Liquid-chromatographic measurement of amino acids in biological samples after formation of phenylthiohydantoin derivatives.

1984 ◽  
Vol 30 (6) ◽  
pp. 851-855 ◽  
Author(s):  
H G Biggs ◽  
L J Gentilcore
Keyword(s):  
Amino Acids ◽  
Biological Samples ◽  
Internal Standard ◽  
Peak Height ◽  
Reversed Phase ◽  
Ultraviolet Absorbance ◽  
Organic Solvent Extraction ◽  
Chromatographic Measurement ◽  
Assay Precision ◽  
Liquid Chromatographic

Abstract In this method for measuring amino acids in urine, serum, and tissue, the amino acids to be assayed and the internal standard, L-norleucine, are converted to phenylthiohydantoins , isolated by organic solvent extraction, separated by reversed-phase "high-pressure" liquid chromatography, and detected by ultraviolet absorbance. The analytes are identified by retention times and quantified by comparing peak heights with that of the internal standard. The peak-height ratios vary linearly with concentrations of 50 to 500 mg/L, corresponding to the concentration range usually found in biological samples. Detection limits are 5 to 20 mg/L. Inter- and intra-assay precision (CV) varies between 1 and 26%. Average analytical recoveries range between 67 and 100%.

Simultaneous liquid-chromatographic quantitation of salicylic acid, salicyluric acid, and gentisic acid in urine.

1980 ◽  
Vol 26 (1) ◽  
pp. 111-114
Author(s):  
B E Cham ◽  
F Bochner ◽  
D M Imhoff ◽  
D Johns ◽  
M Rowland
Keyword(s):  
Salicylic Acid ◽  
Internal Standard ◽  
Peak Height ◽  
Reversed Phase ◽  
Gentisic Acid ◽  
Salicyluric Acid ◽  
Analytical Recovery ◽  
Volume Response ◽  
Assay Precision ◽  
Liquid Chromatographic

Abstract We have developed a specific and sensitive method for the determination of salicylic acid, salicyluric acid, and gentisic acid in urine. Any proteins present are precipitated with methyl cyanide. After centrifugation, an aliquot of the supernate is directly injected into an octadecyl silane reversed-phase chromatographic column, then eluted with a mixture of water, butanol, acetic acid, and sodium sulfate, and quantitated at 313 nm by ultraviolet detection according to peak-height ratios (with internal standard, o-methoxybenzoic acid) or peak heights (no internal standard). The method allows estimates within 25 min. Sensitivity was 0.2 mg/L for gentisic acid, and 0.5 mg/L for both salicyluric and salicylic acid (20-micro L injection volume); response was linear with concentration to at least 2.000 g/L for salicylic acid and metabolites. Analytical recovery of salicylic acid and metabolites from urine is complete. Intra-assay precision (coefficient of variation) is 5.52% at 7.5 mg/L for salicylic acid, 5.01% at 9.33 mg/L for salicyluric acid, and 3.07% at 7.96 mg/L for gentisic acid. Interassay precision is 7.32% at 7.51 mg/L for salicylic acid, 5.52% at 8.58 mg/L for salicyluric acid, and 3.97% at 8.32 mg/L for gentisic acid. We saw no significant interference in urine from patients being treated with various drugs other than aspirin.

Simultaneous liquid-chromatographic quantitation of salicylic acid, salicyluric acid, and gentisic acid in urine.

1980 ◽  
Vol 26 (1) ◽  
pp. 111-114 ◽  
Author(s):  
B E Cham ◽  
F Bochner ◽  
D M Imhoff ◽  
D Johns ◽  
M Rowland
Keyword(s):  
Salicylic Acid ◽  
Internal Standard ◽  
Peak Height ◽  
Reversed Phase ◽  
Gentisic Acid ◽  
Salicyluric Acid ◽  
Analytical Recovery ◽  
Volume Response ◽  
Assay Precision ◽  
Liquid Chromatographic

