Trace level analysis of three glycol ethers in wood stains by APCI-LC-MS/MS†
A direct injection liquid chromatography tandem atmospheric pressure chemical ionization mass spectrometry method was developed for the determination of diethylene glycol methyl ether (DEGME), dipropylene glycol butyl ether (DPGBE), and dipropylene glycol methyl ether (DPGME). This aqueous based method is suitable for many different applications, but was specifically applied to wood stains in the present study. Multiple reaction monitoring (MRM) mode was employed to quantify the glycol ethers by detection of the precursor to product transitions at 121.1 m/z → 59.1 m/z (DEGME), 191.1 m/z → 59.1 m/z (DPGBE), and 149.1 m/z → 59.1 m/z (DPGME). Secondary qualifier ion transitions were used to confirm identity, and the daidzein internal standard demonstrated an excellent correlation to glycol ether responses. Method linearity by (1/x) linear weighted regression showed coefficients ≥ 0.995 in the ranges 0.5 ng mL−1 to 25 ng mL−1, 2.5 ng mL−1 to 50 ng mL−1, and 5.0 ng mL−1 to 50 ng mL−1 for DEGME, DPGBE, and DPGME respectively. A precision of <5% relative standard deviation was demonstrated for quality control samples, which showed excellent accuracy in the recovery of analytes from blind quality assurance samples. The method was proven to be robust and consistent during analysis of eight different commercially available wood stains. All tested wood stains contained <0.002% (w/w) DEGME, verifying compliance with the current Canadian Environment Protection Act of 1% w/w limit in surface coating products. In contrast, significant amounts of DPGBE and DPGME were found in six different woodstains. The presence of propylene glycol ethers in wood stain products is discussed.