Abstract:

A method for the analysis of seven phthalate acid esters (PAEs) including dimethyl phthalate (DMP), diethyl
phthalate (DEP), di-iso-butyl phthalate (DIBP), dibutyl phthalate (DBP), di (2-ethtlhexyl) phthalate (DEHP), butyl benzyl
phthalate (BBP) and di-n-octyl phthalate (DNOP) in oil feedstock by gas chromatography-mass spectrometry (GC-MS) was
established. In this method, sample pretreatment was achieved by organic solvent extraction and subsequent purification by
N-(n-propyl) ethylenediamine (PSA) solid-phase extraction (SPE), and the analytes were analyzed by GC-MS with internal
standard calibration. The proposed calibration curves had good linearity in the range of 0.01–2.0 mg/L with correlation
coefficients between 0.999 8 and 1.000 0. The limits of detection (LODs) (RSN =3) of this method were 0.01–0.02 μg/L
and the limits of quantitation (LOQs) (RSN =10) ranged from 0.03 μg/L to 0.06 μg/L. The average recoveries of 7 PAEs
varied from 77.2% to 98.8% with relative standard deviation (LSDs) of 0.62%–9.37% (n = 6) at the spiked levels 0.1, 0.5,
and 1.0 mg/kg. The contents of 7 PAEs (DMP, DEP, DBP, DIBP, BBP, DEHP, and DNOP) in 76 oil feedstock samples
from different species and geographic origins were determined by this method. The results showed that DBP and DEHP
were detected in all these samples, ranging from (0.015 ± 0.002) to (0.584 ± 0.012) mg/kg and from (0.085 ± 0.006) to
(2.334 ± 0.016) mg/kg, respectively. The detection rates of DIBP, DEP, DMP, BBP, and DNOP were 98.7% (75/76), 64.5%
(49/76), 63.2% (48/76), 32.9% (25/76), and 5.3% (4/76), respectively. Of the 76 samples, the contents of DBP in 17 samples
(22.4%) and DEHP in 1 sample (1.3%) exceeded the maximum limit stipulated in the national standard as 0.3 mg/kg for
DBP and 1.5 mg/kg for DEHP.

Key words: oil feedstock, phthalate acid esters, solid-phase extraction, internal standard method, gas chromatography-mass spectrometry (GC-MS)