Hach Method 10261

Total Organic Carbon in Finished Drinking Water by 

Catalyzed Ozone Hydroxyl Radical Oxidation Infrared 

Analysis
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Hach Company Method 10261

Revision 1.2

December 2015

Organic Carbon in Finished Drinking Water by Hydroxyl Radical Oxidation Infrared 

Analysis

1.0 Scope and Application

1.1 This method is for the determination of total organic carbon (TOC) in finished drinking 

water.

1.2 The method is applicable in the range from 1.0 to 300 mg/L TOC. High TOC values can 

be determined by sample dilution.

1.3 This method is equally effective in performance and use to SM 5310-C and EPA 415.3

for the purposes of regulatory compliance reporting of TOC.

2.0 Summary of Method

2.1 The on-line or laboratory organic carbon analyzer is used to monitor total organic carbon 

from a grab sample or continuous stream. The instrument has an on-board 

manufacturer’s calibration that may be verified and adjusted using independent aqueous 

calibration solutions.

2.2 Ozone and base is added to a stream of water where hydroxyl radicals are formed. The 

hydroxyl radicals oxidize organic carbon to carbon dioxide (CO2) and sodium oxalate. 

Sodium oxalate is further oxidized to CO2 through acidification and a manganese 

catalyst.

2.3 The CO2 produced from oxidation is detected and quantified using non-dispersive 

infrared spectroscopy (NDIR).

3.0 Interferences

3.1 The method is subject to chloride interferences at concentration greater than 30% saline, 

and inorganic carbon at a concentration greater than 1000 mg/L.

3.2 Particulate matter greater than 2 mm (cross sectional diameter) may restrict sample flow 

to the oxidation cell.

4.0 Safety

4.1 The toxicity or carcinogenicity of each reagent used in this method has not been precisely 

determined; however, each chemical should be treated as a potential health hazard. 

Exposure to these chemicals should be reduced to the lowest possible level. It is 

suggested that the laboratory perform personal hygiene monitoring of each analyst using 

this method and that the results of this monitoring be made available to the analyst.

4.2 Unknown samples may contain high concentrations of volatile toxic compounds. Sample 

containers should be opened in a hood and handled with gloves to prevent exposure.
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4.3 This method does not address all safety issues associated with its use. The laboratory is 

responsible for maintaining a safe work environment and a current awareness file of 

OSHA regulations regarding the safe handling of any chemicals specified in this method. 

A reference file of material safety data sheets (MSDSs) should be available to all 

personnel involved in these analyses. Additional information on laboratory safety can be 

found in Sections 16.3 and 16.4.

5.0 Equipment

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

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

materials other than those specified here, but demonstration of equivalent performance 

that meets the requirements of this method is the responsibility of the laboratory.

5.1 Sampling equipment

5.1.1 Sample collection bottles – Collect samples in pre-cleaned glass bottles. Pre-cleaned 

bottles have been acid rinsed, sealed with foil, and baked at 400 °C for at least 1 hour.

6.0 Equipment for sample analysis

6.1 On-line organic carbon analyzer

6.1.1 Hach Company BioTector TOC Analyzer, or equivalent

6.2 Equipment for standard preparation

6.2.1 Volumetric flask – Glass, 500-mL and 200-mL.

6.2.2 Volumetric pipette – Glass, assorted sizes.

7.0 Reagents and Standards

7.1 Organic-free water – Water in which TOC is below the detection limit of this method. 

Water prepared by passage of tap water through ion exchange and UV oxidation has been 

shown to be an acceptable source of reagent water.

7.2 Refer to the on-line organic carbon analyzer operating manual for a list of reagents 

specific to the instrument. Reagent grade chemicals or better should be used.

7.3 Hach Company TOC Standard Solutions: 1000 mg/L as TOC (Cat. No. 2791505) or 

equivalent

7.4 Method detection limit (MDL) solution

7.4.1 If an MDL is required, prepare 7 or more replicate MDL solutions by diluting 1.0 mL of 

the 1000 mg/L stock standard spiking solution (Section 7.3) to 1000 mL. Final 

concentration = 1.0 mg/L TOC.
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7.5 Initial precision and recovery (IPR) solution

7.5.1 Prepare 4 or more replicate IPR solutions by diluting 7.5 mL of the 1000 mg/L stock

standard spiking solution (Section 7.3) to 500 mL. Final concentration = 15 mg/L TOC.

8.0 Sample Collection, Preservation and Storage

8.1 Samples should be collected in pre-cleaned glass bottles. Pre-cleaned bottles have been 

acid rinsed, sealed with foil, and baked at 400 °C for at least 1 hour. Protect samples 

from sunlight. 

8.1.1 Rinse the sample bottle several times with sample. Fill the bottle completely full.

8.2 Analyze samples as soon as possible. If immediate analysis is not possible, preserve 

samples by cooling to <6 o

C, and adjust the pH to < 2 with HCl, H2SO4, or H3PO4.

Analyze the preserved within 28 days of preservation.

