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. 2020 Jan 15:7:928.
doi: 10.3389/fchem.2019.00928. eCollection 2019.

Advancement in Determination of Phthalate Metabolites by Gas Chromatography Eliminating Derivatization Step

Maciej Tankiewicz  1 , Ewa Olkowska  1 , Andrzej Berg  1 , Lidia Wolska  1
Affiliations

Advancement in Determination of Phthalate Metabolites by Gas Chromatography Eliminating Derivatization Step

Maciej Tankiewicz et al. Front Chem. .

Abstract

A gas chromatography-mass spectrometry (GC-MS) method to determine polar and thermally unstable phthalate metabolites [monomethyl phthalate-MMP, monoethyl phthalate-MEP, mono-n-butyl phthalate-MnBP, mono-(2-ethylhexyl) phthalate-MEHP] has been developed. This is the first report presenting the separation of monophthalates without derivatization step and any additional equipment or special injection port. Injection parameters (temperature, pressure, time, and volume of injection), chromatographic separation (retention gap, temperature program), and MS detection/identification (working parameters, ion selection) were investigated. Mechanisms and phenomena occurring under different conditions in the GC injector were evaluated and discussed. The limits of detection (LODs) of MMP, MEP, MnBP, MEHP in the protocol were 0.049, 0.036, 0.038, and 0.029 ng (per 2 μL of injection), respectively. The response of the monophthalates was found to be linear in the tested concentration range (for MMP: 0.15-100 ng, MEP and MnBP: 0.11-100 ng, MEHP: 0.087-100 ng per 2 μL) with the coefficient of determination higher than 0.9817 and inter-day precision in the range of 1.4-5.4%. The developed method is fast, easy and repeatable. Moreover, it allows for the elimination of derivatization agents, reduction of toxic waste production and simplification of analytical procedure.

Keywords: analytical method; derivatization; gas chromatography; injection conditions; phthalate metabolites; separation; thermal stability.

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Figures

Figure 1
Figure 1
Total ion chromatograms of a four monophthalates mixture (100 ng in 2 μL of injection) obtained under classical GC injector conditions, splitless working mode of injector, injection time = 1 min, injection temp.: 190°C (A) and 250°C (B); peak with retention time tr = 7.9 min corresponds to 2-ethylhexanol (2-EH), tr = 9.8 min to phthalic anhydride (PA), tr = 12.4 min monomethyl phthalate (MMP), tr = 13.0 min monoethyl phthalate (MEP), and tr = 14.9 min mono-n-butyl phthalate (MnBP).
Figure 2
Figure 2
Variations in peak areas of monophthalates with increasing injection pressure (in splitless mode), concentration of each analyte 50 mg/L. MMP, monomethyl phthalate; MEP, monoethyl phthalate; MnBP, mono-n-butyl phthalate; MEHP, mono-(2-ethylhexyl) phthalate.
Figure 3
Figure 3
Variations in peak areas of monophthalates with increasing injection temperature (splitless and higher-pressure mode, p = 170 kPa), concentration of each analyte 50 mg/L. MMP, monomethyl phthalate; MEP, monoethyl phthalate; MnBP, mono-n-butyl phthalate; MEHP, mono-(2-ethylhexyl) phthalate.
Figure 4
Figure 4
Total ion chromatogram of mixture of four monophthalates obtained under proposed conditions of GC injector, and, using uncoated fused silica between injector and chromatographic column. MMP, monomethyl phthalate; MEP, monoethyl phthalate; MnBP, mono-n-butyl phthalate; MEHP, mono-(2-ethylhexyl) phthalate.
Figure 5
Figure 5
Total ion chromatogram of mixture of four monophthalates (100 ng in 2 μL of injection) obtained under proposed conditions of GC injector, splitless working mode of injector, injection time = 1 min, injection temp. = 190°C, injection pressure = 170 kPa; peak with retention time tr = 12.4 min corresponds to monomethyl phthalate (MMP), tr = 13.0 min monoethyl phthalate (MEP), tr = 14.9 min mono-n-butyl phthalate (MnBP), and tr = 20.9 min mono-(2-ethylhexyl) phthalate (MEHP).
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