Microcoil NMR coupled with microscale separation techniques for on-line analysis of mass-limited samples.

摘要

Analysis of trace impurities often requires an analytical method that is both sensitive and selective. Although NMR is one of the most powerful methods available for determining molecular structure, it lacks sensitivity and therefore its use as an on-line detection method in separations has been limited. Microcoil NMR probes offer low mass detection limits due to their very small active volume, usually in the muL to nL range. The goal of this dissertation included building solenoidal microcoil NMR probes of high mass sensitivity and successfully using them for on-line detection with microscale separation techniques such as capillary isotachophoresis (cITP) and capillary-LC (capLC).; cITP separates and concentrates components of the sample based on their electrophoretic mobilities, by two to three orders of magnitude, thereby compensating for the poor concentration sensitivity of microcoils. cITP-NMR is therefore a powerful tool for the analysis of trace impurities. On-line cITP-NMR experiments detected 1.9 nanomole of beta-blocker drugs such as atenolol and propranolol with a 250-fold concentration enhancement. cITP-NMR was further used to study inclusion complexation of beta-blocker drugs such as propranolol with beta-cyclodextrin. These results are especially significant considering the widespread use of cyclodextrins as buffer modifiers in electrophoretic separations and as pharmaceutical excipients.; Identifying impurities at levels of 0.1% or lower is one of the many analytical challenges in the pharmaceutical industry and vital for pharmaceutical product development. LC-NMR and capLC-NMR are analytical techniques routinely used to analyze mass-limited samples. However in most cases, the trace impurity has to be separated and identified in the presence of large excess of the parent material, making column overloading a problem for these techniques. cITP-NMR was therefore explored for analysis of 4-aminophenol, a thermal degradation product of acetaminophen. In these experiments 1.8 mug of 4-aminophenol was selectively detected in the presence of a 1000-fold excess of acetaminophen in the tablet matrix. Thus cITP could reduce matrix interferences. To extend the application of cITP-NMR, a contactless conductivity detector was developed and used on-line with NMR detection. Experimental and practical details of the use of these hyphenated techniques and the challenges involved are presented in this dissertation.