9.0 Quality Control

9.1 Each laboratory that uses this method is expected to operate a formal quality assurance 

program (16.1). The minimum requirements of this program consist of an initial 

demonstration of laboratory capability and ongoing analyses of laboratory prepared 

reagent blank water and standards as a test of continued performance to assess accuracy 

and precision. Laboratory performance is compared to established performance criteria 

to determine if the results of analyses meet the performance characteristics of the method.

9.1.1 The analyst shall make an initial demonstration of the ability to generate acceptable 

accuracy and precision with this method. This ability is established as described in 

Sections 9.2 and 9.3. The laboratory shall, on an ongoing basis, demonstrate through 

analysis of the ongoing precision and recovery sample that the analysis system is in 

control.

9.1.2 Accompanying QC for the determination of TOC is required per analytical batch. An 

analytical batch is a set of samples processed during a contiguous 8-hour period. Each 

analytical batch must be accompanied by an ongoing precision and recovery sample

(OPR), matrix spike sample (MS), and matrix spike duplicate sample (MSD) resulting in 

a minimum of four analyses (1 OPR, 1 sample, MS, and MSD).

9.2 Initial demonstration of laboratory capability.

9.2.1 To establish the ability to detect TOC the analyst shall determine the MDL using the 

apparatus, reagents, and standards that will be used in the practice of this method. An 

achieved MDL less than or equal to the MDL in Section 13.0 is recommended prior to 

the practice of this method.

9.2.2 Prepare and measure seven replicates of the MDL standard (Sect. 7.4) according to the 

procedure in Section 11.

9.2.3 Using the results of the set of seven analyses, compute the MDL using the following 

equation:
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MMMMMM =

( )

3.14

1

2

2

× −

− ∑ ∑

n

n

x

x

where:

n = Number of samples (7)

x = measured concentration of each sample

9.3 Initial precision and recovery (IPR) - To establish the ability to generate acceptable 

precision and accuracy, the analyst shall perform the following operations: 

9.3.1 Prepare and analyze a reagent water blank. Compare the reagent water blank 

concentration to the corresponding limit in Table 1 (Section 17). If the result meets the 

acceptance criterion, blank performance is acceptable. If the result is unacceptable, 

identify and correct the issue and repeat the test.

9.3.2 Prepare and measure four samples of the IPR standard (Sect. 7.5) according to the 

procedure in Section 11.

9.3.3 Using the results of the set of four analyses, compute the average percent recovery (x) 

and the standard deviation of the percent recovery (s) for TOC. Use the following 

equation for calculation of the standard deviation of the percent recovery: 

( )

1

2

2

−

−

=

∑ ∑

n

n

x

x

s

where:

n = Number of samples (4)

x = % recovery in each sample

9.3.3.1 Compare s and x with the corresponding limits for initial precision and recovery in Table 

1 (Sect. 17). If s and x meet the acceptance criteria, system performance is acceptable and 

analysis of samples may begin. If, however, s exceeds the precision limit or x falls 

outside the range for recovery, system performance is unacceptable. In this event, correct 

the problem, and repeat the test.

9.4 Ongoing precision and recovery (OPR) - To demonstrate that the analysis system is in 

control, and acceptable precision and accuracy is being maintained with each analytical 

batch, the analyst shall perform the following operations: 
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9.4.1 Prepare a 15 mg/L recovery standard with each analytical batch as described in Sect. 

7.5.1 and measure according to the procedure in Section 11. Calculate the percent 

recovery and compare this value with the limits for ongoing recovery in Table 2 (Sect. 

17). If the percent recovery meets the acceptance criteria, system performance is 

acceptable. If the percent recovery falls outside the acceptance criteria, system 

performance is unacceptable. In this event, correct the problem, and repeat the test.

9.4.1.1 Measure a field sample. After measuring the background concentration, spike the sample 

with a known concentration of TOC. The spike concentration should be 1-5 times the 

background concentration, but still within the reporting range of the method. Prepare a 

duplicate of this spiked sample.

9.4.1.2 Measure the spike duplicates and calculate the spike recovery for each sample and the 

relative percent difference (RPD) between the two results.

Use the following equation to calculate the spike recovery:

SSSSSSSSSS RR RRRRRR RRRR = [CC CC ] − [BB BBBB]

[SSSS] × 100

where:

[Conc] = the measured concentration of the spiked sample

[Bkgd] = the measured concentration of the un-spiked sample

[Sp] = the concentration of the spike

RRRR = |CC CC 1 − CC CC 2|

�

CC CC 1 + CC CC 2

2 �

× 100

where:

Conc1 = the concentration of the first spiked sample

Conc2 = the concentration of the second spiked sample

9.4.1.3 Compare the spike recoveries and RPD with the corresponding limits in Table 2 (Sect. 

17). If recoveries and RPD meet the acceptance criteria, system performance is 

acceptable and analysis of samples may begin. If recoveries or RPD fall outside the 

limits, system performance is unacceptable. In this event, correct the problem, and repeat 

the test.

