Picogram detection of eicosanoids by ultraviolet absorbance after narrow-bore high-performance liquid chromatography

Choosing sample volume to achieve maximum detection sensitivity and resolution with high-performance liquid chromatography columns of 1.0, 2.1 and 4.6 mm I.D

The relationship between sample volume and the chromatographic performance factors of detection sensitivity and resolution were explored for high-performance liquid chromatography (HPLC) columns of 1.0, 2.1 and 4.6 mm I.D. Performance was evaluated for isocratic and gradient elution in systems having low, intermediate and high extracolumn dispersion. Sample volumes ranged from 0.4 microliter to 2 ml. This paper provides guideline for selecting sample injection parameters so that the performance of microbore columns is not needlessly sacrificed by using too small or too large a sample volume. The guidelines are extracted from the works of others and are modified by our own experimental results. Comments are also made on the relative merits of various injection techniques.

Determination of 1-[5-(2-cyclopropyl-5,7-dimethyl-imidazo[4,5-b] pyridin-3-ylmethyl)thiophen-2-yl]cyclopent-3-enecarboxylic acid (CP-191,166), an angiotensin II antagonist, in dog and rat plasma by high-performance liquid chromatography

A simple and precise high-performance liquid chromatographic (HPLC) assay was developed and validated for the determination of a novel angiotensin II antagonist, 1-[5-(2-cyclopropyl-5,7-dimethyl-imidazo[4,5-b]pyridin-3-ylmethyl) thiophen-2-yl]cyclopent-3-enecarboxylic acid (CP-191,166, I), in dog and rat plasma. The internal standard (II, a saturated derivative of I) and analyte were extracted by liquid-liquid extraction using methyl tert.-butyl ether. Samples were analyzed by reversed-phase HPLC using a Zorbax C8 narrow-bore column with ultraviolet detection at 289 nm. The quantitation limit of I was 10 ng/ml and the calibration curve was linear over the range of 0.01-10.0 micrograms/ml (r2 > 0.99). In dog and rat plasma, intra- and inter-assay precision ranged from 0.00 to 3.36% and 0.00 to 4.95%, respectively. The average recoveries were similar (73%) for both I and II and the upper limit of quantification of I can be as high as 500 micrograms/ml. The method described has been successfully applied to the quantification of I in about 2000 dog and rat plasma samples over a nine-month period.

In-vitro evaluation of 5-lipoxygenase and cyclo-oxygenase inhibitors using bovine neutrophils and platelets and HPLC

Inhibition of 5-lipoxygenase has been determined by monitoring the formation of leukotriene B4 and 5-hydroxyeicosatetraenoic acid in bovine polymorphonuclear leucocytes. For evaluating the inhibition of cyclo-oxygenase two different test systems are presented: the first uses 12-hydroxyheptadecatrienoic acid produced by bovine platelets as an indicator of the cyclo-oxygenase activity; the second test system monitors the prostaglandin E2 formation by bovine platelets. All arachidonic acid metabolites are quantified by reverse-phase HPLC with UV-detection.

Determination of prostaglandins in human seminal fluid by solid-phase extraction, pyridinium dichromate derivatization and high-performance liquid chromatography

Prostaglandins of the E type (PGEs) in human seminal fluid have been determined by reversed-phase high-performance chromatography on a C18 column and ultraviolet detection at 230 nm after solid-phase extraction (C18) and oxidation to the corresponding 15-oxoprostaglandin derivatives by pyridinium dichromate in acetonitrile. Under optimized conditions, PGEs from 10-ml seminal samples were extracted into 4 ml of methyl formate with high recoveries (estimated at greater than 95%) and subsequently separated under mild chromatographic conditions (0.5 mM formic acid-acetonitrile, apparent pH 3.8). Comparable analytical sensitivities were obtained with detection at 230 nm with a conventional deuterium lamp spectrophotometer and a photometer equipped with a cadmium emission source, while with a diode-array spectrophotometer, signal-to-noise ratios were reduced with factors between 4.4 and 3.1, depending on the spectral bandwidth of the instrument. Theoretical aspects of signal-to-noise optimization of ultraviolet detectors are discussed. The stability of dilute standard solutions of PGE2 and PGD2 was measured, showing solutions in dichloromethane at 20 degrees C to be as stable as acetonitrile solutions at 5 degrees C over a period of thirty days. Absolute ethanol and acetonitrile were equally suited as solvents.

Identification of reaction products from the pyridinium dichromate derivatization of prostaglandins by high-performance liquid chromatography and direct chemical ionization mass spectrometry

The reaction products from the oxidation of prostaglandins with pyridinium dichromate have been identified by direct chemical ionization mass spectrometry of the underivatized compounds after separation by reversed-phase high-performance liquid chromatography and ultraviolet diode-array detection. The thermal influence on the reproducibility of the dehydration patterns of the mass spectra was studied. The main products from the prostaglandins E1, E2, F1 alpha and F2 alpha were the corresponding 15-oxo derivatives. Minor amounts of the 9,11,15-trioxoprostaglandin were formed from PGE, while the oxidation of PGF was less selective, yielding additional dioxo derivatives. Addition of water to the reagent reduced the reactivity, but increased the selectivity in favour of the formation of 15-oxo-PGF during the oxidation of PGF.

High performance liquid chromatographic determination of thromboxane B2 in human serum as a methoxime-panacylester derivative

A high performance liquid chromatographic (HPLC) method was developed to measure thromboxane B2 (TxB2) levels in human serum. Serum samples (2 mL) were extracted using solid phase extraction columns in a C 18/silica mode sequencing approach. The internal standard, 6-ketoprostaglandin F1 alpha, was added to the serum extracts. The eicosanoids were doubly derivatized, first with panacyl bromide, then with methoxyamine to form methoxime-panacyl ester derivatives. The eicosanoid derivatives were chromatographed using a reverse phase HPLC system with UV detection (254 nm). Assay linearity was demonstrated with fortified TxB2 standards in 3% bovine serum albumin over a range of 25 to 500 ng/mL (r greater than or equal to 0.994). There was no significant interday difference or bias in assay results for pooled standards at 75, 226 and 376 ng/mL concentrations (p greater than 0.05). Pooled estimates of precision at these levels indicate an assay relative standard deviation 6-9%. The HPLC assay was used to quantitate TxB2 levels in human serum. Results were consistent with previously published values when drug-free serum was analyzed to assess ex vivo TxB2 formation.

Stability of leukotrienes C4 and D4 in human urine

The ex vivo stability of leukotrienes (LT) C4 and D4 in human urine was tested in an experimental model. The various LTs were identified/measured by HPLC, liquid scintillation counting, RIA, UV-absorbance and GC-MS. If fresh urine was incubated under physiological conditions added LTC4 was converted in a time-dependent manner to LTD4 (t1/2 about 0.5 h) and to LTE4 (t1/2 about 6 h), respectively. At the end of the 22 h incubation period less than 10% of the initial LTC4 was detectable. LTB4 was stable under these conditions. Therefore the enzymatic urinary metabolism of LTs should be considered in experimental and clinical studies when urine is collected under different conditions.