columnless gc/ims (ii) - B & S Analytik GmbH

IJIMS 5(2002)2,160-174, p. 164“like dissolves like” principle, the withholding/adsorption power of cellulose on thesedrug standards should be stronger than that of Teflon and thus would increase theirretention times more than Teflon.IMPROVEMENT IN THE SEPARATION OF ECGONINE AND ECGONIDINEMETHYL ESTER (EDME)Ecgonine and EDME are two common impurities in seized, smuggled cocaine. Themain structure of both chemicals is an azabicyclo conformation with a methyl group onnitrogen (see Figure 7). In addition, ecgonine also contains a carboxylic acid group anda hydroxyl group and EDME also contains a cycloalkene group and a carboxylic acidmethyl ester group. Ecgonine is therefore more polar than EDME. The molecularweight of ecgonine and EDME are 185.22 and 181.23 amu, respectively. At roomtemperature, ecgonine is a solid and EDME is a liquid. The reduced mobility values ofecgonine and EDME are 1.548 and 1.505, respectively. Figure 8 shows the Ionscan 3Dplasmagram of these two compounds analyzed without the addition of extra layers ofmaterial. An apparent partial overlapping of peaks is observed. Figure 9 depicts thesame data plotted in an Excel 3D plasmagram and zoomed to the drift time regionaround ecgonine and EDME. Figures 10a to 10c show that increasing the thickness ofthe layer material under the sample filter paper enhanced the separation of these twochemicals. Figures 10d to 10f illustrate that not only is the separation enhanced byincreasing the thickness of the layer material added over the sample filter paper, butalso the prolonged withholding of ecgonine exceeds that observed in Figures 10a to10c. The chromatographic effect of M8A2000 is shown in Figure 11. Although theretention time of both chemicals using Teflon above the sample filter paper was lessthan that on a comparable thickness of cellulose, the peaks were narrower (in retentiontime) when Teflon was used. This further indicates that the chromatographic effect wasthe main cause of the separation when these materials were added over the sample filterpaper.SEPARATION OF BENZOYL ECGONINE AND COCAINEBenzoyl ecgonine is another common impurity in seized, smuggled cocaine. Benzoylecgonine can be a precursor of cocaine or a degradation product of cocaine throughhydrolysis of the carboxylic acid methyl ester group (see Figure 12). The molecularweights of benzoyl ecgonine and cocaine are 289.34 and 303.36 amu, respectively.Both of these chemicals are solid at room temperature. The melting point of benzoylecgonine and cocaine are 86-92 o C and 98 o C 2respectively. The reduced mobilityvalues of benzoyl ecgonine and cocaine are 1.188 and 1.160, respectively. Figure 13ashows the 3D plasmagram zoomed to the drift time region of the benzoyl ecgonine andcocaine peaks. Although it was very difficult to visually resolve these two chemicalson Figure 13a, the Excel 3D plasmagram (Figure 13b) confirms that they are barelyseparated along the retention time axis. Such a minor separation still allowed theIonscan software to detect both chemicals and no false identification occurred whenthey were individually analyzed. Figures 14a and 14b show how the addition of one ortwo layers under the sample filter paper affects the separation of benzoyl ecgonine andcocaine. Because the addition of more layers of material under the sample filter paperincreased the retention times of both chemicals in a similar fashion, there is noimprovement in their separation. Figures 14c and 14d show a substantial improvementin the separation of these two chemicals when extra layer(s) of material are added overthe sample filter paper. The retention times of both chemicals were increaseddramatically along with a broadening in their peak shape. Although the thickness of