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This study describes the development of a sensitive and accurate dispersive liquid-liquid microextraction strategy for the preconcentration and determination of selected pesticides in wastewater and lake water samples by gas chromatography-mass spectrometry. Determination of these pesticides at high accuracy and precision is important because they can be still be found in environmental samples. The type of extraction solvent and type of disperser solvent were optimized using the univariate approach. Furthermore, a Box-Behnken experimental design was used to set up a working model made up of 18 combinations of three variables, tested at three levels. The parameters fitted into the design model were volume of extraction solvent, disperser solvent volume, and mixing period. Analysis of variance was used to evaluate the experimental data to determine the significance of extraction variables and their interactions, before selecting optimum extraction conditions. The method was then applied to aqueous standard solutions between 2.0 and 500 μg L -1 , and the limit of detection (LOD) and quantification (LOQ) values obtained for the analytes were between 0.37-2.8 and 1.2-9.4 μg L -1 , respectively. The percent recoveries were calculated in the range of 92-114 and 96-110% for wastewater and lake water, respectively. These results validated the accuracy and applicability of the method to the selected matrices.

A laboratory study was designed to assess the following: i) the degradation kinetics of chlorotoluron and flufenacet at two different temperatures, 6 °C and 16 °C, in an unamended agricultural soil and one amended with spent mushroom substrate (SMS) and green compost (GC), and ii) the formation of the main metabolites of both herbicides with potential risk for water pollution over degradation time. The aim was to determine the dependence of these herbicide degradations on temperature (Q 10 factor) using kinetic parameters, which is essential information for the later simulation of herbicide environmental fate with FOCUS models. SMS and GC were applied in situ to the natural soil as organic amendments at rates of 140 or 85 t residue ha -1 , respectively. Unamended and amended soils were taken from the 0-10 cm topsoil of experimental plots (three replicates/treatment) located on an agricultural farm. Samples of soil + herbicides were incubated at 6 °C or 16 °C under laboratory conditions. The degradation curves of chlorotoluron and flufenacet were fitted to single first-order and first-order multicompartment kinetic models, respectively. The flufenacet degradation, the more hydrophobic herbicide, was slower than that of chlorotoluron in all the treatments. The application of the organic amendments to soil increased the half-lives (DT 50 ) for both herbicides incubated at 6 °C (1.3-1.9 times) and 16 °C (1.4-1.9 times) due to their higher sorption and lower bioavailability for degradation in amended soils. The herbicides recorded a faster degradation at 16 °C than at 6 °C (Q 10  = 1.9-2.8) due to the increased microbial biomass and/or activity with temperature. The metabolites desmethyl chlorotoluron, flufenacet ESA and flufenacet OA were detected in all the soil treatments at both incubation temperatures. The determination of Q 10 factors in amended soils is very valuable for generating accurate input data for pesticide fate models such as FOCUS in order to improve the evaluation of the leaching of herbicides and their transformation products, which is a relevant goal to maintain the sustainability of agricultural systems., (Copyright © 2018 Elsevier B.V. All rights reserved.)

A simultaneous analytical method based on LC-MS/MS was developed for the determination of flufenacet and its metabolites, [(4-fluorophenyl)(1-methylethyl) amino]oxo-acetic acid and [N-(4-fluorophenyl)-N-(1-methylethyl) acetamide]-2-sulfinylacetic acid, in agricultural products. The compounds were extracted from samples with methanol. The crude extracts were purified using Bond Elut C18 and InertSep GC/PSA, then determined by LC-MS/MS. The average recoveries (n=5) from 4 kinds of agricultural products (wheat, soybean, potato and tomato) spiked at the level of the MRLs or the uniform limits (0.01 μg/g) were 70.6-97.0%, and the relative standard deviations were less than 5%. The lower limits of quantitation of flufenacet and its metabolites were 0.01 μg/g.

In this work, bismerthiazol was firstly assayed by a fast and portable method employing protein-capping gold nanoculsters as probes. The luminescent intensity of the nanoclusters showed a correlative response towards bismerthiazol from 5 to 4000 μg/mL with a linear relation in the range of 5 - 100 μg/mL. As little as 5 μg/mL of bismerthiazol could be quantified. The high affinity of bismerthiazol to interact with the soybean protein-capped gold nanoclusters contributed to the excellent selectivity of this method over other common pesticides. The recoveries in several cabbage samples were 101 - 135%, indicating good performance in practical applications. By comparison to previous reported approaches, this method bears advantages including simple operation, fast response, visual readout and good selectivity.

