微分ガスクロマトグラフ法によるカラム温度の適否の判別

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The effect of sample amount and column temperature on the shape of chromatographic peak and the retention time was investigated experimentally by means of a derivative method. As well known, Cruickshank and Everett proposed to express the peak distortion by skew ratio, R, shown by eqn. (1) and Fig. 1. The skew ratio can simply be measured in the derivative method as the ratio of the derivative peak heights, as given by eqn. (2). In the present work, the peak distortion was discussed in terms of the degree of asymmetry, S, defined as the logarithm of skew ratio. A close correlation between the shift of retention time and the distortion of peak shape was observed, especially when the column temperature was too high or too low, and this tendency became more remarkable with increasing amount of sample injected. As shown in Fig. 3, when the column temperature is lower than the optimum one, with increasing sample amount the peak shows a leading shape more prominently and the retention time becomes longer. On the contrary, when the temperature is higher, a more remarkable tailling of the peak is observed and the retention time becomes shorter. The experimental conditions and the data obtained are given in Figs 5 9. As tabulated in Table II, it was confirmed experimentally with several samples that there is a temperature T1, at which the degree of asymmetry S does not depend on the amount of sample injected. At this optimum temperature, the degree of asymmetry shows a value S° that lies very closely to zero. Further, a temperature T2, at which the retention time shows a constant value independent of the sample amount injected was measured. Two optimum temperatures T1 and T2 were found to be almost identical in the range of experimental error. It can be judged simply and rapidly whether the column temperature is suitable or not from these results. For a given sample component under a certain column packing condition, if S°, i. e. the least value of degree of asymmetry, is known, one can easily find whether the temperature is higher or lower than the optimum one, from the measurement of S under the given temperature, as tabulated in Table III. If S° has not been evaluated, by comparing two values of S, namely, SA obtained for A-μl sample and SB for B-μl sample, respectively, one can know the suitability of the column temperature. Most simply, if the absolute value of S be nearly zero, one may judge that the column temperature is not far from the optimum. Thus, it could be said that by an aid of the derivatives gas chromatographic method one can easily obtain an important information concerning the column temperature. An example with a three-component mixture is reproduced in Fig. 10.
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微分ガスクロマトグラフ法によるカラム温度の適否の判別

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