Results of Selenate Determination

The discussion focused on how to reduce selenite to selenate efficiently and calculate the recovery. Since a selenite calibrant was used to verify the efficiency of the reduction process, the laboratories were recommended to apply the same analytical procedure to both samples and calibrants. It was stressed that the HCl molarity and the reduction temperature should be strictly controlled. HCl molarities ranging between 4 and 6 mol L and temperatures ranging between 60 and 100 °C (with different heating times) were found to be suitable to ensure complete reduction of selenate to selenite. 

The determination of selenate by difference between total inorganic selenium content and selenite was questioned. Although this method is quite commonly used and acceptable for selenate determination, this does not correspond to a direct measurement of the species hence, this method would not be accepted for certification and it was proposed that the results obtained by difference would be used as confirmative v ues of results obtained by techniques actually separating the Se species e.g. HPLC-ICP-MS or HPLC-HGAAS). 

For solution A, the CV between laboratories (raw data) was 31.9% it decreased to 4.1% after removing outliers on technical grounds. The mean of laboratory means was (6.2 0.3) pg which overlapped the expected value of 6.0 pg 

---