Abstract We have developed a specific and sensitive method for the determination of salicylic acid, salicyluric acid, and gentisic acid in urine. Any proteins present are precipitated with methyl cyanide. After centrifugation, an aliquot of the supernate is directly injected into an octadecyl silane reversed-phase chromatographic column, then eluted with a mixture of water, butanol, acetic acid, and sodium sulfate, and quantitated at 313 nm by ultraviolet detection according to peak-height ratios (with internal standard, o-methoxybenzoic acid) or peak heights (no internal standard). The method allows estimates within 25 min. Sensitivity was 0.2 mg/L for gentisic acid, and 0.5 mg/L for both salicyluric and salicylic acid (20-micro L injection volume); response was linear with concentration to at least 2.000 g/L for salicylic acid and metabolites. Analytical recovery of salicylic acid and metabolites from urine is complete. Intra-assay precision (coefficient of variation) is 5.52% at 7.5 mg/L for salicylic acid, 5.01% at 9.33 mg/L for salicyluric acid, and 3.07% at 7.96 mg/L for gentisic acid. Interassay precision is 7.32% at 7.51 mg/L for salicylic acid, 5.52% at 8.58 mg/L for salicyluric acid, and 3.97% at 8.32 mg/L for gentisic acid. We saw no significant interference in urine from patients being treated with various drugs other than aspirin.

Liquid Chromatographic Determination of Diclazuril in Premix and Supplemented Feed: Interlaboratory Study

1994 ◽  
Vol 77 (6) ◽  
pp. 1359-1361 ◽  
Author(s):  
Andre Fontaine ◽  
Karel Haustraete
Keyword(s):  
Solid Phase ◽  
Collaborative Study ◽  
Internal Standard ◽  
Chromatographic Determination ◽  
Peak Height ◽  
Reversed Phase ◽  
Poultry Feed ◽  
Uv Detector ◽  
Relative Standard ◽  
Liquid Chromatographic

Abstract Diclazuril, Janssen Research Compound R 64433 (Clinacox), is analyzed by liquid chromatography (LC). Compound R 062646, with a structure analogous to that of diclazuril, is used as internal standard. The drug is extracted from feed with acidified methanol. Diclazuril is then isolated by solid-phase extraction (SPE) with a cartridge containing a C18 phase. The eluate is evaporated, and the residue is redissolved in dimethylformamide. An aliquot is injected onto a reversed-phase ODS LC column, and the drug quantitated at 280 nm with a UV detector. Peak areas are obtained at the retention times corresponding to the internal standard and diclazuril. The quantity of active ingredient is determined by comparing the ratio of the peak height of diclazuril to that of internal standard in the sample with the same ratio in a single calibration solution. SPE is not necessary for the analysis of premixes. Eleven laboratories participated in the collaborative study. Laboratories were provided with 2 samples of premixes and 3 samples of feed for poultry. Feed sample K1 was sent to only 6 laboratories. The reproducibility relative standard deviations (RSDRS) were 7.38 and 7.53% for the 2 premixes and 9.67,13.65, and 18.61% for the 3 samples of supplemented feed.

Liquid-chromatographic measurement of endogenous and exogenous glucocorticoids in plasma.

1979 ◽  
Vol 25 (11) ◽  
pp. 1944-1947 ◽  
Author(s):  
F J Frey ◽  
B M Frey ◽  
L Z Benet
Keyword(s):  
Therapeutic Response ◽  
Methylene Chloride ◽  
Internal Standard ◽  
Peak Height ◽  
Specific Method ◽  
Silica Column ◽  
Acid And Base ◽  
Chromatographic Measurement ◽  
Liquid Chromatographic ◽  
Lower Limits

Abstract The therapeutic response to and side effects of glucocorticoids will be better recognized and the recovery of the adrenals during the tapering of therapy with steroids better evaluated if endogenous and exogenous glucocorticoids are separately assessed. We describe a specific method for simultaneously measuring the concentrations of cortisone, cortisol, prednisone, and prednisolone in plasma by "high-pressure" liquid chromatography. The steroids, together with an internal standard, dexamethasone, are extracted from 1 mL of plasma with methylene chloride-ether, washed with acid and base, and separated isocratically on a normal-phase silica column with a mobile phase consisting of methylene chloride/tetrahydrofuran/methanol/glacial acetic acid (96.85/1/2.1/0.05 by vol) at a flow rate of 1.3 mL/min. The steroids are detected at 254 nm and quantitated by peak-height measurements; their retention times range from 6 to 20 min. The lower limits for routine detection of all four compounds is 10 microgram/L. The analytical recoveries are about 75%; the intra-day variability (CV) is 1 to 9%, and the inter-day variability 2 to 11%. Of 26 drugs and 20 steroids tested, only theophylline presents an interference problem.