β-Cyclodextrin and its derivatives can selectively bind to various organic molecules in its cavity and provide good applications in sample preparation. Surface-enhanced Raman spectroscopy is a sensitive technique and has received increasing attention in the last decade. Herein, 3,5-dimethyl phenyl carbamoylated β-cyclodextrin bonded silica gel was used as a ssorbent in solid-phase extraction to selectively enrich forchlorfenuron and thidiazuron followed by determination with surface-enhanced Raman spectroscopy. It showed excellent selectivity for forchlorfenuron and thidiazuron and the adsorption capacities were 40.0 and 30.0 μg/g, respectively. A rapid and sensitive method based on the modified β-cyclodextrin solid-phase extraction coupled with surface-enhanced Raman spectroscopy was developed. The linear ranges were 30.0-300.0 μg/L for forchlorfenuron and thidiazuron at 1005 and 640 cm(-1) , respectively. Both of the limits of detection were 15.0 μg/L, which were significantly lower than the maximum permitted by the National Standard. The recoveries of forchlorfenuron and thidiazuron were 78.9-87.9% for the spiked grape, kiwi, cucumber and tomato, with relative standard deviations of 8.1-13.2%. The results show that this method is sensitive, selective, and relatively time saving, and has great potential in the analysis of trace amounts of plant growth regulators in fruits and vegetables., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

This study aimed to develop a rapid, specific and sensitive method for the residue determination of benzo-1,2,3-thiadiazole-7-carboxylic acid 2-benzoyloxyethyl ester in soil, vegetable, and water by using gas chromatography with tandem mass spectrometry. During the extraction procedure, modified quick, easy, cheap, effective, rugged, and safe method using acetonitrile was compared with classical oscillating extraction using ethyl acetate and acetone, respectively. Before injection, a solid-phase extraction cartridge of Bond Elut Florisil was used for sample clean-up. The method was fully validated and showed satisfactory linearity (r(2) > 0.99) over the range to be assayed (10-1000 ng/mL), with the limits of detection ranging from 0.092-0.229 ng/mL and the limits of quantification ranging from 0.307-0.763 ng/mL. Recovery values at the spiked concentrations of 10, 100 and 1000 ng/g varied from 85.9-109.3%, 81.0-108.2%, 74.2-113.4% for water, soil and vegetable, respectively, with the maximum relative standard deviations of 12.2%. Results indicated that the established modified quick, easy, cheap, effective, rugged, and safe method coupled to gas chromatography with tandem mass spectrometry was promising for the residue monitoring of benzo-1,2,3-thiadiazole-7-carboxylic acid 2-benzoyloxyethyl ester in the environment and vegetable products., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The surface enhanced Raman scattering (SERS) spectra of biologically and industrially significant 5-methylthio-1, 3, 4-thiadiazole 2-thiol molecule have been investigated. The SERS spectra at various concentrations of the adsorbate are compared with the Fourier transform Infrared (FTIR) and normal Raman spectra (NRS) of the probe molecule recorded in different environmental conditions. The optimized molecular structures of the most probable thione and the thiol forms of the molecule have been estimated from the density functional theory (DFT) calculations. The vibrational signatures of the molecule have been assigned from the potential energy distributions (PEDs). The detail vibrational analyses reveal that ∼54% of the thione form of the molecule is prevalent in the solid state and its population increases to ∼65% in ACN solvent medium. Concentration dependent SERS, together with the 2-dimensional correlation spectra (2D-COS), corroborate the presence of both the thione and the thiol forms of the molecule even in the surface adsorbed state. The orientations of the thione and the thiol forms of the molecule on the nanocolloidal silver surface have been predicted from the surface selection rule. The selective enhancement of Raman bands in the SERS spectra have been explored from the view of the Albrecht's "A" and Herzberg-Teller (HT) charge transfer (CT) contribution., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A simple and accurate method for the determination of bismerthiazol and its metabolite 2-amino-5-mercapto-1,3,4-thiadiazole was developed in Chinese cabbage and soil by high-performance liquid chromatography-diode array detection in this study. The limits of detection were 0.06 mg/kg for bismerthiazol and 0.03 mg/kg for 2-amino-5-mercapto-1,3,4-thiadiazole, respectively. Recoveries of cabbage and soil were investigated at three spiking levels and were in the range of 84.0-96.0% for bismerthiazol and 71.0-74.6% for 2-amino-5-mercapto-1,3,4-thiadiazole, with relative standard deviations below 7.0%. For field experiments, the half-life of bismerthiazol was 2.4-2.5 days in Chinese cabbage and 2.5-4.8 days in soil at the two experimental locations in China. Dissipation residues of 2-amino-5-mercapto-1,3,4-thiadiazole were lower than 0.72 mg/kg. Terminal residues of bismerthiazol and its metabolite were less than 3.0 and 0.3 mg/kg in Chinese cabbage, respectively. No bismerthiazol or metabolite residues were detected in soil on days 5, 7, 10, and 14 after the last spraying at the two dosage levels.

