 ... 330 362 394 ... ... ...

1 Column: 30 m x 0.25 mm ID; 94% methyl, 5% phenyl, 1% vinyl bonded phase fused silica capillary

Conditions: 5 min at 30°C; 30 - 280 at 8°C per min; isothermal at 280°C until benzo(ghi)perylene elutes

 Gas velocity: 30 cm/sec at 30°C (at constant pressure).

2 See Section 1.2; included for tailing factor testing

Method 625.1 43 December 2014
Table 5 – Chromatographic Conditions and Characteristic m/z’s for Acid Extractables

Analyte

Retention 

Time (sec) 1

Characteristic m/z’s

Electron impact ionization Chemical ionization

Prime Second Second Methane

2-Chlorophenol 705 128 64 130 129 131 157

Phenol 700 94 65 66 95 123 135

2-Nitrophenol 900 139 65 109 140 168 122

2,4-Dimethylphenol 924 122 107 121 123 151 163

2,4-Dichlorophenol 947 162 164 98 163 165 167

4-Chloro-3-methylphenol 1091 142 107 144 143 171 183

2,4,6-Trichlorophenol 1165 196 198 200 197 199 201

2,4-Dinitrophenol 1325 184 63 154 185 213 225

4-Nitrophenol 1354 65 139 109 140 168 122

2-Methyl-4,6-dinitrophenol 1435 198 182 77 199 227 239

Pentachlorophenol 1561 266 264 268 267 265 269

Column: 30 m x 0.25 mm ID; 94% methyl, 5% phenyl, 1% vinyl bonded phase fused silica capillary

Conditions: 5 min at 30°C; 30 - 250 at 8°C per min; isothermal at 280°C until pentachlorophenol elutes

Gas velocity: 30 cm/sec at 30°C (at constant pressure)

Method 625.1 44 December 2014
Table 6 – QC Acceptance Criteria – Method 625 1

X Range for

P, Ps (%) 3

Limit for 

Analyte RPD (%)

