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Biomedical subjects

L R Snyder

Publications and source records attributed to L R Snyder.

At least 73 records · Page 4Linked to original sources
PubMed1982

Automated analysis of acetaminophen and caffeine in serum using the FAST-LC system: contributions to assay imprecision in procedures based on HPLC with sample pretreatment.

Two procedures are described for the fully automated analysis of several therapeutic drugs in serum, using HPLC with on-line pretreatment (solvent extraction) of the sample. The FAST-LC system (Technicon Instruments) was used for the assay of mixtures of 1) acetaminophen, theophylline, and/or caffeine, or 2) phenylethylmalonamide, primidone, phenobarbital, carbamazepine epoxide, phenyltoin, and/or carbamazepine. The rate of sample analysis was 15/hr for the theophylline group of drugs and 12/hr for the six anticonvulsants. The precision of resulting assays was about 3% (CV), and only 75 microliter of sample was required. The precision of resulting assays, in terms of a previously reported model, is also discussed.

Acetaminophen↗
PubMed1981

Liquid-chromatographic analysis for common tricyclic antidepressant drugs and their metabolites in serum or plasma with the technicon "FAST-LC" system.

We describe a single procedure for assay of seven tricyclic antidepressant drugs and metabolites in serum or plasma: protriptyline, nortriptyline, amitriptyline, desmethyldoxepin, doxepin, desipramine, and imipramine. With the Technicon "FAST-LC" system, samples are aspirated directly into the unit and pretreated via double extraction; the concentration of each drug is then determined by "high-performance" liquid chromatography. Final chromatograms are monitored at 205 nm, at analysis rates of 7.5 samples/h. Concentration and absorbance are linearly related for each drug from 0 to 1400 micrograms/L. Day-to-day CVs averaged 5 to 6% for each drug, and there is good correlation of FAST-LC values with those obtained by gas-chromatographic methods. Total sample volume is 750 microliters.

Amitriptyline↗
PubMed1981

Precision of "high-performance" liquid-chromatographic assays with sample pretreatment. Error analysis for the Technicon "FAST-LC" system.

A comprehensive theory has been presented elsewhere (Anal. Chem. 53: 877-884, 1981) for the various contributions to assay imprecision in procedures that are based on sample extraction followed by "high-performance" liquid chromatography. Experimental data (1800 assays, 8400 results) for the Technicon FAST-LC system are used with this theory in an effort to understand and control the precision of clinical-laboratory procedures, both automated and manual. This study provides specific conclusions and recommendations on matters such as: standardization procedures and protocols, physical properties requires in internal standards, the relative importance of different sources of imprecision and means for improving precision, the relative importance of temperature control in pretreatment and liquid-chromatographic analysis, and the precision obtainable with small sample volumes or with samples containing very low concentrations of analyte (e.g., in assays for free drugs). Automation evidently can lead to twofold greater assay precision, other factors being equal, for liquid-chromatographic procedures that include sample pretreatment. Similarly, internal standardization, properly applied, can decrease assay imprecision by twofold.

Anticonvulsants↗
PubMed1980

Evolutionary conservation of linkage groups: additional evidence from murid and cricetid rodents.

In Mus musculus, family Muridae, the glucosephosphate isomerase (Gpi-l), pink-eyed dilution (p), albinism (c), and beta-type globin (Hbb) loci are known to be linked in the order Gpi-l-p-c-Hbb. In Rattus norvegicus, another murid rodent, the p, c, and Hbb loci are known to be linked in the same order and with similar recombination frequencies. In Peromyscus maniculatus, family Cricetidae, it was previously known that p and c are linked and by analogy to Mus musculus that linkage group should be bounded by Gpi-l near p and by a beta-globin locus near c. Linkage has now been established between Gpi-l and the Hbe globin locus in Peromyscus. However, the observed recombination frequency in Peromyscus (16.3%) is significantly lower than in Mus, suggesting that perhaps a chromosomal inversion has occurred during the evolutionary divergence of the two rodent families. Linkage relationships were also tested between the Hbc1, Hbd1, and Hbe1 globin variants. Hbc1 (presumably an alpha-type globin) segregated independently from Hbd1 and Hbe1 (presumably beta-type globins). No recombination was observed between Hbd1 and Hbe1. Those two globin genes may be alleles at a single locus, although circumstantial evidence suggests that they represent tightly linked duplicate loci.

