Reverse phase liquid chromatography method, development

Others have examined the necessary parameters that should be optimized to make the two-dimensional separation operate within the context of the columns that are chosen for the unique separation applications that are being developed. This is true for most of the applications shown in this book. However, one of the common themes here is that it is often necessary to slow down the first-dimension separation system in a 2DLC system. If one does not slow down the first dimension, another approach is to speed up the second dimension so that the whole analysis is not gated by the time of the second dimension. Recently, this has been the motivation behind the very fast second-dimension systems, such as Carr and coworker s fast gradient reversed-phase liquid chromatography (RPLC) second dimension systems, which operate at elevated temperatures (Stoll et al., 2006, 2007). Having a fast second dimension makes CE an attractive technique, especially with fast gating methods, which are discussed in Chapter 5. However, these are specialized for specific applications and may require method development techniques specific to CE. 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

Matthijs, N., Perrin, C., Maftouh, M., Massart, D.L., Vander Heyden, Y. Definition and system implementation of strategies for method development of chiral separations in normal- or reversed-phase liquid chromatography using polysaccharide-based stationary phases. 7. Chromatogr. A 2004, 1041, 119-133. 

The stationary phase may be a solid or liquid on a solid support. The mechanisms responsible for distribution between phases include surface absorption, ion exchange, relative solubilities and steric affects . High performance liquid chromatography is a useful method for quinolizidine alkaloid analysis, especially when pure standards are available". This method was recently used for alkaloid metabolite extraction and analysis . A simple reversed-phase liquid chromatographic method has been developed for the simultaneous quantitation of four anticancerous alkaloids vincristine, vinblastine, and their precursors catharanthine and vindoline using a specific HPLC column . 

Reverse-phase liquid chromatography is now virtually the only method used in the analysis of the TG mixtures. The first paper on TG-HPLC analysis was published in 1975 by Pei et al. (81). Triglycerides were separated on a VYDAC reverse-phase (35 - 44 /xm) column and eluted with methanol-water (9 1). Since Pei et al. first applied RP-HPLC to the separation of triacyl-glycerols, a number of reverse-phase systems have been developed as rapid and efficient resolution of complex triacylglycerol mixtures can be achieved. 

Tang, L., Fitch, W. L., Alexander, M. S., and Dolan, J. W. (2000). Expediting the method development and quality control of reversed-phase liquid chromatography electrospray ionization mass spectrometry for pharmaceutical analysis by using an LC/MS performance test mix. Anal. Chem. 72 5211-5218. 

Macek et al. [120] developed a method to quantitate omeprazole in human plasma using liquid chromatography-tandem mass spectrometry. The method is based on the protein precipitation with acetonitrile and a reversed-phase liquid chromatography performed on an octadecylsilica column (55 x 2 mm, 3 /im). The mobile phase consisted of methanol-10 mM ammonium acetate (60 40). Omeprazole and the internal standard, flunitra-zepam, elute at 0.80 0.1 min with a total rim time 1.35 min. Quantification was through positive-ion made and selected reaction monitoring mode at m/z 346.1 —> 197.9 for omeprazole and m/z 314 —> 268 for flunitrazepam, respectively. The lower limit of quantification was 1.2 ng/ml using 0.25 ml of plasma and linearity was observed from 1.2 to 1200 ng/ml. The method was applied to the analysis of samples from a pharmacokinetic study. 

Hultman et al. [130] developed a LC/MS/MS method for the quantitative determination of esomeprazole and its two main metabolites 5-hydro-xyesomeprazole and omeprazole sulfone in 25 /il human, rat, or dog plasma. The analytes and their internal standards were extracted from plasma into methyl ferf-butyl ether-dichloromethane (3 2). After evaporation and reconstitution of the organic extract, the analytes were separated on a reversed-phase liquid chromatography column and measured by atmospheric-pressure positive ionization mass spectrometry. 

Reverse phase liquid chromatography has typically been used for the separation of PFCs, employing either Cg or Cig columns [96], although the use of perfluoroalkyl columns has also been reported [115]. Mobile phases are typically mixtures of methanol-water or acetonitrile-water and are often modified with ammonium acetate to improve chromatographic separation and MS sensitivity. Both isocratic and gradient elution methodologies have been employed [96]. LC-MS/MS methods [116, 117] have also been developed for the separation of PFSA and PFCA isomers and generally employ linear perfluorooctyl stationary phases and acidified mobile phases. 

Heinisch, S. et al. Effect of temperature on the retention of ionizable compounds in reversed-phase liquid chromatography application to method development. J. Chromatogr. A. 2006, 1118, 234—243. 

It seems that the recent investigations made on the AED have resulted in the development of an important new tool for the investigation of mildly heterogeneous surfaces such as modern packing materials used in HPLC. This method has already allowed the derivation of important new results regarding retention mechanisms in reversed phase liquid chromatography [61,117] and on molec-ularly imprinted polymers [56,118]. Its application in preparative liquid chromatography should be fruitful. 

Michalke, B., Schramel, P., Witte, H. Method developments for iodine speciation by reversed-phase liquid chromatography-ICP-mass spectrometry. Biol Trace Elem Res 2000, 78, 61-19. Michalke, B., Schramel, P., Witte, H. Iodine speciation in human serum by reversed-phase hquid chromatography-ICP-mass spectrometry. Biol Trace Elem Res 2000, 78, 81-91. 

Ogiso, H., Suzuki, T., and Taguchi, R., Development of a reverse-phase liquid chromatography electrospray ionization mass spectrometry method for lipidomics, improving detection of phosphatidic acid and phosphatidylserine, Anal. Biochem., 375(1), 124, 2008. 

Kampo medicines in which A.fangchi root or A. manshuriensis stem may be misused [492], Moreover, LC-PDA and LC-EIMS detection methods both were effective in distinguishing AAI (5) and AAII (5) peaks by their spectra. Very recently, we have reported the extensive analysis of aristolochic acids and aristolactams in the various Chinese medicinal plants and crude drugs using different techniques. A method has been developed using reversed phase liquid chromatography coupled with atmospheric pressure chemical ionization (APCI) tandem mass spectrometry under the positive ion detection mode [LC/(+)APCI/MS/MS] to determine the amount of AA-1(5) in Xinxin, a traditional Chinese medicine that originate from nine Asarum species... 

Grogg-Sulser, K. Helmlin, H.-J. Clerc, J.-T. Qualitative and quantitative determination of illicit heroin street samples by reversed-phase high-performance liquid chromatography method development by CARTAGO-S. [Pg.9]

Michalke B, Witte H and Schramel P (2000) Method developments for iodine speeiation by reversed phase liquid chromatography-ICP-mass spectrometry. Biol Trace Elem Res 78/1-3 67-79. 

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