Biomedical subjects

M Jemal

Publications and source records attributed to M Jemal.

At least 19 recordsLinked to original sources

PubMed1998

Gas chromatography-mass spectrometric method for quantitative determination in human urine of dicarboxylic (dioic) acids produced in the body as a consequence of cholesterol biosynthesis inhibition.

A capillary gas chromatography-mass spectrometric (GC-MS) method in human urine has been developed and validated for the quantitative determination of dicarboxylic acids (dioic acids) which are produced in the body as a consequence of the administration of an inhibitor of the enzyme squalene synthase, which is involved in the biosynthesis of cholesterol. The standards and quality control (QC) samples were prepared by adding dioic acids into human urine. Internal standard (sebacic acid) was added to each urine sample (0.1 ml) and then dried by evaporation under nitrogen. The dried sample was reacted with pentafluorobenzyl (PFB) bromide under conditions that maximized the formation of the di-PFB ester (at the expense of the mono-PFB ester) of the dioic acids. After drying by evaporation, each sample residue was reconstituted in mesitylene and injected into a capillary GC-MS system via a splitless injection. The detection was by negative ion chemical ionization mass spectrometry with selected ion monitoring (SIM) of the [M-PFB]- of the analytes and the internal standard.

Acyclic Monoterpenes↗

PubMed1998

High performance liquid chromatography mobile phase composition optimization for the quantitative determination of a carboxylic acid compound in human plasma by negative ion electrospray high performance liquid chromatography tandem mass spectrometry.

A systematic investigation was undertaken to study the effects of varying concentrations of additives in the acetonitrile/water high performance liquid chromatography mobile phase, especially formic acid and ammonium formate, on the negative ion electrospray response of a carboxylic acid compound. The study showed that the response progressively decreased with increase in the formic acid concentration. While such a decrease in the response could be qualitatively explained by the decrease in the concentration of the ionized form of the carboxylic acid compound due to the lower pH of the mobile phase, the change in response was not as large as expected from the change of the concentration of the ionized form. The response also progressively decreased with increase in the ammonium formate concentration but the decrease cannot be explained by the change in the pH of the mobile phase. Although the best negative ion electrospray response was obtained with a water/acetonitrile mobile phase that contained no additives at all, the retention time of the analyte was not found to be adequately reproducible on repeated injections. Thus, this mobile phase was deemed unacceptable for practical, routine use. Comparing formic acid against ammonium formate, the former was preferable since it caused a smaller attenuation of the negative ion response. Equally important was the fact that addition of formic acid had the desirable effect of maintaining a reasonably high capacity factor (k') for the analyte even at a relatively high acetonitrile concentration. A concentration of 1 mM formic acid in the mobile phase was large enough to achieve the reproducible elongated retention time for the analyte, with a loss in the analyte response of about 60% only. It should be noted that the sensitivity achieved with the 1 mM formic acid mobile phase, in which the carboxylic acid is expected to be about 10% in the ionized form, is about 9 times better than the sensitivity achieved in the 1 mM ammonium formate mobile phase, in which the carboxylic acid is expected to be about 99% in the ionized form.

Carboxylic Acids↗

PubMed1998

The use of high-flow high performance liquid chromatography coupled with positive and negative ion electrospray tandem mass spectrometry for quantitative bioanalysis via direct injection of the plasma/serum samples.