Range for Q 

(%) 2

Limit for s 

(%) 3

Range for

(%) 3

Acenaphthene 70-130 29 60-132 47-145 48

Acenaphthylene 60-130 45 54-126 33-145 74

Aldrin 7-152 39 7-152 D-166 81

Anthracene 58-130 40 43-120 27-133 66

Benzo(a)anthracene 42-133 32 42-133 33-143 53

Benzo(b)fluoranthene 42-140 43 42-140 24-159 71

Benzo(k)fluoranthene 25-146 38 25-146 11-162 63

Benzo(a)pyrene 32-148 43 32-148 17-163 72

Benzo(ghi)perylene 13-195 61 D-195 D-219 97

Benzyl butyl phthalate 43-140 36 D-140 D-152 60

beta-BHC 42-131 37 42-131 24-149 61

delta-BHC D-130 77 D-120 D-120 129

bis(2-Chloroethyl)ether 52-130 65 43-126 12-158 108

bis(2-Chloroethoxy)methane 52-164 32 49-165 33-184 54

bis(2-Chloroisopropyl) ether 63-139 46 63-139 36-166 76

bis(2-Ethylhexyl) phthalate 43-137 50 29-137 8-158 82

4-Bromophenyl phenyl ether 70-130 26 65-120 53-127 43

2-Chloronaphthalene 70-130 15 65-120 60-120 24

4-Chlorophenyl phenyl ether 57-145 36 38-145 25-158 61

Chrysene 44-140 53 44-140 17-168 87

4,4’-DDD D-135 56 D-135 D-145 93

4,4’-DDE 19-130 46 19-120 4-136 77

4,4’-DDT D-171 81 D-171 D-203 135

Dibenz(a,h)anthracene 13-200 75 D-200 D-227 126

Di-n-butyl phthalate 52-130 28 8-120 1-120 47

3,3’-Dichlorobenzidine 18-213 65 8-213 D-262 108

Dieldrin 70-130 38 44-119 29-136 62

Diethyl phthalate 47-130 60 D-120 D-120 100

Dimethyl phthalate 50-130 110 D-120 D-120 183

2,4-Dinitrotoluene 53-130 25 48-127 39-139 42

2,6-Dinitrotoluene 68-137 29 68-137 50-158 48

Di-n-octyl phthalate 21-132 42 19-132 4-146 69

Endosulfan sulfate D-130 42 D-120 D-120 70

Endrin aldehyde D-189 45 D-189 D-209 75

Fluoranthene 47-130 40 43-121 26-137 66

Fluorene 70-130 23 70-120 59-121 38

Heptachlor D-172 44 D-172 D-192 74

Heptachlor epoxide 70-130 61 71-120 26-155 101

Hexachlorobenzene 38-142 33 8-142 D-152 55

Hexachlorobutadiene 68-130 38 38-120 24-120 62

Hexachloroethane 55-130 32 55-120 40-120 52

Indeno(1,2,3-cd)pyrene 13-151 60 D-151 D-171 99

Isophorone 52-180 56 47-180 21-196 93

Naphthalene 70-130 39 36-120 21-133 65

Nitrobenzene 54-158 37 54-158 35-180 62

N-Nitrosodi-n-propylamine 59-170 52 14-198 D-230 87

Method 625.1 45 December 2014
Table 6 – QC Acceptance Criteria – Method 625 1

Analyte

Range for Q 

(%) 2 

Limit for s 

(%) 3

Range for X

(%) 3

Range for

P, Ps (%) 3

Limit for 

RPD (%)

PCB-1260 19-130 77 19-130 D-164 128

Phenanthrene 67-130 24 65-120 54-120 39

Pyrene 70-130 30 70-120 52-120 49

1,2,4-Trichlorobenzene 61-130 30 57-130 44-142 50

4-Chloro-3-methylphenol 68-130 44 41-128 22-147 73

2-Chlorophenol 55-130 37 36-120 23-134 61

2,4-Dichlorophenol 64-130 30 53-122 39-135 50

2,4-Dimethylphenol 58-130 35 42-120 32-120 58

2,4-Dinitrophenol 39-173 79 D-173 D-191 132

2-Methyl-4,6-dinitrophenol 56-130 122 53-130 D-181 203

2-Nitrophenol 61-163 33 45-167 29-182 55

4-Nitrophenol 35-130 79 13-129 D-132 131

Pentachlorophenol 42-152 52 38-152 14-176 86

Phenol 48-130 39 17-120 5-120 64

2,4,6-Trichlorophenol 69-130 35 52-129 37-144 58

1 Acceptance criteria are based upon method performance data in Table 7 and from EPA Method 1625. Where 

necessary, limits for recovery have been broadened to assure applicability to concentrations below those used 

to develop Table 7. 2 Test concentration = 100 μg/mL 3 Test concentration = 100 μg/L

Q = Calibration verification (Sections 7.3.1 and 13.4)

s = Standard deviation for four recovery measurements in the DOC test (Section 8.2.4).

X = Average recovery for four recovery measurements in the DOC test (Section 8.2.4).

P, Ps = MS/MSD recovery (Section 8.3.2, Section 8.4.2).

RPD = MS/MSD relative percent difference (RPD; Section 8.3.3).

D = Detected; result must be greater than zero.

Method 625.1 46 December 2014
Table 7 – Precision and Recovery as Functions of Concentration – Method 625 1

Analyte Recovery, X' (μg/L)

Single analyst 

precision, sr' (μg/L)

Overall precision,

S' (μg/L)

