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Query: KEGG:D01453 (caffeine)
 21,611 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A method was developed for determining theobromine and caeffine in cocoa and chocolate products by high pressure liquid chromatography. After a simple hot water extraction, both theobromine and caffeine were separated by using a reverse phase C18 column and a mobile phase of methanol-water-acetic acid (20 + 79 + 1). Theobromine and caffeine were quantitated at 280 nm; average recoveries were 98.7 and 95.0%; and coefficients of variation were 2.31 and 3.91%, respectively.
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PMID:High pressure liquid chromatographic determination of theobromine and caffeine in cocoa and chocolate products. 73 Jun 47

A simple, rapid assay for serum theophylline is described. Optimisation of the high-performance liquid chromatographic system has allowed the analysis of minimun sample volume (50 micronl) in the shortest time (8 min) with good between-batch precision (C.V. = 8.3%)and accuracy (recovery ca. 100%). The behaviour of theophylline and other xanthine derivatives, theobromine, caffeine and 8-chlorotheophylline, on a bonded octadecyl reversed-phase system suggests that C18 phase effects solute separation by mixed retention mechanisms rather than by pure reversed-phase chromatography. This behaviour is attributed to the participation of underivatised silanol groups in the chromatographic process, and observation corroborated by independent investigation. The mechanism of the silanol participation is difficult to rationalise; however, a normal-phase liquid partition system complies with the experimental data.
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PMID:Retention behaviour of a bonded reversed phase in a high-performance liquid chromatographic assay of serum theophylline. 87 25

A reverse phase high-pressure liquid chromatographic method is presented for the simultaneous separation and determination of sacchrain, sodium benzoate, and caffeine in soft drinks, fruit juices, fruit cocktails, fruit punches, coffee, and artificial sweetener concentrates. Decarbonated soft drinks, fruit punches, and artificial sweetener concentrates are injected directly into the chromatograph. Fruit juices and coffee solutions require filtration through a 0.45 mum pore membrane filter prior to injection. Samples are eluted from a mu-Bondapak/C18 column with 5% glacial acetic acid and are quantitated with an ultraviolet detector. The results of saccharin, sodium benzoate, and caffeine determinations in 34 soft drinks (representing 11 manufacturers and 20 flavors); 8 fruit juices, cocktails, and punches; 7 coffees; and 6 artificial sweetener concentrates are presented. Average recoveries of saccharin, sodium benzoate, and caffeine from soft drinks are 99.0, 99.3, and 100.2%, respectively.
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PMID:Determination of saccharin, sodium benzoate, and caffeine in beverages by reverse phase high-pressure liquid chromatography. 124 28

A high performance liquid chromatographic method for the analysis of unconjugated bilirubin in neonatal serum is presented. Bilirubin was dissociated from protein with caffeine reagent and extracted with chloroform. An isocratic, reversed-phase HPLC system based on a C18 column was used. Bilirubin was detected at 450 nm. Bilirubin SRM 916a from National Institute of Standards and Technology, USA was the primary calibrator. An average recovery factor of 0.996 (SD = 0.018; N = 16) was obtained for bilirubin added to neonatal cord sera. The measurement range extended from 25 to 500 mumol l-1 L-1. The method is proposed as a reference method for unconjugated bilirubin in neonatal sera.
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PMID:Analysis of unconjugated bilirubin in serum by reversed-phase high performance liquid chromatography. 141 Dec 67

A new method for the determination of theophylline (1,3-dimethyl-1H-purine-2,6-dione) in human plasma is described, free from interference by theobromine (3,7-dimethyl-1H-purine-2,6-dione) and caffeine (1,3,7-trimethyl-1H-purine-2,6-dione). The method makes use of ion-interaction reversed-phase high-performance liquid chromatography (octylamine-orthophosphate being the interaction reagent and a C18 reversed-phase column the stationary phase) with spectrophotometric detection at 274 nm. The quantitative results obtained in the analysis of samples of plasma from patients undergoing treatment with theophylline were compared with those obtained for the same samples with the TDx fluorescence polarization immunoassay procedure (using the Abbot Therapeutic Drug Monitoring system), which is generally employed in hospitals and clinical laboratories. Statistical F-test and t-test for multiple samples were applied to the data obtained by the two methods. The results showed no significant difference between the two methods at the 95% confidence level.
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PMID:Quantification of theophylline in human plasma by reversed-phase ion-interaction high-performance liquid chromatography and comparison with the TDx fluorescence polarization immunoassay procedure. 152 27

