Quantitative Analysis of Dialkylmercaptothiadiazole in Lubricating Oils by HPLC Directly Coupled with GPC.

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  • ＧＰＣ直結型ＨＰＬＣによる潤滑油中のジアルキルメルカプトチアジアゾールの定量分析

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Dialkylmercaptothiadiazole(DAMT) in Lubricating oils has been analyzed quantitatively using a High Preformance Liquid Chromatograph coupled directly with a Gel Permeation Chromatograph (GPC-HPLC). Both chromatographs were connected with a 3-way valve and a 6-way valve (Fig. 1).<br>The DAMT rich fraction of a lubricating oil sample separated by GPC was trapped at once in the loop with the 6-way valve by switching the 3-way valve, and the fraction was then introduced into the HPLC column by switching the 6-way valve.<br>Analytical conditions of two Chromatographs are listed in Table 1. The loop volume (HPLC injection volume) was found to have an effect on resolution of DAMT elution peak on HPLC Chromatogram, and the optimum volume which brings about good resolution with high sensitivity was 10μl (Fig. 3). The most appropriate time for switching of the 3-way valve was found to be among 14 minutes 45 seconds and 14 minutes 50 seconds (Table 2, Figs. 5, 6). On the basis of these data, all subsequent experiments were carried out at the switching time of 14 minutes 45 seconds.<br>Precision of the method were established by 5 repeated runs with lubricating oil samples of four different DAMT concentration levels. The coefficient of variation (CV%) of the four concentration levels lies in the range 1.4-2.4%. The difference between throretical and observed values of DAMT content could be regarded as insignificant (Table 3).<br>The limit of detection was found to be 0.01% of DAMT.<br>Several additives in lubricating oils were determined by this method, and the results showed better resolution than that could be obtained by HPLC alone (Figs. 7-11).

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