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D C Locke

Publications and source records attributed to D C Locke.

16 recordsLinked to original sources
PubMed2001

Adsorption of SO2 on sewage sludge-derived materials.

Sewage sludge-derived materials carbonized at temperatures between 400 and 950 degrees C were used for adsorption of sulfur dioxide from dry and moist air. The materials were characterized using sorption of nitrogen and thermal analysis. The sulfur dioxide capacity was measured according to a laboratory-developed breakthrough test. It was found that the capacity of the adsorbents increases with increasing temperature of carbonization. It is likely that during carbonization at high temperatures such catalytic metals as calcium become active. They play a significant role in the SO2 removal process by neutralization of sulfuric acid formed as a result of oxidation of sulfur dioxide in wet conditions. Besides sulfuric acid, various sulfur-containing salts are formed. It was shown that, after their removal using waterwashing,the SO2 capacitysignificantly decreased.

Adsorption↗
PubMed2001

Sewage sludge-derived materials as efficient adsorbents for removal of hydrogen sulfide.

Sewage sludge-derived materials were used as adsorbents of hydrogen sulfide from moist air. The adsorbent obtained by carbonization at 950 degrees C has a capacity twice of that of coconut-shell-based activated carbon. The capacity of the sludge-derived materials increases with increasing carbonization temperature. It is likelythatduring carbonization at 950 degrees C a mineral-like phase is formed that consists of such catalytically active metals as iron, zinc, and copper. The results obtained demonstrate that the presence of iron oxide significantly increases the capacity of commercial carbon and activated alumina. The sludge-derived adsorbents are efficient for hydrogen sulfide removal until the pore entrances are blocked with sulfur as the product of oxidation reaction. For materials in which the catalytic effect is predominant, hydrogen sulfide is adsorbed until all pores are filled with sulfur. There is also indication that chemisorption plays a significant role in the removal of hydrogen sulfide from moist air.

Adsorption↗
PubMed1998

Separation of paclitaxel and related taxanes by micellar electrokinetic capillary chromatography.

Micellar electrokinetic capillary chromatography is used to separate paclitaxel (trade name Taxol, Bristol-Myers Squibb) and 14 related taxanes in 11.5 min. An aqueous acetonitrile (ACN) buffer containing sodium dodecyl sulfate (SDS) surfactant allows resolution of the 15 taxanes from each other and from the principal matrix ingredient in the injectable dosage form of the drug, Cremophor EL (polyethoxylated castor oil). Although the precise effect of high concentrations of ACN on micelle size and structure is not clear, the separation achieved is not possible in the absence of the organic modifier. The migration order is apparently the of decreasing aqueous-phase solubility, which is related to the presence of a side chain at the carbon 13-position, to the addition of a xylosyl group at the 7-position, and to the number of acetylated hydroxyl groups; it is also related to the increasing affinity of the taxane side chain for the micellar phase. The retention factors, k', increase linearly with SDS concentration above the critical micelle concentration. With increasing concentration of ACN, k' values for the taxanes without side chain decrease; for the most hydrophobic taxanes, k' increases up to 20% (v/v) ACN and then decreases sharply at higher concentrations; for the others, k' varies little up to 10% ACN, and then decreases rapidly with added ACN. Similar behavior was observed with methanol, but the break in k' occurred between 30% and 40% (v/v). Resolution was unacceptably poor if the samples dissolved in methanol were injected; samples dissolved in buffer containing SDS were well-behaved, probably because of stacking of the micelles during injection. Van't Hoff plots (in k' vs 1/T) were linear and allowed calculation of the delta H degree of transfer of taxane from aqueous to micelle phase. However, similar to the situation in HPLC, uncertainty in the micelle/aqueous phase ratio precludes reliable determination of the corresponding delta S degree.

Acetonitriles↗
PubMed1997

Determination of paclitaxel and related taxanes in bulk drug and injectable dosage forms by reversed phase liquid chromatography.