Acenaphthene 0.96C+0.19 0.15 X -0.12 0.21 X -0.67

Acenaphthylene 0.89C+0.74 0.24 X -1.06 0.26 X -0.54

Aldrin 0.78C+1.66 0.27 X -1.28 0.43 X +1.13

Anthracene 0.80C+0.68 0.21 X -0.32 0.27 X -0.64

Benzo(a)anthracene 0.88C-0.60 0.15 X +0.93 0.26 X -0.28

Benzo(b)fluoranthene 0.93C-1.80 0.22 X +0.43 0.29 X +0.96

Benzo(k)fluoranthene 0.87C-1.56 0.19 X +1.03 0.35 X +0.40

Benzo(a)pyrene 0.90C-0.13 0.22 X +0.48 0.32 X +1.35

Benzo(ghi)perylene 0.98C-0.86 0.29 X +2.40 0.51 X -0.44

Benzyl butyl phthalate 0.66C-1.68 0.18 X +0.94 0.53 X +0.92

beta-BHC 0.87C-0.94 0.20 X -0.58 0.30 X -1.94

delta-BHC 0.29C-1.09 0.34 X +0.86 0.93 X -0.17

bis(2-Chloroethyl)ether 0.86C-1.54 0.35 X -0.99 0.35 X +0.10

bis(2-Chloroethoxy)methane 1.12C-5.04 0.16 X +1.34 0.26 X +2.01

bis(2-Chloroisopropyl)ether 1.03C-2.31 0.24 X +0.28 0.25 X +1.04

bis(2-Ethylhexyl)phthalate 0.84C-1.18 0.26 X +0.73 0.36 X +0.67

4-Bromophenyl phenyl ether 0.91C-1.34 0.13 X +0.66 0.16 X +0.66

2-Chloronaphthalene 0.89C+0.01 0.07 X +0.52 0.13 X +0.34

4-Chlorophenyl phenyl ether 0.91C+0.53 0.20 X -0.94 0.30 X -0.46

Chrysene 0.93C-1.00 0.28 X +0.13 0.33 X -0.09

4,4’-DDD 0.56C-0.40 0.29 X -0.32 0.66 X -0.96

4,4’-DDE 0.70C-0.54 0.26 X -1.17 0.39 X -1.04

4,4’-DDT 0.79C-3.28 0.42 X +0.19 0.65 X -0.58

Dibenz(a,h)anthracene 0.88C+4.72 0.30 X +8.51 0.59 X +0.25

Di-n-butyl phthalate 0.59C+0.71 0.13 X +1.16 0.39 X +0.60

3,3’-Dichlorobenzidine 1.23C-12.65 0.28 X +7.33 0.47 X +3.45

Dieldrin 0.82C-0.16 0.20 X -0.16 0.26 X -0.07

Diethyl phthalate 0.43C+1.00 0.28 X +1.44 0.52 X +0.22

Dimethyl phthalate 0.20C+1.03 0.54 X +0.19 1.05 X -0.92

2,4-Dinitrotoluene 0.92C-4.81 0.12 X +1.06 0.21 X +1.50

2,6-Dinitrotoluene 1.06C-3.60 0.14 X +1.26 0.19 X +0.35

Di-n-octyl phthalate 0.76C-0.79 0.21 X +1.19 0.37 X +1.19

Endosulfan sulfate 0.39C+0.41 0.12 X +2.47 0.63 X -1.03

Endrin aldehyde 0.76C-3.86 0.18 X +3.91 0.73 X -0.62

Fluoranthene 0.81C+1.10 0.22 X +0.73 0.28 X -0.60

Fluorene 0.90C-0.00 0.12 X +0.26 0.13 X +0.61

Heptachlor 0.87C-2.97 0.24 X -0.56 0.50 X -0.23

Heptachlor epoxide 0.92C-1.87 0.33 X -0.46 0.28 X +0.64

Hexachlorobenzene 0.74C+0.66 0.18 X -0.10 0.43 X -0.52

Hexachlorobutadiene 0.71C-1.01 0.19 X +0.92 0.26 X +0.49

Hexachloroethane 0.73C-0.83 0.17 X +0.67 0.17 X +0.80

Method 625.1 47 December 2014
Table 7 – Precision and Recovery as Functions of Concentration – Method 625 1

Analyte Recovery, X' (μg/L)

Single analyst 

precision, sr' (μg/L)

Overall precision,

S' (μg/L)