9.4.1.4 The laboratory should add results that pass to IPR and previous OPR data and update QC 

charts to form a graphic representation of continued laboratory performance. The 

laboratory should also develop a statement of laboratory data quality for each analyte by 

calculating the average percent recovery (R) and the standard deviation of the percent 

recovery (sr). Express the accuracy as a recovery interval from R - 2sr to R + 2sr. For 

example, if R = 95% and sr = 5%, the accuracy is 85% to 105%. Control charts are 

acceptable for evaluating process control, but under no circumstances can the control 

limits be widened beyond those established in the acceptance criteria defined in Section 

13. 
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10.0 Calibration and Standardization

10.1 The Hach BioTector TOC Analyzer has a built-in calibration. No further initial 

calibration is required. However, the instruments have the capability of developing a 

user-calibration. See manufacturer’s manual for instructions.

10.2 Calibration Verification

10.2.1 To verify that the instrument is measuring TOC properly, analyze a 1.0 mg/L (Sect. 7.4)

and 15.0 mg/L (Sect. 7.5) TOC standard. Results should be within 15 percent of the 

actual value. Perform this calibration verification daily while instrument is in use. If the 

calibration verification standard result is outside the limit, it is unacceptable. In this 

event, correct the problem, and repeat the test.

11.0 Procedure

11.1 Instrument Setup – follow the instrument manufacturer’s instructions for instrument

setup.

11.2 Follow the manufacturer’s instructions for sample analysis.

12.0 Data Analysis and Calculations

12.1 TOC concentration is calculated automatically against internal instrument calibration.

13.0 Method Performance

Performance of the method was demonstrated in multi-lab studies comparing the method 

against EPA Reference Method SM 5310-C. The method was evaluated in low ionic 

strength reference matrix as well as multiple geographically diverse finished drinking 

water samples obtained from both surface water and ground water sources.

Validation Results Section Limit 

Method Detection Limit 9.2 0.02 mg/L 

Initial Recovery 9.3 100%

Initial Recovery Range 9.3 99.3% - 101%

Initial Precision 95% 9.3 0.01

Matrix Spike Recovery 9.4.1 102%

Matrix Recovery Range 9.4.1 96.5% - 107%

Matrix Recovery Precision 95% 9.4.1 0.02

14.0 Pollution Prevention

14.1 Follow guidelines in Section 15.

15.0 Waste Management

15.1 It is the laboratory’s responsibility to comply with all federal, state, and local regulations 

governing waste management, particularly the hazardous waste identification rules and 

land disposal restrictions, and to protect air, water, and land by minimizing and control 
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all releases from fume hoods and bench operations. Compliance with all sewage 

discharge permits and regulations is also required.

15.2 For further information on waste management, consult “The Waste Management manual 

for Laboratory Personnel”, and “Less is Better: Laboratory Chemical Management for 

Waste Reduction”, both available from the American Society’s Department of 

Government Relations and Science Policy, 1155 16th Street N.W., Washington, D.C. 

20036.

16.0 References

16.1 “Protocol for the Evaluation of Alternate Test Procedures for Organic and Inorganic 

Analytes in Drinking Water,” USEPA, EPA-815-R-15-007, February 2015.

16.2 40 CFR 136, Appendix B.

16.3 “OSHA Safety and Health Standards, General Industry,” (29 CFR 1910), Occupational 

Safety and Health Administration, OSHA 2206 (Revised, January 1976)

16.4 “Safety in Academic Chemistry Laboratories,” American Chemical Society, Committee 

on Chemical Safety, 3rd Edition, 1979.

16.5 “Water Analysis Handbook,” Hach Company, 8th Edition, 2013.

17.0 Tables

17.1 Acceptance Criteria for Performance tests – The QC performance criteria for this method 

were performed with a Hach Company BioTector TOC Analyzer.

Table 1. Initial Precision and Recovery Acceptance Criteria

Parameter Acceptance Criteria

Reagent Blank ≤ 0.5 mg/L C

Percent Recovery 90% - 110%

Relative Standard Deviation ≤ 10%

Table 2. Ongoing Precision and Recovery Acceptance Criteria

Parameter Acceptance Criteria

Reagent Blank ≤ 0.5 mg/L C

Lab Fortified Blank Recovery 90-110%

Sample Matrix Spike Recovery 70-130%

Sample Matrix Spike Recovery RPD ≤ 10%
18.0 Glossary of Definitions and Purposes

The definitions and purposes are specified to this method but have been conformed to common 

usage as much as possible.

18.1 Units of weight and measure and their abbreviations

18.1.1 Symbols

o

C: degrees Celsius

18.1.2 Alphabetical characters

mg/L: milligram per liter

18.2 Definitions, acronyms, and abbreviations

18.2.1 MDL: Method detection limit

18.2.2 IPR: Initial precision and recovery

18.2.3 OPR: On-going precision and recovery

18.2.4 MS: Matrix spike

18.2.5 MSD: Matrix spike duplicate

18.2.6 LIS: Low ionic strength, deionized water

18.2.7 HIS: High ionic strength, 250 mg/L CO3, 250 mg/L CaCO3