Method 624.1 – Purgeables 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-14-014

Method 624.1 i December 2014
METHOD 624.1 – PURGEABLES BY GC/MS

1. Scope and Application

1.1 This method is for determination of purgeable 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 previous protocols (References 1 - 3), on 

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

validation study (Reference 4). 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 Table 1. The method may be extended to determine the 

analytes listed in Table 2; however, poor purging efficiency or gas chromatography of some of 

these analytes may make quantitative determination difficult. For example, an elevated temperature 

may be required to purge some analytes from water. If an elevated temperature is used, calibration 

and all quality control (QC) tests must be performed at the elevated temperature. EPA encourages 

the use of this method to determine additional compounds amenable to purge-and-trap GC/MS.

1.3 The large number of analytes in Tables 1 and 2 of this method makes testing difficult if all analytes 

are determined simultaneously. Therefore, it is necessary to determine and perform QC tests for 

“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 Table 1 must be determined, at a minimum, and QC testing must be performed for these 

analytes. The analytes in Table 1 and some of the analytes in Table 2 have been identified as Toxic 

Pollutants (40 CFR 401.15), expanded to a list of Priority Pollutants (40 CFR 423, appendix A). 

1.4 Method detection limits (MDLs; Reference 5) for the analytes in Table 1 are listed in that table. 

These MDLs were determined in reagent water (Reference 6). 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 version 

promulgated in 1984 (40 FR 43234). The MDL for a specific wastewater may differ from those 

listed, depending on the nature of interferences in the sample matrix. 

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 in Section 13.2 are focused on such monitoring needs and 

may not be relevant to other uses of the method. 

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

(see the glossary in Section 20). Table 1 contains MDL values and ML values for many of 

the analytes. The MDL for an analyte in a specific wastewater may differ from that listed 

in Table 1, depending upon the nature of interferences in the sample matrix. 

1.5 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. 

1.5.1 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. 

Method 624.1 1 December 2014
1.5.2 Any modification beyond those expressly allowed at 40 CFR 136.6 or in Section 8.1.2 of 

this method shall be considered a major modification that is subject to application and 

approval of an alternate test procedure under 40 CFR 136.4 and 136.5.

1.5.3 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).

1.6 This method is restricted to use by or under the supervision of analysts experienced in the operation 

of a purge-and-trap system and a gas chromatograph/mass spectrometer and in the interpretation of 

mass spectra. Each analyst must demonstrate the ability to generate acceptable results with this 

method using the procedure in Section 8.2. 

1.7 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 gas is bubbled through a measured volume of water in a specially-designed purging chamber 

(Figure 1). The purgeables are efficiently transferred from the aqueous phase to the vapor phase. 

The vapor is swept through a sorbent trap where the purgeables are trapped (Figure 2). After 

purging is completed, the trap is heated and backflushed with the gas to desorb the purgeables onto 

a gas chromatographic column (Figures 3 and 4). The column is temperature programmed to 

separate the purgeables which are then detected with a mass spectrometer.

2.2 Different sample sizes in the range of 5 - 25 mL are allowed in order to meet differing sensitivity 

requirements. Calibration and QC samples must have the same volume as field samples.

3. Interferences

3.1 Impurities in the purge gas, organic compounds outgassing from the plumbing ahead of the trap, 

and solvent vapors in the laboratory account for the majority of contamination problems. The 

analytical system must be demonstrated to be free from contamination under the conditions of the 

analysis by analyzing blanks as described in Section 8.5. Fluoropolymer tubing, fittings, and thread 

sealant should be used to avoid contamination. 

3.2 Samples can be contaminated by diffusion of volatile organics (particularly fluorocarbons and 

methylene chloride) through the septum seal into the sample during shipment and storage. Protect 

samples from sources of volatiles during collection, shipment, and storage. A reagent water field 

blank carried through sampling and analysis can serve as a check on such contamination.

3.3 Contamination by carry-over can occur whenever high level and low level samples are analyzed 

sequentially. To reduce the potential for carry-over, the purging device and sample syringe must be 

rinsed with reagent water between sample analyses. Whenever an unusually concentrated sample is 

encountered, it should be followed by an analysis of a blank to check for cross contamination. For 

samples containing large amounts of water-soluble materials, suspended solids, high boiling 

compounds or high purgeable levels, it may be necessary to wash the purging device with a 

detergent solution, rinse it with distilled water, and then dry it in a 105°C oven between analyses. 

The trap and other parts of the system are also subject to contamination; therefore, frequent bakeout 

and purging of the entire system may be required. Screening samples at high dilution may prevent 

introduction of contaminants into the system. 

Method 624.1 2 December 2014
4. Safety

4.1 The toxicity or carcinogenicity of each reagent used in this method has 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. 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: benzene; carbon tetrachloride; chloroform; 1,4-

dichlorobenzene; 1,2-dichloroethane; 1,2-dichloropropane; methylene chloride; tetrachloroethylene; 

trichloroethylene; and vinyl chloride. Primary standards of these 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 5.3.1.2). 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 cited for illustration purposes only. No 

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

materials other than those specified here. Demonstration of equivalent performance that 

meets the requirements of this method is the responsibility of the laboratory. Suppliers for

equipment and materials in this method may be found through an on-line search. 

5.1 Sampling equipment for discrete sampling. 

5.1.1 Vial – 25 or 40 mL capacity, or larger, with screw cap with a hole in the center (Pierce 

#13075 or equivalent). Unless pre-cleaned, detergent wash, rinse with tap and reagent 

water, and dry at 105°C before use.

5.1.2 Septum – Fluoropolymer-faced silicone (Pierce #12722 or equivalent). Unless pre-cleaned, 

detergent wash, rinse with tap and reagent water, and dry at 105 ± 5°C for one hour before 

use.

5.2 Purge-and-trap system – The purge-and-trap system consists of three separate pieces of equipment: 

A purging device, trap, and desorber. Several complete systems are commercially available. Any 

system that meets the performance requirements in this method may be used.

5.2.1 The purging device should accept 5- to 25-mL samples with a water column at least 3 cm 

deep. The purge gas must pass though the water column as finely divided bubbles. The 

purge gas must be introduced no more than 5 mm from the base of the water column. The 

purging device illustrated in Figure 1 meets these design criteria. Purge devices of a 

different volume may be used so long as the performance requirements in this method are 

met.

Method 624.1 3 December 2014
5.2.2 The trap should be at least 25 cm long and have an inside diameter of at least 0.105 in. The 

trap should be packed to contain the following minimum lengths of adsorbents: 1.0 cm of 

methyl silicone coated packing (Section 6.3.2), 15 cm of 2,6-diphenylene oxide polymer 

(Section 6.3.1), and 8 cm of silica gel (Section 6.3.3). The minimum specifications for the 

trap are illustrated in Figure 2. A trap with different dimensions and packing materials is 

acceptable so long as the performance requirements in this method are met.

5.2.3 The desorber should be capable of rapidly heating the trap to the temperature necessary to 

desorb the analytes of interest, and of maintaining this temperature during desorption. The 

trap should not be heated higher than the maximum temperature recommended by the 

manufacturer. The desorber illustrated in Figure 2 meets these design criteria.

5.2.4 The purge-and-trap system may be assembled as a separate unit or coupled to a gas 

chromatograph as illustrated in Figures 3 and 4. 

5.3 GC/MS system

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

programmable gas chromatograph and all required accessories, including syringes and 

analytical columns. Autosamplers designed for purge-and-trap analysis of volatiles also 

may be used. 

5.3.1.1 Injection port – Volatiles interface, split, splitless, temperature programmable 

split/splitless (PTV), large volume, on-column, backflushed, or other. 

