Study On The Methods For Testing Liquid Chromatographic Peak Purity Of Explosives And Their Applications

When using liquid chromatography to separate and quantify explosives, chromatographers are typically faced with a problem of peak purity testing. It is important to study the methods of checking chromatographic peak purity of explosives for preparations qualitative and quantitative analysis of the substance. The correlation of peak purity, chromatographic separation and detection has been investigated. On the base of the need of explosive analysis and the level of detectors, a peak shape analysis method that can be applied to two-diversion chromatographic peak is presented. The methods of testing peak purity reported on the references are improved to overcome their shortcomings. The application of these methods to explosives and related materials is studied in this paper. The following results and conclusions have been reached: 1. The correlation of peak purity, chromatographic separation and detection has been investigated. The effect of different chromatographic conditions on resolution has also been described. The resolution, which is determined by retention characteristics of explosive, and the overlapping of peak shape, which is caused by the change of the resolution of conjoint chromatographic peaks, are proved to be the essence of the problem of peak purity testing. The component identity of peak is not equal to the concept of peak purity. Corresponding disposal ways are proposed according to various possible cases when the peak purity is tested. 2. A new method for chromatographic peak purity determination by means of peak shape analysis is presented on the basis of the EMG model. Directly measurable parameters, i.e. peak width and asymmetry factor, are first utilized for the peak shape analysis. It is showed from theoretical and experimental results that for an impure peak, in comparing the peak shape of impure peak with the standard one, its purity can beidentified. It has some advantages for chromatographers lacked multiple channel detectors to test two-dimensional chromatographic peak purity. According to relative derivative of asymmetry factor it can point out the position of impurity in the chromatographic peak. 3. The technique essentials of comparative spectra method, which is applied to test peak purity of explosives, are investigated, and its characteristics and limitation are summarized. Two problems have been discussed in detailed and corresponding disposal means have been proposed. The first is the assessment of complete coelute chromatograpbic peak purity, and the second is the effect of the little impurity hidden in two end of peak on purity checking. The limitation of detection of comparative spectra method is also reviewed. The result indicates it can detect 0.5% RDX in HMX peak under suitable conditions. 4. The characteristics of comparative absorbance ratio method and absorbance ratio plOt method are investigated. The results indicate that the absorbance ratio method is simple and effective. The sensitivity of this method is largely dependent on the wavelength pair chosen and the differences in absorptivity of the coelute solutes. The methods of absorbance ratio calculated from the peak area and comparative absorbanceratios calculated at points through the chromatographic peak can provide more full-scale information of peak purity compared with the method of absorbance ratio calculated from peak height. 5. The basic principles of derivative spectroscopy are introduced. The application of derivative spectroscopy to actual explosive samp...