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Biomedical subjects

C M Riley

Publications and source records attributed to C M Riley.

At least 55 records · Page 3Linked to original sources
PubMed1990

Multidimensional liquid chromatography of opioid peptides: fluorogenic labelling, retention prediction and separation optimization.

The ultra-trace analysis of opioid peptides in biological samples can be achieved by multidimensional liquid chromatography with pre-column fluorogenic derivatization with naphthalene-2,3-dicarboxaldehyde in the presence of cyanide ion. However, in order to take full advantage of the high sensitivity possible with detectors based on laser-induced fluorescence or chemiluminescence, each component of the analytical method must be carefully optimized. In this study, strategies are presented for the prediction of retention time and the optimization of separations of derivatized opioid peptides in multidimensional LC systems.

Acetonitriles↗
PubMed1990

High potency dipeptide sweeteners. 1. L-aspartyl-D-phenylglycine esters.

Twenty esters of L-aspartyl-D-phenylglycine, as well as two substituted analogues, an o-fluoro and a p-hydroxy-phenylglycine ester, were prepared. The L-aspartyl-D-phenylglycine (-)-alpha- and (+)-beta-fenchyl esters had the highest sweetness potency at 1200 and 3700 times that of sucrose, respectively. The high potency of these sweeteners is surprising as the phenyl group occupies a position previously believed to accommodate only much smaller groups.

Animals↗
PubMed1990

High-potency dipeptide sweeteners. 2. L-aspartylfuryl-, thienyl-, and imidazolylglycine esters.

Eight L-aspartyl dipeptides derived from heterocyclic glycine esters were prepared and evaluated as sweeteners. The fenchyl esters of L-aspartyl-2-furyl-, 2- and 3-thienyl-, and imidazolylglycine were all potently sweet with the D-2-furylglycine (+)-beta-fenchyl ester being the most potent at 16,500 times the potency of sucrose. The requirement for a planar heterocyclic group directly attached to the glycine carbon atom was demonstrated by the observation that the tetrahydrofuryl and beta-thienylalanine fenchyl esters were not sweet. The heteroaromatic glycine esters join the phenylglycine esters as a novel class of dipeptide sweeteners with very high potency.

Animals↗
PubMed1990

Field efficacy of Vectobac-12AS and Vectobac-24AS against black fly larvae in New Brunswick streams (Diptera: Simuliidae).

The control of black fly larvae using 2 aqueous suspension formulations of Bacillus thuringiensis, serotype H-14 was evaluated in 6 trials on small and large sized streams in New Brunswick. Applications equivalent to 25 ppm (Vectobac-12AS) or 12.5 ppm (Vectobac-24AS) over a 1-min period resulted in 100% control of black fly larvae up to 3 km downstream of the application point. Over the 6 trials, effective carry was seen to increase with increased stream discharge which varied from as low as 0.8 m3/min in the small stream to 108.6 m3/min in the large stream.

Animals↗
PubMed1989

Multi-dimensional high-performance liquid chromatography of opioid peptides following pre-column derivatization with naphthalene-2,3-dicarboxaldehyde in the presence of cyanide ion. Preliminary results on the determination of leucine- and methionine-enkephalin-like fluorescence in the striatum region of the rat brain.

The reversed-phase high-performance liquid chromatography of three synthetic opioid peptides, 5leucine-enkephalin, 5methionine-enkephalin and [D-2alanine]-5methionine enkephalin, has been studied after their pre-column fluorogenic derivatization with naphthalene-2,3-dicarboxaldehyde in the presence of cyanide to the corresponding 1-cyanobenz[f]isoindole (CBI) derivatives. The chromatographic properties of the three synthetic CBI-peptides were characterized using three different stationary phases, ODS Hypersil, CPS Hypersil and Spherisorb Phenyl, eluted with mobile phases containing various concentrations of methanol, tetrahydrofuran or acetonitrile in 26 mM trifluoroacetic acid, adjusted to pH 3.5. The data obtained using single chromatographic columns were used to design a multi-dimensional system in which the three synthetic CBI-peptides of interest were transferred as a single fraction from one column to a second. The first column served to separate the peptides from the majority of the material in the samples, and the second column was used to separate the three CBI-peptides from each other. The best separation was achieved in which the first column was Spherisorb Phenyl and the second column was ODS Hypersil. Both columns were eluted with a mobile phase of 45% acetonitrile (v/v) in 26 mM trifluoroacetic acid (pH 3.5) at a flow-rate of 1.0 ml/min. The method has been applied to the determination of leucine- and methionine-enkephalin-like fluorescence in the striatum of the rat brain.

