Standard electrochemical behavior of high-quality, boron-doped polycrystalline diamond thin-film electrodes

Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove nondiamond carbon impurity phases and to hydrogen terminate the surface. The boron-doping level of the NRL film was estimated to be in the mid 1019 B/cm3 range, and the boron-doping level of the USU films was approximately 5 x 10(20) B/cm(-3) based on boron nuclear reaction analysis. The electrochemical response was evaluated using Fe-(CN)6(3-/4-), Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, dopamine, ascorbic acid, Fe(3+/2+), and chlorpromazine. Comparisons are made between the apparent heterogeneous electron-transfer rate constants, k0(app), observed at these high-quality diamond films and the rate constants reported in the literature for freshly activated glassy carbon. Ru(NH3)6(3+/2+), IrCl6(2-/3-), methyl viologen, and chlorpromazine all involve electron transfer that is insensitive to the diamond surface microstructure and chemistry with k0(app) in the 10(-2)-10(-1) cm/s range. The rate constants are mainly influenced by the electronic properites of the films. Fe(CN)6(3-/4-) undergoes electron transfer that is extremely sensitive to the surface chemistry with k0(app) in the range of 10(-2)-10(-1) cm/s at the hydrogen-terminated surface. An oxygen surface termination severely inhibits the rate of electron transfer. Fe(3+/2+) undergoes slow electron transfer at the hydrogen-terminated surface with k0(app) near 10(-5) cm/s. The rate of electron transfer at sp2 carbon electrodes is known to be mediated by surface carbonyl functionalities; however, this inner-sphere, catalytic pathway is absent on diamond due to the hydrogen termination. Dopamine, like other catechol and catecholamines, undergoes sluggish electron transfer with k0(app) between 10(-4) and 10(-5) cm/s. Converting the surface to an oxygen termination has little effect on k0(app). The slow kinetics may be related to weak adsorption of these analytes on the diamond surface. Ascorbic acid oxidation is very sensitive to the surface termination with the most negative Ep(ox) observed at the hydrogen-terminated surface. An oxygen surface termination shifts Ep(ox) positive by some 250 mV or more. An interfacial energy diagram is proposed to explain the electron transfer whereby the midgap density of states results primarily from the boron doping level and the lattice hydrogen. The films were additionally characterized by scanning electron microscopy and micro-Raman imaging spectroscopy. The cyclic voltammetric and kinetic data presented can serve as a benchmark for research groups evaluating the electrochemical properties of semimetallic (i.e., conductive), hydrogen-terminated, polycrystalline diamond.

Two-year stability of borderline personality measures.

Two-year stability coefficients were computed for several measures of borderline personality disorder within a nonclinical sample (n = 65) that included individuals with significant borderline features. Overall, the stability coefficients were modest (r ranging from .28 to .62; intraclass correlations ranging from .26 to .62). Stability values for each of the self-report measures under study were higher than those for the interview-based measure of BPD features, and, in some cases, these values varied as a function of the prototypicality of the subsamples examined. Analyses conducted to identify moderator effects provided no evidence that the stability of BPD scores was moderated by change in personal distress level; however, changes in BPD self-report scores were related to changes in level of negative affectivity.

Turbidimetric assay of penicillin in feeds: addition of magnesium sulfate to eliminate chlortetracycline interference.

The official AOAC method for extracting penicillin from feeds allows some chlortetracycline to be co-extracted if the latter is also present in the sample. This can cause a high bias in results obtained by using the turbidimetric assay in which the test organism is sensitive to both antibiotics. In this report, we show that magnesium ions can be used to circumvent the interference of chlortetracycline in the turbidimetric assay for penicillin.

Role of purine base excretion in regulation of purine pools.

Wild type and mutant strains of Neurospora crassa excrete hypoxanthine, xanthine, and uric acid, but not adenine or inosine, when exogenous adenine is added to growing cultures. No detectable excretion occurs in the absence of adenine. The de novo pathway of purine biosynthesis was found to influence the excretion, in that a metabolic block immediately prior to IMP significantly decreased the excretion, while a metabolic block immediately after IMP significantly increased the excretion over that of wild type. The purine catabolic pathway, which is sensitive to ammonia regulation, was found to be a key determinant in the amount and type of excretion. Recently, it was suggested that hypoxanthine accumulation is the result of a mechanism to regulate the adenylate pool size (Leung and Schramm, 1978). In this report, the possibility that hypoxanthine excretion controls adenylate and guanylate pool sizes is discussed and the role of the purine nucleotide cycle in hypoxanthine excretion is examined.