The electrochemical behavior of new generation fungicide acibenzolar-s-methyl (S-methyl 1,2,3-benzothiadiazole-7-carbothioate, ASM) on the hanging mercury drop electrode (HMDE) was investigated using square wave adsorptive stripping voltammetry. This method of determination is based on the irreversible reduction of ASM at the HMDE. The well-defined ASM peak was observed at -0.4 V (vs. Ag/AgCl) in BR buffer at pH 2.2. The reduction peak current was proportional to concentration of ASM from 1.0 × 10(-8) to 6.0 × 10(-8) mol L(-1) with detection and quantification limit 3.0 × 10(-9) and 1.0 × 10(-8) mol L(-1), respectively. The applicability of the developed method for analysis of spiked samples of tap water, river water, and soil is illustrated. The effect of adsorption on the mercury electrode was studied in detail using the AC impedance method. Possible interferences with other common pesticides and heavy metal ions were examined. Clarification of the electrode mechanism was made using cyclic voltammetry (CV) technique.

A rapid, sensitive and reliable analytical method for thidiazuron residues in apple and soil was established. The residual levels of the pesticide in apple and soil were determined by high performance liquid chromatography (HPLC) with UV detector. Samples of apple and soil were extracted with acetonitrile-water solutions, and then cleaned up by Florisil or C(18) cartridges. The results showed good linearity (r(2)=1.000) over the concentration range of 0.01-5.0 mg/L. Limits of quantification (LOQ) of the method were 0.01 mg/kg for both soil and apple. Recovery from the apple and soil samples were 83.36%-84.08% and 85.27%-89.83%, respectively, and the corresponding relative standard deviations (RSDs) of the recovery data were 0.155%-0.524% and 0.475%-4.79% for the three fortified levels (0.01, 0.1, 0.5 mg/kg). The analyte in the samples were further confirmed by electrospray ionization tandem mass spectrometry (ESI-MS/MS). It was demonstrated that the proposed method was simple and efficient, and particularly suitable for detecting thidiazuron residues in apple and soil., (© Springer Science+Business Media, LLC 2011)

We report on the electronic structure of poly[2,6-(4,4-bis- (2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), a promising low-band-gap donor material for efficient bulk heterojunction organic solar cells. Electronic properties of interfaces formed between PCPDTBT and prototypical electrodes [Au, indium-tin-oxide and poly(ethylene-dioxythiophene): poly(styrenesulfonate)], obtained from X-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy, are evaluated. The formation of interface dipoles is observed, and their consequences for device performance are discussed. For the system PCPDTBT/Au chemical interactions occur, which may affect in particular the charge extraction at the corresponding interface., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A simple and accurate method for the analysis of acibenzolar-S-methyl (benzo[1,2,3]thiadiazole-7-carbothioic acid-S-methyl ester; CGA 245 704; ASM) and its major conversion product, benzo[1,2,3]thiadiazole-7-carboxylic acid (CGA 210 007; BTC), in soils is presented. ASM extraction from soil samples was performed using acetonitrile and BTC was extracted with a mixture of potassium phosphate buffer (0.5 M, pH 3) and acetonitrile (70:30 %, v/v). Both extracts were directly analyzed in a high-performance liquid chromatography-diode array detection (HPLC-DAD) system. Pesticide separation was achieved on a C18 (4.6 mm × 150 mm, 5 μm) analytical column with a isocratic elution of acetonitrile:water 40:60 % (v/v) with 0.6 mL L⁻¹ acetic acid at a flow rate of 1 mL min⁻¹. Linear regression coefficients (r (2)) of the external calibration curves were always above 0.9997. The limits of detection (LOD) and quantification (LOQ) of the method were 0.005 and 0.02 mg kg⁻¹ for ASM, and 0.01 and 0.05 mg kg⁻¹ for BTC, respectively. Recoveries were investigated at six fortification levels and were in the range of 90-120 % for ASM and 74-96 % for BTC with relative standard deviations (RSDs) below 11 % in all cases. The method was also validated by analyzing freshly spiked soil samples with 2.7% organic matter content at 0.5 mg kg⁻¹ level, with slightly lower recovery values only for ASM. Moreover, recoveries for intermediate aged residues of the analytes were similar to fresh residues. This method was also applied to determine ASM half-life (t(½) = 8.7 h) and the rate of the acidic metabolite formation.