5.3.1.2 Carrier gas – Data in the tables in this method were obtained using helium carrier 

gas. If another carrier gas is used, analytical conditions may need to be adjusted 

for optimum performance, and calibration and all QC tests must be performed 

with the alternate carrier gas. See Section 4.3 for precautions regarding the use 

of hydrogen as a carrier gas.

5.3.2 GC column – See the footnote to Table 3. Other columns or column systems may be used 

provided all requirements in this method are met.

5.3.3 Mass spectrometer – Capable of repetitively scanning from 35-260 Daltons (amu) every 2 

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

ionization mode, and producing a mass spectrum which meets all criteria in Table 4 when 

50 ng or less of 4-bromofluorobenzene (BFB) is injected through the GC inlet. If acrolein, 

acrylonitrile, chloromethane, and vinyl chloride are to be determined, it may be necessary 

to scan from below 25 Daltons to measure the peaks in the 26 - 35 Dalton range for reliable 

identification.

5.3.4 GC/MS interface – Any GC to MS interface that meets all performance requirements in this 

method may be used. 

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

continuous acquisition and storage of mass spectra 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.

Method 624.1 4 December 2014
5.4 Syringes – Graduated, 5 - 25 mL, glass hypodermic with Luerlok tip, compatible with the purging 

device.

5.5 Micro syringes – Graduated, 25 - 1000 μL, with 0.006 in. ID needle. 

5.6 Syringe valve – Two-way, with Luer ends 

5.7 Syringe – 5 mL, gas-tight with shut-off valve.

5.8 Bottle – 15 mL, screw-cap, with Teflon cap liner. 

5.9 Balance – Analytical, capable of accurately weighing 0.0001 g. 

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. It may be generated by passing 

deionized water, distilled water, or tap water through a carbon bed, passing the water through a 

water purifier, or heating the water to between 90 and 100°C while bubbling contaminant free gas 

through it for approximately 1 hour. While still hot, transfer the water to screw-cap bottles and seal 

with a fluoropolymer-lined cap. 

6.2 Sodium thiosulfate – (ACS) Granular.

6.3 Trap materials

6.3.1 2,6-Diphenylene oxide polymer – Tenax, 60/80 mesh, chromatographic grade, or 

equivalent. 

6.3.2 Methyl silicone packing – 3% OV-1 on Chromosorb-W, 60/80 mesh, or equivalent. 

6.3.3 Silica gel – 35/60 mesh, Davison, Grade-15 or equivalent. 

Other trap materials are acceptable if performance requirements in this method are met.

6.4 Methanol – Demonstrated to be free from the target analytes and potentially interfering compounds.

6.5 Stock standard solutions – 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. Stock solution concentrations alternate to those 

below may be used. Prepare stock standard solutions in methanol using assayed liquids or gases as 

appropriate. Because some of the compounds in this method are known to be toxic, 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:

6.5.1 Place about 9.8 mL of methanol in a 10-mL ground-glass-stoppered volumetric flask. 

Allow the flask to stand, unstoppered, for about 10 minutes or until all alcohol wetted 

surfaces have dried. Weigh the flask to the nearest 0.1 mg.

6.5.2 Add the assayed reference material. 

Method 624.1 5 December 2014
6.5.2.1 Liquids – Using a 100 μL syringe, immediately add two or more drops of assayed 

reference material to the flask. Be sure that the drops fall directly into the 

alcohol without contacting the neck of the flask. Reweigh, dilute to volume, 

stopper, then mix by inverting the flask several times. Calculate the 

concentration in μg/μL from the net gain in weight.

6.5.2.2 Gases – To prepare standards for any of compounds that boil below 30°C, fill a 

5-mL valved gas-tight syringe with reference standard vapor to the 5.0 mL mark. 

Lower the needle to 5 mm above the methanol meniscus. Slowly introduce the 

vapor above the surface of the liquid (the vapor will rapidly dissolve in the 

methanol). Reweigh, dilute to volume, stopper, then mix by inverting the flask 

several times. Calculate the concentration in μg/μL from the net gain in weight. 

6.5.3 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. 

6.5.4 Prepare fresh standards weekly for the gases and 2-chloroethylvinyl ether. All standards 

should be replaced after one month, or sooner if the concentration of an analyte changes by 

more than 10 percent. 

Note: 2-Chloroethylvinyl ether has been shown to be stable for as long as one month if prepared 

as a separate standard, and the other analytes have been shown to be stable for as long as 

2 months if stored at less than -10°C with minimal headspace in sealed, miniature inertvalved vials. 

6.6 Secondary dilution standards – Using stock solutions, prepare secondary dilution standards in 

methanol that contain the compounds of interest, either singly or mixed. Secondary dilution 

standards should be prepared at concentrations such that the aqueous calibration standards prepared 

in Section 7.3.2 will bracket the working range of the analytical system. 

6.7 Surrogate standard spiking solution – Select a minimum of three surrogate compounds from Table 

5. The surrogates selected should match the purging characteristics of the analytes of interest as 

closely as possible. Prepare a stock standard solution for each surrogate in methanol as described in 

Section 6.5, and prepare a solution for spiking the surrogates into all blanks, LCSs, and MS/MSDs. 

The spiking solution should be prepared such that spiking a small volume will result in surrogate 

concentrations near the mid-point of the calibration range. For example, adding 10 μL of a spiking 

solution containing the surrogates at a concentration of 15 μg/mL in methanol to a 5-mL aliquot of 

water would result in a concentration of 30 μg/L for each surrogate. Other surrogate concentrations 

may be used. 

6.8 BFB standard – Prepare a solution of BFB in methanol as described in Sections 6.5 and 6.6. The 

solution should be prepared such that an injection or purging from water will result in introduction 

of ≤ 50 ng into the GC. BFB may be included in a mixture with the internal standards and/or 

surrogates.

6.9 Quality control check sample concentrate – See Section 8.2.1. 

6.10 Storage – When not being used, store standard solutions (Sections 6.5 - 6.9) at -10 to -20°C, 

protected from light, in fluoropolymer-sealed glass containers with minimal headspace.

Method 624.1 6 December 2014
7. Calibration 

7.1 Assemble a purge-and-trap system that meets the specifications in Section 5.2. Prior to first use, 

condition the trap overnight at 180°C by backflushing with gas at a flow rate of at least 20 mL/min. 

Condition the trap daily prior to use.

7.2 Connect the purge-and-trap system to the gas chromatograph. The gas chromatograph should be 

operated using temperature and flow rate conditions equivalent to those given in the footnotes to 

Table 3. Alternative temperature and flow rate conditions may be used provided that performance 

requirements in this method are met.

7.3 Internal standard calibration

7.3.1 Internal standards

7.3.1.1 Select three or more internal standards similar in chromatographic behavior to 

the compounds of interest. Suggested internal standards are listed in Table 5. 

Use the base peak m/z as the primary m/z for quantification of the standards. If 

interferences are found at the base peak, use one of the next two most intense 

m/z’s for quantitation. Demonstrate that measurement of the internal standards 

are not affected by method or matrix interferences. 

7.3.1.2 To assure accurate analyte identification, particularly when selected ion 

monitoring (SIM) is used, it may be advantageous to include more internal 

standards than those suggested in Section 7.3.1.1. 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. 

7.3.1.3 Prepare a stock standard solution for each internal standard surrogate in methanol 

as described in Section 6.5, and prepare a solution for spiking the internal 

standards into all blanks, LCSs, and MS/MSDs. The spiking solution should be 

prepared such that spiking a small volume will result in internal standard 

concentrations near the mid-point of the calibration range. For example, adding 

10 μL of a spiking solution containing the internal standards at a concentration of 

15 μg/mL in methanol to a 5-mL aliquot of water would result in a concentration 

of 30 μg/L for each internal standard. Other concentrations may be used. The 

internal standard solution and the surrogate standard spiking solution (Section 

6.7) may be combined, if desired. Store the solution at <6°C in fluoropolymersealed glass containers with a minimum of headspace. Replace the solution after 

1 month, or more frequently if comparison with QC standards indicates a 

problem. 

