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R B McComb

Publications and source records attributed to R B McComb.

At least 37 records · Page 2Linked to original sources
PubMed1983

Falsely high serum creatinine concentration associated with severe methanol intoxication.

A case of severe methanol intoxication (1300 mg/L) was associated with markedly increased serum creatinine (490 mg/L) despite normal urea values and the absence of any other signs of renal disease. These values declined progressively to normal, and the patient recovered with no visual impairment. Additional laboratory experimentation suggested that the high creatinine value was probably ascribable to some unknown foreign material(s) in the patient's blood that reacted with the alkaline picrate used in the measurement of creatinine. One of the presumed metabolites of methanol, formaldehyde, reacts with creatinine but the product does not react with picrate. We believe that the foreign material was derived from either commercial preparations of methanol or contaminants in the patient's drinking water.

Alcoholic Intoxication↗
PubMed1981

Urinary metanephrines as measured by liquid chromatography with an on-line post-column reaction detector.

In this method for measuring metanephrine and normetanephrine in urine, they are freed from their conjugates by hydrolysis in acid, neutralized, and isolated on a cation-exchange resin. Both metanephrines are co-eluted with ammoniacal methanol and the eluate is concentrated 10-fold with respect to the original urine volume by evaporation and reconstitution. The recovered metanephrines ae separated by reversed-phase (C18) "high-pressure" liquid chromatography with use of a mobile phase consisting of 10 mmol/L trichloroacetate, pH 2.7, containing 30 mL of acetonitrile per liter. The metanephrines are detected at 365 nm after being converted to vanillin in a post-column reaction with alkaline periodate. Total metanephrine values for most patients were appreciably lower than values obtained by the comparison procedure, that of Pisano (Clin. Chim. Acta 5: 406, 1970); however, results obtained by the two methods for two patients with pheochromocytomas agreed well.

Adrenal Gland Neoplasms↗
PubMed1981

4-nitrophenyl phosphate--characterization of high-purity materials for measuring alkaline phosphatase activity in human serum.

We studied 53 lots of 4-nitrophenyl phosphate (I), obtained from 20 different commercial suppliers, and used this information to set specifications for it. Using these well-defined specifications, we classified 21 lots of I as "unacceptable," 26 lots as "borderline," and six as "acceptable." All lots were shown to contain some 4-nitrophenol and inorganic phosphate. However, "acceptable" I had < 0.3 mmol of 4-nitrophenol and < 10 mmol of inorganic phosphate per mole of I. The mole concentration of I (based on disodium hexahydrate, formula weight 371) was determined by enzymic conversion to 4-nitrophenol in five lots of "acceptable" materials. The mole fraction of I ranged from 0.982 to 0.998. From these measurements and from estimates of impurities that absorb at 311 nm, as determined by liquid chromatography and spectrophotometry at other wavelengths, our best estimate of the molar absorptivity of I at 311 nm in 10 mmol/L NaOH at 25 degrees C was 9867 L x mol-1 x cm-1, with a total uncertainty of 76 L x mol-1 x cm-1. We recommend that I used in clinical laboratories for measurement of alkaline phosphatase activity in serum meet the specifications given in this paper: I content > 98%, maximum activity > 98% in comparative testing with other "acceptable" lots of I, and impurities not to exceed the values cited above.

Alkaline Phosphatase↗
PubMed1980

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

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.

Chromatography, High Pressure Liquid↗
PubMed1980

High-purity 4-nitrophenol: purification, characterization, and specifications for use as a spectrophotometric reference material.

We describe specifications for high-purity 4-nitrophenol, which is suitable for spectrophotometric standardization. Such a reference material is needed in clinical enzymology to establish the proper molar absorptivity of 4-nitrophenol under final reaction conditions, particularly for measuring alkaline phosphatase activity in human serum. Some lots of 4-nitrophenol available commercially met these specifications, but several did not. The latter can be purified to meet our specifications by recrystallization or sublimation. The molar absorptivity of 4-nitrophenol (35 mumol/L) IN 10 mmol/L NaOH at 25 degrees C at 401 nm is 18380 +/- 90 L.mol-1.cm-1.

Alkaline Phosphatase↗
PubMed1979

Urinary 3-methoxy-4-hydroxymandelic acid as measured by liquid chromatography, with on-line post-column reaction.

We describe a method for measurement of 3-methoxy-4-hydroxymandelic acid (vanillylmandelic acid, VMA) in urine. After the pH of the urine is adjusted to 2.7 and the sample is filtered, exactly 15 microL is injected onto a C-18 reversed-phase column. VMA is eluted from the column with 10 mmol/L phosphate buffer, pH 2.7, containing 30 mL of acetonitrile per liter. The eluate stream is combined with alkaline periodate and then passed through a 60 degrees C water bath. The VMA is completely oxidized to vanillin, which is detected and quantitiated by its absorbance at 360 nm. No deterioration of the column was noted after 167 such injections of urine samples. Long-term control data indicate a CV of 12 and 10% at VMA concentrations of 1.5 and 5.8 mg/L, respectively. Although results correlate well (r = 0.976) with those by the method of Pisano et al. [Clin. Chim. Acta 7, 285 (1962)], they average 10% lower. Of 20 compounds tested, only methyl dopa interfered with the procedure as described.

Chromatography, Liquid↗
PubMed1979

Increase in dialyzable calcium associated with therapy with lithium.

We measured total and dialyzable calcium concentrations in consecutive sera submitted for routine lithium analysis. Of 98 samples from 61 different individuals, six (6.1%) total calcium results and 32 (33%) dialyzable calcium results were above the respective reference intervals. By comparison, when both total and dialyzable calcium were measured on 50 different apparently healthy volunteers, no results were outside either reference interval (2.20--2.58 mmol/L for total and 1.30--1.47 mmol/L for dialyzable calcium). These increases were not due to age or sex differences between the patients and controls. From the dialyzable calcium data, there appears to be an even higher incidence of mild hypercalcemia in patients receiving oral lithium salts than is indicated by the total calcium concentration alone.

Adult↗
PubMed1977

Formation and properties of lactate dehydrogenase inhibitors in NADH.

We describe some characteristics of the mode of formation of inhibitors of lactate dehydrogenase from commercial NADH. Inhibitor formation is time- and concentration-dependent and also varies with the commercial source of NADH. At least two inhibitory components can form in concentrated NADH solutions. One of these can be separated from NADH by chromatography on either diethylaminoethyl-celluose or diethylaminoethyl-Sephadex; the second cannot. The NADH-associated inhibitor appeared to be present in each of the three commercial NADH preparations studied. The 260 nm/340 nm absorbance ratio was of no help in locating this inhibitor during chromatography.

Chromatography, Ion Exchange↗
PubMed1976

Determination of the molar absorptivity of NADH.

The molar absorptivity of NADH at 340 nm has been determined by an indirect procedure in which high-purity glucose is phosphorylated by ATP in the presence of hexokinase, coupled to oxidation of the glucose-6-phosphate by NAD+ in the presence of glucose-6-phosphate dehydrogenase. The average value from 85 independent determinations is 6317 liter mol-1 cm-1 at 25 degrees C and pH 7.8. The overall uncertainty is -4.0 to +5.5 ppt (6292 to 6352 liter mol-1 cm-1), based on a standard error of the mean of 0.48 ppt and an estimate of systematic error of -2.6 to +4.1 ppt. Effects of pH, buffer, and temperature on the molar absorptivity are also reported.

Absorption↗