Spectrophotometric determination of polyoxyethylene nonionic surfactants in ground waters using triple-stage solid-phase extraction followed by an improved ferric thiocyanate complexation method

A practical spectrophotometric determination method for polyoxyethylene nonionic surfactants in ground waters was established, which is based on a ferric thiocyanate complexation colorimetric method preceded by a triple-stage solid-phase extraction technique using SCX, SAX, and C18 cartridges interconnected. Cationic and anionic surfactants interfere with the determination and were therefore effectively trapped and isolated by the SCX and SAX solid phases, respectively. Nonionic surfactants (NSs) were finally introduced and concentrated in the C18 cartridge. The analyte was quantitatively eluted from the C18 sorbent, and the residue was subjected to the colorimetric determination. The calibration line was linear (r(2) = 0.9997) up to 200 mu g L-1 of heptaoxyethylenedodecylether when analyzing sample sizes of 100 mL. Overall recoveries were 95-97% with an RSD of less than 3%. The method was applied to the analysis of river water, and 6.4 mu g L-1 of NSs as heptaoxyethylenedodecylether was found by means of the standard addition method. The proposed method is very practical and features minimum consumption of chemicals.