Simultaneous liquid-chromatographic determination of three antiarrhythmic drugs: disopyramide, lidocaine, and quinidine.

1980 ◽  
Vol 26 (2) ◽  
pp. 197-200
Author(s):  
J G Flood ◽  
G N Bowers ◽  
R B McComb
Keyword(s):  
Mobile Phase ◽  
Antiarrhythmic Drugs ◽  
Internal Standard ◽  
Chromatographic Determination ◽  
Peak Height ◽  
Reversed Phase ◽  
Multiple Drug ◽  
Evaporation Technique ◽  
Liquid Chromatographic Determination ◽  
Liquid Chromatographic

Abstract We report a common methodology for determining three antiarrhythmic drugs: disopyramide, lidocaine, and quinidine. Alkalinized serum and internal standard (p-chlorodisopyramide) are extracted into dichloromethane, the organic phase is evaporated, and the redissolved residue is injected onto a reversed-phase column (micron Bondapack C18). Quantitation is via peak-height ratios of analyte vs internal standard (as detected at 205 nm) referenced to a serum-based multiple-drug standard. A mobile phase of 30 mmol/L phosphate buffer and acetonitrile (72/28 by vol) is used. These conditions yiel; optimum separation and band symmetry for the analytes and some of their metabolites. Crucial factors in this simultaneous assay include pH of the mobile phase and injected solution, extraction time, and evaporation technique. Day-to-day precision (CV) for all drugs was less than 5%, and correlation with other assay techniques for each drug is reported. The method enables more efficient use of personnel and instrumentation without sacrificing analytical quality.

scholarly journals Simultaneous liquid-chromatographic determination of three antiarrhythmic drugs: disopyramide, lidocaine, and quinidine.

1980 ◽  
Vol 26 (2) ◽  
pp. 197-200 ◽  
Author(s):  
J G Flood ◽  
G N Bowers ◽  
R B McComb
Keyword(s):  
Mobile Phase ◽  
Antiarrhythmic Drugs ◽  
Internal Standard ◽  
Chromatographic Determination ◽  
Peak Height ◽  
Reversed Phase ◽  
Multiple Drug ◽  
Evaporation Technique ◽  
Liquid Chromatographic Determination ◽  
Liquid Chromatographic

Abstract We report a common methodology for determining three antiarrhythmic drugs: disopyramide, lidocaine, and quinidine. Alkalinized serum and internal standard (p-chlorodisopyramide) are extracted into dichloromethane, the organic phase is evaporated, and the redissolved residue is injected onto a reversed-phase column (micron Bondapack C18). Quantitation is via peak-height ratios of analyte vs internal standard (as detected at 205 nm) referenced to a serum-based multiple-drug standard. A mobile phase of 30 mmol/L phosphate buffer and acetonitrile (72/28 by vol) is used. These conditions yiel; optimum separation and band symmetry for the analytes and some of their metabolites. Crucial factors in this simultaneous assay include pH of the mobile phase and injected solution, extraction time, and evaporation technique. Day-to-day precision (CV) for all drugs was less than 5%, and correlation with other assay techniques for each drug is reported. The method enables more efficient use of personnel and instrumentation without sacrificing analytical quality.

Improved liquid-chromatographic method for determination of serum cortisol.

1979 ◽  
Vol 25 (7) ◽  
pp. 1293-1296 ◽  
Author(s):  
P M Kabra ◽  
L L Tsai ◽  
L J Marton
Keyword(s):  
Limit Of Detection ◽  
Internal Standard ◽  
Serum Cortisol ◽  
Peak Height ◽  
Reversed Phase ◽  
Column Temperature ◽  
Coefficients Of Variation ◽  
Liquid Chromatographic Method ◽  
Liquid Chromatographic