Animals↗
PubMed1989

Analysis of 5-fluorouracil in plasma by precolumn derivatization with 4-bromomethyl-7-methoxycoumarin, followed by multi-dimensional high-performance liquid chromatography.

An assay for 5-fluorouracil (5-FU) has been developed that utilizes a double extraction with ethyl acetate, followed by precolumn derivatization with 4-bromo-methyl-7-methoxycoumarin. The reaction mixture was quenched with 5% acetic acid, extracted with hexane, and analyzed by multi-dimensional high-performance liquid chromatography. Derivatized 5-FU was injected into a cyanopropyl column and a heart cut containing the analyte was then switched to an octadecyl column and quantitated by fluorescence detection. The assay had a limit of detection of 0.5 ng 5-FU/ml plasma and was linear to 20 micrograms/ml. It was shown to be free of interferences from the other anticancer agents commonly used in combination with 5-FU. This assay should have the sensitivity needed to measure the low levels that occur after low-dose, continuous infusion of 5-FU.

Animals↗
PubMed1989

High-performance liquid chromatography of 5-fluorouracil after derivatization with 4-bromomethyl-7-methoxycoumarin. Characterization of the derivative and the use of column switching for the improvement of resolution and the enhancement of sensitivity.

The derivatization of 5-fluorouracil with 4-bromomethyl-7-methoxycoumarin has been reported previously; however, the structure of the derivative was not confirmed. The synthesis and purification of the 5-FU derivative is described along with the spectroscopic (MS and NMR) determination that it is labelled at both heterocyclic nitrogens as expected. A column switching HPLC system is also presented which consists of primary separation on a cyanopropyl column followed by a final separation on an ODS column with fluorescence detection. This system removes all interferences from the derivatization system and has a limit of detection for the pure derivative of less than 50 fmol (injection volume = 100 microliters).

Chromatography, High Pressure Liquid↗
PubMed1989

Diode array spectroscopy in pharmaceutical analysis: determination of acetaminophen/codeine phosphate tablets.

The use of diode array spectrophotometry for the analysis of tablets containing acetaminophen and codeine has been investigated. The technique was found to be applicable to the analysis of tablets which nominally contain 300 mg acetaminophen and 15, 30 or 60 mg codeine phosphate (Tylenol Nos 2-4, respectively). The concentration of codeine in extracts of Tylenol No. 1, which contains 7.5 mg codeine phosphate, was found to be too low for precise determination. First-derivative spectroscopy is required for the analysis of Tylenol Nos 2 and 3. Tylenol No. 4 can be determined using either the zero or the first-derivative spectra; however, the former was found to give consistently lower values for each component. The influence of derivative order and analytical wavelength range on the precision was investigated. The accuracy of the procedure was assessed by comparing the results from spectroscopy with those from liquid chromatography. Finally, some general conclusions on the applicability of diode array spectroscopy for the multicomponent analysis of pharmaceuticals are presented.

Acetaminophen↗
PubMed1988

High-performance liquid chromatography of bis[1,2-bis-(diphenylphosphino)ethane]gold(I) chloride, a potential antineoplastic agent.

The chromatography of [Au(dppe)2]+ (I), a potential antineoplastic drug, was studied on a variety of stationary phases (ODS Hypersil, PLRP-S, Partisil SAX and Partisil SCX) using aqueous mobile phases containing 60% acetonitrile, 15% tetrahydrofuran and various electrolytes. The effects of both the concentration (0-20 mM) and the nature of the electrolytes, added to the mobile phase, on the chromatography of I were investigated. A wide variety of electrolytes were investigated in which the hydrophobicity of both the anion and the cation were varied. The analyte of interest was found to be unretained by the like-charged Partisil SAX column. On the other hand, I was retained on the Partisil SCX by an ion-exchange mechanism and retention could be controlled by manipulating the electrolyte composition of the mobile phase. I was retained on the two reversed-phase materials by a mixture of solvophobic and electrostatic interactions but, under the conditions studied, the latter mechanism was the dominant one. The retention of I on the two reversed-phase materials was influenced much more by the nature and concentration of the cation added to the mobile phase than it was by the nature and concentration of the anion. Therefore, manipulation of the nature and concentration of the cationic species in the mobile phase appears to afford the most useful means of manipulating the retention of I, and presumably its analogues, on reversed-phase columns.

Antineoplastic Agents↗
PubMed1988

Bioanalysis of cisplatin analogues--a selective review.