7.3.2 Calibration

7.3.2.1 Calibration standards 

7.3.2.1.1 Prepare calibration standards at a minimum of five concentration 

levels for each analyte of interest by adding appropriate volumes of 

one or more stock standards to a fixed volume (e.g., 40 mL) of 

reagent water in volumetric glassware. Fewer levels may be

necessary for some analytes based on the sensitivity of the MS. The 

concentration of the lowest calibration standard for an analyte should 

Method 624.1 7 December 2014
be at or near the ML value in Table 1 for an analyte listed in that 

table. 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 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 does not exceed the MLs in Table 1, 

and provided that the resulting calibration meets the acceptance 

criteria in Section 7.3.4, based on the RSD, RSE, or R2

. 

 The concentrations of the higher standards 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. 

7.3.2.1.2 To each calibration standard or standard mixture, add a known 

constant volume of the internal standard spiking solution (Section 

7.3.1.3) and surrogate standard spiking solution (Section 6.7) or the 

combined internal standard solution and surrogate spiking solution 

(Section 7.3.1.3). Aqueous standards may be stored up to 24 hours, 

if held in sealed vials with zero headspace as described in Section 

9.1. If not so stored, they must be discarded after one hour. 

7.3.2.2 Prior to analysis of the calibration standards, analyze the BFB standard (Section 

6.8) and adjust the scan rate of the MS to produce a minimum of 5 mass spectra 

across the BFB GC peak, but do not exceed 2 seconds per scan. Adjust 

instrument conditions until the BFB criteria in Table 4 are met. 

Note: The BFB 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 BFB peak. 

The BFB 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 BFB spectrum so long as the spectrum is not distorted to meet 

the criteria in Table 4.

7.3.2.3 Analyze the mid-point 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

2) 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; 3 to 5 m/z’s assure 

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

Table 6 as the primary m/z. For analytes in Table 6 that do not have a secondary 

m/z, acquire a mass spectrum and enter one or more secondary m/z’s for more 

reliable identification. 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. 

Method 624.1 8 December 2014
7.3.2.4 For SIM operation, determine the analytes in each descriptor, the quantitation 

m/z for each analyte (the quantitation m/z can be the same as for full-scan 

operation; Section 7.3.2.3), 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 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, the number of m/z’s in a 

descriptor should be limited. 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 Dalton) that can occur at each m/z 

monitored. 

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

to meet requirements in Sections 7.3.2.2 - 7.3.2.4. 

7.3.3 Analyze each calibration standard according to Section 10 and tabulate the area at the 

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

standard. Calculate the response factor (RF) for each compound at each concentration 

using Equation 1. 

Equation 1 

RF = (AsxCis)

(AisxCs)

where:

As = Area of the characteristic m/z for the analyte to be measured.

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

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

Cs = Concentration of the analyte to be measured (μg/L).

7.3.4 Calculate the mean (average) and relative standard deviation (RSD) of the response 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 (1/C). The coefficient of 

determination (R2

) of the weighted regression must be greater than 0.920 (this value 

roughly corresponds to the RSD limit of 35%). Alternatively, the relative standard error 

(Reference 10) 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.

Method 624.1 9 December 2014
7.4 Calibration verification – Because the analytical system is calibrated by purge of the analytes from 

water, calibration verification is performed using the laboratory control sample (LCS). See Section 

8.4 for requirements for calibration verification using the LCS, and the Glossary for further 

definition. 

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.

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 1.5 and 40 CFR 

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

include an alternate purge-and-trap device, and changes in both column and type of mass 

spectrometer (see 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 8.9). 

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 

at least as low as the MDLs listed 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 a 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 internal standards and 

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

LCS samples must be fortified with the analytes of interest (Section 

Method 624.1 10 December 2014
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 alternate materials) but any 

laboratory using that specific 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-l).

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

(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 7, and recoveries for 

surrogates that do not have recovery limits specified in Table 7, 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 7 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.

Method 624.1 11 December 2014
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/LCS (Section 8.4).

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).

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) Analysis dates and times.

c) Analysis sequence/run chronology.

d) Sample volume (Section 10).

e) Sample dilution (Section 13.2).

f) Instrument and operating conditions.

g) Column (dimensions, material, etc).

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

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

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

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

the raw data to the results reported.

l) A written Standard Operating Procedure (SOP).

8.1.2.2.6 The 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 7 for the analytes of interest 

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

MDLs in Table3 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 analyzed or reagents are changed, a blank must be 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 batch of samples run during a given 12-hour shift (see the note at 

Section 8.4). 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. 

Method 624.1 12 December 2014
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 8.8. 

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. Results for regulatory compliance must 

be accompanied by QC results that meet all acceptance criteria.

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 Table 1 for those analytes which list MDL values, or lower than one-third the 

regulatory compliance limit, whichever is greater. For MDLs not listed in Table 1, 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 Table 1. All procedures used in 

the analysis 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 methanol. 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/LCS (Sections 7.4 and 8.4). 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). 

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 aliquots of reagent water. 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 volume of 5 mL and a concentration of 20 μg/L were used to develop the 

QC acceptance criteria in Table 7. An alternative volume and sample concentration may be 

used, provided that all QC tests are performed and all QC acceptance criteria in this method 

are met. Also add an aliquot of the surrogate spiking solution (Section 6.7) and internal 

standard spiking solution (Section 7.3.1.3) to the reagent-water aliquots. 

8.2.3 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 7. For analytes in Tables 1 and 2 not listed in Table 7, DOC QC 

Method 624.1 13 December 2014
acceptance criteria must be developed by the laboratory. EPA has provided guidance for 

development of QC acceptance criteria (References 11 and 12). If s and X

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 falls outside the range for recovery, system performance is unacceptable for 

that analyte.

Note: The large number of analytes in Tables 1 and 2 present a substantial probability that one 

or more will fail at least one of the acceptance criteria when many or all 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 batch of samples analyzed on a given 12-hour shift with the analytes in Table 

1. 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, or in a permit. 

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 7. A laboratory may 

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

desired.

Method 624.1 14 December 2014
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 7 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 13). If spiking is 

performed at a concentration lower than 20 μg/L, the laboratory must use either 

the QC acceptance criteria in Table 7, 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 8, substituting 

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

equation in Table 8, substituting X’ for X ; (3) Calculate the range for recovery 

at the spike concentration as (100 X’/T) ± 2.44(100 S’/T)% (Reference 4). For 

analytes of interest in Tables 1 and 2 not listed in Table 7, QC acceptance criteria 

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

development of QC acceptance criteria (References 11 and 12).

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 7. If an in-house QC 

limit for the RPD is greater than the limit in Table 7, then the limit in Table 7 must be used. 

Similarly, if an in-house lower limit for recovery is below the lower limit in Table 7, then 

the lower limit in Table 7 must be used, and if an in-house upper limit for recovery is above 

the upper limit in Table 7, then the upper limit in Table 7 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 Calibration verification/laboratory control sample (LCS) – The working calibration curve or RF 

must be verified at the beginning of each 12-hour shift by the measurement of an LCS. 

Note: The 12-hour shift begins after analysis of the blank that follows the LCS and ends 12 hours 

later. The blank is outside of the 12-hour shift. The MS and MSD are treated as samples 

and are analyzed within the 12-hour shift.