Two bioanalytical methods have been developed and validated utilizing high flow high performance liquid chromatography (HPLC) for on-line purification of plasma and serum samples and electrospray tandem mass spectrometry for detection and quantitation. Each plasma or serum sample, after mixing with an aqueous solution of the internal standard, was injected into a small diameter (1 x 50 mm) column packed with large particles of OASIS (30 microns), with a 100% aqueous mobile phase at a high flow rate (3-4 mL/min). The combination of the high linear speed (6-8 cm/s) of the aqueous mobile phase and the large particle size resulted in the rapid passage of the proteins and other large biomolecules through the column while the small-molecule analytes were retained on the column. During this purification period, the HPLC effluent was directed to waste. After the purification step, the HPLC mobile phase was rapidly changed from 100% aqueous to < or = 100% organic, the flow was reduced to 0.5-0.8 mL/min, and the column effluent was directed towards the mass spectrometer. The small molecule analytes were eluted during this period. In the method developed and validated for the quantitative determination of compound I in rat plasma (method A), the same OASIS column (1 x 50 mm, 30 microns) served as the purification and analytical (elution) column. In the method developed for the simultaneous determination of pravastatin and its positional isomer biotransformation product (SQ-31906) in human serum (method B), the purification column was connected to a conventional C18 analytical column (3.9 x 50 mm, 5 microns) to achieve the required chromatographic separation between the two isomers. For method A, where 50 microL of rat plasma mixed 1:1 with water containing the internal standard was injected, the standard curve range was 1 to 1,000 ng/mL. For method B, where 200 microL of a human serum sample mixed 4:1 with water containing the internal standard was injected, the standard curve range was 0.5 to 100 ng/mL. The total analysis time for each method was < or = 5 min per sample. The accuracy, inter-day precision and intra-day precision were within 10% for both methods.

Animals↗

PubMed1997

Negative ion electrospray high-performance liquid chromatography-mass spectrometry method development for determination of a highly polar phosphonic acid/sulfonic acid compound in plasma. Optimization of ammonium acetate concentration and in-source collision-induced dissociation.

A method, based on negative ion electrospray ionization (ESI) single-stage mass spectrometry coupled with HPLC, was developed for the determination of a squalene synthase inhibitor, BMS-187745, in human plasma. BMS-187745, a highly polar compound with both phosphonic acid and sulfonic acid groups, presented difficulties in developing plasma extraction and HPLC procedures. Precipitation of the plasma protein with methanol was finally chosen as the basis for sample preparation since extraction with water-immiscible solvents or with solid-phase extraction columns failed. It was essential to add ammonium acetate to the HPLC mobile phase, not only to enhance the retention of BMS-187745 but also to ensure a well-shaped chromatographic peak. While the use of ammonium acetate had the desired chromatographic effects, it had the undesirable consequence of suppressing the negative ion ESI signal. With the plasma extracts, the [M-H2O-H]- ion (m/z 367) showed significantly lower chemical noise than the [M-H]- ion (m/z 385), and was thus chosen as the analytical ion for the selected ion monitoring. The signal of the m/z 367 ion was significantly enhanced by the optimization of the in-source collision-induced dissociation (CID) of m/z 385 to m/z 367.

Acetates↗

PubMed1997

Quantitative determination of BMS-186716, a thiol compound, in rat plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after hydrolysis of the methyl acrylate adduct by the native esterases.

During method development in support of non-clinical studies in animal models, BMS-186716 was found to be extremely unstable in blood and plasma. Stabilization of the compound was achieved by reacting the compound with methyl acrylate (MA) in blood, from which the plasma was then prepared. While the resulting BMS-186716-MA adduct was found to be stable in dog plasma, and hence it was used as the basis for the method developed for analysis of dog plasma samples, the BMS-186716-MA adduct was found to be unstable in rat plasma as it was readily hydrolyzed to BMS-186716-acrylic acid (AA) by native esterases found in rat plasma. Although the finding of the instability of BMS-186716-MA in rat plasma was not the result of prospective planning, we were able to successfully develop a quantitative bioanalytical method using BMS-186716-AA as the analyte instead of the originally planned BMS-186716-MA analyte. The standard and quality-control (QC) samples were prepared by spiking blank plasma with BMS-186716-MA, and then allowing them to stand at room temperature for 1 h to convert BMS-186716-MA to BMS-186716-AA. After adding the internal standard BMS-188035-AA, each sample was acidified with HCl and then extracted with methyl tert.-butyl ether. The reconstituted extract was injected into a HPLC-electrospray ionization mass spectrometric system for detection by positive ion electrospray ionization. A lower limit of quantitation (LLQ) of 5 ng/ml was achieved, using 0.1 ml plasma and a standard curve range of 5-5000 ng/ml.

Acrylates↗

PubMed1997

Quantitative determination of BMS186716, a thiol compound, in dog plasma by high-performance liquid chromatography-positive ion electrospray mass spectrometry after formation of the methyl acrylate adduct.