A variety of analytical procedures have been described for the determination of cisplatin and its analogues in biological fluids (plasma, plasma ultrafiltrate and urine), as well as in solid tissues. This paper attempts to review those methods which have been most commonly used in practice. These analytical methods may be conveniently divided into non-selective methods which detect only the platinum metal and selective methods which are capable of detecting the intact compounds. The non-selective methods include X-ray fluorescence, proton induced X-ray emission, flameless atomic absorption (FAA) and high-performance liquid chromatography (HPLC). The latter method requires pre-column derivatization with diethyldithiocarbamate. The selective methods generally employ a fractionation step using HPLC followed by either on-line or off-line detection. Off-line detection by FAA requires the collection of fractions from the HPLC column and is somewhat tedious. On the other hand, sample preparation is minimal and biological fluids may be injected directly onto the column. The most sensitive HPLC methods for the determination of cisplatin and its analogues in biological fluids employ on-line electrochemical detection or post column derivatization with bisulphite.

Journal Article↗
PubMed1988

Stability of milrinone and digoxin, furosemide, procainamide hydrochloride, propranolol hydrochloride, quinidine gluconate, or verapamil hydrochloride in 5% dextrose injection.

The stability of milrinone and digoxin, furosemide, procainamide hydrochloride, propranolol hydrochloride, quinidine gluconate, or verapamil hydrochloride in 5% dextrose injection containing milrinone was studied. Milrinone admixtures with digoxin, furosemide, propranolol hydrochloride, quinidine gluconate, and verapamil hydrochloride were studied at two concentrations. Admixtures of milrinone and procainamide hydrochloride were studied at four concentrations. Duplicate solutions of each admixture and each control were prepared and stored in glass containers for four hours at room temperature (22-23 degrees C), under normal fluorescent lights. The samples were analyzed immediately by visual inspection, tested for pH, and assayed by high-performance liquid chromatography (HPLC). Milrinone 0.35 mg/mL-furosemide 4 mg/mL and milrinone 0.1 mg/mL-furosemide 5 mg/mL admixtures precipitated immediately after preparation and were not studied by HPLC. No changes in pH or visual appearance were observed in the remaining admixtures after storage at room temperature for four hours. Admixtures containing milrinone 0.175 or 0.2 mg/mL and procainamide hydrochloride 1, 2, or 4 mg/mL satisfied the USP standard for procainamide hydrochloride injection USP assay after one hour but failed this test in all cases after four hours. No degradation of milrinone was observed in any of the admixtures containing procainamide hydrochloride. Milrinone and furosemide are incompatible in 5% dextrose injection and should be administered separately. The remaining admixtures were compatible, and all except those containing procainamide hydrochloride were stable for four hours at room temperature.

Digoxin↗
PubMed1987

High-performance liquid chromatography of anthracycline antibiotics with electrochemical detection. Application to the clinical pharmacokinetics of 4'-deoxydoxorubicin.

The high-performance liquid chromatography with electrochemical detection (HPLC-EC) of six anthracycline antibiotics is described. All the compounds of interest may be analysed using a reversed-phase column (ODS Hypersil or Zorbax ODS) and a mobile phase consisting of acetonitrile-isopropanol-0.1 M phosphate buffer (pH 4.5). The use of short columns (7.5 cm) allowed short analysis times and improved sensitivity, such that detection limits of between 1 and 2 ng ml(-1) could be achieved. Sample preparation involved an alkaline extraction into chloroform, followed by a back extraction into acid solution. Final clean-up of the samples is achieved by shaking the final acidic extract with an organic solvent. The precision of the assay for the compounds studied ranges between 1.22 and 6.46% and the accuracy ranges between 94.5 and 106.0%. The analytical methodology developed is applied to the clinical pharmacokinetics of 4'-deoxydoxorubicin. The correlation between plasma levels found by HPLC-EC and those found by HPLC with fluorescence detection is excellent (r(2) = 0.990).

Journal Article↗
PubMed1987

Stability indicating assay for fetindomide (NSC 373965), a potential prodrug of mitindomide (NSC 284356), employing high-performance liquid chromatography.

A stability indicating assay for fetindomide using reversed-phase high-performance liquid chromatography (HPLC) has been developed. The chromatography was performed on a MOS Hypersil (C(8)) column and was optimized by investigating the effects of methanol (7.5-20%), acetonitrile (5-7%), tetrabutylammonium hydrogen-sulphate (TBA, 0-90 mM) and acetate buffer (pH 3.5, 60-100 mM) on the retention of fetindomide and mitindomide. The optimum mobile phase was 5% acetonitrile in an aqueous solution containing 100 mM acetate buffer (pH 3.5) and 40 mM TBA. Complete resolution of fetindomide, and its degradation products, phenylalanine, the two isomers of N-phenylalanyloxymethylmitindomide and mitindomide was achieved within 10 min at a flow rate of 2 ml/min. The method is linear, accurate and precise for the determination of fetindomide and mitindomide and was applied to study the stability of fetindomide in various aqueous media.

Journal Article↗