QUANTITATIVE INJECTIONS OR CALIBRATIONS IN GAS-CHROMATOGRAPHY - ANOMALY ASSOCIATED WITH SYRINGE TYPE

When syringes with open needles are used for quantitative injections, e.g. to calibrate gas chromatographic pe:lh areas against the volume o f liquid injected, the resultant plot may display an intercept. Curren t studies on cyclohexane have shown that this effect is so severe that it can make the major contribution to the total signal. Since the mag nitude of the anomaly increases with the volatility of the liquid, thi s means that calibrations of liquid mixtures. or the use of an interna l standard. will be unreliable when moderately volatile components are injected with syringes of the above type. The problem is shown to be caused by volatilisation from the needle a whilst it is inserted in th e heated injection Fort, and is exacerbated by increasing the temperat ure of the port or increasing the residence time of the needle. The an omaly is totally avoided if the calibration is performed using a syrin ge of the type in which the piston passes down the needle. Somewhat si milar effects to the ones described can also arise for other reasons, and literature references to such situations are given.