Determination of carbendazim in blueberries by reversed-phase high-performance liquid chromatography.

A fluorescent reversed-phase high-performance liquid chromatographic method was developed for the analysis of carbendazim in blueberries. Recoveries of fortified blueberries at 27 and 810 ng/g were more than adequate with good precision. Forty commercial blueberry samples were analyzed and the amount of carbendazim ranged from none detected (detection limit of 15 ng/g) to 155 ng/g. Confirmation of carbendazim in the blueberry samples was made by enzyme immunoassay and UV photodiode array.     

Determination of Penicillium roqueforti toxin by reversed-phase high-performance liquid chromatography.

A method for the detection and quantification of Penicillium roqueforti toxin (PRT) using reversed-phase high-performance liquid chromatography has been established. The limit of quantitation of this method was 3 ng of PRT, while the limit of detection was 2 ng of toxin. The precision of the analysis based on numerous runs was good. Retention times for PRT were highly reproducible with an average coefficient of variation of about 1.6%. Analysis of PRT in liquid and solid samples showed no interference of the sample matrix. The accuracy of the method was 98.6%, with mean PRT recoveries of 96.8%, and 100.4% for the spiked culture medium and blue cheese extracts, respectively.     

Determination of p-chloronitrobenzene in plasma by reversed-phase high-performance liquid chromatography.

A simple, accurate and precise isocratic reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of p-chloronitrobenzene (p-CNB) in rat plasma. A plasma sample was deproteinized with methanol containing the internal standard (p-bromonitrobenzene). The resulting methanol eluate obtained after centrifugation was filtered and injected into a high-performance liquid chromatograph (50 microliters each). A column packed with 5 microns octadecylsilane (ODS) spherical particles was used with isocratic elution of methanol-water (45:55, v/v) at a flow-rate of 1.0 ml/min. The compounds were detected by ultraviolet absorbance at 280 nm. The retention times of p-CNB and the internal standard were 12.5 and 15.5 min, respectively, at a column oven temperature of 30 degrees C. The results were linear from 0.05 to 100 micrograms/ml (r = 0.999), and the detection limit was 0.01 microgram/ml. The relative error and the coefficient of variation on replicate assays were less than 7 and 10%, respectively, for all concentrations studied. The overall recoveries of p-CNB were between 97 and 105%. Plasma samples could be stored for up to one month at -20 degrees C.     

Determination of overt carnitine palmitoyltransferase by reversed-phase high-performance liquid chromatography

A method for the determination of carnitine palmitoyltransferase I (CPT I; EC 2.3.1.19) in isolated rat liver mitochondria by reversed-phase high-performance liquid chromatography is described. Enzyme activity is assayed by direct determination of coenzyme A (CoA) released from palmitoyl-CoA within 60 min by a linear gradient system. CPT 1 in rat liver mitochondria can be assayed from only 30 micrograms of mitochondrial protein per millilitre of assay mixture. The changes in the kinetic parameters of CPT I, including Ki for malonyl-CoA, resulting from the fasting-feeding cycle are also discussed.     

Determination of tetracycline antibiotics by reversed-phase high-performance liquid chromatography with fluorescence detection.

A highly sensitive method for the determination of tetracycline antibiotics (TCs) using reversed-phase high-performance liquid chromatography with fluorescence detection is presented. This method was based on the use of disodium ethylenediaminetetraacetate (EDTA) and calcium chloride as fluorescence-increasing reagents in the mobile phase. The concentrations of each reagent in the mobile phase greatly influenced the fluorescence intensity of TCs. When the concentration of EDTA and calcium chloride were 25 and 35 mM, respectively, and the pH of the mobile phase was 6.5, the maximum fluorescence intensity was obtained. The column temperature hardly influenced the fluorescence intensity. At 3.75 ng of TCs injected, the precision (relative standard deviation) ranged from 1.12 to 2.20%. In the range 0.075-37.5 ng for tetracycline and oxytetracycline and 0.225-37.5 ng for chlortetracycline, a linear response was observed. The detection limits of this method were 49-190 pg for three different TCs. The proposed method was applied to the determination of one of the TCs in pharmaceuticals by the internal standard method using other TCs as internal standards and was also applied to determination of TCs added to fish tissue.     

Determination of paraquat in sunflower seeds by reversed-phase high-performance liquid chromatography

The herbicide paraquat was determined with extracts from 1-g samples of sunflower seeds. The liquid chromatography procedure utilized a microparticle (10 micron) C18 reversed-phase column and isocratic elution with 27% acetonitrile in water, 10 mM in the sodium salt of octanesulfonic acid. Eluted paraquat was detected at 254 and 280 nm and quantitated by paraquat internal standard peak height ratios. This procedure provided linear working curves over the concentration range of 0-20 microgram/g of paraquat. Recovery of paraquat varied from 89-101%, with an average recovery of 93%. Good agreement was obtained in the comparison of results of the described procedure with those from a well established UV procedure.     

Determination of cortisol in human plasma by reversed-phase high-performance liquid chromatography

A method is described for the measurement of cortisol in human plasma using 45% aqueous methanol eluent on a 120 mm x 4.5 mm I.D. Hypersil octadecylsilane column with UV detection at 239 nm after a simple dichloromethane extraction and evaporation with a prednisone internal standard. The sample preparation time and chromatography time are each about 15 min and linear correlations have been obtained with plasma samples assayed by the Mattingly fluorimetric technique and a commercial-kit competitive protein binding method. Concentration down to 30 nmol/l may be measured and the method can be used when fluorimetry is invalidated by interference, particularly from spironolactone.     

Determination of deuterium oxide in water by reversed-phase high-performance liquid chromatography

Refractive index detection allows > 0.1% D₂O to be determined in a few microliters of enriched water with a C₁₈ column when pure water is used as the mobile phase.     

Faster analysis by reversed-phase high-performance liquid chromatography

Summary Many analysts are not taking full advantage of the high speed possibilities of modern LC. Some analytical procedures reported in the literature, and many in regular use in control laboratories, could be achieved in less time without loss in precision. Some factors which affect retention times are discussed and the advantages and disadvantages of employing shorter column lengths and finer packing materials in reversed-phase HPLC are examined. The effect on efficiency of increased flow rates with 10,5 and 3 m ODS materials is shown. The ability to couple shorter column lengths without loss of efficiency is also demonstrated. This allows a minimum length to be selected that gives adequate resolution. Examples of high speed separations are shown and limitations in state of the art HPLC equipment and chromatographic data systems are discussed briefly.Presented at the 14th International Symposium on Chromatography London, September, 1982     

The separation of nonapeptides by reversed-phase high-performance liquid chromatography.

The separation properties of five nonapeptides on commercial reversed-phase materials have been investigated and the effects of pH, salt concentration and solvent composition have been studied. With appropriate variation of the pH and salt concentration in the mobile phase, it is possible to resolve all of the peptides investigated and their by-products. Mixtures of water and organic solvents (acetonitrile, dioxan, methanol and n-propanol) have been used. The choice of the organic solvent does not strongly influence the separation pattern. The simplicity, speed and quality of the separations and the favourable detection limits (ca. 30 ng) at 220 nm render this technique suitable to routine quantitative analysis.