Indeno(1,2,3-cd)pyrene 0.78C-3.10 0.29 X +1.46 0.50 X +0.44

Isophorone 1.12C+1.41 0.27 X X

X X

X

+0.77 0.33 +0.26

Naphthalene 0.76C+1.58 0.21 -0.41 0.30 -0.68

Nitrobenzene 1.09C-3.05 0.19 +0.92 0.27 X +0.21

N-Nitrosodi-n-propylamine 1.12C-6.22 0.27 X +0.68 0.44 X +0.47

PCB-1260 0.81C-10.86 0.35 X +3.61 0.43 X +1.82

Phenanthrene 0.87C-0.06 0.12 X +0.57 0.15 X +0.25

Pyrene 0.84C-0.16 0.16 X +0.06 0.15 X +0.31

1,2,4-Trichlorobenzene 0.94C-0.79 0.15 X +0.85 0.21 X +0.39

4-Chloro-3-methylphenol 0.84C+0.35 0.23 X +0.75 0.29 X +1.31

2-Chlorophenol 0.78C+0.29 0.18 X +1.46 0.28 X +0.97

2,4-Dichlorophenol 0.87C+0.13 0.15 X +1.25 0.21 X +1.28

2,4-Dimethylphenol 0.71C+4.41 0.16 X +1.21 0.22 X +1.31

2,4-Dinitrophenol 0.81C-18.04 0.38 X +2.36 0.42 X +26.29

2-Methyl-4,6-Dinitrophenol 1.04C-28.04 0.05 X +42.29 0.26 X +23.10

2-Nitrophenol 1.07C-1.15 0.16 X +1.94 0.27 X +2.60

4-Nitrophenol 0.61C-1.22 0.38 X +2.57 0.44 X +3.24

Pentachlorophenol 0.93C+1.99 0.24 X +3.03 0.30 X +4.33

Phenol 0.43C+1.26 0.26 X +0.73 0.35 X

X X

+0.58

2,4,6-Trichlorophenol 0.91C-0.18 0.16 +2.22 0.22 +1.81

1 Regressions based on data from Reference 2

X' = Expected recovery for one or more measurements of a sample containing a concentration of C, in μg/L.

sr' = Expected single analyst standard deviation of measurements at an average concentration found of X , in μg/L.

S' = Expected interlaboratory standard deviation of measurements at an average concentration found of X , in 

μg/L.

C = True value for the concentration, in μg/L.

X = Average recovery found for measurements of samples containing a concentration of C, in μg/L.

Method 625.1 48 December 2014
Table 8 – Suggested Internal and Surrogate Standards

