USEPA Validation Study Report for Hach Method 10261 Total Organic 

Carbon in Finished Drinking Water by Catalyzed Ozone

Hydroxyl Radical Oxidation Infrared Analysis

Submitted by:

Hach Company

5600 Lindbergh Drive

Loveland Colorado 80538

Cary Jackson 

and

Luke Johnson

December 2015
Hach Company Validation Study Report

Measurement of TOC in Water and Wastewater, Method 10261

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Background

Purpose of Study

The purpose of this study is to validate proposed Hach Method 10261, Measurement of Total 

Organic Carbon (TOC) in Water and Wastewater for approval and use in USEPA regulatory 

drinking water compliance and reporting programs.

Method Summary

The 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.

Ozone and base are 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.

The CO2 is detected and quantified by non-dispersive infrared spectroscopy.

Method Justification

The EPA Reference Method SM 5310-C for the measurement of TOC is laborious and does not 

completely oxidize certain organic compounds. A simple, more efficient and lower cost

analytical method is desirable. The proposed method uses an advanced oxidation process 

which ensures complete oxidation.

Scope of Method

Method 10261 is applicable for use in drinking water, surface, and municipal and industrial 

wastewaters. 

Study Design and Objectives

The design and objectives of this validation study are detailed in the Validation Study Plan0F

1

appended to this report.

Study Implementation

Study Sponsor

The organizational sponsor responsible for managing this study is Hach Company.

 1 Hach Validation Study Plan, March 2015
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Measurement of TOC in Water and Wastewater, Method 10261

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Study Participants

The participants, laboratories, and test matrices were selected from geographically diverse

regions of the United States and are listed in the following table.

Treated Drinking 

Water Matrix 

Facility

Laboratory Source of Treated 

Test Water

Loveland, Colorado Hach Company Surface Water

Keokuk, Iowa Test America-Cedar Falls, Hach Company Surface Water

Brighton, Colorado Test America-Pittsburgh, Hach Company Ground Water

Sample Collection and Distribution

Matrix samples for this validation study were collected, preserved, and stored per SM 5310-C 

protocols.

Analysis Description

The description of the type and number of analyses are described in the Validation Study Plan 

appended to this report.

Data Reporting and Validation

Data Collection, Laboratory Submission, and Validation

For each laboratory performing analyses, results from each test measurement were read from a 

BioTector 3500 analyzer and manually transferred to an electronic spread sheet. Each 

laboratory then submitted the electronic spread sheet to the Hach Study Director for review 

and statistical evaluation. 

Results

Summary results of the validation study are listed in Tables 1-5. Initial demonstration of 

capability is demonstrated by accuracy (bias) and precision data which are generated 

throughout the calibration range in several matrices. These data were collected at the Hach 

laboratory and are included in Table 1. The quantitation range and method reporting limits for 

this method are 0.1-300 mg/L TOC.
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Table 1 – Initial Demonstration of Capability for Hach Method 10261

Parameter Concentration 

(mg/L)

Average Percent Recovery by Matrix

LIS 250 mg/L CO3

250 mg/L 

CaCO3

Method Blank 0 0.0 0.0 0.0

Average Percent Bias by Matrix

LIS 250 mg/L CO3

250 mg/L 

CaCO3

Accuracy (bias) 

Low 3.0 2.1 4.0

Mid 3.8 4.7 1.8

High 2.2 1.0 1.0

Percent Relative Standard Deviation by Matrix

LIS 250 mg/L CO3

250 mg/L 

CaCO3

Precision 

Low 0.9 1.2 3.1

Mid 0.3 1.0 0.4

High 2.8 0.3 0.3

Average Percent Bias by Matrix

Loveland DW Brighton DW Keokuk DW

Matrix Spike 

Accuracy (bias)

Low 4.7 2.5 1.2

Mid 7.3 7.0 1.1

High 1.0 6.4 2.1

Percent Relative Standard Deviation by Matrix

Loveland DW Brighton DW Keokuk DW

Matrix Spike 

Precision

Low 4.1 2.1 0.5

Mid 0.5 0.2 0.6

High 2.0 0.6 0.6
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Measurement of TOC in Water and Wastewater, Method 10261

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 Table 2 – Loveland Colorado Tap Water Performance Results 

Method 

Detection 

Limit (mg/L)

Method 

Detection 

Limit (mg/L)

Low Ionic Strength 

Reagent Water

0.17 0.02

High Ionic Strength 

Reagent Water 0.09 0.06

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Low Ionic Strength 

Reagent Water 102 2 1 100 0 0.3

High Ionic Strength 

Reagent Water 105 5 5 100 0 1

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

102 0.3 101 0.8

Matrix Spike Analysis Matrix Spike Analysis

Matrix

SM 5310-C Hach Method 10261

Initial Precision and Recovery Initial Precision and Recovery

Loveland Treated 

Tap Water
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Table 3 – Keokuk Drinking Water Plant Summary Results 

Method 

Detection 

Limit (mg/L)

Method 

Detection 

Limit (mg/L)

Low Ionic Strength 

Reagent Water

0.054 0.03

High Ionic Strength 

Reagent Water 0.06 0.12

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Low Ionic Strength 

Reagent Water 100 0 0 100 0 1

High Ionic Strength 

Reagent Water 102 2 1 100 0 1

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

103 9.3 101 0.1

Matrix

SM 5310-C Hach Method 10261

Initial Precision and Recovery Initial Precision and Recovery

Keokuk Treated 

Tap Water

Matrix Spike Analysis Matrix Spike Analysis
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Table 4 – Brighton Colorado Drinking Water Plant Summary Results

Development of QC Acceptance Criteria

Quality control acceptance criteria for method detection limit (MDL), initial precision and 

recovery (IPR), and matrix spike recovery are described in Table 5. Calibration verification is 

demonstrated through the accuracy (bias) data. These criteria are based on intra-laboratory 

data. 

