Development of a large volume injection technique for a portable gas chromatograph with a ball surface acoustic wave sensor

Most portable gas chromatographs (GCs) were designed exclusively for gas samples. If they can handle liquid samples too, the range of application is expected to expand substantially. However, in general, the injection volume of liquid samples in GCs is limited to about 1 μl or less to prevent the loss of analytical precision and instrument contamination. Therefore, it is difficult to achieve sufficient sensitivity with the limited resources of the portable GCs. In this study, we developed a large volume injection (LVI) technique applicable to portable GCs, fabricated a compact LVI-GC using a spherical surface acoustic wave (SAW) sensor (the ball SAW sensor) as the detector, and confirmed its basic operation. Using a sample mixture of linear alkanes with 7-13 carbons in a pentane solvent, we evaluated measurement conditions without the loss of analyte in a sample volume range of ∼5-50 μl and confirmed the linearity of the response with respect to the sample volume. In addition, 1,2-methylenedioxybenzene, a simulant of a hallucinogen, 3,4-methylenedioxymethamphetamine (MDMA), was analyzed for an application in drug analysis in urine, and a detection limit of ∼23 ng/ml, well below the cutoff value of ∼250 ng/ml for MDMA, was achieved. Furthermore, we found a correlation between the response of the ball SAW sensor and the retention index and investigated the possibility of quantitative analysis using retention indices.