Range for Surrogate Recovery (%) 1

Base/neutral fraction Calibration verification Recovery from samples

Acenaphthalene-d8 66 - 152 33 - 168

Acenaphthene-d10 71 - 141 30 - 180

Aniline-d5

Anthracene-d10 58 - 171 23 - 142

Benzo(a)anthracene-d12 28 - 357 22 - 329

Benzo(a)pyrene-d12 32 - 194 32 - 194

4-Chloroaniline-d4 1 - 145 1 - 145

bis(2-Chloroethyl) ether-d8 52 - 194 25 - 222

Chrysene-d12 23 - 290 23 - 290

Decafluorobiphenyl

4,4’-Dibromobiphenyl

4,4’-Dibromooctafluorobiphenyl

1,4-Dichlorobenzene-d4 65 - 153 11 - 245

2,2’-Difluorobiphenyl

Dimethyl phthalate-d6 47 - 211 1 - 500

Fluoranthene-d10 47 - 215 30 - 187

Fluorene-d10 61 - 164 38 - 172

4-Fluoroaniline

1-Fluoronaphthalene

2-Fluoronaphthalene

2-Methylnaphthalene-d10 50 - 150 50 - 150

Naphthalene-d8 71 - 141 22 - 192

Nitrobenzene-d5 46 - 219 15 - 314

2,3,4,5,6-Pentafluorobiphenyl

Perylene-d12

Phenanthrene-d10 67 - 149 34 - 168

Pyrene-d10 48 - 210 28 - 196

Pyridine-d5

Acid fraction

2-Chlorophenol-d4 55 - 180 33 - 180

2,4-Dichlorophenol-d3 64 - 157 34 - 182

4,6-Dinitro-2-methylphenol-d2 56 - 177 22 - 307

2-Fluorophenol

4-Methylphenol-d8 25 - 111 25 - 111

2-Nitrophenol-d4 61 - 163 37 - 163

4-Nitrophenol-d4 35 - 287 6 - 500

Pentafluorophenol

2-Perfluoromethylphenol

Phenol-d5 48 - 208 8 - 424

1 Recovery from samples is the wider of the criteria in the CLP SOW for organics or in Method 1625

Method 625.1 49 December 2014
Table 9A – DFTPP Key m/z’s and Abundance Criteria for Quadrupole Instruments 1

m/z Abundance criteria

51 30 - 60 percent of m/z 198

68 Less than 2 percent of m/z 69

70 Less than 2 percent of m/z 69

127 40 - 60 percent of base peak m/z 198

197 Less than 1 percent of m/z 198

198 Base peak, 100 percent relative abundance

199 5 - 9 percent of m/z 198

275 10 - 30 percent of m/z 198

365 Greater than 1 percent of m/z 198

441 Present but less than m/z 443

442 40 - 100 percent of m/z 198

443 17 - 23 percent of m/z 442

1 Criteria in these tables are for quadrupole and time-of-flight instruments. Alternative tuning criteria may be used 

for other instruments, provided method performance is not adversely affected.

Table 9B – DFTPP Key m/z’s and Abundance Criteria for Time-of-flight Instruments 1

m/z Abundance criteria

51 10 - 85 percent of the base peak

68 Less than 2 percent of m/z 69

70 Less than 2 percent of m/z 69

127 10 - 80 percent of the base peak

197 Less than 2 percent of Mass 198

198 Base peak, or greater than 50% of m/z 442

199 5 - 9 percent of m/z 198

275 10 - 60 percent of the base peak

365 Greater than 0.5 percent of m/z 198

441 Less than 150 percent of m/z 443

442 Base peak or greater than 30 percent of m/z 198

443 15 - 24 percent of m/z 442

1 Criteria in these tables are for quadrupole and time-of-flight instruments. Alternative tuning criteria may be used 

for other instruments, provided method performance is not adversely affected.

Method 625.1 50 December 2014
21. Figures

Figure 1 Tailing factor calculation

Method 625.1 51 December 2014
Figure 2 Chromatogram of combined acid/base/neutral standard 

Method 625.1 52 December 2014
22. Glossary

These definitions and purposes are specific to this method but have been conformed to common usage 

to the extent possible.

22.1 Units of weight and measure and their abbreviations

22.1.1 Symbols

oC degrees Celsius

μg microgram

μL microliter

< less than

> greater than

≤ less than or equal to

% percent

22.1.2 Abbreviations (in alphabetical order)

cm centimeter

g gram

h hour

ID inside diameter

in. inch

L liter

M Molecular ion

m mass or meter

mg milligram

min minute

mL milliliter

mm millimeter

ms millisecond

m/z mass-to-charge ratio

N normal; gram molecular weight of solute divided by hydrogen equivalent of solute, 

per liter of solution

ng nanogram

pg picogram

ppb part-per-billion

ppm part-per-million

ppt part-per-trillion

psig pounds-per-square inch gauge

22.2 Definitions and acronyms (in alphabetical order)

Analyte – A compound or mixture of compounds (e.g., PCBs) tested for by this method. The analytes are 

listed in Tables 1 - 3.

Batch – See Extraction

Blank – An aliquot of reagent water that is treated exactly as a sample including exposure to all glassware, 

equipment, solvents, reagents, internal standards, and surrogates that are used with samples. The blank is 

Method 625.1 53 December 2014
used to determine if analytes or interferences are present in the laboratory environment, the reagents, or the 

apparatus.

