Isocratic mode, liquid chromatography

Figure 10.279 Isocratic separation of pharmaceutically relevant inorganic and organic anions by mixed-mode liquid chromatography. Separator column Acclaim Mixed-Mode WAX-1, S m column dimensions 150 mm X4.6 mm i.d. column temperature 30°C eluent 50 50 (v/v) MeCN/buffer (2.68 g potassium monophosphate-I-0.2 g sodium...

A liquid chromatography-mass spectrometry (LC-MS) method that can quantitatively analyze urinar y normal and modified nucleosides in less than 30 min with a good resolution and sufficient sensitivity has been developed. Nineteen kinds of normal and modified nucleosides were determined in urine samples from 10 healthy persons and 18 breast cancer patients. Compounds were separ ated on a reverse phase Kromasil C18 column (2.1 mm I.D.) by isocratic elution mode using 20 mg/1 ammonium acetate - acetonitrile (97 3 % v/v) at 200 p.l/min. A higher sensitivity was obtained in positive atmospheric pressure chemical ionization mode APCI(-i-). 

Liquid chromatography has a number of different configurations with regard to technical (instrumental) as well as separation modes. The HPLC system can be operated in either isocratic mode, i.e. the same mobile phase composition throughout the chromatographic ran, or by gradient elution (GE), i.e. the mobile phase composition varies with run time. The choice of operation... 

Normal-phase (NP) and reversed-phase (RP) liquid chromatography are simple divisions of the LC techniques based on the relative polarities of the mobile and stationary phases (Figure 4.10). Both NPLC and RPLC analysis make use of either the isocratic or gradient elution modes of separation (i.e. constant or variable composition of the mobile phase, respectively). Selection from these four available separation techniques depends on many variables but basically on the number and chemical structure of the compounds to be separated and on the scope of the analysis. 

High performance liquid chromatography in reversed phase mode was performed isocratically with 82% acetonitrile in water. Detection wavelengths of 254 and 280nm... 

Liquid chromatography Analyses of chlorogenic acids are carried out with reversed-phase LC systems, both in gradient and isocratic modes. The typical analytical system employs Cig columns of 5 pm packing, with a mobile-phase gradient of 25-47.5% methanol in pH 2.5 citrate buffer (0.025 mol 1 ), or isocratic elution with 30% methanol in pH 2.5 citrate buffer (0.025 mol 1 ), with UV detection at 310-330 nm. 

Liquid chromatography Separation and quantitative analysis of flavanols and polyphenols may be conducted by Cig reversed-phase LC methods, using either isocratic or gradient modes. In one example of the isocratic separation method, the solvent system used consists of acetic acid-methanol-dimethylform-amide-water (1 2 40 157 v/v/v/v). Eluting peaks are monitored by UV absorption at 254 nm. 

Figure 4 Different modes in liquid chromatography of biomolecules (A) isocratic elution, (B) linear gradient elution, (C) stepwise elution, and (D) displacement development.

A sensitive, selective, and fast LC-MS/MS method and a simple sample treatment were proposed for the analysis of amprolium in food samples. Hydrophilic interaction liquid chromatography allowed the retention of this cationic coccidiostat. The method provided an efficient chromatographic analysis in less than 3 min using isocratic elution mode (118). 

Later, the method of liquid adsorption chromatography, both in the isocratic and the gradient separation modes, was applied to investigate the FTD of oligomers, mainly of the first and the third types, with —OH, —COOH, —C=N and —SH functional groups. 

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