Animals↗
PubMed1980

On-line liquid-chromatographic analysis for drugs in serum with the Technicon "FAST-LC" system: performance data for theophylline and for four commonly used anticonvulsants and their metabolites.

We describe a new instrument for use in assay of therpeutic drugs in serum by "high-performance" liquid chromatography, the "FAST-LC" system (Technicon). Serum samples are aspirated directly into the unit, extracted with solvent, and the evaporated and redissolved extract is injected onto a chromatographic column. We illustrate the performance of the system by assays in serum for theophylline and four anticonvulsants (primidone, phenobarbital, phenytoin, and carbamazepine) plus two of their active metabolites (phenylethylmalonamide and carbamazepine epoxide). For theophylline, final chromatograms are monitored at 270 nm, at analysis rates of 10/h. Concentration and absorbance are linearly related from 0 to 130 mg of theophylline per liter. For the anticonvulsants, chromatograms are monitored at 200 nm, at analysis rates of 7.5/h. The six individual determinations are each linear beyond the therapeutic range. For both drug panels, day-to-day CV's were 4 to 6%. Results correlate well with those by enzyme immunoassay. A total sample volume of 150 microL is required.

Anticonvulsants↗
PubMed1980

Continuous-flow analysis for glucose in serum, with use of hexokinase and glucose-6-phosphate dehydrogenase co-immobilized in tubular form.

Hexokinase and glucose-6-phosphate dehydrogenase, co-immobilized at the inner wall of plastic tubing, were used with continuous-flow analyzers to measure serum glucose. The performance of the enzyme-containing coils meets the hydraulic requirements of the continuous-flow instruments, and the average carryover does not exceed 2.2%. A glucose concentration change of 1 g/L yields a 0.08 change in absorbance. There is no significant deviation from linearity for glucose concentrations up to 5 g/L. The method is similar to the Reference Method proposed by the Food and Drug Administration, and results by the two methods agree and correlate well (r = 0.999). The operational stability of the enzyme tubes is sufficient to allow the analysis of at least 10 000 serum samples. We investigated in detail the effect of reagent concentrations and temperature on the performance of the enzyme coils, and the results shed light on the nature of the heterogeneous dual-enzymic reaction.

Autoanalysis↗
PubMed1979

Polychromatic analysis: new applications of an old technique.

As a means of correcting for many potential interferences, polychromatic analysis offers an effective alternative to either sample pretreatment or separate blank determinations. Because of the differing spectral characteristics of each interfering species, and the nature of these interferences (static vs. kinetic), the application of polychromatic analysis must be optimized for each analytical procedure to minimize all residual errors. Overall assay precision can be maximized by proper use of flagging procedure to minimize all residual errors. Overall assay precision can be maximized by proper use of flagging procedures (also based on polychromatic analysis). By using a second wavelength measurement, the analyst can also verify the accuracy of an analytical measurement in selected situations. These applications of polychromatic analysis are a departure from conventional analytical procedures in allowing for correction of various interferences in the actual reaction mixture, without making assumptions about the recovery of analyte during pretreatment or the equivalent absorptivity of interferent in both blank and assay solutions.

Aspartate Aminotransferases↗
PubMed1978

Genetics of hemoglobin in the deer mouse, Peromyscus maniculatus. I. Multiple alpha- and beta-globin structural loci.

Genetic data, together with molecular structure studies, have demonstrated that the complex hemoglobin phenotypes in four subspecies of P. maniculatus are generated by at least four, and probably five, globin structural loci. The Hba and Hbc loci apparently arose by duplication of an ancestral alpha-type locus, while Hbb, Hbd, and Hbe apparently were derived from a beta-type locus. The Hba and Hbb structural loci are electrophoretically monomorphic, while Hbc, Hbd, and Hbe are each polymorphic for at least two electrophoretic alleles. Alleles at Hbc and Hbd segregate independently. The globin products of Hbc and Hbd are electrophoretically indistinguishable; therefore, it is impossible to enumerate true gene frequencies in population surveys. Combined evidence from Peromyscus, Mus and Rattus indicates a remarkable similarity in the numbers of duplicated globin structural loci and in their linkage relationships to coat color loci.