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 solution (Section 6.7) and internal standard solution (Section 

7.3.1.3). The concentration of the analytes in reagent water should be the same as the 

concentration in the DOC (Section 8.2.2). 

Method 624.1 15 December 2014
8.4.2 Analyze the LCS prior to analysis of field samples in the batch of samples analyzed during 

the 12-hour shift (see the Note at Section 8.4). Determine the concentration (A) of each 

analyte. Calculate the percent recovery (Q) as 100 (A/T) %, where T is the true value of 

the concentration in the LCS.

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

criterion in Table 7. For analytes of interest in Tables 1 and 2 not listed in Table 7, 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 Q falls outside the range, proceed 

according to Section 8.4.4. 

Note: The large number of analytes in Tables 1 - 2 present a substantial probability that one or 

more will fail the acceptance criteria when all analytes are tested simultaneously. Because 

a re-test is allowed in event of failure (Sections 8.1.7 and 8.4.3), it may be prudent to 

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 (Q). 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 calibration verification/LCS test 

(Section 8.4). If the acceptance criteria for Q cannot be met, re-calibrate the instrument 

(Section 7). If failure of the LCS indicates a systemic problem with samples analyzed 

during the 12-hour shift, re-analyze the samples analyzed during that 12-hour shift. 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.

8.4.5 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 7. 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 7, 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 7, the lower limit in Table 7 must be used, and if an in-house upper 

limit for recovery is higher than the upper limit in Table 7, the upper limit in Table 7 must be 

used. 

8.5 Blank – A blank must be analyzed at the beginning of each 12-hour shift to demonstrate freedom 

from contamination. A blank must also be analyzed after a sample containing a high concentration 

of an analyte or potentially interfering compound to demonstrate freedom from carry-over.

8.5.1 Spike the internal standards and surrogates into the blank. 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. 

Method 624.1 16 December 2014
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 analyzed 

during the 12-hour shift (Section 8.4), whichever is greater; analysis of samples must be 

halted and samples affected by the blank must be 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 Surrogate recoveries – Spike the surrogates into all samples, blanks, LCSs, and MS/MSDs. 

Compare surrogate recoveries against the QC acceptance criteria in Table 7. For surrogates in 

Table 5 without QC acceptance criteria in Table 7, and for other surrogates that may be used by the 

laboratory, limits must be developed by the laboratory. EPA has provided guidance for 

development of QC acceptance criteria (References 11 and 12). 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. 

8.7 Internal standard responses 

8.7.1 Calibration verification/LCS – The responses (GC peak heights or areas) of the internal 

standards in the calibration verification/LCS 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 

LCS test using a fresh QC check sample (Section 8.4.1) or perform and document system 

repair. Subsequent to repair, repeat the calibration verification/LCS test (Section 8.4). If 

the responses are still not within 50% to 200%, re-calibrate the instrument (Section 7) and 

repeat the calibration verification/LCS test.

8.7.2 Samples, blanks, 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 standard 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.

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

wastewater samples must be assessed and records maintained periodically (see 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

X X

X

) and the standard deviation of the percent recovery (sp). 

Express the accuracy assessment as a percent interval from -2sp to +2sp. For example, 

if = 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).

8.9 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.

Method 624.1 17 December 2014
9. Sample Collection, Preservation, and Handling

9.1 Collect the sample as a grab sample in a glass container having a total volume of at least 25 mL. 

Fill the sample bottle just to overflowing in such a manner that no air bubbles pass through the 

sample as the bottle is being filled. Seal the bottle so that no air bubbles are entrapped in it. 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 analysis, but do not freeze. If 

residual chlorine is present, add sodium thiosulfate preservative (10 mg/40 mL is sufficient for up 

to 5 ppm Cl2) to the empty sample bottle just prior to shipping to the sampling site. Any method 

suitable for field use may be employed to test for residual chlorine (Reference 14). Field test kits 

are also available for this purpose. If sodium thiosulfate interferes in the determination of the 

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

preservative has been added, shake the sample vigorously for one minute. Maintain the hermetic 

seal on the sample bottle until time of analysis.

9.3 If acrolein is to be determined, analyze the sample within 3 days. To extend the holding time to 14 

days, acidify a separate sample to pH 4 - 5 with HCl using the procedure in Section 9.7. 

9.4 Experimental evidence indicates that some aromatic compounds, notably benzene, toluene, and 

ethyl benzene are susceptible to rapid biological degradation under certain environmental 

conditions (Reference 3). Refrigeration alone may not be adequate to preserve these compounds in 

wastewaters for more than seven days. To extend the holding time for aromatic compounds to 14 

days, acidify the sample to approximately pH 2 using the procedure in Section 9.7. 

9.5 If halocarbons are to be determined, either use the acidified aromatics sample in Section 9.4 or 

acidify a separate sample to a pH of about 2 using the procedure in Section 9.7. Aqueous samples 

should not be preserved with acid if the ethers in Table 2, or the alcohols that they would form upon 

hydrolysis, are of analytes of interest.

9.6 The ethers listed in Table 2 are prone to hydrolysis at pH 2 when a heated purge is used. Aqueous 

samples should not be acid preserved if these ethers are of interest, or if the alcohols they would 

form upon hydrolysis are of interest and the ethers are anticipated to present.

9.7 Sample acidification – Collect about 500 mL of sample in a clean container and adjust the pH of the 

sample to 4 - 5 for acrolein (Section 9.3), or to about 2 for the aromatic compounds (Section 9.4) by 

adding 1+1 HCl while swirling or stirring. Check the pH with narrow range pH paper. Fill a 

sample container as described in Section 9.1. Alternatively, fill a precleaned vial (Section 5.1.1) 

that contains approximately 0.25 mL of 1+1 HCl with sample as in Section 9.1. If preserved using 

this alternative procedure, the pH of the sample can be verified to be <2 after some of the sample is 

removed for analysis. Acidification will destroy 2-chloroethylvinyl ether; therefore, determine 

2-chloroethylvinyl ether from the unacidified sample. 

9.8 All samples must be analyzed within 14 days of collection (Reference 3), unless specified otherwise 

in Sections 9.3 - 9.7. 

10. Sample Purging and Gas Chromatography

10.1 The footnote to Table 3 gives the suggested GC column and operating conditions. Included in 

Table 3 are retention times and MDLs that can be achieved under these conditions. Sections 10.2 

through 10.7 suggest procedures that may be used with a manual purge-and-trap system. AutoMethod 624.1 18 December 2014
samplers and other columns or chromatographic conditions may be used if requirements in this 

method are met.

10.2 Attach the trap inlet to the purging device, and set the purge-and-trap system to purge (Figure 3). 

Open the syringe valve located on the purging device sample introduction needle.

10.3 Allow the sample to come to ambient temperature prior to pouring an aliquot into the syringe. 

Remove the plunger from a syringe and attach a closed syringe valve. Open the sample bottle (or 

standard) and carefully pour the sample into the syringe barrel to just short of overflowing. Replace 

the syringe plunger and compress the sample. Open the syringe valve and vent any residual air 

while adjusting the sample volume. Since this process of taking an aliquot destroys the validity of 

the sample for future analysis, the analyst should fill a second syringe at this time to protect against 

possible loss of data. Add the surrogate spiking solution (Section 6.7) and internal standard spiking 

solution (Section 7.3.1.3) through the valve bore, then close the valve. The surrogate and internal 

standards may be mixed and added as a single spiking solution. Autosamplers designed for purgeand-trap analysis of volatiles also may be used. 

10.4 Attach the syringe valve assembly to the syringe valve on the purging device. Open the syringe 

valve and inject the sample into the purging chamber. 