Calibration – The process of determining the relationship between the output or response of a measuring 

instrument and the value of an input standard. Historically, EPA has referred to a multi-point calibration 

as the “initial calibration,” to differentiate it from a single-point calibration verification.

Calibration standard – A solution prepared from stock solutions and/or a secondary standards and containing 

the analytes of interest, surrogates, and internal standards. The calibration standard is used to calibrate the 

response of the GC/MS instrument against analyte concentration.

Calibration verification standard – The mid-point calibration standard used to verify calibration. See 

Sections 7.3 and 13.4.

Descriptor – In SIM, the beginning and ending retention times for the RT window, the m/z’s sampled in 

the RT window, and the dwell time at each m/z.

Extracted ion current profile (EICP) – The line described by the signal at a given m/z.

Extraction Batch – A set of up to 20 field samples (not including QC samples) started through the 

extraction process on a given 12-hour shift (Section 3.1). Each extraction batch must be accompanied by 

a blank (Section 8.5), a laboratory control sample (LCS, Section 8.4), and a matrix spike and duplicate 

(MS/MSD; Section 8.3), resulting in a minimum of five analyses (1 sample, 1 blank, 1 LCS, 1 MS, and 1 

MSD) and a maximum of 24 analyses (20 field samples, 1 blank, 1 LCS, 1 MS, and 1 MSD) for the 

batch. If greater than 20 samples are to be extracted in a 12-hour shift, the samples must be separated into 

extraction batches of 20 or fewer samples.

Field Duplicates – Two samples collected at the same time and place under identical conditions, and 

treated identically throughout field and laboratory procedures. Results of analyses the field duplicates 

provide an estimate of the precision associated with sample collection, preservation, and storage, as well 

as with laboratory procedures.

Field blank – An aliquot of reagent water or other reference matrix that is placed in a sample container in 

the field, and treated as a sample in all respects, including exposure to sampling site conditions, storage, 

preservation, and all analytical procedures. The purpose of the field blank is to determine if the field or 

sample transporting procedures and environments have contaminated the sample.

GC – Gas chromatograph or gas chromatography

Internal standard – A compound added to an extract or standard solution in a known amount and used as a 

reference for quantitation of the analytes of interest and surrogates. In this method the internal standards 

are stable isotopically labeled analogs of selected method analytes (Table 8). Also see Internal standard 

quantitation.

Internal standard quantitation – A means of determining the concentration of an analyte of interest (Tables 

1 - 3) by reference to a compound not expected to be found in a sample.

DOC – Initial demonstration of capability (Section 8.2); four aliquots of reagent water spiked with the 

analytes of interest and analyzed to establish the ability of the laboratory to generate acceptable precision 

and recovery. An DOC is performed prior to the first time this method is used and any time the method or 

instrumentation is modified.

Method 625.1 54 December 2014
Laboratory Control Sample (LCS; laboratory fortified blank; Section 8.4) – An aliquot of reagent water 

spiked with known quantities of the analytes of interest and surrogates. The LCS is analyzed exactly like a 

sample. Its purpose is to assure that the results produced by the laboratory remain within the limits specified 

in this method for precision and recovery.

Laboratory fortified sample matrix – See Matrix spike

Laboratory reagent blank – A blank run on laboratory reagents; e.g., methylene chloride (Section 11.1.5).

Matrix spike (MS) and matrix spike duplicate (MSD) (laboratory fortified sample matrix and duplicate) –

Two aliquots of an environmental sample to which known quantities of the analytes of interest and 

surrogates are added in the laboratory. The MS/MSD are prepared and analyzed exactly like a field 

sample. Their purpose is to quantify any additional bias and imprecision caused by the sample matrix. 

The background concentrations of the analytes in the sample matrix must be determined in a separate 

aliquot and the measured values in the MS/MSD corrected for background concentrations.

May – This action, activity, or procedural step is neither required nor prohibited.