As it is extremely unstable in blood, the thiol compound BMS186716 was stabilized by the addition of methyl acrylate (MA) to blood samples. The blood samples were then kept in ice for 10-15 min for completion of the Michael addition reaction to occur between the thiol group of BMS186716 and MA, after which the plasma was separated by centrifugation under refrigeration. For sample analysis, the standard and quality control samples were prepared by spiking blank plasma with the BMS186716-MA adduct. After addition of the internal standard, BMS 188035-MA, each sample was acidified with HCI and then extracted with methyl tert.-butyl ether. Each reconstituted extract was injected into a high-performance liquid chromatography-positive ion electrospray ionization mass spectrometric system. The electrospray condition was chosen to enhance the [M+NH4]+ signal at the expense of the [M+H]+ signal. Monitoring the [M+NH4]+ signal, a lower limit of quantitation of 2.5 ng/ml was achieved, with 0.5 ml plasma. We have thus shown that a sulfhydryl compound (BMS186716) in blood can successfully be stabilized by reacting it with MA and that the adduct produced is adequately stable in blood and plasma to allow the development of a rugged quantitative bioanalytical method.

Acrylates↗

PubMed1997

Quantitative bioanalysis utilizing high-performance liquid chromatography/electrospray mass spectrometry via selected-ion monitoring of the sodium ion adduct [M+Na]+.

A high-performance liquid chromatography (HPLC)/electrospray mass spectrometric method for quantitative determination of a compound in dog plasma was developed and validated via the selected-ion monitoring of the electrospray-generated [M+Na]+ adduct of the compound. The plasma samples were acidified with HCl and then extracted with methyl tert-butyl ether. The reconstituted extracts were injected into an HPLC/positive-ion electrospray ionization mass spectrometry system. The HPLC mobile phase consisted of acetonitrile, water, formic acid (3 mM) and sodium acetate (0.3 mM). This composition of mobile phase provided the optimum electrospray condition for the formation of the [M+Na](+)-ion. This work demonstrates that the addition of sodium acetate into the HPLC mobile phase and the subsequent selected-ion monitoring of the sodium ion adduct of the analyte is a viable approach in quantitative bioanalysis. The facile formation of the sodium ion adduct of the analyte, which does not contain functional groups that are known to be strong proton acceptors, appears to be a function of the particular electrospray instrument used.

Acrylates↗

PubMed1995

Direct injection for high sample throughput capillary gas chromatographic-mass spectrometric bioanalysis.

Because of the drawback of the relatively long analysis times inherent to temperature-programmed splitless injection capillary GC-MS, isothermal direct injection capillary GC-MS was investigated for quantitative bioanalysis. Using extracts from spiked plasma samples, we showed that high quality chromatography with a run time much shorter than that achievable with splitless injection can be achieved with direct injection. Sensitivity and other performance parameters were as good as or better than those of the splitless method. Since sample throughput is of great importance in laboratories that analyze thousands of biological samples, it is recommended that, when possible, splitless injection, which has traditionally been used in trace level GC-MS bioanalytical methods, be replaced by direct injection.

Bridged Bicyclo Compounds, Heterocyclic↗

PubMed1995

Determination of BMS-186318 in dog, rat and monkey plasma by liquid chromatography-ionspray mass spectrometry.

BMS-186318 is a member of the recently discovered "aminodiol" class of HIV protease inhibitors. A simple but sensitive method was developed for the determination of BMS-186318 in dog plasma and then applied to monkey and rat plasma. The compound was extracted from dog plasma with methyl tert-butyl ether at basic pH. The dried extract was reconstituted in mobile phase and injected into a 150 x 2.1 mm i.d. Zorbax Rx-C18 HPLC column. A portion of the effluent was directed into the LC-ionspray MS system, where the [M+H]+ ion of the secondary amine compound was monitored. The HPLC conditions were chosen in order to achieve a short run time and large sample throughput, with both analyte and internal standard eluting within 1.5 min. The liquid-liquid extraction procedure provided very clean extracts so that sufficient signal-to-noise ratio was obtained with single-stage mass spectrometry instead of the more costly tandem mass spectrometry. The required lower limit of quantitation of 2.5 ng ml-1 was easily achieved. The method has also been validated for BMS-186318 in monkey plasma without modification. The method has been modified for rat plasma. Owing to irreproducibility observed when applying the liquid-liquid extraction method to rat plasma, a solid-phase extraction method was developed. The addition of phenylmethylsulfonyl fluoride was necessary to stabilize BMS-186318 in rat blood and plasma.

