cleaning method for nonionic surfactant with derivatization

[parsely10]

I am trying to develop a swab method for equipment cleaning. The peak of interesting is Poly(oxy-1,2-ethanediyl), a-undecyl-w-hydroxy, C11O(CH2CH2O)7H, . I use Phenyl Isocyanate as derivatization reagent (1,2 dicholoethane as solvent) since we only have UV detector in our lab. The sample solution is incubated in water bath at 60C for three hours and the reaction was quenched with methanol at the end.

I have difficults to control the reaction: the precision from multiple sample preparations is pretty bad (RSD >15%) even though i prepared them at the same time. I tried eicosanol (C20-OH) as internal std but the results are even worse. Any recommendation?

thanks in advance

[Consumer Products Guy]

How about a colorimetric test specific for nonionic surfactants, like the ammonium cobalt thiocyanate test?

[parsely10]

thanks for your guidance and i really appreciate it.