Calorimetric study of Sb-modified Ge–Se–Te glassy alloys

The glassy compositions of Ge ₁₆ Se ₅₂ Te _32?x Sb _x system, obtained using rapid melt quenching technique, have been characterized by calorimetric study at different heating rates in this study. A systematic investigation of the crystallization kinetics is carried out for these compositions. Composition corresponding to atomic % 8 of Sb has good thermal stability. The material exhibits the unique thermal properties, which makes it suitable to use for electrical or memory switching devices. Various thermal parameters, activation energies of glass transition and crystallization are calculated using relevant approaches.     

Thermoanalytical investigations of niobium(V) chloride aryloxides

Niobium(V) chloride aryloxides [NbCl₃(OAr)₂] and [NbCl₂(OAr)₃] (Oar = —OC₆H₄Bu ^t -4 and —OC₆H₄OMe-4) have been prepared by reacting NbCl₅ with two and three equivalents of the respective phenol in CCl₄. The complexes have been characterized by elemental analysis, molecular weight determination, i.r., ¹H-n.m.r., u.v.–vis. and MS techniques. Thermal behaviour (t.g.–d.t.) of the complexes has also been studied and decomposition schemes proposed. The kinetic and thermodynamic parameters namely, the activation energy 'E ^*', the frequency factor 'A', entropy of activation 'S' and specific rate constant 'kr' etc. have been calculated employing the Coats–Redfern equation. The non-isothermal t.g. data has also been utilized to determine the most probable mechanism and corresponding activation energy for the decomposition of niobium(V) complexes by testing seven different theoretically possible decomposition mechanisms.     

Simultaneous detection of a wide variety of commonly abused drugs in a urine screening program using thin-layer identification techniques.

A single-step extraction method and thin-layer identification techniques capable of testing a wide variety of drugs of abuse are presented. These techniques are well suited for large and/or small drug programs involved in urine testing because they provide substantial economic benefits and improve clinical functioning. The drugs are absorbed on a 6 X 6 cm piece of paper loaded with cation-exchange resin and then eluted from the paper at pH 10.1 using ammonium chloride-ammonia buffer. The simultaneous thin-layer detection of sedatives, hypnotics, narcotic analgesics, central nervous system stimulants and miscellaneous drugs is accomplished by spotting the solution of extracted residue on a 20 X 20 cm Gelman pre-coated silica gel glass microfiber sheet (ITLC Type SA). A two-stage solvent system is used in order to obtain a chromatogram with optimum separation of a wide range of drugs. This system can separate methadone and/or cocaine from propoxyphene, methaqualone, methylphenidate, pentazocine, pipradrol, Doxepin, chlorpromazine, phenazocine, naloxone, naltrexone, imipramine and trimeprazine; amphetamine from phenylpropanolamine and dimethyltryptamine; codeine from dextromethorphan; methamphetamine from dimethyltryptamine, etc. Different detection reagents are then applied in succession to different marked areas of the developed chromatogram. This elegant method of extraction and spraying has enabled us to detect morphine base at a sensitivity level of 0.15 mug/ml, amphetamine sulfate at 1.0 mug/ml, methamphetamine hydrochloride at 0.5 mug/ml, phenmetrazine hydrochloride at 0.5 mug/ml, codeine phosphate at 0.5 mug/ml, methadone hydrochloride at 1.0 mug/ml, secobarbital at 0.36 mug/ml and phenobarbital at 0.5 mug/ml in urine. The minimum volume of urine needed to achieve these sensitivities is 20 ml. The cost of analysis per urine specimen using these techniques for concomitant screening of these drugs is less than US$ 1.     

Thin-layer detection of diazepam and/or chilordiazepoxide alone or in combination with major drugs of abuse in drug abuse urine screening programs

Three extraction procedures for the detection of diazepam, oxazepam, chlorazepate and/or chlordiazepoxide in human urines are presented. All three procedures are based on the acid hydrolysis of benzodiazepines and/or their conjugated metabolites to give the corresponding benzophenones. Procedure I involves the direct acid hydrolysis of raw urine and is recommended when the aim is to test the abuse of benzodiazepine derivatives only. Procedure II Is a two-step extraction method in which a wide variety of drugs of abuse including cocaine (test based on the detection of benzoylecgonine) are extracted by the first step using paper loaded with cation-exchange resin and the benzodiazepines are tested in the second step by the acid hydrolysis of the spent urine left after removing the ion-exchange paper. Procedure III involves the use of inert fibrous matrix and then its acid hydrolysis. The detection procedure is based on the identification of methylaminochlorobenzophenone (MACB) and aminochlorobenzophenone (ACB). MACB is detected as a yellow-colored compound while ACB is detected by spraying with Bratton-Marshall reagent. Specificity of detection of ACB has been achieved by the selection of a thin-layer developing solvent system in which sulfonamides with primary aromatic amino groups remain at the origin.     

Process intensification in PSA processes for upgrading synthetic landfill and lean natural gases

Process intensification aims at reducing the size of equipment by orders of magnitude and is actively perused in separation processes. Its feasibility in Pressure Swing Adsorption (PSA) processes has been explored. A 4-bed PSA and a 3-bed PSA, which emulate the moving bed processes, and duplex PSA and a modified duplex PSA have been selected for the exploratory studies. Simulation studies on the separation of a mixture of CH₄–CO₂ over 5A zeolite were carried out to compare the performance of these processes. An index has been proposed to quantify the process intensification. The 3-bed PSA and the modified duplex PSA exhibited superior performance compared to the other two for a purity of 99.9 mol% of both the products. However, the performances of the processes other than duplex were comparable when purities were set at 95 mol%. In 3-bed PSA a modest process intensification of four times reduction in size and two times reduction in energy requirement appears to be feasible if benchmarked against the PSA based on the variant of the Skarstrom cycle.     

Comparison of costs for testing a wide variety of drugs of abuse per urine specimen in a drug abuse urine screening program and frequent urine collections.

Existing urine testing techniques in a drug abuse urine screening program with their capacity to analyze urine specimens per day are discussed. The start-up cost using each technique and cost per specimen are presented. A single step extraction technique using ion-exchange paper to absorb drugs prior to thin-layer chromatography (TLC) as reported by these laboratories will cost $0.58 per specimen, for testing the entire aray of drugs of abuse (at least 9-14 tests per specimen). Sensitivity reported using TLC technique for the morphine base is 0.15 mug/ml (minimum volume of urine needed 20 ml), 0.10 mug/ml if the volume of urine available is 30-35 ml, and 0.07 mug/ml if the volume of urine available is 43-50 ml.