Animals↗

PubMed1992

Determination of SQ 33,600, a phosphinic acid containing HMG CoA reductase inhibitor, in human serum by high-performance liquid chromatography combined with ionspray mass spectrometry.

A method for the determination of SQ 33,600 in human serum is presented. This compound, which contains both carboxylic and phosphinic acid functional groups, is an HMG CoA reductase inhibitor currently under clinical investigation at the Bristol-Myers Squibb Pharmaceutical Research Institute. Human serum extracts prepared using solid-phase techniques were analyzed by combining high-performance liquid chromatography and atmospheric pressure ionization mass spectrometry. Under the conditions of the analysis, SQ 33,600 and its fluorinated analog, SQ 33,547, used as the internal standard, existed as anions in solution and could be sampled directly using the ionspray technique. The method utilized a simple isocratic mobile-phase system. No sample derivatization was required for these polar molecules. The retention time of the analytes was 3.5 min with a total analysis time of 5 min. The limit of detection was 0.5 ng ml-1 serum with a minimum quantifiable limit of 2.0 ng ml-1. The method was linear to at least 400 ng ml-1.

Chromatography, High Pressure Liquid↗

PubMed1992

Effect of the amount of internal standard on the precision of an analytical method.

In an earlier published paper, a confidence interval approach was used to show that the use of a large amount of internal standard (relative to the analyte) would adversely affect the precision of the analytical method. However, the confidence intervals were not calculated correctly. The authors recalculated the confidence intervals and found that there is no effect on the precision as measured by the confidence intervals.

Chemistry Techniques, Analytical↗

PubMed1991

Stereoisomeric purity determination of captopril by capillary gas chromatography.

The GC method developed for the stereoisomeric purity determination of captopril is based on the combined information derived from the analyses of the captopril sample on two GC systems, one with a chiral and the other with an achiral column. The limit of detection has been determined to be 0.02% (w/w) for (R,S) or (S,R) and 0.03% for (R,R), with corresponding minimum quantifiable levels of 0.08% and 0.09%.

Capillary Action↗

PubMed1989

Determination of lovastatin acid in serum by gas chromatography/mass spectrometry.

The acid form of lovastatin, an HMG-CoA reductase inhibitor, was analyzed by gas chromatography/negative-ion chemical ionization mass spectrometry after derivatization with pentafluorobenzyl bromide and bis-(trimethylsilyl)trifluoroacetamide (BSTFA). Mass spectrometry of this derivative produced a dominant [M-181]- ion under chemical ionization conditions using ammonia as the reagent gas. The limit of detection was approximately 2 pg injected on column.

Gas Chromatography-Mass Spectrometry↗

PubMed1988

Simultaneous determination of the prodrug zofenopril and its active drug in plasma by capillary gas chromatography-mass-selective detection.

After oral administration of zofenopril, the active sulfhydryl angiotensin-converting enzyme inhibitor is released. Zofenopril is currently under clinical investigation as an antihypertensive. Blood samples are reacted with N-ethylmaleimide, immediately after collection, processed into plasma and stored frozen for subsequent analysis. After addition of two internal reference standards, one each for the prodrug and the active compound, the plasma samples are purified by a combination of liquid-liquid and solid-phase extractions. The dried methylated extracts are reconstituted with tetramethylbenzene and chromatographed by automated splitless injection on a fused-silica capillary column, connected to a mass-selective detector. The analytes and the internal reference standards are chromatographically resolved and a common fragment ion is monitored for the analytes. A limit of quantitation of approximately 1 ng/ml of plasma is achieved.

Angiotensin-Converting Enzyme Inhibitors↗

PubMed1987