Baseline separation of 15 taxanes including paclitaxel (Taxol) was achieved on pentafluorophenyl (PFP) HPLC columns. Methods using aqueous acetonitrile gradients on each of two commercial PFP columns were developed that are suitable for the determination of potency, content uniformity, and degradation profile of the paclitaxel bulk drug and injectable dosage form. The elution order is apparently related to molecular size, the number of acetylated hydroxyl groups, and the substitution of a xylosyl group at the 7-position. The resolution of several of the taxanes is a sensitive function of the starting eluent composition and the programming rate, which requires optimization of the methods on both columns. Retention of 10 of the taxanes was studied over the temperature range from 30 to 70 degrees C, and enthalpies of transfer, delta H degree, were determined. Conversion of a hydroxy group to an acetyl group, which can interact more strongly with the fluorines on the PFP, has a large effect on the delta H degree, as does the addition of a xylosyl derivative to the 7-hydroxy. The methods developed for the injectable drug form allow good resolution of the taxanes from the excipient Cremophor EL, a polyethoxylated castor oil used with ethanol to solubilize the paclitaxel. The methods for the bulk drug were fully validated in terms of accuracy, precision, specificity including forced degradation, limits of detection and quantitation, and linearity and range.

Antineoplastic Agents, Phytogenic↗
PubMed1995

Separation of the eleven priority pollutant phenols by capillary zone electrophoresis.

Capillary zone electrophoresis (CZE) provides highly efficient separation of the eleven US EPA priority pollutant phenols. All of these phenols are completely resolved in fewer than 15 min in a 100 cm x 75 microns I.D. uncoated fused-silica capillary at 22.5 kV using a pH 9.8 phosphate-borate buffer. Buffer pH is the most critical parameter controlling resolution and separation time. A simple theoretical treatment greatly simplifies the pH optimization procedure. The effects on the separation of buffer concentration, applied voltage, and sample quantity injected were studied. Good calibration data were obtained for phenol concentrations up to 50 mg/l. Limits of detection for all phenols were less than 1 ppm.

Buffers↗
PubMed1990

Design of a photoionization detector for high-performance liquid chromatography using an automated liquid-to-vapor phase interface and application to phenobarbital in an animal feed and to amantadine.

An automated liquid-to-vapor phase interface system forms the basis for a new high-performance liquid chromatography (HPLC)-photoionization detection (PID) system. The system incorporates a six-valve interface enabling peak trapping, solvent switching and thermal desorption of the solute of interest into a vapor phase PID. For reversed-phase HPLC, the eluted solute peak is isolated on a Tenax trap after dilution of the effluent with water; the water is then evaporated, following which the trapped solute is flash-evaporated into the PID system. For normal-phase HPLC, the column effluent is diluted with hexane, the solute peak is concentrated on a short column packed with a propyl-amino/cyano bonded phase and the solvent is evaporated. The solute is then eluted with water onto the Tenax trap, and the above procedure for reversed-phase HPLC followed. All operations are controlled with a microcomputer. The advantages of the new detector system include completely automated operation, fast sample preparation, high sensitivity, and inherent selectivity. The system was applied to phenobarbital, which was extracted with acetonitrile from spiked laboratory animal feed, and to amantadine. The phenobarbital assay used a normal-phase separation with hexane-methyl tert.-butyl ether-methanol eluent. The manual sample preparation time was 5 min and the limit of detection was 2 ng phenobarbital injected; a conventional HPLC assay with UV detection required a longer sample preparation time and had a detection limit of 700 ng. Amantadine was assayed using a reversed-phase HPLC system with a water-methanol-triethylamine-orthophosphoric acid mobile phase. The detection limit was 25 ng injected.

Amantadine↗
PubMed1988

Determination of menadione in an animal feed using supercritical fluid extraction and HPLC with electrochemical detector.

Menadione (vitamin K3) is extracted from spiked rat chow using supercritical fluid carbon dioxide at 8000 psi and 60 degrees C. Quantitative extraction requires only 20 min. The extraction does not suffer from the problems associated with conventional solvent extraction of lipophilic materials from animal feeds. Menadione is determined in the extract, which does not require further cleanup, using reversed-phase high-performance liquid chromatography (HPLC) with reductive mode electrochemical detection at a silver electrode at -0.75 V vs. calomel. The minimum detectable quantity by the detector is 125 pg of menadione, and the response is linear over at least 4 orders of magnitude; however, the minimum quantity extractable is about 20 micrograms/g of feed. Repetitive extracts of a spiked feed sample over a five-day period show an average recovery of 90.5% with a relative standard deviation of 2.2% at the 1 mg/g level.

