Hach Method 10267

Spectrophotometric Measurement of Total Organic Carbon 

(TOC) in Finished Drinking Water 
Hach Company Method 10267

TNTplus 810/811

Revision 1.2

December 2015

Spectrophotometric Measurement of TOC in Finished Drinking Water 

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 25.0 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 Hach TNTplus TOC chemistry follows acid persulfate digestion to oxidize TOC to carbon 

dioxide (CO2). The generated CO2 passes through a gas-permeable membrane into an indicator 

solution is measured spectrophotometrically. Inorganic carbon (IC) is removed from the sample 

prior to digestion by acidification and agitation. 

2.2 The CO2 produced from oxidation is detected and quantified using visible spectrum 

spectrophotometry at 435 nm.

3.0 Interferences

3.1 The items listed in the Interfering substances table have been individually checked up to the given 

concentrations and do not cause interference. The cumulative effects and influence of other ions 

have not been determined. Measurement results can be verified using sample dilutions or standard 

additions.

Interfering substance Interference level (mg/L)

NH4

+ 200

Ca+ 2000 as CaCO3

Cl- 1000

Mg+ 2000 as CaCO3

Inorganic Carbon 250 CO3

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.
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 Hach Company DR 6000, DR 3900, DR 1900 spectrophotometer, or equivalent

6.2 Hach Company DRB200 reactor, or equivalent

6.3 Hach Company TOC X-5 shaker or equivalent

6.4 Equipment for standard preparation

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

6.4.2 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 Hach Company TNTplus TOC, Cat. No. TNT810 and TNT811.

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 and measure 7 or more replicates of an MDL stock solution by 

diluting 3.0 mL of the 1000 mg/L standard spiking solution (Section 7.3) to 1000 mL. Final 

concentration = 3.0 mg/L TOC.

7.5 Initial precision and recovery (IPR) solution
7.5.1 Prepare and measure 4 or more replicates of an IPR stock solution by diluting 7.5 mL of the 1000 

mg/L 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 oC, 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 water 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:

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 measure four samples of the IPR standard (Sect. 7.5) according to the procedure in 

Section 11.

9.3.2 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

9.3.2.1 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: 

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. 

10.0 Calibration and Standardization

10.1 The Hach DR series spectrophotometers have a built-in calibration that is automatically used when 

the TNTplus TOC vial is inserted into the instrument. 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 3.0 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 Preparation 

11.2.1 Low Range TNT 810: Pipet 2.0 or 2.5 mL of sample into the reagent vial, use volume as indicated 

in manufacturer’s instructions. 

11.2.2 High Range TNT 811: Pipet 1.0 mL of sample into the reagent vial.

11.3 Total Inorganic Carbon Removal

11.3.1 Place the uncapped reagent vial into the TOC-X5 shaker, raise the fan assembly, and turn the 

shaker on. The shaker will run for 5 min.

11.4 Reaction

11.4.1 Place the membrane cap on the indicator vial.

11.4.2 Invert the indicator vial and screw the other side of the membrane cap to the shaken reagent vial. 

Do not invert or shake the assembled vials.

11.4.3 Heat the reactor block to 100 °C.

11.4.4 Place the assembled vials into the reactor block, reagent vial down.

11.4.5 React for 120 minutes.

11.5 Analysis

11.5.1 Carefully remove the assembled vials from the reactor.

11.5.2 Invert the assembly so that the indicator vial is down.

11.5.3 Wipe the indicator vial and insert into the spectrophotometer. The instrument reads the barcode, 

then selects and performs the correct test. No zero is required. Results are reported in mg/L TOC.

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 a 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 0.33 mg/L TOC

Initial Recovery 9.3 103%

Initial Recovery Range 9.3 97.5% - 109%

Initial Precision 95% 9.3 0.03

Matrix Recovery 9.4.1 99.5%

Matrix Recovery Range 9.4.1 94.3 – 105%

Matrix Recovery Precision 95% 9.4.1 0.06

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 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 was 

performed with a Hach Company DR3900 Spectrophotometer and TNTplus 810 Reagent.

Table 1. Initial Precision and Recovery Acceptance Criteria

Parameter Acceptance Criteria

Relative Standard Deviation ≤ 10%

Percent Recovery 90-110%

Table 2. Ongoing Precision and Recovery Acceptance Criteria

Parameter Acceptance Criteria

Lab Fortified Blank Recovery 90-110%

Sample Matrix Spike Recovery 70-130%

Sample Matrix Spike 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