Animals↗
PubMed1978

Genetics of hemoglobin in the deer mouse, Peromyscus maniculatus. II. Multiple alleles at regulatory loci.

Deer mice are polymorphic for electrophoretic hemoglobin phenotypes showing one, two, or three bands. Within the multibanded phenotypes, there is considerable variation in the hemoglobin partitioning, defined as the fraction of total hemoglobin made up by the secondary and tertiary bands. In subspecies sonoriensis, for example, hemoglobin partitionings range from 0.03 to 0.38. The inheritance of partitioning values is under remarkably strict genetic control. The genetic variation is additive and the narrow heritability is close to 1.0. The inheritance data can be modeled in precise detail by postulating multiple-allele polymorphisms at globin regulatory loci. Comparison of simulated versus actual inheritance data demonstrates that the so-called null structural alleles actually produce functional globins.--The genetic controls in Peromyscus may be analogous to those in primates. Unfortunately, the molecular mechanisms effecting the regulation are unknown. Different subspecies of P. maniculatus show strikingly different arrays of partitioning values, but the role of natural selection in maintaining the quantitative polymorphisms remains obscure.

Alleles↗
PubMed1977

Rapid chromatographic method to determine polyamines in urine and whole blood.

A procedure is described for the rapid determination of putrascine, spermine and spermidine in ruine and whole blood. The samples are hydrolyzed with barium hydroxide and are neutralized with sulfuric acid. The polyamines are concentrated and separated from amino acids on a small bed of ion-exchange resin that then serves to load the samples on a two-channel, automated ion-exchange chromatography apparatus. As many as 100 samples can be analyzed in a 24-h period. The method has been shown to be applicable to the analysis of urine and whole blood samples, but further development is needed for application to serum samples.

Autoanalysis↗
PubMed1977

Continuous-flow analysis for glucose, triglycerides, and ATP with immobilized enzymes in tubular form.

Small-bore ("Autozyme") tubes with immobilized enzymes at the inner wall have been developed and studied for application in the Technicon "SMAC" high-speed continuous-flow biochemical analyzer. Tubes coated with glucose oxidase (D-glucose:oxygen oxidoreductase, EC 1.1.3.4) have been prepared for the assay of glucose, with colorimetric assay of the hydrogen peroxide produced; tubes coated with glycerol kinase (ATP:glycerol phosphotransferase, EC 2.7.1.30) for the enzymatic assay of triglycerides; tubes coated with hexokinase (ATP:D-hexose-6-phosphotransferase, EC 2.7.1.1) and glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NAD+ oxidoreductase EC 1.1.1.49) for the measurement of ATP, an intermediate product in assays for creatine kinase. With use of 10-15 cm lengths of Autozyme tube and SMAC hydraulics (150 samples per hour), assay sensitivity and carryover were similar to values for the corresponding free-enzyme methods. These immobilized enzymes were sufficiently stable for one to eight weeks of continuous use before replacemnt. We conclude that suitable bound-enzyme tubes can replace either single or multiple free-enzyme reagents in many continuous-flow assays at high sampling rates.

Adenosine Triphosphate↗
PubMed1976

Derivatives of 1-naphthyl ethylenediamine dihydrochloride for standardization of direct-bilirubin assays done with the Technicon "SMAC".

The Jendrassik--Groff assay for direct bilirubin was adapted for analysis rates of 150/h on the Technicon "SMAC" continuous-flow analyzer. This requires development of a standard that is compatible with the other 19 channels on this analyzer. N-1-Naphthyl ethylenediamine dihydrochloride has been used for standardization of direct bilirubin assays, but we found it to be unsuitable because values for potassium are falsely elevated when potassium is determined with a valinomycin ion-selective electrode. This interference can be eliminated by alkylating the aliphatic amine group in the standard. The resulting compounds undergo the coupling reaction in the same way as the original compound and function equally well as standards for the direct bilirubin reaction. The only limitation of these analogs is their decreased solubility at physiological pH in some cases. Thus only certain alkyl groups are suitable.

Autoanalysis↗