Animal Feed↗
PubMed1977

Separation of aza-arenes by high-pressure liquid chromatography.

Fast, efficient liquid chromatographic separations of aza-arenes were obtained using both, reversed-phase, and adsorbent packings. Aza-arenes with 2-5 rings are separated within 20 minutes. Sample recovery is quantitative and permits subsequent uv and fluorescence spectrophotometric identifications. The detection limit for most aza-arenes was 1 ng with a 254-nm uv detector. An application to an air pollution problem demonstrates the usefulness of this approach.

Air Pollution↗
PubMedDate not supplied

Determination of vitamin K1 in powdered infant formulas, using supercritical fluid extraction and liquid chromatography with electrochemical detection.

Vitamin K1 (phylloquinone) is extracted from commercial soy protein-based and milk-based powdered infant formulas by using supercritical fluid extraction with CO2 at 8000 psi and 60 degrees C. Quantitative extraction requires only 15 min, and does not suffer from the problems associated with conventional solvent extraction of lipophilic materials from media such as formulas. Vitamin K1 is determined in the extracts by using reverse-phase liquid chromatography (LC) with reductive mode electrochemical detection at a silver electrode polarized at -1.1 V vs SCE. LC run time is 9 min. The minimum detectable quantity is 80 pg, and response is linear over at least 5 orders of magnitude. Recovery of vitamin K1 from a milk-based powdered formula was 95.6% with RSD of 7.4%, and from a soy protein-based product, 94.4% recovery with RSD of 6.5%.

Adsorption↗
PubMedDate not supplied

Liquid chromatographic determination of benzoyl peroxide in acne preparations.

A rapid, precise, and accurate liquid chromatographic (LC) method is described for the determination of benzoyl peroxide (BP) in acne preparations. BP is extracted from a water dispersion of the preparation with dichloromethane (DCM), and an aliquot is eluted from a C-18 reverse phase LC column with acetonitrile-0.10 M aqueous NaClO4. Selective and sensitive quantitation is accomplished with a reductive mode electrochemical detector. This detector is an order of magnitude more sensitive than a 240 nm UV absorption detector; the lower limit of detection is 2 ng for a 4 microL injection. The recovery of BP is 99.4% and the detector response is linear to at least 2 micrograms per 4 microL injection.

Acne Vulgaris↗
PubMedDate not supplied

Separation of cis-/trans-diastereomers and enantiomers of aminoindanol and aminoindan using capillary electrophoresis.

Aminoindanol poses an interesting separation problem because it contains two chiral centers and exists as four stereoisomers. The capillary electrophoretic separation of the cis- and the larger trans-diastereomers of aminoindanol is simply achieved by pH control of the tris buffer background electrolyte. In accordance with theory, maximum separation occurs at the pH equal to the mean value of the pKA values of the isomers. The separation of the enantiomers of both the cis- and trans-diastereomers is effected using the chiral selector alpha-cyclodextrin (alpha-CD). The cis-enantiomeric pair is better separated than the trans-pair, as reflected by the larger difference in the binding constants, K, for the cis-enantiomers with the alpha-CD, K values were measured from the change in electrophoretic mobility with selector concentration, over the temperature range 15 degrees C-35 degrees C. The associated delta H degrees and delta S degrees values were determined for the transfer of each enantiomer from the aqueous buffer phase to the alpha-CD phase. The corresponding K values and associated thermodynamic quantities were also measured for the aminoindan enantiomers, which lack the hydroxyl group of aminoindanol. The effect of chiral selector size was evaluated for the aminoindanols by measuring K and the associated values using beta-CD, which has a larger cavity than the alpha-CD. The better fit of the larger trans-isomers leads to larger K values for the trans-isomers but reduced Ks for the cis-. The gamma-CD cavity is too large to produce chiral discrimination. The low solubility of the beta-CD requires the addition of high concentrations of urea to the tris buffer. Urea has little effect on the K values of the trans-aminoindanols with alpha-CD, but leads to larger values for the cis-isomers.

Electrophoresis, Capillary↗