High pressure liquid chromatographic determination of ethopabate in feeds.

A high pressure liquid chromatographic (HPLC) method is described for determining ethopabate in poultry feeds. Feed samples containing ethopabate are finely ground, extracted 30 min by sonification with methanol-water (80 + 20), and filtered. The extract is cleaned up on an alumina column, and the first 4 ml eluate collected is analyzed. The drug is eluted through a muBondapak C18 column with acetonitrile-water (30 + 70) at a flow rate of 1.4 ml/min and detected by ultraviolet absorption at 280 nm. Chromatography is complete in 7 min, and detector response is linear. The drug is quantitated by peak height ratios. The procedure described is reproducible and shows good agreement with the official AOAC colorimetric method. The lower limit of detection is 2 ng by HPLC, making the method applicable to residue analyses.

High pressure liquid chromatographic determination of sulfanitran and dinsed in medicated feeds and premixes.

A simple reverse phase high pressure liquid chromatographic method is described for determining sulfanitran (acetyl-p-nitrophenylsulfanilamide) and Dinsed (dinitrodiphenylsulfonylethylenediamine) in a variety of feed premixes and formulations. Feed premixes are extracted with dimethylformamide, and formulated feeds are extracted with hot methanol. The extract is filtered through medium porosity paper and injected into a liquid chromatograph equipped with a 254 nm ultraviolet detector and a 30 cm column packed with muBondapak C18. The mobile phase is acetonitrile-water (45 + 55) at a flow rate of 1.0 ml/min. Chromatography was complete in 10 min and peak heights were used for quantitation. Comparison of analyses of commercial samples by this method and by the AOAC colorimetric method, 42.176-42.179, showed close agreement. Recovery of spiked feed samples ranged from 98 to 105%. Butynorate and roxarsone, 2 other drugs which are normally found in combination with sulfanitran and Dinsed, do not interfere.

Gas-liquid chromatographic determination of strychnine in grain baits.

A simple and rapid gas-liquid chromatographic procedure, using a 6' times 1/4'' glass column packed with 5% SE-30 on Chromosorb W (DMCS) and a flame ionization detector, is described. Grain baits containing strychnine alkaloid are ground, mixed, and extracted by shaking with chloroform containing an internal standard, 1,3,5-triphenylbenzene. Without further cleanup, extract filtrates are injected directly into a gas chromatograph. Peak height ratios are used for quantitation of strychnine. The analysis of commercial samples shows that the method compares well with a commonly employed ultraviolet spectrophotometric method; good precision, with recoveries ranging from 89.9 to 91.7%, is obtained in the analysis of prepared samples. The method is sensitive to 2 mug strychnine.

High-performance liquid chromatographic determination of strychnine in grain baits.l.

A simple and rapid high-performance liquid chromatographic procedure is described for the determination of strychnine. Grain baits containing strychnine alkaloid are ground, mixed, and extracted by shaking with chloroform. Without further cleanup, extract filtrates are injected directly into a liquid chromatograph. Chromatography is complete within 7 min and peak heights are used for quantitation. Separations were made on a 30 cm times 4 mm id stainless steel column packed with mu Porasil (8-12 mum silica). The eluting solvent was methanol-chloroform (10+90) at a flow rate of 2.0 ml/min. Recovery of spiked samples ranged from 91.5 to 95.2%. Confirmation of strychnine from a commercial sample was made by high resolution mass spectrometry with mass agreement to 1.2 ppm.

Separation of rotenoids and the determination of rotenone in pesticide formulations by high-performance liquid chromatography.

The rotenoids deguelin, B-dihydrorotenone, dehydrorotenone, rotenone, 6alpha beta, 12alpha beta-rotenolone, and tephrosin were chromatographed on 8-12 mum silica. A mobile phase of chloroform-isooctane (35+65) pumped at a flow rate of 1 ml/min through a 30 cm column was used and the absorbance of the eluate was monitored at 294 nm. Rotenone, B-dihydrorotenone, deguelin, and dehydrorotenone are completely resolved while 6alpha beta, 12alpha beta-rotenolone and tephrosin chromatograph as one peak. This method has potential as a preparative separation technique for rotenoids. Also described is a procedure to quantitatively measure rotenone in pesticide formulations. Samples were extracted with chloroform and chromatographed at a flow of 2.5 ml/min. The method is rapid (rotenone is eluted in 12 min) and reproducible.