Chromatography Forum

I've been doing 515.4 for decades and once in a while a sample will fail the 30% acceptance range for 2,4-dcpaa. Spikes for these samples also fail the surrogate, but the 7 calibrated herbicides are all acceptable. The internal response for these samples are very close to the average of calibration. In these samples there is a very large peak about 4 minutes before the surrogate, but is not present in our method preserved blank water.
Anyone else see this? It seems as if 2,4-DCPAA does not track the other herbicides in the method.

Thanks

Not sure if you had any responses to this old one but we found the following issue with preservation in the method - more is not better. Other analytes were not affected.


Laboratory 515.4 Preservative Study
Table of % Recoveries of Surrogates and Spiked Analytes
Sample Type and mg of Na2SO3 Added
Austin tap DI Water
3 10 20 3 10 20
DCAA surrogate 96 51 33 101 55 31
2,4-DB 90 17 12 102 19 12
Chloramben 98 71 52 109 65 39