10.5 Close both valves and purge the sample at a temperature, flow rate, and duration sufficient to purge 

the less-volatile analytes onto the trap, yet short enough to prevent blowing the more-volatile 

analytes through the trap. The temperature, flow rate, and time should be determined by test. The 

same purge temperature, flow rate, and purge time must be used for all calibration, QC, and field 

samples.

10.6 After the purge, set the purge-and-trap system to the desorb mode (Figure 4), and begin to 

temperature program the gas chromatograph. Introduce the trapped materials to the GC column by 

rapidly heating the trap to the desorb temperature while backflushing the trap with carrier gas at the 

flow rate and for the time necessary to desorb the analytes of interest. The optimum temperature, 

flow rate, and time should be determined by test. The same temperature, desorb time, and flow rate 

must be used for all calibration, QC, and field samples. If heating of the trap does not result in 

sharp peaks for the early eluting analytes, the GC column may be used as a secondary trap by 

cooling to an ambient or subambient temperature. To avoid carry-over and interferences, maintain 

the trap at the desorb temperature and flow rate until the analytes, interfering compounds, and 

excess water are desorbed. The optimum conditions should be determined by test. 

10.7 Start MS data acquisition at the start of the desorb cycle and stop data collection when the analytes 

of interest, potentially interfering compounds, and water have eluted (see the footnote to Table 3 for 

conditions). 

10.8 Cool the trap to the purge temperature and return the trap to the purge mode (Figure 3). When the 

trap is cool, the next sample can be analyzed.

11. Performance Tests

11.1 At the beginning of each 12-hour shift during which analyses are to be performed, GC/MS 

performance must be verified before blanks or samples may be analyzed (Section 8.4). Use the 

instrument operating conditions in the footnotes to Table 3 for these performance tests. Alternate 

conditions may be used so as long as all QC requirements are met.

Method 624.1 19 December 2014
11.2 BFB – Inject 50 ng of BFB solution directly on the column. Alternatively, add BFB to reagent 

water or an aqueous standard such that 50 ng or less of BFB will be introduced into the GC. 

Analyze according to Section 10. Confirm that all criteria in Section 7.3.2.2 and Table 4 are met. 

If all criteria are not met, perform system repair, retune the mass spectrometer, and repeat the test 

until all criteria are met.

11.3 GC resolution – There must be a valley between 1,2-dibromoethane and chlorobenzene, and the 

height of the valley must not exceed 25 percent of the shorter of the two peaks. For an alternate GC 

column, apply this valley height criterion to two representative GC peaks separated by no more 

than 7 seconds.

11.4 Verify calibration with the LCS (Section 8.4) after the criteria for BFB are met (Reference 15) and 

prior to analysis of a blank or sample. After verification, analyze a blank (Section 8.5) to 

demonstrate freedom from contamination and carry-over at the MDL.

12. Qualitative Identification

12.1 Target analytes are identified by comparison of results from analysis of a sample or blank with data 

stored in the GC/MS data system (Section 7.3.2.3). Identification of an analyte is confirmed per 

Sections 12.1.1 through 12.1.4.

12.1.1 The signals for all characteristic m/z’s stored in the data system (Section 7.3.2.3) for each 

analyte of interest must be present and must maximize within the same two consecutive 

scans.

12.1.2 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 LCS run at the beginning of the shift (Section 8.4). 

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 7.3.1.2). 

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 LCS or other standard. 

12.1.3 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 

7.3.2.3), 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.

12.1.4 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 1.6) must determine the presence or absence of the 

compound. 

12.2 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 

Method 624.1 20 December 2014
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.

13. Calculations 

13.1 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 5 or 6. Calculate the 

concentration using the response factor (RF) determined in Section 7.3.3 and Equation 2. If a 

calibration curve was used, calculate the concentration using the regression equation for the curve. 

If the concentration of an analyte exceeds the calibration range, dilute the sample by the minimum 

amount to bring the concentration into the calibration range, and re-analyze. 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 

Cs (μg/L)=

As x Cis x DF

Ais x RF

where:

Cs = Concentration of the analyte in the sample, and the other terms are as defined in Section 

7.3.3. 

13.2 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. 

13.2.1 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.

13.2.2 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. 

13.2.2.1 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 

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.

13.2.2.2 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.

Method 624.1 21 December 2014
13.2.2.3 Report a result for an analyte found in a sample 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 7). This may require 

reporting results for some analytes from different analyses.

13.2.3 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. 

14. Method Performance

14.1 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 - 600 μg/L (References 4 and 

16). 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 8.

14.2 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.

15. Pollution Prevention

15.1 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.

15.2 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.

15.3 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. 

16. Waste Management 

16.1 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 

Method 624.1 22 December 2014
and regulations. An overview of requirements can be found in Environmental Management Guide 

for Small Laboratories (EPA 233-B-98-001).

16.2 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.

16.3 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.

16.4 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.

17. References

1. Bellar, T.A. and Lichtenberg, J.J. “Determining Volatile Organics at Microgram-per-Litre Levels 

by Gas Chromatography,” Journal American Water Works Association, 66, 739 (1974).

2. “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.

3. Bellar, T.A. and Lichtenberg, J.J. “Semi-Automated Headspace Analysis of Drinking Waters and 

Industrial Waters for Purgeable Volatile Organic Compounds,” Measurement of Organic Pollutants 

in Water and Wastewater, C.E. Van Hall, editor, American Society for Testing and Materials, 

Philadelphia, PA. Special Technical Publication 686, 1978.

4. “EPA Method Study 29 EPA Method 624-Purgeables,” EPA 600/4-84-054, National Technical 

Information Service, PB84-209915, Springfield, Virginia 22161, June 1984.

5. 40 Code of Federal Regulations 136, Appendix B

6. “Method Detection Limit for Methods 624 and 625,” Olynyk, P., Budde, W.L., and Eichelberger, 

J.W. Unpublished report, May 14, 1980.

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. 40 Code of Federal Regulations 136.6(b)(5)(x)

Method 624.1 23 December 2014
11. 40 Code of Federal Regulations 136.6(b)(2)(i)

12. Protocol for EPA Approval of New Methods for Organic and Inorganic Analytes in Wastewater and 

Drinking Water (EPA-821-B-98-003) March 1999

13. Provost, L.P. and Elder, R.S. “Interpretation of Percent Recovery Data,” American Laboratory, 15,

58-63 (1983).

14. 40 CFR 136.3(a), Table IB, Chlorine - Total residual

15. Budde, W.L. and Eichelberger, J.W. “Performance Tests for the Evaluation of Computerized Gas 

Chromatography/Mass Spectrometry Equipment and Laboratories,” EPA-600/4-80-025, U.S. 

Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, 

Ohio 45268, April 1980.

16. “Method Performance Data for Method 624,” Memorandum from R. Slater and T. Pressley, U.S. 

Environmental Protection Agency, Environmental Monitoring and Support Laboratory, Cincinnati, 

Ohio 45268, January 17, 1984.

