LC Conditions Research Articles

Dietary carbohydrate and postexercise synthesis of proglycogen and macroglycogen in human skeletal muscle.

This study examined the role of carbohydrate (CHO) ingestion on the resynthesis of two pools of glycogen, proglycogen (PG) and macroglycogen (MG), in human skeletal muscle. Nine males completed an exhaustive glycogen depletion exercise bout at 70% maximal O2 consumption on two occasions. Subsequent 48-h dietary interventions consisted of either high (HC, 75% of energy intake) or low (LC, 32% of energy intake) CHO diets. Muscle biopsies were taken at exhaustion (EXH) and 4, 24, and 48 h later. The total muscle glycogen (Gt) at EXH for the HC and LC conditions was not significantly different, and the MG represented approximately 12% of the Gt. From EXH to 4 h, there was an increase in the PG only for HC and no change in MG in either diet (P < 0.05). From 4 to 24 h, the concentration of PG increased in both conditions (P < 0.05). Between 24 and 48 h, in HC the majority of the increase in Gt was due to the MG pool (P < 0.05). The MG and PG concentrations for HC were significantly greater than for LC at 24 and 48 h (P < 0.05). At 48 h the MG represented 40% of the Gt for the HC diet and only 21% for the LC diet. There was no change in the net rates of synthesis of PG or MG over 48 h for LC (P < 0.05). The net rate of PG synthesis from 0 to 4 h for HC was 16 +/- 1.68 mmol glucosyl units . kg dry wt-1 . h-1, which was threefold greater than for LC (P < 0. 05). The net rate of PG synthesis decreased significantly from 4 to 24 h for HC, whereas the net rate of MG synthesis was not different over 48 h but was significantly greater than in LC (P < 0.05). The two pools are synthesized at very different rates; both are sensitive to CHO, and the supercompensation associated with HC is due to a greater synthesis in the MG pool.

Evaluation of particle beam high-performance liquid chromatography–mass spectrometry for analysis of cholesterol oxides

The capabilities of using particle beam (PB) liquid chromatography–mass spectrometry (LC–MS) was investigated for the analysis of cholesterol and oxycholesterols; normal-phase (NP) and reversed-phase (RP) chromatographic methods making use of narrow-bore columns were set up for the simultaneous separation of these compounds. The influence of PB interface parameters, LC conditions (solvent composition and flow-rate) and MS conditions was explored. PB mass spectra were recorded in electron impact (EI), positive-ion chemical ionization (PCI) and negative-ion chemical ionization (NCI) modes and the corresponding spectral data discussed. Better performance in terms of ion abundance were observed in EI mode both under NP and RP conditions. Using EI source and operating in selected-ion monitoring (SIM) mode, linearity, sensitivity and precision of the analysis were explored. The experimental data fitted a quadratic model in the overall range studied. Using the RP-LC–PB-MS method detection limits at the low-ng level were achieved for all the analytes; in addition, repeatability ranging from 3% for triol to 9% for cholesterol and 7-ketocholesterol at the 4 ng level was obtained.

Liquid chromatographic analysis and isolation of diastereoisomers obtained by an aldolization reaction

A new route using an aldolization reaction has been investigated in order to synthesize a precursor of pilocarpin, an alkaloid having sympathomimetic properties. To study the stereoselectivity of this route and to propose a mechanism, liquid chromatography has been used to analyse and to isolate each diastereoisomer for a structural determination by NMR. To further investigate the reaction mechanism, seven different aldehydes (or ketones) were used in the aldolization reaction, producing seven different mixtures. This paper describes the improvement of LC conditions with diol- and amino-bonded silica and the nonaqueous mobile phases required for the isolation of each isomer. Keywords: diastereoisomers, pilocarpin precursor, normal phase liquid chromatography, diol- and amino-bonded silicas.

Liquid Chromatographic Method for Determination of Biogenic Amines in Fish and Fish Products

A liquid chromatographic method with postcolumn derivatization is described for determination of biogenic amines in fish and fish products. Histamine, tyramine, serotonin, beta-phenylethylamine, tryptamine, putrescine, cadaverine, agmatine, spermine, and spermidine can be determined in less than 60 min. Routine sample preinjection treatment implies only 2 extractions with 0.6N perchloric acid and filtration through a 0.45 micron filter. Lack of interferences from volatile amines, amino acids, and dipeptides was verified. Results of reliability study were satisfactory. The proposed method was linear for each amine between 0.25 and 8.00 mg/L. Average recoveries ranged from 92 to 103%. Precisions (coefficients of variation) ranged from 0.70 to 9.75%. Determination limits were < or = 1 mg/kg. A modification in LC conditions was necessary to apply the method to ripened fish products to avoid interferences from food matrixes. In addition, stability of biogenic amines in fresh anchovies and hake during short-term frozen storage was studied. Results showed that, except for agmatine, frozen storage is suitable for keeping samples before analysis.

Evaluation of analytical methods: Liquid chromatography of cefalexin

A comparative study of three isocratic liquid Chromatographic methods for the analysis of cefalexin is described. Two methods, taken from the European Pharmacopoeia and the US Pharmacopeia, use classical alkyl bonded phases (C 18) as the stationary phase. The third method uses poly(styrene-divinylbenzene). Poor reproducibility of the selectivity towards cefalexin and its related substances was observed for the C 18 columns. In both C 18 methods, none of the columns was able to separate all the potential related substances from cefalexin under the prescribed LC conditions. The copolymer columns on the other hand showed good selectivity, independent of the origin or age of the columns. Four bulk samples of cefalexin were analysed by these three methods and the results were compared. Although the selectivity of polymer columns was better, for the samples examined no significant differences were observed for the assay results obtained with the three methods.