May not – This action, activity, or procedural step is prohibited.

Method blank – See blank.

Method detection limit (MDL) – A detection limit determined by the procedure at 40 CFR 136, Appendix 

B. The MDLs determined by EPA in the original version of the method are listed in Tables 1, 2 and 3. As 

noted in Sec. 1.5, use the MDLs in Tables 1, 2, and 3 in conjunction with current MDL data from the 

laboratory actually analyzing samples to assess the sensitivity of this procedure relative to project objectives 

and regulatory requirements (where applicable).

Minimum level (ML) – The term “minimum level” refers to either the sample concentration equivalent to 

the lowest calibration point in a method or a multiple of the method detection limit (MDL), whichever is 

higher. Minimum levels may be obtained in several ways: They may be published in a method; they may be 

based on the lowest acceptable calibration point used by a laboratory; or they may be calculated by 

multiplying the MDL in a method, or the MDL determined by a laboratory, by a factor of 3. For the 

purposes of NPDES compliance monitoring, EPA considers the following terms to be synonymous: 

“quantitation limit,” “reporting limit,” and “minimum level.” 

MS – Mass spectrometer or mass spectrometry, or matrix spike (a QC sample type)

MSD – Matrix spike duplicate (a QC sample type)

Must – This action, activity, or procedural step is required.

m/z – The ratio of the mass of an ion (m) detected in the mass spectrometer to the charge (z) of that ion

Preparation blank – See blank

Quality control check sample (QCS) – See Laboratory Control Sample

Reagent water – Water demonstrated to be free from the analytes of interest and potentially interfering 

substances at the MDLs for the analytes in this method.

Method 625.1 55 December 2014
Regulatory compliance limit (or regulatory concentration limit) – A limit on the concentration or amount 

of a pollutant or contaminant specified in a nationwide standard, in a permit, or otherwise established by a 

regulatory/control authority.

Relative retention time (RRT) – The ratio of the retention time of an analyte to the retention time of its 

associated internal standard. RRT compensates for small changes in the GC temperature program that 

can affect the absolute retention times of the analyte and internal standard. RRT is a unitless quantity.

Relative standard deviation (RSD) – The standard deviation times 100 divided by the mean. Also termed 

“coefficient of variation.”

RF – Response factor. See Section 7.2.2.

RSD – See relative standard deviation

Safety Data Sheet (SDS) – Written information on a chemical’s toxicity, health hazards, physical properties, 

fire, and reactivity, including storage, spill, and handling precautions that meet the requirements of OSHA, 

29 CFR 1910.1200(g) and Appendix D. United Nations Globally Harmonized System of Classification and 

Labelling of Chemicals (GHS), third revised edition, United Nations, 2009.

Selected Ion Monitoring (SIM) - An MS technique in which a few m/z’s are monitored. When used with 

gas chromatography, the m/z’s monitored are usually changed periodically throughout the 

chromatographic run, to correlate with the characteristic m/z’s of the analytes, surrogates, and internal 

standards as they elute from the chromatographic column. The technique is often used to increase 

sensitivity and minimize interferences.

Signal-to-noise ratio (S/N) – The height of the signal as measured from the mean (average) of the noise to 

the peak maximum divided by the width of the noise.

Should – This action, activity, or procedural step is suggested but not required.

SPE – Solid-phase extraction; an extraction technique in which an analyte is extracted from an aqueous 

solution by passage over or through a material capable of reversibly adsorbing the analyte. Also termed 

liquid-solid extraction.

Stock solution – A solution containing an analyte that is prepared using a reference material traceable to 

EPA, the National Institute of Science and Technology (NIST), or a source that will attest to the purity, 

authenticity, and concentration of the standard.

Surrogate – A compound unlikely to be found in a sample, and which is spiked into sample in a known 

amount before extraction or other processing, and is quantitated with the same procedures used to 

quantify other sample components. The purpose of the surrogate is to monitor method performance with 

each sample.

Method 625.1 56 December 2014