Biomedical subjects

R W Stringham

Publications and source records attributed to R W Stringham.

8 recordsLinked to original sources

PubMed2001

Effect of mobile phase acidic additives on enantioselectivity for phenylalanine analogs.

The use of acidic mobile phase additives allows the chiral separation of underivatized phenylalanine analogs on a common amylosic column. In addition to decreasing retention and band-broadening arising from non-ideal interactions, acidic additives may also increase selectivity. This appears to be due to the minimization of non-selective binding in the recognition site. Effects of the additives are related to additive pKa and size. Ethanesulfonic acid was typically the most effective additive with trifluoroacetic acid being one of the least effective.

Acids↗

PubMed2001

The role of modifiers in high selectivity chiral separations on Pirkle-type columns.

Atypically high selectivity (alpha > 2) chiral separations have been observed on Pirkle type supports. These separations were examined in terms of their response to various modifiers, thermodynamic behavior and LSER modeling. Atypical thermodynamic and LSER results were observed along with large changes in selectivity between modifiers. The use of bulky modifiers gave increased selectivity resulting from dramatic increases in the retention of the second eluting enantiomer. These findings lead to the conclusion that increased retention is due to an inability of bulky modifers to penetrate a tight complex between selector and this enantiomer.

Journal Article↗

PubMed1999

Empirical relationship between chiral selectivity and mobile phase modifier properties.

An empirical relationship was derived which relates properties of the mobile phase modifier to the chiral selectivity factor for a given analyte/chiral selector combination. Using carbon dioxide and heptane-based mobile phases, the effect of various mobile phase modifiers on Pirkle-type stationary phases may be accurately modeled using a two-parameter equation. Similar results are obtained using cellulosic stationary phases with carbon dioxide-based mobile phases. Modeling separations performed using heptane-based mobile phases with cellulosic stationary phases were not successful. The predictive ability of this modeling approach was demonstrated using novel modifiers and chiral analytes.

Chromatography, Liquid↗

PubMed1987

Selective non-adsorption preparative chromatography of bovine immunoglobulin Gl.

Bovine immunoglobulin Gl (IgGl) was purified from blood serum by isocratic elution through a mixed-bed ion-exchange column at low ionic strength. Selection of a mobile phase pH near the isoelectric point of IgG precluded its binding to the strong cation- and anion-exchange sorbents and allowed IgGl to be eluted isocratically. Under these conditions most of the other components in the serum sample were retained on the mixed-bed column. This approach gives excellent throughput and purity.

Adsorption↗

PubMed1982

Use of post-column derivatization in liquid chromatographic determination of sulfamethazine and sulfathiazole in feeds and feed premixes.

Sulfonamide drugs are extracted from feed and feed premixes by shaking with 0.15N HCl in 25% methanol. The extract is diluted, clarified, and chromatographed on a reverse phase C18 column. Mobile phases used are methanol-2% acetic acid (35 + 65) and acetonitrile-2% acetic acid (18 + 82) for sulfamethazine (SMT) and sulfathiazole (STZ), respectively. A solution of dimethylaminobenzaldehyde (DMAB) is added to the column eluate and the resulting sulfonamide-DMAB complex is detected at 450 nm. The method was tested for linearity, recovery, and precision across a broad sample range. Recovery was 100.6 +/- 2.3% and 96.3 +/- 1.6% for STZ and SMT, respectively. Linearity was excellent (r2 = 0.9985 for STZ and r2 = 0.9996 for SMT) as was within-day precision (RSD = 2.00% for STZ and 1.52% for SMT). The method was compared with the Bratton-Marshall colorimetric method. Analysis of 14 STZ and 15 SMT samples failed to detect any bias between the 2 methods. Some practical aspects of the use of this technique are discussed.

Animal Feed↗

PubMed1981

High performance liquid chromatographic determination of furazolidone in feed and feed premixes.

Furazolidone is separated from finished feeds by acetone-water extraction on a Goldfisch apparatus. Extracting solvent is removed, and the residue is dissolved in dimethylformamide-5% tetraethylammonium bromide (1 +1), clarified, and chromatographed on a reverse phase C1 column. The mobile phase is CH3CN-2% acetic acid (20 + 80) with detection at 365 nm. The method was tested for linearity, recovery, and ruggedness, and compared with the AOAC colorimetric assay by using field samples containing 0.0055-0.055% furazolidone. Precision data suggest a cumulative relative standard deviation of 1.43% within days and 1.78% between days. The ruggedness test predicts a between-laboratory relative standard deviation of 3.67%. Recovery was 97.5 +/- 2.0% and linearity was excellent (r2 = 0.9994) up to 0.06% furazolidone. Premixes are extracted by shaking with dimethylformamide. An aliquot of the extract is diluted (1 + 1) with 5% tetraethylammonium bromide, clarified, and chromatographed.

Animal Feed↗

PubMedDate not supplied

Liquid chromatographic determination of cholecalciferol in rodent baits.

Cholecalciferol (vitamin D3) is extracted in acetonitrile on a Goldfisch apparatus, diluted to volume, and determined by reverse phase liquid chromatography (LC). The sum of the peak heights of pre-vitamin D3 and cis-vitamin D3 is used for quantitation. The method was tested for precision, linearity, and recovery. Quadruplicate analyses of 5 formulation samples gave relative standard deviations of 1.56-2.65%. Linearity was excellent with regression and correlation coefficients of 0.9997 and 0.9998, respectively. Recovery was 98.0 +/- 2.7%. The method is applicable to 0.075% cholecalciferol rodent baits.

Cholecalciferol↗

PubMedDate not supplied

Sulfamethazine and sulfathiazole determination at residue levels in swine feeds by reverse-phase liquid chromatography with post-column derivatization.

Twenty g sample, to which sulfamerazine has been added as internal standard, is extracted with 0.3N HCl + 1.5% diethylamine in 25% methanol. The sample extract is chilled (to aid clarification), centrifuged, and filtered. The sulfonamides are separated from each other and from co-extracted materials on a C-18 reverse-phase column and detected at 450 nm following post-column derivatization with dimethylaminobenzaldehyde. Two isocratic mobile phases have been tested: (1) acetonitrile-2% acetic acid (17 + 83), with an analysis time of 13 min; and (2) acetonitrile-methanol-2% acetic acid (4 + 16 + 80), with an analysis time of 20 min but an improved analysis for some samples. As many as 40 samples have been analyzed at one time unattended with the aid of an autosampler. A total of about 1500 field samples have been assayed using the method. Method sensitivity is 0.1 ppm for either analyte in a hog finishing fed. Linearity for each of the analytes is satisfactory over a range of 0.4-25 ppm in spiked feeds. Coefficients of variation range from 13% at 0.5 ppm to 2% at 13 ppm as tested over a period of time in naturally contaminated samples. The absolute recovery of sulfamerazine varies with sample matrix, but, in the presence of sulfamerazine as internal standard, recovery has been 96.7-99.7% over the range of 0.1-10 ppm. Sulfamerazine and sulfamoxole were tested for their suitability as internal standards. Sulfamerazine is a good internal standard for sulfamethazine; neither is ideal for sulfathiazole.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal Feed↗