High performance liquid chromatography operating modes

High-performance liquid chromatography-tandem mass spectrometry method for the determination of gemifloxacin in human plasma was based on the protein precipitation of plasma samples with acetonitrile containing [ C Ha] gemifloxacin as an internal standard. The supernatant was injected onto a PLRP-S column without any further clean-up. The mass spectrometer was operated in positive ion mode, and the ions were detected in multiple reaction-monitoring (MRM) mode. The assay requires 50 gl of plasma and is precise and accurate within the range 10-5000 ng/ml [15]. 

High-performance liquid chromatography (HPLC) uses high pressure to force the mobile phase through a closed column packed with micrometresized particles. This allows rapid separation of complex mixtures. Several operating modes of HPLC are possible (see also p. 205). These are ... 

A method that uses high performance liquid chromatography/ mass spectrometry (HPLC/MS) for the analysis of chlorinated phenoxyacid herbicides is described. During method development different techniques were used to increase both the sensitivity and the specificity of thermospray HPLC/MS for chlorinated acid herbicides. These included the operation of the instrument in the negative chemical ionization (NCI) mode initiated by discharge and the use of a wire-repeller in the ion source for efficient extraction of positive ions. Single quadrupole repeller-induced and multiple quadrupole collision activated dissociation (CAD) experiments were also performed to increase the structural information of the mass spectra. 

With its different modes of operation, high-performance liquid chromatography (HPLC) is a most suitable technique for the separation of less volatile, polar, or even ionic analytes. HPLC separation provides a continuous eluent flow of typically up to 1 mL min which can easily be introduced into the nebuHser of a flame AAS system. The interface design generally is a critical factor, since it may induce additional peak broadening which reduces both sensitivity and resolution. 

Many simple carbohydrates and other polyhydroxy compounds can be oxidized at a silver oxide surface. The oxidation is via an electrocatalytic mechanism involving a Ag(I) oxide. This forms the basis of a flow stream detector operated in an amperometric mode which may be used for either flow injection or high performance liquid chromatography (HPLC) applications. The title electrode has been applied to the detection of simple carbohydrates, triglycerides and nucleic acid components. 

Samples are analysed by LC-MS. For the samples discussed below, the system consisted of an Agilent 1100 high-performance liquid chromatography (HPLC) system and a Waters Quattromicro triple quadrupole mass spectrometer. The HPLC was operated in reversed phase mode using a CIS column. In most cases gradient elution was used with a binary mobile phase consisting of (A) water with 0.1% formic acid and (B) acetonitrile with 0.1% formic acid. This results in a retention time for nicotinic acid of about 2.5 minutes. Nicotinic acid is fairly hydrophilic and its retention time in this case corresponds to about... 

Due to the absence of hydrogen donor capabilities [31], cyanopropyl silica phases are less retentive in normal-phase liquid chromatography than under-ivatized silica or other NP packing materials. Therefore, very few applications have been reported that utilize cyanopropyl-bonded silica in the HILIC mode [32,33]. The limited number of applications may also be attributed to the mechanical instabiUty of cyanopropyl-bonded silica when operated with solvents of intermediate polarity. This instabihty is caused by a decrease in the adhesion of particles to each other that maintain the integrity of the column bed in either nonpolar or highly polar solvents [25]. Dinh et al. [34] performed a multivariate modeling of column selectivity by principal component analysis of chromatographic data from polar compounds of various structures on 20 commercially available HILIC columns and verified the low potential of cyanopropyl-bonded silica columns due to insufficient hydrophilicity. 

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