Ion-pair chromatography of methotrexate in a column-switching system using an alkyl-diol silica precolumn for direct injection of plasma

The retention behaviour of methotrexate as an ion-pair with tetrabutylammonium in a column-switching system, based on an alkyl-diol silica C8 precolumn, combined with an analytical column, LiChrospher RP 18, was studied. Methotrexate is mainly present as a divalent anion at pH 7.4, however, the rete...

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Bibliographic Details
Published in:Journal of Chromatography A 1996-08, Vol.742 (1-2), p.113-120
Main Authors: Yu, Zuoxiang, Westerlund, Douglas
Format: Article
Language:English
Subjects:
Acetonitriles - chemistry
Anions - chemistry
Chromatography, High Pressure Liquid - instrumentation
Chromatography, High Pressure Liquid - methods
Column switching
Hydrogen-Ion Concentration
Ion-pair adsorption
Linear Models
Methotrexate
Methotrexate - analysis
Methotrexate - chemistry
Methotrexate - metabolism
Models, Chemical
Plasma - chemistry
Quaternary Ammonium Compounds - chemistry
Retention models
Sample enrichment
Silicon Dioxide - chemistry
Spectrophotometry, Ultraviolet
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Summary:The retention behaviour of methotrexate as an ion-pair with tetrabutylammonium in a column-switching system, based on an alkyl-diol silica C8 precolumn, combined with an analytical column, LiChrospher RP 18, was studied. Methotrexate is mainly present as a divalent anion at pH 7.4, however, the retention data was consistent with the formation of a 1+1 ion pair with the counter ion. The concentration of the tetrabutylammonium and the acetonitrile in the mobile phase could be used to regulate the retention in the system. Relevant chromatographic parameters to estimate the enrichment effect in the column-switching system are also identified and discussed. The column-switching system was applied to direct injection of plasma (100 μl) giving a limit of detection of 10 ng/ml for methotrexate using UV detection at 307 nm.
ISSN:0021-9673
DOI:10.1016/0021-9673(96)00257-9