Xu X, et al. Analytical Methods, 2012, 4(11), 3688-3694.
It's useful for monitoring methanol (MeOH) concentration in wastewater because methanol is an industrially popular source of carbon for denitrification. In wastewater samples as low as µg mL-1, headspace solid phase microextraction (HS-SPME) and direct liquid injection coupled with gas chromatography and mass spectrometry (GC/MS) was tested. Reliability and recovery of the two methods were checked with methanol-d3 (MeOH-d3) or acetonitrile as internal standards.
· Selection of Internal Standards
The base ions for methanol-d3 appeared at m/z 35, 33 and 30. Retention times were a bit different for methanol-d3 and methanol: 4.25 and 4.35 minutes, respectively, for liquid injection and 4.65 and 4.75 minutes, respectively, for Headspace-Solid Phase Microextraction (HS-SPME). Such a difference could be explained by a hydrogen and deuterium steric effect. In scan mode (particularly at low levels) methanol-d3 and methanol were difficult to clearly discriminate. Therefore, it was used acetonitrile (CH3CN) with base ions of m/z 41 and 40 as the internal standard for low-concentration methanol.
· Method Validation: Linear Range
Linearity of calibration curves was measured at different concentrations of methanol. Liquid injection and HS-SPME both had linear ranges of 5-1000 g mL-1. Our internal standard for the low concentrations (5-50 g mL-1) was acetonitrile, and for the high concentrations (50-1000 g mL-1), we used methanol-d3. All correlation coefficients squared (R2) were above 0.995 which means excellent linearity for both HS-SPME and liquid injection.