Newly designed 2,1,3-benzothiadiazole-containing fluorescent probes with four excited state intramolecular proton transfer (ESIPT) sites were successfully tested in live cell-imaging assays using a confluent monolayer of human stem-cells (tissue). All tested dyes were compared with the commercially available DAPI and gave far better results., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

This article reports the determination of uric acid (UA) in the presence of ascorbic acid (AA) using a self-assembled submonolayer of heteroaromatic dithiol, 2,5-dimercapto-1,3,4-thiadiazole (DMcT), on gold (Au) electrode. Submonolayer to multilayers of DMcT can be prepared on Au electrode by varying the soaking time of Au electrode in 1mM aqueous solution of DMcT. The formation of submonolayer, monolayer, and multilayers of DMcT on Au electrode was confirmed from its reductive desorption measurements and electrochemical blocking behavior toward ferricyanide. Interestingly, submonolayer of DMcT separates the voltammetric signal of UA from AA by 210 mV, whereas monolayer and multilayers of DMcT fail to separate them. The voltammetric signals of AA and UA are highly stable and reproducible at submonolayer of DMcT. Fast electron transfer, weak hydrogen bonding interactions with AA and UA, and prevention of fouling effect caused by oxidized product of AA can be achieved at submonolayer of DMcT, and thus it successfully separates the voltammetric signals of AA and UA. The practical application of the current system is demonstrated by measuring the concentration of UA in human urine samples without any treatment.

2,5-Dimercapto-1,3,4-thiadiazol (DMTD) can bind on the surface of a gold electrode through the strong gold-sulfur interaction. The fabrication and electrochemical characteristics of the DMTD self-assembled monolayer (SAM)-modified gold electrode were investigated. The DMTD SAM electrode exhibited a significantly increased sensitivity. Cu(II) was accumulated in phosphate buffer (pH 4.6) at a potential of -0.6 V (vs. Ag/AgCl) for 40 s and then determined by anodic stripping voltammetry (ASV) in copper-free phosphate buffer (pH 5.0). The effects of various parameters, such as the pH values of the preconcentration solution and measurement solution, the accumulation potential, and the accumulation time, were investigated. Under the optimum conditions, a linear calibration graph was obtained in the concentration range of 8.0 x 10(-6) to 8.0 x 10(-5) mol l(-1) with a correlation coefficient of 0.9978. The relative standard deviations for eight successive determinations were 4.3 and 2.9% for 1.0 x 10(-5) and 2.0 x 10(-5) mol l(-1) Cu(II), respectively. The detection limit (three times signal to noise) was 4.0 x 10(-7) mol l(-1). The proposed voltammetric method was utilized successfully to detect the concentration of Cu(II) ions in tap water samples.