Method 624.1 24 December 2014
18. Tables

Table 1 – Purgeables1

Analyte CAS Registry No. MDL (μg/L)2 ML (μg/L)3

Acrolein 107-02-8

Acrylonitrile 107-13-1

Benzene 71-43-2 4.4 13.2

Bromodichloromethane 75-27-4 2.2 6.6

Bromoform 75-25-2 4.7 14.1

Bromomethane 74-83-9

Carbon tetrachloride 56-23-5 2.8 8.4

Chlorobenzene 108-90-7 6.0 18.0

Chloroethane 75-00-3

2-Chloroethylvinyl ether 110-75-8

Chloroform 67-66-3 1.6 4.8

Chloromethane 74-87-3

Dibromochloromethane 124-48-1 3.1 9.3

1,2-Dichlorobenzene 95-50-1

1,3-Dichlorobenzene 541-73-1

1,4-Dichlorobenzene 106-46-7

1,1-Dichloroethane 75-34-3 4.7 14.1

1,2-Dichloroethane 107-06-2 2.8 8.4

1,1-Dichloroethene 75-35-4 2.8 8.4

trans-1,2-Dichloroethene 156-60-5 1.6 4.8

1,2-Dichloropropane 78-87-5 6.0 18.0

cis-1,3-Dichloropropene 10061-01-5 5.0 15.0

trans-1,3-Dichloropropene 10061-02-6

Ethyl benzene 100-41-4 7.2 21.6

Methylene chloride 75-09-2 2.8 8.4

1,1,2,2-Tetrachloroethane 79-34-5 6.9 20.7

Tetrachloroethene 127-18-4 4.1 12.3

Toluene 108-88-3 6.0 18.0

1,1,1-Trichloroethane 71-55-6 3.8 11.4

1,1,2-Trichloroethane 79-00-5 5.0 15.0

Trichloroethene 79-01-6 1.9 5.7

Vinyl chloride 75-01-4

1 All the analytes in this table are Priority Pollutants (40 CFR 423, Appendix A) 2 MDL values from the 1984 promulgated version of Method 624 3 ML = Minimum Level – see Glossary for definition and derivation

Method 624.1 25 December 2014
Table 2 – Additional Purgeables

Analyte CAS Registry

Acetone 1 67-64-1

Acetonitrile 2 75-05-8

Allyl alcohol 1 107-18-6

Allyl chloride 107-05-1

t-Amyl ethyl ether (TAEE) 919-94-8

t-Amyl methyl ether (TAME) 994-058

Benzyl chloride 100-44-7

Bromoacetone 2 598-31-2

Bromobenzene 108-86-1

Bromochloromethane 74-97-5

1,3-Butadiene 106-99-0

n-Butanol 1 71-36-3

2-Butanone (MEK) 1,2 78-93-3

t-Butyl alcohol (TBA) 75-65-0

n-Butylbenzene 104-51-8

sec-Butylbenzene 135-98-8

t-Butylbenzene 98-06-6

t-Butyl ethyl ether (ETBE) 637-92-3

Carbon disulfide 75-15-0

Chloral hydrate 2 302-17-0

Chloroacetonitrile 1 107-14-2

1-Chlorobutane 109-69-3

Chlorodifluoromethane 75-45-6

2-Chloroethanol 2 107-07-3

bis (2-Chloroethyl) sulfide 2 505-60-2

1-Chlorohexanone 20261-68-1

Chloroprene (2-chloro-1,3-butadiene) 126-99-8

3-Chloropropene 107-05-1

3-Chloropropionitrile 542-76-7

2-Chlorotoluene 95-49-8

4-Chlorotoluene 106-43-4

Crotonaldehyde 1,2 123-73-9

Cyclohexanone 108-94-1

1,2-Dibromo-3-chloropropane 96-12-8

1,2-Dibromoethane 106-93-4

Dibromomethane 74-95-3

cis-1,4-Dichloro-2-butene 1476-11-5

trans-1,4-Dichloro-2-butene 110-57-6

cis-1,2-Dichloroethene 156-59-2

Dichlorodifluoromethane 75-71-8

Method 624.1 26 December 2014
Table 2 – Additional Purgeables

Analyte CAS Registry

1,3-Dichloropropane 142-28-9

2,2-Dichloropropane 590-20-7

1,3-Dichloro-2-propanol 2 96-23-1

1,1-Dichloropropene 563-58-6

cis-1,3-Dichloropropene 10061-01-5

1:2,3:4-Diepoxybutane 1464-53-5

Diethyl ether 60-29-7

Diisopropyl ether (DIPE) 108-20-3

1,4-Dioxane 2 123-91-1

Epichlorohydrin 2 106-89-8

Ethanol 2 64-17-5

Ethyl acetate 2 141-78-6

Ethyl methacrylate 97-63-2

Ethylene oxide 2 75-21-8

Hexachlorobutadiene 87-63-3

Hexachloroethane 67-72-1

2-Hexanone 2 591-78-6

Iodomethane 74-88-4

Isobutyl alcohol 1 78-83-1

Isopropylbenzene 98-82-8

p-Isopropyltoluene 99-87-6

Methacrylonitrile 2 126-98-7

Methanol 2 67-56-1

Malonitrile 2 109-77-3

Methyl acetate 79-20-9

Methyl acrylate 96-33-3

Methyl cyclohexane 108-87-2

Methyl iodide 74-88-4

Methyl methacrylate 78-83-1

4-Methyl-2-pentanone (MIBK) 2 108-10-1

Methyl-t-butyl ether (MTBE) 1634-04-4

Naphthalene 91-20-3

Nitrobenzene 98-95-3

N-Nitroso-di-n-butylamine 2 924-16-3

2-Nitropropane 79-46-9

Paraldehyde 2 123-63-7

Pentachloroethane 2 76-01-7

Pentafluorobenzene 363-72-4

2-Pentanone 2 107-19-7

2-Picoline 2 109-06-8

Method 624.1 27 December 2014
Table 2 – Additional Purgeables

Analyte CAS Registry

1-Propanol 1 71-23-8

2-Propanol 1 67-63-0

Propargyl alcohol 2 107-19-7

beta-Propiolactone 2 57-58-8

Propionitrile (ethyl cyanide) 1 107-12-0

n-Propylamine 107-10-8

n-Propylbenzene 103-65-1

Pyridine 2 110-86-1

Styrene 100-42-5

1,1,1,2-Tetrachloroethane 630-20-6

Tetrahydrofuran 109-99-9

o-Toluidine 2 95-53-4

1,2,3-Trichlorobenzene 87-61-6

Trichlorofluoromethane 75-69-4

1,2,3-Trichloropropane 96-18-4

1,2,3-Trimethylbenzene 526-73-8

1,2,4-Trimethylbenzene 95-63-6

1,3,5-Trimethylbenzene 108-67-8

Vinyl acetate 108-05-4

m-Xylene 3 108-38-3

o-Xylene 3 95-47-6

p-Xylene 3 106-42-3

m+o- Xylene 3 179601-22-0

m+p- Xylene 3 179601-23-1

o+p- Xylene 3 136777-61-2

1 Determined at a purge temperature of 80°C 2 May be detectable at a purge temperature of 80°C 3 Determined in combination separated by GC column. Most 

GC columns will resolve o-xylene from m+p-xylene. 

Report using the CAS number for the individual xylene or 

the combination, as determined. 

