Abstract
The present work reports capillary liquid chromatographic (LC) column switching methodology tailored for sensitive and selective determination of the four phthalic acid monoesters monoethyl phthalate (MEP), monobutyl phthalate (MBP), monobenzyl phthalate (MBzP) and monoethylhexyl phthalate (MEHP) in human urine using electrospray ionization (ESI) mass spectrometry (MS). Method validation was performed utilizing quadropole ion trap (QIT) MS detection. Sample volumes of 200 µL of deconjugated and 10 times diluted urine were loaded onto a preconcentration column of 34 mm x 0.32 mm inner diameter (ID) packed with Hypercarb 5 µm particles using a loading mobile phase consisting of H2O/ACN (85/15, v/v, adjusted to pH 2.5 using HCl) with a flow rate of 20 µL/min. Backflushed elution onto a 75 mm x 0.32 mm ID analytical column packed with 5 µm Hypercarb particles was conducted using a H2O/THF gradient (0.5-90% THF) where both solvents contained 10 mM ammonium acetate, at a flow rate of 4 µL/min. Elution of the monophthalates was provided within 8 min and the total analysis time was less than 25 min with manual operation. Ionization was performed in the negative mode and MEP, MBP, MBzP and MEHP were observed as [M–H]- at m/z 192.9, 220.9, 255.0 and 277.1, respectively. Quantification was performed in the multiple reaction monitoring (MRM) mode monitoring the fragments at m/z 120.9, 176.9, 182.9 and 233.0 for MEP, MBP, MBzP and MEHP, respectively. The method was validated over the concentration range 2.5–125 ng/mL in pre-treated diluted urine, yielding correlation coefficients in the range 0.996-0.999. The within-assay (n=6) and between-assay (n=6) repeatabilities were in the range 4.0-24% and 4.8-15%, respectively. The mass limits of detection (mLOD) for MEP, MBP, MBzP and MEHP using QIT-MS and MRM were 70, 32, 50 and 40 pg respectively, corresponding to a concentration limit of detection (cLOD) of 3.5, 1.6, 2.5, and 2.0 ng/mL urine, utilizing a 200 ìL sample loop.