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Biomedical subjects

G D Christian

Publications and source records attributed to G D Christian.

At least 19 recordsLinked to original sources
PubMed1992

Sequential injection immunoassay utilizing immunomagnetic beads.

A novel sequential injection immunoassay (SIIA) method is described which utilizes immunomagnetic beads to investigate short-time antibody binding. The method is versatile and flexible and may therefore be adapted to many different applications. Initial results for a competitive assay are also presented. The immunomagnetic bead reactor is created within the flowing stream by retaining immunomagnetic beads with an electromagnet to form an open tube reactor. Thus, the spent beads may be discharged after each analysis. This eliminates the problems of instability of reaction surfaces and eliminates the need for additional time traditionally required for regeneration of the solid-reacting phase in order to not only save time and increase sampling frequency but also to provide each individual sampling cycle with a fresh, uniform portion of beads. The spent beads are collected off line and may be regenerated later. Short-time binding kinetic studies demonstrate linear initial binding under 1 min, which then begins to reach saturation in approximately 10 min. Competitive binding assays of monoclonal mouse IgG (MRC OX-19) to polyclonal sheep anti-mouse IgG immobilized to the immunomagnetic beads show reproducible linear displacement in 30-120-s reactions. Fluorescence detection is utilized with a detection limit of 155 ng/mL, and since the reaction time is typically 2 min or shorter, the sampling frequency is 30 samples/h.

Animals↗
PubMed1991

Fundamentals of sinusoidal flow sequential injection spectrophotometry.

A rational design of the sequential injection analyzer is based on description of the mutual penetration of sample and reagent zones, which are sequentially stacked into a tubular conduit and then injected into a reactor and transported toward the detector by means of a carrier stream, flowing at a preprogrammed rate. Variables governing zone penetration have been identified by a series of dispersion experiments, for sequential injection of two and three zones, thus outlining the conditions for performing single- and double-reagent-based assays. A parallel is drawn between conventional flow injection and corresponding sequential injection colorimetric determinations of chloride and phosphate, with the aim of suggesting guidelines for the development of spectrophotometric- and fluorescence-based sequential injection methods.

Flow Injection Analysis↗
PubMed1991

New modified polymeric electrodes selective to local anaesthetic compounds.

New polymeric electrodes responding to the cationic forms of tetracaine (TC), lidocaine (LD), and procaine (PC) were constructed by incorporating their ion-pair complexes (the salts of TC, LD and PC with phosphotungstic acid) into ethylene-vinyl acetate (E/VAC) copolymer. Other ion pairing agents investigated were silicotungstate and tetraphenylborate. The phosphotungstic acid resulted in the best linear and Nernstian response. A 1:1 (v/v) mixture of dioctyl phthalate (DOP) and nitrobenzene (NB) was used as plasticizer. The electrodes exhibited linear response over the concentration ranges 10(-2)-5.6 x 10(-6), 10(-2)-2.5 x 10(-5) and 10(-2)-1.8 x 10(-5) M of TC, LD and PC, respectively. pH did not affect the electrode performances within the ranges 2.7-6.3, 2.6-6.7 and 2.8-7.5 for the three electrodes, respectively. Interferences are negligible for many organic base and alkali metal cations. Cations of similar structure interfere with LD and PC, but not appreciably with TC. Direct potentiometry was used to determine these compounds in pharmaceutical preparations with accurate results.

Electrodes↗
PubMed1988

Acetaminophen and analogs as cosubstrates and inhibitors of prostaglandin H synthase.