Method 

Detection 

Limit (mg/L)

Method 

Detection 

Limit (mg/L)

Low Ionic Strength 

Reagent Water

0.12 0.03

High Ionic Strength 

Reagent Water 0.17 0.14

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Average 

Percent (%) 

Recovery

Percent Bias Standard 

Deviation

Low Ionic Strength 

Reagent Water 100 0 0 100 0 0

High Ionic Strength 

Reagent Water 100 0 0 100 0 0

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

Average 

Percent (%) 

Recovery

Relative 

Percent 

Difference

110 2.6 104 0.5

Matrix

Brighton Treated 

Tap Water

Matrix Spike Analysis Matrix Spike Analysis

SM 5310-C Hach Method 10261

Initial Precision and Recovery Initial Precision and Recovery
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Table 5 – Quality Control Performance Criteria for Hach Method 10261

Data Analysis/Discussion

MDL Results

The low ionic strength matrix MDL results for each of the three facilities ranged from 0.04 mg/L 

to 0.16 mg/L for the EPA Reference Method SM 5310-C, and 0.02 mg/L to 0.03 mg/L for Hach 

Method 10261. The high ionic strength matrix MDL results ranged from 0.06 mg/L to 0.17 mg/L 

for the EPA Reference Method SM 5310-C and 0.06 mg/L to 0.14 mg/L for Hach Method 10261. 

The pooled MDL results for EPA Reference Method SM 5310-C were determined to be 0.10

mg/L for low ionic strength matrix water and 0.09 mg/L for high ionic strength matrix water. 

The pooled MDL results for Hach Method 10261 were determined to be 0.02 mg/ for low ionic 

strength matrix water and 0.09 mg/L for high ionic strength matrix water. 

Initial Precision and Recovery Results

The IPR average recovery results for low ionic strength matrix water for each of the three 

facilities ranged from 100% to 102% for EPA Reference Method SM 5310-C and 100% for Hach 

Method 10261. The IPR average recovery results for high ionic strength matrix water ranged 

Low Ionic Strength 

Reagent Water

High Ionic Strength 

Reagent Water

Initial Precision and 

Recovery Analysis

Average 

Percent (%) 

Recovery

Percent Bias

Lower Limit 

of % 

Recovery

Upper Limit 

of % 

Recovery

95% 

Precision of 

Recovery

Average 

Percent (%) 

Recovery

Percent Bias

Lower Limit 

of % 

Recovery

Upper Limit 

of % 

Recovery

95% 

Precision of 

Recovery

Low Ionic Strength 

Reagent Water 101 1 96.2 105 0.01 100 0 99.3 101 0.01

High Ionic Strength 

Reagent Water 102 2 93.2 111 0.06 100 0 99.7 100 0.02

Average 

Percent (%) 

Recovery

Percent Bias

Lower Limit 

of % 

Recovery

Upper Limit 

of % 

Recovery

95% 

Precision of 

Recovery

Average 

Percent (%) 

Recovery

Percent Bias

Lower Limit 

of % 

Recovery

Upper Limit 

of % 

Recovery

95% 

Precision of 

Recovery

105 5 89.6 121 0.04 102 2 96.5 107 0.02

Matrix

SM 5310-C Hach Method 10261

Initial Precision and Recovery (IPR) Initial Precision and Recovery (IPR)

Drinking Water 

Matrix Analysis

Matrix Spike Recovery Matrix Spike Recovery

Method Detection Limit (MDL) 

mg/L

0.10

0.09

Method Detection Limit (MDL) 

mg/L

0.02

0.09
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Measurement of TOC in Water and Wastewater, Method 10261

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from 100% to 105% for EPA Reference Method SM 5310-C and 100% for the Hach Method 

10261. 

The pooled low ionic strength matrix recovery results for EPA Reference Method SM 5310-C 

was determined to be 101% with a 95% precision of 0.01, and 100% with a 95% precision of 

0.01 for Hach Method 10261. The pooled high ionic strength matrix recovery results for the 

EPA Reference Method SM 5310-C was determined to be 102% with a 95% precision of 0.06

and 100% with a 95% precision of 0.02 for Hach method 10261.

Matrix Spike Results

The average matrix spike recovery results of the three facilities ranged from 102% to 110% for 

EPA Reference Method SM 5310-C and 101% to 104% for Hach method 10261. The relative 

percent difference for matrix spike recoveries ranged from 0.3 to 9.3 for EPA reference method 

SM 5310-C and 0.1 to 0.8 for Hach method 10261. 

The pooled matrix spike results of recovery for EPA Reference Method SM 5310-C was 

determined to be 105% and 102% for Hach Method 10261. The 95% Precision of Recovery 

results for the EPA Reference Method 5310-C and Hach Method 10261 were determined to be 

0.04 and 0.02 respectively.

Conclusion

A validation study was conducted to compare the performance of Hach Method 10261 for the 

measurement of TOC in water to that of the EPA Reference Method SM 5310-C. The results of 

the study indicate that Hach Method 10261 is equally effective to that of the EPA Reference 

Method SM 5310-C for Safe Drinking Water Act monitoring and compliance reporting 

programs.