Page 1 of 2 Office of Ground Water and Drinking Water

February 18

, 201 6

MEMORANDUM

SUBJECT: Basis for Expedited Approval of Thermo Fisher Scientific Orthophosphate Discrete

Analyzer Method for Drinking Water

FROM: William A. Adams

, Chemist,

SRMD/TSC

TO: The Record

Thermo Fisher Scientific submitted an orthophosphate discrete analyzer method as an alternate test

proce dure to S tandard M ethod (SM) 4500

- P E a nd S tandard M ethod (SM) 4500

- P F

. SM 4500

- P E and

SM 4500

- P F are approved in the national primary drinking water regulations at 40 CFR 141.23(k)(1) for the determination of orthophosphate by ascorbic acid reduction followed by colorimetr ic
detection

.

In t he Thermo Fisher discrete analyzer o rthophosphate method, orthophosphate is reacted with ammonium molybdate and antimony potassium tartrate in an acidic medium to form an antimony

phospho

- molybdate complex. The complex is then reduced by ascorbic acid to form an intensely
blue

- colored complex that can be measured spectrophotometrically (880 nm). Only orthophosphate forms the blue color in the analysis. The Thermo Fisher orthophosphate method uses a n automated discrete analyzer, which decreases cost through minimizing the us e of chemical reagents and generation of waste products

, along with a decreased possibility of human error compared to the approved manual SM 4500

- P E method. In turn, the analysis of drinking water samples becomes easier without risking the quality of res ults.

A validation study was conducted to compare the performance of the Thermo Fisher

o rthophosphate method with SM 4500

- P E

. An initial demonstration of capability was performed using different ma trixes ( e.g. tap water from surface and ground water sources ) at various orthophosphate concentrations. Reagent blank data to evaluate contamination , p recision and

recovery data, and detection limit data were ; in addition, a method minimum reporting level ( MRL )
was confirmed

. The complete data summary is pro vided in the Thermo Fisher Scientific ATP
Validation Report. Briefly, the results are as follows:

 The detection limit calculated as MDL for the Thermo Fisher Scientific method was determined to be 0.00036 mg P/L compared to 0.0032 mg P/L for the reference SM 4500

- P

E

. MR Ls were confirmed at 0.01 mg P / L for the Thermo Fisher Scientific method and 0.015 mg P/L for the reference SM 4500

- P E

.

 The recovery for initial precision and recovery ( IPR ) samples ranged from 102 % to 103 %
with 0.1 to 1. 0 %RSD for the Thermo Fisher Scientific method and 101% to 102 % with 0.4
%RSD for the reference SM 4500

- P E

. The recovery for precision and accuracy laboratory fortified blank ( LFB ) samples ranged from 102% to 103% with 0.2 to 1.1 %RSD for thePage 2 of 2

Thermo Fishe r Scientific method and 92 .0 % to 104% with 0.29 to 0.96 %RSD for the
reference SM 4500

- P E.

 Mid

- level continuing calibration check ( CCC ) recovery results ranged from 100% to 105%
with 1.3 to 1.9 %RSD for the Thermo Fisher Scientific method and 97 .5 % to 104% with 1.5
%RSD for the reference SM 4500

- P E.

 The average matrix spike recovery results ranged from 92 .0% to 97.9 % with 0.1 to
0 .7 %RSD for the Thermo Fisher Scientific method and 94 .4 % to 101 % with 0.24 to 3 .0
%RSD for the reference SM 4500

- P E

.

Based on the results of the validation study, the T hermo Fisher Scientific discrete analyzer method was determined to be equally as effective as the reference SM 4500

- P E for the determin ation of orthophosphate in drinking water.