Previous studies have shown that acetaminophen (APAP) is converted by prostaglandin H synthase (PGHS) to both one-electron oxidized products and the two-electron oxidized product, N-acetyl-p-benzoquinone imine (NAPQI). The present study further characterizes this reaction and shows that relatively low concentrations (20-200 microM) of APAP stimulate PGHS activity in ram seminal vesicle microsomes, whereas high concentrations (greater than 10 mM) inhibit the conversion of arachidonic acid (AA) to 15-hydroperoxy-9,11-peroxidoprosta-5,13-dienoic acid (PGG2). Stimulatory and inhibitory activities apparently involve the reduction of oxidized complexes of PGHS, and stimulatory and inhibitory activities roughly correlate with the electrochemical half-wave oxidation potentials of a series of hydroxyacetanilides. Using APAP as a probe, it was found that at low concentrations, APAP is converted in a cooxidation reaction with arachidonic acid to a dimer, 4'4"'-dihydroxy-3', 3"'-biacetanilide (bi-APAP), and other polymeric products. Moreover, an electrophilic metabolite of acetaminophen, NAPQI, was detected directly and also detected indirectly by its reaction with glutathione (GSH) to form 3'-(S-glutathionyl)acetaminophen (GS-APAP). The formation of all products was inhibited by indomethacin and the reductants, ascorbic acid and butylated hydroxyanisole (BHA). However, in the presence of GSH, ascorbic acid only partially inhibited the formation of GS-APAP while almost completely inhibiting the formation of bi-APAP. The same products of APAP (bi-APAP and NAPQI) were formed by PGHS and hydrogen peroxide in reactions that were not inhibited by indomethacin. At high concentrations of APAP that inhibit PGHS, the formation of products in the presence of arachidonic acid but not H2O2 was inhibited. These findings are generally consistent with a mechanism of acetaminophen oxidation by PGHS that involves common intermediate enzyme forms for both cyclooxygenase- and hydroperoxidase-catalyzed reactions. At least one of the intermediate complexes is reduced by relatively low concentrations of APAP and stimulates PGHS, whereas another intermediate complex is reduced by APAP at higher concentrations to inhibit the enzyme.

Acetaminophen↗
PubMed1988

Flame atomic absorption determination of manganese in whole blood using solvent extraction into acetone.

Whole blood sample (2 mL) is dry ashed and taken up in 3 M hydrochloric acid. The volume is adjusted to 2 mL with water, and 3 mL of saturated calcium chloride solution (previously saturated with acetone) is added. Iron is removed first by solvent extraction from the acid solution with 100 ppm dithizone in acetone. The pH of the aqueous phase is adjusted to 8.0 with 0.2 mL of 0.4 M tris buffer, and the manganese is extracted with dithizone in 2 mL acetone and is measured in the acetone phase at 278.8 nm by atomic absorption spectrometry using an air-acetylene flame. The mean manganese value found for 14 samples was 32 +/- 7 ppb. The detection limit is 2 ppb manganese.

Acetone↗
PubMed1979

A coupled enzymatic method to measure blood lactate by amperometric monitoring of the rate of oxygen depletion with a Clark oxygen electrode.

A rapid, sensitive and reliable method to measure lactate in blood is described. The method is based on the enzymatic oxidation of lactate to pyruvate in the presence of nicotinamide adenine dinucleotide (NAD+) and lactate dehydrogenase (LDH). The reaction product, NADH, is then oxidized by molecular oxygen, carried in the buffered reagent medium, in the presence of horeseradish peroxidase and other cofactors. The maximum rate of oxygen depletion, which is directly proportional to the amount of lactate ion present in the sample, is amperometrically monitored by a membrane oxygen electrode. No sample pretreatment is required in the present procedure other than dilution, and a comparison study between the described method and a spectrophotometric method shows good correlation.

Buffers↗
PubMed1978

Enzymatic determination of blood ethanol, with amperometric measurement of rate of oxygen depletion.

A rapid electrochemical measurement of blood ethanol is proposed. Alcohol is oxidized by NAD+ in the presence of alcohol dehydrogenase; and the NADH produced is aerobically oxidized by horseradish peroxidase. The rate of depletion of buffer-carried oxygen, which is directly proportional to the alcohol concentration in the sample, is amperometrically monitored with a membrane oxygen-sensing electrode. Only a 5-microliter sample of whole blood is required, with no deproteinization, incubation, extraction, or dilution. Results, obtained in less than 1 min, correlate well with those obtained by gas-chromatographic and spectrophotometric methods.

Alcohol Oxidoreductases↗
PubMed1977

Enzymatic assay of total cholesterol in serum or plasma by amperometric measurement of rate of oxygen depletion following saponification.

A method for serum or plasma cholesterol assay involving amperometric measurement of the rate of oxygen depletion in the cholesterol oxidase-catalyzed oxidation of cholesterol is described. The hydrolysis of the serum cholesterol esters is accomplished by saponification of 50 mul of sample with 0.2 ml of ethanolic KOH (1.0 mol/1) containing 0.5% Triton X-100 for 5 min at 75 degrees C. The rate of oxygen consumption in a 25-mul aliquot of this is measured with a Clark electrode in a Beckman Glucose Analyzer and the assay takes about one minute after incubation; results are read digitally on the instrument. The analyzer cell contains 1 ml of 1 M phosphate buffer, pH 7.4, with 100 mg sodium cholate/100 ml and 0.1-0.2 U cholesterol oxidase.

Buffers↗