Validation Study Plan for Proposed ATP Method Hach 10225 for the Colorimetric 

Measurement of Fluoride Ion Using SPANDNS Reagent and an Arsenite-free Interferent 

Reduction Option

Introduction

This validation study plan (Plan) follows in part, follows the guidelines set forth in the 

United States Environmental Protection Agency (EPA) document Protocol for EPA Approval of 

Alternate Test Procedures for Organic and Inorganic Analytes in Wastewater and Drinking 

Water.

1

 The Plan is part of the application for requesting expedited approval of Hach Method 

10225 for the Colorimetric Measurement of Fluoride Using SPADNS and an Arsenite-free 

Interferent Reduction Option.

Method Justification

EPA reference method SM4500-F D and ATP Hach Method 8029 are colorimetric 

methods that use SPADNS chemistry for the measurement of fluoride. As part of these methods, 

sodium arsenite is used for the removal of residual chlorine, as it is an interferent in the analysis 

for fluoride. Hach Method 10225 for the Measurement of Fluoride uses the exact same core 

chemistry as the EPA reference and ATP methods cited above, but differs by replacing the 

sodium arsenite with a green non-hazardous chlorine scavenger.

Program Use

This method is currently approved for use in 40 CFR part 136 wastewater programs 

under section 136.6. It is being proposed as an alternative method under the EPA Office of 

Drinking Water Expedited Rule for 40 CFR 141 drinking water monitoring programs.

Single Laboratory Performance Data and Results

In the development of this test method, a single laboratory side-by-side study was 

performed with the EPA reference SM4500-F D and ATP 8029 methods. The summary of the 

results are listed in Table 1. 

 

11 EPA-821-B-98-002, March 1998.
Table1. Summary of Results from Fluoride Side-by-side Study

Performance Test

Reference Method Results

SM 4500-F D/Hach 8029

Proposed ATP Method 

Results Hach 10225

MDL – 7 reps at 0.03 mg/L F- 0.014 mg/L F- 0.014 mg/L FQL – 3.18 X MDL rounded up 0.05mg/L F- 0.04 mg/L FIPR – 4 reps at 1.0 mg/L FAverage 100.3% 99.8%

IPR – 4 reps at 1.0 mg/L FStdev 0.50 0.50

IPR – 4 reps at 1.0 mg/L F-

%RSD 0.49% 0.50%

Matrix Spikes – Duplicates at 

5.0 mg/L Cl2

Fall City, Washington spiked 

@ 1.0 mg/L FDuplicate Average 94.5% 97.0%

Duplicate %RSD 0.75% 0.00%

Sandy Springs, Georgia spiked 

@ 0.50 mg/L FDuplicate Average 90.0% 96.0%

Duplicate %RSD 3.14% 0.00%

Dallas, Texas spiked @ 0.50 

mg/L FDuplicate Average 92.0% 92.0%

Duplicate %RSD 3.07% 0.00%

Proposed Validation Test Plan

Test Analyte – Fluoride ion

Number of test matrices – 3

Number of test laboratories – 3

Geographic locations – California, Colorado, Iowa

Reference Method – SM4500-F D/Hach 8029

ATP Method – 10225
Comparative Test

Validation performed by laboratories in three geographically distinct regions (CA, CO, 

IA)

Calibration verification at 0.5 and 1.5 mg/L FMDL – 7 replicates spiked @ 0.1 mg/L F- with low ionic strength water and a minimum 

of 2.0 mg/L Cl2

MDL – 7 replicates spiked @ 0.1 mg/L F- with high ionic strength water* and a 

minimum of 2.0 mg/L Cl2

IPR – 4 replicates spiked @ 1.0 mg/L F- with low ionic strength water and a minimum of 

2.0 mg/L Cl2

IPR – 4 replicates spiked @ 1.0 mg/L F- with high ionic strength water and a minimum of 

2.0 mg/L Cl2

Matrix – 4 replicates of tap water with fluoride fortification levels of 0.5 – 1.0 mg/L Fand residual chlorine levels of 0.02 – 2.00 mg/L Cl2

One laboratory to distill matrix samples

* High ionic strength water was prepared by weighing 0.70 g sodium bicarbonate, 0.74 g 

sodium sulfate and 0.77 g sodium chloride into a 1-L volumetric flask and bringing to 

volume with reagent water. The stock solution was diluted by a factor of 10x and used for 

the analyses.