Abstract We describe a specific and precise method for measuring concentrations of cortisol in serum or plasma by liquid chromatography. Cortisol, together with an internal standard, equilenin, is extracted from 1 mL of serum or plasma and analyzed isocratically on a reversed-phase column with a mobile phase of acetonitrile/phosphate buffer (30/70, by vol.), at a flow rate of 2.0 mL/min. The eluted cortisol is detected by its absorption at 254 nm and quantitated by peak height measurements. Each analysis requires no longer than 15 min at the optimum column temperature of 50 degrees C. The lower limit of detection for cortisol is about 2 ng/sample for a standard solution; sensitivity is routinely 5 micrograms/L of serum. Analytical recoveries exceeded 95%, with good day-to-day precision (coefficients of variation between 4 and 7%). Of more than 50 drugs and steroids tested for possible interference, only the steroids cortisone, prednisone, and prednisolone may interfere with the analysis of cortisol.

Improved liquid-chromatographic determination of mexiletine, an antiarrhythmic drug, in plasma.

1984 ◽  
Vol 30 (2) ◽  
pp. 319-322 ◽  
Author(s):  
W Mastropaolo ◽  
D R Holmes ◽  
M J Osborn ◽  
J Rooke ◽  
T P Moyer
Keyword(s):  
Methylene Chloride ◽  
Limit Of Detection ◽  
Internal Standard ◽  
Chromatographic Determination ◽  
Peak Height ◽  
Reversed Phase ◽  
Internal Standard Peak ◽  
Chromatographic Procedure ◽  
Liquid Chromatographic

Abstract In this improved reversed-phase liquid-chromatographic procedure for determination of mexiletine in plasma, mexiletine and an internal standard, chlorodisopyramide, are extracted with methylene chloride from 0.5 mL of serum or plasma; the extract is then concentrated and injected onto a C18 chromatographic column. Mexiletine in the column effluent is detected by monitoring absorbance at 210 nm. It is quantified by use of mexiletine-internal standard peak-height ratios. The relation between this ratio and mexiletine concentration is linear from 0.1 to 5.0 mg/L. The lower limit of detection is about 50 micrograms/L. At a mexiletine concentration of 2.0 mg/L in serum, intrarun precision (CV) is 2.9% and inter-run precision is 5.9%; at 0.5 mg/L, these CVs are 5.7% and 9.6%, respectively. Analytical recovery of added mexiletine in serum is 68-88%. Therapeutic concentrations of some commonly administered drugs in patients' specimens did not interfere. In serum from 38 patients receiving mexiletine for cardiac arrhythmia, concentrations measured by this method correlated with therapeutic efficacy.

Reversed-Phase Liquid Chromatographic Determination of Vitamin D in Milk

1994 ◽  
Vol 77 (4) ◽  
pp. 1047-1051 ◽  
Author(s):  
Arthur F Hagar ◽  
Lee Madsen ◽  
Louis Wales ◽  
Henry B Bradford
Keyword(s):  
Vitamin D ◽  
Solid Phase ◽  
Internal Standard ◽  
Slight Modification ◽  
Chromatographic Determination ◽  
Reversed Phase ◽  
Fat Content ◽  
Extraction Column ◽  
Assay Precision ◽  
Liquid Chromatographic

Abstract Vitamin D in milk is determined by a slight modification of the method of Sliva et al. [J. AOAC Int. (1992) 75,566–571] for infant formula and enteral nutritional products. The sample is saponified for 30 min at 60°C and extracted overnight into 60 mL of hexane. The hexane layer is washed, neutralized, and taken to dryness with a rotary evaporator. The sample is reconstituted in hexane and applied to 500 mg of Florisil in a solid-phase extraction column. Vitamin D is eluted with isopropyl alcohol. The eluate is evaporated to dryness under N2, and the sample is reconstituted in 1.0 mL of acetonitrile. The extract is analyzed on a C18 liquid chromatographic column (250 × 4.6 mm, 5 μm particle size) with UV detection at 265 nm. Milk samples of various fat content (i.e., skim, low fat, and whole milk) were analyzed. Spiked recoveries gave means of 81–96%; recoveries were inversely related to fat content. Assay precision ranged from 3.2 to 8.6%. The method can measure vitamins D2 and D3 individually, and no difference in the recoveries of the 2 vitamins was observed. Thus, vitamin D2 can be used as an internal standard for quantitating vitamin D3, and vice versa. The method is satisfactory for use in screening of milk for vitamin D content.

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