Propylene glycol monomethyl ether isomers in workplace air determined by solvent desorption-gas chromatography

Background Propylene glycol monomethyl ether (PGME) is a widely used organic solvent. It exists in the form of two isomers in the workplace, which will cause adverse effects such as eye and upper respiratory tract irritation in workers. However, there is still a lack of standard detection methods for simultaneous detection of two isomers of PGME in China.

Objective To establish a solvent desorption-gas chromatographic method for two isomers of PGME 1-methoxy-2-propanol (α-PGME), 2-methoxy-1-propanol (β-PGME) in workplace air.

Methods A method of solvent desorption-gas chromatography for α-PGME and β-PGME in workplace air were proposed. Air samples were collected with solvent desorption activated carbon tubes, desorbed using a desorption solution of dichloromethane/methanol (85:15), and then separated on a free fatty acid phase (FFAP) fused silica capillary chromatography column , detected with a flame ionization detector (FID), and quantified by peak area. Standard evaluation protocol was followed to obtain key indicators: standard curve, limit of detection, lower limit of quantification, relative standard deviation (RSD) that measures precision, and spiked recovery of sample solutions that measures accuracy. Desorption efficiency, sampling efficiency, and adsorption capacity tests were conducted, sample stability was evaluated using spiked activated carbon tube preservation test, and interference test was also assessed. The developed method was then applied to field air sample testing.

Results In this method, using dichloromethane/methanol (85:15) as the sample desorption solution, the quantitative detection ranges of α-PGME and β-PGME were 0.95-923.0 μg·mL⁻¹ and 0.97-912.0 μg·mL⁻¹ with both correlation coefficients of 0.999 9, the method limits of detection were 0.28 µg·mL⁻¹ and 0.29 µg·mL⁻¹, and the lower limits of quantification were 0.95 µg·mL⁻¹ and 0.97 µg·mL¹, respectively. The lowest concentrations detected were both 0.19 mg·m⁻³, and the lowest concentrations quantified were 0.63 mg·m⁻³ and 0.65 mg·m⁻³, respectively, under the conditions of sampling volume of 1.5 L and the volume of desorption solution of 1.0 mL. The intra-batch precisions for α-PGME and β-PGME were 2.8%-4.9% and 2.8%-5.1%, the inter-batch precisions were 4.2%-5.7% and 4.5%-5.9%, the spiked recoveries were 98.8%-100.3% and 96.4%-102.9%, and the desorption efficiencies were 92.7%-97.3% and 92.2%-98.1%, respectively. The average sampling efficiency was 100%, and the samples could be stored at room temperature (25-30 ℃) for at least 7 d and at 4 ℃ for at least 15 d. The adsorption capacities of the activated carbon sampling tube for α-PGME and β-PGME were greater than 13.9 mg and 2.7 mg (100 mg of activated carbon adsorbent), respectively. Possible co-existing components in workplace did not interfere with the determination of α-PGME and β-PGME. The short-time exposure concentrations of α-PGME and β-PGME in the spray painting unit of an automobile manufacturing company were determined to be 18.69 mg·m⁻³ and 2.19 mg·m⁻³, and the time-weighted average concentrations were 6.03 mg·m⁻³ and 1.08 mg·m⁻³ respectively.

Conclusion This method is accurate, precise and suitable for on-site monitoring of the two isomers of PGME in workplace air.