Continuous flow microextraction (CFME) combined with high-performance liquid chromatography-ultraviolet (HPLC-UV) detection has been applied to the analysis of five widely used pesticides, simazine, fensulfothion, etridiazole, mepronil and bensulide, present at trace levels in water samples. CFME employs a single organic solvent drop positioned at the tip of a polyether ether ketone (PEEK) tubing, which is immersed in a continuous flowing aqueous sample solution in a 0.5-ml glass chamber. The PEEK tubing acts as the organic drop holder and fluid delivery duct. Analytes are partitioned between the organic drop and the bulk sample solution. Important extraction factors including type of solvent, its volume, sample solution flow rate, extraction time, its pH and addition of salt were investigated. All pesticides exhibit good linearity in the investigated concentration range of 25-250 ng ml(-1) with coefficients of determination (R2) ranging from 0.9879 to 0.9999 under the optimized conditions. Detection limits lower than 4 ng ml(-1) were obtained for all analytes. The method was evaluated by analyzing natural water sample collected from a reservoir in Singapore. This study for the first time demonstrated the compatibility of CFME procedure and HPLC separation.

U.S. Environmental Protection Agency (EPA) Method 535 has been developed in order to provide a method for the analysis of "Alachlor ESA and other acetanilide degradation products," which are listed on EPA's 1998 Drinking Water Contaminant Candidate List. Method 535 uses solid-phase extraction with a nonporous graphitized carbon sorbent to extract the ethane sulfonic acid (ESA) and oxanilic acid degradates of propachlor, flufenacet, dimethenamid, alachlor, acetochlor, and metolachlor from finished drinking water matrixes. Separation and quantitation of the target analytes are achieved with liquid chromatography/tandem mass spectrometry. Dimethachlor ESA and butachlor ESA were chosen during the method development as the surrogate and internal standard. Drinking water samples were dechlorinated with ammonium chloride without adversely affecting the analyte recoveries. Typical mean recoveries of 92-116% in deionized water and 89-116% in ground water were observed with relative standard deviations of <5%.

Proteins are particularly attractive targets for product analysis, which is used to understand pathology. Protein modifications, such as advanced glycation end products (AGEs), serve as footprints of biochemical processes and also help in the search for novel agents that efficiently inhibit protein damage. Interestingly, several medical agents that are used clinically interfere with oxidative protein damage through different mechanisms characteristic of their chemical structures. We recently found that angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs) lower the in vitro formation of the AGEs pentosidine and carboxymethyllysine. Their inhibition for AGE formation is more striking than aminoguanidine. Unlike aminoguanidine, ARBs and ACEIs do not trap reactive carbonyl precursors of AGEs. Rather, they inhibit AGE formation, possibly as a result of their potent ability to scavenge hydroxyl radicals and to chelate the transition metals necessary for the Fenton reaction. We tested their AGE-lowering ability in vivo in a unique type-2 diabetic model with nephropathic SHR/NDmcr-cp rats, which exhibits the metabolic syndrome (obesity, hyperglycemia, hyperlipidemia, hyperinsulinemia) in addition to hypertension. Obesity and associated metabolic derangements, in addition to hypertension, markedly accelerate renal injury. Expectedly, correction of hyperglycemia and hyperinsulinemia partially but significantly improves renal injury. A low-calorie diet greatly improves renal injury despite persistent hypertension. Among antihypertensive agents, ARBs, unlike nifedipine and atenolol, are renoprotective despite persistent metabolic syndrome, but their action is independent of blood pressure lowering and is observed in a dose-dependent manner despite the complete blockade of angiotensin II receptor. Interestingly, the improvement of renal injury by ARBs as well as a low-calorie diet is associated with a significant reduction in local oxidative stress and AGE formation in the kidney. During the characterization of the AGE-lowering profile of our chemical compound libraries ( approximately 2000), we identified several inhibitors of oxidative stress and advanced glycation. They are indeed renoprotective, independently of correction of hypertension and metabolic syndrome, in experimental diabetic nephropathy and other nephritis models. Altogether, our data are in good agreement with the recent therapeutic concept for diabetic nephropathy that multiple risk factor interventions are critical in the treatment of diabetic renal injury, and further implicate a therapeutic potential of inhibition of oxidative stress and advanced glycation.

