Pitfalls and solutions for the trace determination of phthalates in water samples

A method based on liquid-liquid extraction (LLE) and automated large volume injection (LVI)GC-MS analysis was developed for the trace determination of phthalate di-esters in water samples at sub-mu g L-1 (ppb) levels. Strategies applied to reduce contamination include (i) careful selection of tools, glassware and solvents, (ii) systematic blank checks of the chromatographic system, glassware and solvents and (iii) frequent verifications of blanks during sequences. Background levels could be reduced to those present in the extraction solvent. For phthalates not present in the extraction solvent the limits of quantitation (LOQ) are 6 ng L-1 for di-methyl phthalate (DMP), 3 ng L-1 for benzylbutyl phthalate (BzBP) and 45 ng L-1 for the isomeric phthalate mixtures di-isononyl phthalate (DiNP) and di-isodecyl phthalate (DOP). For the other phthalates, the LOQ was set at twice the blank (extraction solvent) level and are 20 ng L-1 for di-ethyl phthalate (DEP), 60 ng L-1 for di-isobutyl phthalate (DiBP), 80 ng L-1 for di-n-butyl phthalate (DBP) and 30 ng L-1 for bis-(2-ethylhexyl) phthalate (DEHP).