After giving a survey of the literature of the HPLC methods for the determination of caffeine, theophylline and theobromine two methods are presented for their purity test, i.e. their detection in each other at the trace level. In the reversed-phase system the stationary phase was C18-silica and the 2:3 mixture of methanol and water was used as the eluent at a detection wavelength of 254 nm. The k' values for theobromine, theophylline and caffeine are 0,25, 0,62 and 1,12, respectively. This system enables the detection of 0,2% of theobromine and 0,1% of theophylline in caffeine and 0,2% of caffeine in theobromine or theophylline. In the normal phase system silica was used as the stationary phase while the eluent was 85:15:0,05 mixture of chloroform, dioxane and formic acid. The wavelength of the detection was 273 nm. The k' values of caffeine, theobromine and theophylline are 1,5 4,0 and 5,6, respectively. This system also enables the detection of 0,1% of theophylline and theobromine in caffeine or 0,2% of caffeine in the former. Theophyline and theobromine can be detected in each other at the 0,1% level.
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PMID:[HPC purity tests for caffeine, theophylline and theobromine]. 187 88

Cotinine is a sensitive and specific biochemical marker of exposure to cigarette smoke. We describe a simple solid-phase extraction of cotinine from plasma before quantification by HPLC. Extraction recovery was 97.9% +/- 11.0% for plasma concentrations of 5-400 micrograms/L. Baseline separation of cotinine and caffeine was achieved within 11 min of injection onto a C18 reversed-phase column. The mobile phase was citric acid/dibasic potassium phosphate (30 mmol/L each, pH 6.0) containing 100 mL of acetonitrile per liter. Within-day and day-to-day precision (CV) were 4.7% and 8.4%, respectively. We also describe a modification of the Nicotine Metabolite RIA kit (Diagnostic Products Corp.) for quantifying cotinine in plasma. Recovery of cotinine from supplemented plasma was within 10% of the expected value with this RIA kit. Interassay precision averaged 8.1% for samples in the range 50-400 micrograms/L; intra-assay precision averaged 3.6% at 230 micrograms/L and 8.7% at 53 micrograms/L. Correlation between the two methods was RIA = 1.13 HPLC + 14.8 (n = 128, r = 0.957, P less than 0.001). Both methods are technically simple to perform.
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PMID:High-performance liquid-chromatographic method compared with a modified radioimmunoassay of cotinine in plasma. 193 77

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 x 4.6 mm I.D., reversed-phase C18 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 micrograms of cholesterol (loop injection) and on every peak of a five-steroid mixture of 5 micrograms 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 micrograms of cholesterol at m/z 386. Similarly the B/E linked scan of the same ion was recorded on 2.5 micrograms and 500 ng.
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PMID:Particle beam liquid chromatography-mass spectrometry on a double-focusing sector instrument. 202 86

A convenient high performance liquid chromatographic method for the determination of methylxanthines in biological samples is described. Separation was achieved by reversed phase chromatography using a mobile phase consisting of tetrahydrofuran + methanol + 0.01M potassium dihydrogen phosphate, pH 3.5 (1:20:79, v/v/v), on a 7 microns C18 column and a C18 Lichrosorb precolumn at a flow rate of 0.8 mL/min. Levels varying from 0.25-16 mg/L could be detected by UV at 280 nm. In this range, standard curves were established for 4 methylxanthines: theobromine, paraxanthine, theophylline and caffeine in 4 media: mobile phase, serum, gastric and pancreatic juices, and were found to be linear (r greater than or equal to 0.9975). Overall characteristics of the method were determined as: percent recovery (89.54%), accuracy (greater than or equal to 99.4%) and reproducibility (greater than or equal to 95%). Retention times ranged from 4.21 +/- 0.01 (1-methyluric acid) to 10.8 +/- 0.03 min (caffeine). Animal experiments (5 and 10 mg/kg boluses) were used to determine caffeine half life in dog's blood (310 +/- 46 and 453 +/- 59 min, respectively) and its secretion into pentagastrin stimulated gastric juice (mean concentrations 2.51 and 6.04 mg/L; mean outputs 351 and 1206 micrograms/2.25 h; both statistically different at p less than 0.001 level).
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PMID:High performance liquid chromatographic determination of methylxanthines in canine serum, gastric and pancreatic juices. 227 48

A sensitive and specific high-performance liquid chromatographic (HPLC) procedure is developed for simultaneously quantitating the levels of caffeine, theophylline, theobromine and paraxanthine in breast milk. The method involved the precipitation of proteins present in the milk samples with a 6% v/v perchloric acid solution containing the internal standard, proxyphylline, followed by centrifugation at 12,800 Xg for 10 minutes. The clear supernatant was then chromatographed on a C18 reversed-phase analytical column at ambient temperature using a wavelength of 272 nm. Samples were eluted from the column at a constant flow rate of 1.5 mL/min using a gradient program in which the concentration of methanol in the mobile phase varied from 0 to 16%. The mean recoveries of the methylxanthines averaged over all the concentrations examined were generally excellent and ranged from 96.3 +/- 5.4% for caffeine to 102.3 +/- 8.9% for paraxanthine. The assay precision was very good and the peaks of interest were extremely well resolved. The method is recommended for assessing the total caffeine and dimethylxanthine load to which the nursing infant is exposed in mothers ingesting typical amounts of caffeine.
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PMID:HPLC analysis of methylxanthines in human breast milk. 229 10


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