A comparative study of LC methods for analysis of cefradine

A comparative study of two isocratic liquid chromatographic methods for the analysis of cefradine is described. The first method is prescribed by the European Pharmacopoeia for the assay of cefradine, using classical alkyl bonded phase (C 18) as the stationary phase. Poor reproducibility of the selectivity towards cefradine and its related substances was observed when this method was used and none of the C 18 columns examined was able to separate cefradine completely from its potential related substances under the prescribed LC conditions. On the other hand, the second method, which uses poly(styrene-divinylbenzene) as the stationary phase, shows good selectivity even when using columns from different manufacturers and of different age. Four bulk samples of cefradine were analysed following both methods and the results were compared.

Reversed-phase liquid chromatography of the opioid peptides--2. Quantitative structure-retention relationships and isocratic retention prediction.

The ability of Snyder's theory of linear gradient elution to predict the starting isocratic reversed-phase LC conditions (k' = 4-10) for the opioid peptides was investigated. The errors in predicting the concentration of acetonitrile (phi) required to elute the peptides with a k' value of 4 were high, ranging from 13.5 to 38.1%. At k' = 10 the errors were generally reduced to less than 20%. This analysis was repeated with the same peptides after conversion to their fluorescent 1-cyanobenz[f]isoindoles (CBIs) by reaction with naphthalene-2,3-dicarboxaldehyde/cyanide. For the CBI derivatives, the errors in predicting the required concentration of acetonitrile for isocratic elution were markedly reduced and ranged from 0 to 14.3 for k' = 4 and 0 to 11.9% for k' = 10. The errors in the model in predicting the required isocratic mobile phase accurately were attributed to a mixed mechanism of retention involving solvophobic and silanophilic interactions and leading to non-linear relationships between log k' and phi. Even when the errors in predicting the required value of phi were relatively high, the Snyder approach was found to be very useful in predicting the initial starting conditions for the reversed-phase LC of the native opioid peptides as well as their fluorescence CBI derivatives.

Influence of temperature on the separation properties of immobilized Carbowax 20M open tubular column liquid chromatography

AbstractProperties of Carbowax 20M stationary phase immobilized with pluriisocyanates were investigated in the temperature interval 20–80°C. Phase transition was observed under both GC and LC conditions. Depending on the type of crosslinking agent, different phase transition temperature intervals were found with the same end point transition temperature of 55°C in the GC system and 60°C in the LC system. In contrast to GC, the retention behavior of the columns in the LC system is not significantly influenced by phase transition. A severe drop of the height equivalent to a theoretical plate was observed near the phase transition in both systems. It was due to the increase in diffusivity of the stationary phase.

Particle beam liquid chromatography—mass spectrometry on a double-focusing sector instrument

A commercially available particle beam interface developed by the Vestec Corporation has been coupled to a double-focusing high-resolution mass spectrometer (VG ZAB 2F) via a momentum separator. An ultraviolet detector was in-line with the interface and allowed monitoring of the eluting materials. With this instrumentation, complete electron-impact (EI) mass spectra on synthetic mixtures of steroids, nucleosides, and several derivatives of amino acids were recorded. Amongst these the EI mass spectra of 2,4-dinitrophenyl, 9-fluorenylmethoxycarbonyl and phenylthiohydantoin derivatives were obtained. The standard LC conditions used here (250 mm × 4.6 mm I.D., reversed-phase C 18 column, 1.0 or 1.5 ml/min flow-rate, isocratic or gradient programming) allowed separation of the mixtures. The resulting mass spectra were compared with those obtained using a direct insertion probe. The agreement was excellent in most cases. Sensitivity measurements were performed on cholesterol and caffeine. A complete low-resolution mass spectrum can be obtained on 100 ng of cholesterol. Single-ion monitoring of the M + of 200 pg of caffeine gave a 4:1 signal-to-noise ratio at m/z 194. Complete high-resolution mass spectra were obtained on 5 μg of cholesterol (loop injection) and on every peak of a five-steroid mixture of 5 μg each. The accuracy of the mass measurements were better than 5 m.m.u. for most cases. Three to four scans could be obtained for each liquid chromatographic peak. Mass-analyzed ion kinetic energy spectra were recorded on the M + of 2.5 μg of cholesterol at m/z 386. Similarly the B/E linked scan of the same ion was recorded on 2.5 μg and 500 ng.

Near field and far field induced mismatch on O + e → e second harmonic waves

The inhomogeneities induced in the process of second harmonic generation (SHG) in collimated light beams (Rw &gt; 1) of Gaussian nature is studied for O + e → e type interactions. The coherence length lc and phase matching conditions Δk change considerably and degrade harmonic conversion efficiency. The results are obtained in terms of τD (dimensionless temperature), Rw (collimation), and ξF (field variable) in the near field (NF) and far fields (FF) respectively. This work extends previous work on inhomogeneity mismatch on plane-wave approximations for O + O → e interactions.