Method 624.1 28 December 2014
Table 3 – Example Retention Times

Analyte Retention time (min)

Chloromethane 3.68

Vinyl chloride 3.92

Bromomethane 4.50

Chloroethane 4.65

Trichlorofluoromethane 5.25

Diethyl ether 5.88

Acrolein 6.12

1,1-Dichloroethene 6.30

Acetone 6.40

Iodomethane 6.58

Carbon disulfide 6.72

3-Chloropropene 6.98

Methylene chloride 7.22

Acrylonitrile 7.63

trans-1,2-Dichloroethene 7.73

1,1-Dichloroethane 8.45

Vinyl acetate 8.55

Allyl alcohol 8.58

2-Chloro-1,3-butadiene 8.65

Methyl ethyl ketone 9.50

cis-1,2-Dichloroethene 9.50

Ethyl cyanide 9,57

Methacrylonitrile 9.83

Chloroform 10.05

1,1,1-Trichloroethane 10.37

Carbon tetrachloride 10.70

Isobutanol 10.77

Benzene 10.98

1,2-Dichloroethane 11.00

Crotonaldehyde 11.45

Trichloroethene 12.08

1,2-Dichloropropane 12.37

Methyl methacrylate 12.55

p-Dioxane 12.63

Dibromomethane 12.65

Bromodichloromethane 12.95

Chloroacetonitrile 13.27

2-Chloroethylvinyl ether 13.45

cis-1,3-Dichloropropene 13.65

4-Methyl-2-pentanone 13.83

Method 624.1 29 December 2014
Table 3 – Example Retention Times

Analyte Retention time (min)

Toluene 14.18

trans-1,3-Dichloropropene 14.57

Ethyl methacrylate 14.70

1,1,2-Trichloroethane 14.93

1,3-Dichloropropane 15.18

Tetrachloroethene 15.22

2-Hexanone 15.30

Dibromochloromethane 15.68

1,2-Dibromoethane 15.90

Chlorobenzene 16.78

Ethylbenzene 16.82

1,1,1,2-Tetrachloroethane 16.87

m+p-Xylene 17.08

o-Xylene 17.82

Bromoform 18.27

Bromofluorobenzene 18.80

1,1,2,2-Tetrachloroethane 18.98

1,2,3-Trichloropropane 19.08

trans-1,4-Dichloro-2-butene 19.12

Column: 75 m x 0.53 mm ID x 3.0 μm wide-bore DB-624

Conditions: 40°C for 4 min, 9°C/min to 200°C, 20°C/min (or 

higher) to 250°C, hold for 20 min at 250°C to remove 

water

Carrier gas flow rate: 6 - 7 mL/min at 40°C 

Inlet split ratio: 3:1

Interface split ratio: 7:2

Method 624.1 30 December 2014
Table 4 – BFB Key m/z Abundance Criteria 1

m/z Abundance criteria

50 15 - 40% of m/z 95.

75 30 - 60% of m/z 95.

95 Base Peak, 100% Relative Abundance.

96 5 - 9% of m/z 95.

173 <2% of m/z 174.

174 >50% of m/z 95.

175 5 - 9% of m/z 174.

176 >95% but <101% of m/z 174.

177 5 - 9% of m/z 176.

1

 Abundance criteria are for a quadrupole mass 

spectrometer; contact the manufacturer for criteria for 

other types of mass spectrometers

Table 5 – Suggested Surrogate and Internal Standards

Analyte Retention time (min)1 Primary m/z Secondary m/z’s

Benzene-d6 10.95 84

4-Bromofluorobenzene 18.80 95 174, 176

Bromochloromethane 9.88 128 49, 130, 51

2-Bromo-1-chloropropane 14.80 77 79, 156

2-Butanone-d5 9.33 77

Chloroethane-d5 4.63 71

Chloroform13C 10.00 86

1,2-Dichlorobenzene-d4 152

1,4-Dichlorobutane 18.57 55 90, 92

1,2-Dichloroethane-d4 10.88 102

1,1-Dichloroethene-d2 6.30 65

1,2-Dichloropropane-d6 12.27 67

trans-1,3-Dichloropropene-d4 14.50 79

1,4-Difluorobenzene 114 63, 88

Ethylbenzene-d10 16.77 98

Fluorobenzene 96 70

2-Hexanone-d5 15.30 63

Pentafluorobenzene 168

1,1,2,2-Tetrachloroethane-d2 18.93 84

Toluene-d8 14.13 100

Vinyl chloride-d3 3.87 65

1 For chromatographic conditions, see the footnote to Table 3.

Method 624.1 31 December 2014
Table 6 – Characteristic m/z’s for Purgeable Organics

Analyte Primary m/z Secondary m/z’s

Chloromethane 50 52

Bromomethane 94 96

Vinyl chloride 62 64

Chloroethane 64 66

Methylene chloride 84 49, 51, and 86

Trichlorofluoromethane 101 103

1,1-Dichloroethene 96 61 and 98

1,1-Dichloroethane 63 65, 83, 85, 98, and 100

trans-1,2-Dichloroethene 96 61 and 98

Chloroform 83 85

1,2-Dichloroethane 98 62, 64, and 100

1,1,1-Trichloroethane 97 99, 117, and 119

Carbon tetrachloride 117 119 and 121

Bromodichloromethane 83 127, 85, and 129

1,2-Dichloropropane 63 112, 65, and 114

trans-1,3-Dichloropropene 75 77

Trichloroethene 130 95, 97, and 132

Benzene 78

Dibromochloromethane 127 129, 208, and 206

1,1,2-Trichloroethane 97 83, 85, 99, 132, and 134

cis-1,3-Dichloropropene 75 77

2-Chloroethylvinyl ether 106 63 and 65

Bromoform 173 171, 175, 250, 252, 254, and 256

1,1,2,2-Tetrachloroethane 168 83, 85, 131, 133, and 166

Tetrachloroethene 164 129, 131, and 166

Toluene 92 91

Chlorobenzene 112 114

Ethyl benzene 106 91

1,3-Dichlorobenzene 146 148 and 111

1,2-Dichlorobenzene 146 148 and 111

1,4-Dichlorobenzene 146 148 and 111

Method 624.1 32 December 2014
Table 7 – LCS (Q), DOC (s and X ), and MS/MSD (P and RPD) Acceptance Criteria 1

Analyte

Range for Q 

(%)

Limit for s 

(%)

Range for

X (%)

Range for 

P (%)

Limit for 

RPD

Benzene 65-135 33 75-125 37-151 61

Benzene-d6 70-130

Bromodichloromethane 65-135 34 50-140 35-155 56

Bromoform 70-130 25 57-156 45-169 42

Bromomethane 15-185 90 D-206 D-242 61

2-Butanone-d5 60-140

Carbon tetrachloride 70-130 26 65-125 70-140 41

Chlorobenzene 65-135 29 82-137 37-160 53

Chloroethane 40-160 47 42-202 14-230 78

Chloroethane-d5 60-140

2-Chloroethylvinyl ether D-225 130 D-252 D-305 71

Chloroform 70-135 32 68-121 51-138 54

Chloroform13C 70-130

Chloromethane D-205 472 D-230 D-273 60

Dibromochloromethane 70-135 30 69-133 53-149 50

1,2-Dichlorobenzene 65-135 31 59-174 18-190 57

1,2-Dichlorobenzene-d4 70-130

1,3-Dichlorobenzene 70-130 24 75-144 59-156 43

1,4-Dichlorobenzene 65-135 31 59-174 18-190 57

1,1-Dichloroethane 70-130 24 71-143 59-155 40

1,2-Dichloroethane 70-130 29 72-137 49-155 49

1,2-Dichloroethane-d4 70-130

1,1-Dichloroethene 50-150 40 19-212 D-234 32

1,1-Dichloroethene-d2 70-130

trans-1,2-Dichloroethene 70-130 27 68-143 54-156 45

1,2-Dichloropropane 35-165 69 19-181 D-210 55

1,2-Dichloropropane-d6 60-140

cis-1,3-Dichloropropene 25-175 79 5-195 D-227 58

trans-1,3-Dichloropropene 50-150 52 38-162 17-183 86

trans-1,3-Dichloropropene-d4 70-130

Ethyl benzene 60-140 34 75-134 37-162 63

2-Hexanone-d5 60-140

Methylene chloride 60-140 192 D-205 D-221 28

1,1,2,2-Tetrachloroethane 60-140 36 68-136 46-157 61

1,1,2,2-Tetrachloroethane-d2 70-130

Tetrachloroethene 70-130 23 65-133 64-148 39

Toluene 70-130 22 75-134 47-150 41

Toluene-d8 70-130

1,1,1-Trichloroethane 70-130 21 69-151 52-162 36

1,1,2-Trichloroethane 70-130 27 75-136 52-150 45

Trichloroethene 65-135 29 75-138 70-157 48

Trichlorofluoromethane 50-150 50 45-158 17-181 84

Vinyl chloride 5-195 100 D-218 D-251 66

Vinyl chloride-d3 70-130

1

Criteria were calculated using an LCS concentration of 20 μg/L Notes:

Q = Percent recovery in calibration verification/LCS (Section 8.4) 1. Criteria for pollutants are based upon the method 

s = Standard deviation of percent recovery for four recovery performance data in Reference 4. Where necessary, 

measurements (Section 8.2.4) limits for recovery have been broadened to assure 

applicability to concentrations below those used to X = Average percent recovery for four recovery measurements develop Table 7. (Section 8.2.4)

P = Percent recovery for the MS or MSD (Section 8.3.3) 2. Criteria for surrogates are from EPA CLP 

D = Detected; result must be greater than zero SOM01.2D

Method 624.1 33 December 2014
Table 8 – Recovery and Precision as Functions of Concentration

Analyte

Recovery, X'

(μg/L)

Single analyst 

precision, sr'

(μg/L)

Overall 

precision, 

S' (μg/L)

Benzene 0.93C+2.00 20.26 X -1.74 0.25 X -1.33

Bromodichloromethane 1.03C-1.58 0.15 X +0.59 0.20 X +1.13

Bromoform 1.18C-2.35 0.12 X +0.36 0.17 X +1.38

Bromomethanea 1.00C 0.43 X 0.58 X

Carbon tetrachloride 1.10C-1.68 0.12 X +0.25 0.11 X +0.37

Chlorobenzene 0.98C+2.28 0.16 X -0.09 0.26 X -1.92

Chloroethane 1.18C+0.81 0.14 X +2.78 0.29 X +1.75

2-Chloroethylvinyl ethera 1.00C 0.62 X 0.84 X

Chloroform 0.93C+0.33 0.16 X +0.22 0.18 X +0.16

Chloromethane 1.03C+0.81 0.37 X +2.14 0.58 X +0.43

Dibromochloromethane 1.01C-0.03 0.17 X -0.18 0.17 X +0.49

1,2-Dichlorobenzeneb 0.94C+4.47 0.22 X -1.45 0.30 X -1.20

1,3-Dichlorobenzene 1.06C+1.68 0.14 X -0.48 0.18 X -0.82

1,4-Dichlorobenzeneb 0.94C+4.47 0.22 X -1.45 0.30 X -1.20

1,1-Dichloroethane 1.05C+0.36 0.13 X -0.05 0.16 X +0.47

1,2-Dichloroethane 1.02C+0.45 0.17 X -0.32 0.21 X -0.38

1,1-Dichloroethene 1.12C+0.61 0.17 X +1.06 0.43 X -0.22

trans-1,2,-Dichloroethene 1.05C+0.03 0.14 X +0.09 0.19 X +0.17

1,2-Dichloropropanea 1.00C 0.33 X 0.45 X

cis-1,3-Dichloropropenea 1.00C 0.38 X 0.52 X

trans-1,3-Dichloropropenea 1.00C 0.25 X 0.34 X

Ethyl benzene 0.98C+2.48 0.14 X +1.00 0.26 X -1.72

Methylene chloride 0.87C+1.88 0.15 X +1.07 0.32 X +4.00

1,1,2,2-Tetrachloroethane 0.93C+1.76 0.16 X +0.69 0.20 X +0.41

Tetrachloroethene 1.06C+0.60 0.13 X -0.18 0.16 X -0.45

Toluene 0.98C+2.03 0.15 X -0.71 0.22 X -1.71

1,1,1-Trichloroethane 1.06C+0.73 0.12 X -0.15 0.21 X -0.39

1,1,2-Trichloroethane 0.95C+1.71 0.14 X +0.02 0.18 X +0.00

Trichloroethene 1.04C+2.27 0.13 X +0.36 0.12 X +0.59

Trichlorofluoromethane 0.99C+0.39 0.33 X -1.48 0.34 X -0.39

Vinyl chloride 1.00C 0.48 X 0.65 X

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

X

X

, in μg/L. 

S' = Expected interlaboratory standard deviation of measurements at an average concentration found of , in μg/L.

C = True value for the concentration, in μg/L.

 = Average recovery found for measurements of samples containing a concentration of C, in μg/L. a Estimates based upon the performance in a single laboratory (References 4 and 16).

b Due to coelutions, performance statements for these isomers are based upon the sums of their concentrations.

Method 624.1 34 December 2014
19. Figures

Method 624.1 35 December 2014
Method 624.1 36 December 2014
Method 624.1 37 December 2014
20. Glossary

These definitions and purposes are specific to this method, but have been conformed to common usage to 

the extent possible.

20.1 Units of weight and measure and their abbreviations

20.1.1 Symbols 

oC degrees Celsius

μg microgram

μL microliter

< less than

> greater than

% percent

20.1.2 Abbreviations (in alphabetical order) 

cm centimeter

g gram

h hour

ID inside diameter

in. inch

L liter

M Molecular ion

m mass

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

v/v volume per unit volume

w/v weight per unit volume

20.2 Definitions and acronyms (in alphabetical order)

Analyte – A compound tested for by this method. The analytes are listed in Tables 1 and 2.

Analyte of interest – An analyte of interest is an analyte required to be determined by a regulatory/control 

authority or in a permit, or by a client. 

Analytical batch – The set of samples analyzed on a given instrument during a 12-hour period that begins 

and ends with analysis of a calibration verification/LCS. See Section 8.4. 

Method 624.1 38 December 2014
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 

used to determine if analytes or interferences are present in the laboratory environment, the reagents, or the 

apparatus. See Section 8.5.

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 laboratory control sample (LCS) used to verify calibration. See 

Section 8.4.

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.

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 of 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 a sample in a known amount and used as a reference for 

quantitation of the analytes of interest and surrogates. Internal standards are listed in Table 5. Also see 

Internal standard quantitation.

Internal standard quantitation – A means of determining the concentration of an analyte of interest (Tables 1 

and 2) by reference to a compound added to a sample and not expected to be found in the sample.

DOC – Initial demonstration of capability (DOC; 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. A DOC is performed prior to the first time this method is used and any time the 

method or instrumentation is modified. 

Laboratory control sample (LCS; laboratory fortified blank (LFB); on-going precision and recovery sample; 

OPR) – 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. In this method, the 

LCS is synonymous with a calibration verification sample (See Sections 7.4 and 8.4).

Laboratory fortified sample matrix – See Matrix spike

Method 624.1 39 December 2014
Laboratory reagent blank – See Blank

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 (laboratory reagent 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 Table 1. As noted in 

Sec. 1.4, use the MDLs in Table 1 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

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.

Quality control sample (QCS) – A sample containing analytes of interest at known concentrations. The 

QCS is obtained from a source external to the laboratory or is prepared from standards obtained from a 

different source than the calibration standards. 

The purpose is to check laboratory performance using test materials that have been prepared independent 

of the normal preparation process.

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.

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.

Method 624.1 40 December 2014
Relative standard deviation (RSD) – The standard deviation times 100 divided by the mean. Also termed 

“coefficient of variation.” 

RF – Response factor. See Section 7.3.3.

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 for 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.

SIM – See Selection Ion Monitoring 

Should – This action, activity, or procedural step is suggested but not required.

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 and 

authenticity of the reference material.

Surrogate – A compound unlikely to be found in a sample, and which is spiked into sample in a known 

amount before purge-and-trap. The surrogate is quantitated with the same procedures used to quantitate 

the analytes of interest. The purpose of the surrogate is to monitor method performance with each 

sample.

Method 624.1 41 December 2014