Effect of concentration, moisture and soil type on dissipation of flufenacet from soil has been studied under laboratory condition. The treated soil samples (1 and 10 microg/g levels) were incubated at 25+/-1 degrees C. The effect of moisture was studied by maintaining the treated soil samples (10 microg/g level) at field capacity and submerged condition. In general, flufenacet persisted for 60-90 days at lower and beyond 90 days at high rate. The dissipation of flufenacet from soil followed first order kinetics with half-life (DT50) values ranging from 10 to 31 days. The dissipation of flufenacet was faster at low rate than high rate of application. The slow dissipation at high rate could be attributed to inhibition of microbial activity at high rate. There was little overall difference in rate of dissipation in Ranchi and Nagpur soil maintained at field capacity and submerged condition moisture regimes. In Delhi soil net dissipation was faster under field capacity moisture than submerged condition. Soil types greatly influenced the dissipation of flufenacet. Dissipation was fastest in Delhi soil (DT50 10.1-22.3 days) followed by Ranchi soil (DT50 10.5-24.1 days) and least in Nagpur soil (DT50 29.2-31.0 days). The difference in dissipation could be attributed to the magnitude of adsorption and desorption of flufenacet in these soils.

Dimethenamid [2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide] and flufenacet [N-(4-fluorophenyl)-N-(1-methylethyl)-2-(5-(trifluoromethyl)-1,3,4-thiadiazol-2-yl)oxy] were isolated by C-18 solid-phase extraction and separated from their ethanesulfonic acid (ESA) and oxanilic acid (OXA) degradates during their elution using ethyl acetate for the parent compound, followed by methanol for the polar degradates. The parent compounds were detected using gas chromatography-mass spectrometry in selected-ion mode. The ESA and OXA degradates were detected using high-performance liquid chromatography--electrospray mass spectrometry (HPLC-ESPMS) in negative-ion mode. The method detection limits for a 123-mL sample ranged from 0.01 to 0.07 microg/L. These methods are compatible with existing methods and thus allow for analysis of 17 commonly used herbicides and 18 of their degradation compounds with one extraction. In a study of herbicide transport near the mouth of the Mississippi River during 1999 and 2000, dimethenamid and its ESA and OXA degradates were detected in surface water samples during the annual spring flushes. For flufenacet, the only detections at the study site were for the ESA degradates in samples collected at the peak of the herbicide spring flush in 2000. The low frequency of detections in surface water likely is due to dimethenamid and flufenacet being relatively new herbicides. In addition, detectable amounts of the stable degradates have not been detected in ground water.

An analytical procedure for detecting residues of a new herbicide, flufenacet, in soil, wheat grain and straw by gas chromatographic method using various solvents and extraction methods was standardized. The best results were obtained when samples fortified with flufenacet and were extracted with acetone-0.2 M HCl (95:5) using a horizontal shaker for soil and Soxhlet extractor for plant samples. The clean up was done by partitioning with dichloromethane. The GC equipped with an electron-capture detector and a column packing of HP-1 as stationary phase and nitrogen as a carrier gas at a flow-rate of 15 ml min(-1) was used. Temperatures of oven, injector and detector were adjusted at 190, 210 and 270 degrees C, respectively. The retention time of flufenacet was 2.07 min. The herbicide recoveries ranged between 81 to 100% from the three matrices.

A rapid and accurate voltammetric method for the quantitative determination of 2-mercapto-5-phenylammino-1,3,4-thiadiazole (MPATD) with carbon paste electrodes (CPE) has been developed. The study was made by cyclic voltammetry between -0.4 and +0.6 V with 50 mV s(-1) sweep rate in aqueous solution. After successive oxidation/reduction cycles we found a total oxidation of MPATD at +0.45 V. As the compound is oxidated, the reduction current peak increases at +0.13 V, indicating an irreversible process. Following only the oxidation process in the -0.1 to +0.6 V range, we investigated the optimum scan rates at different current densities and pH values (realised with buffers, pH between 1.0 and 10.0) with CPE versus Ag/AgCl reference electrode using linear sweep voltammetry. We found a good linear relation between the current peak height and concentration in a 2.5 x 10(-9)-1.25 x 10(-7) mol ml(-1). This method allows the quantitative detection of the MPATD as it or from dosage forms and biological media.

The polarographic behavior of the product of N,N'-methylene-bis(2-amino-1,3,4-thiadiazole) (I) with nitrite and N-(1-naphthyl)-ethylendiamine is reported. The effects of acidity and reagents on the polarography was studied, and a polarographic method was established for the determination of (I). The relative standard deviation was 2.2-8.4%, and the recovery in the range of 80-103%. The proposed method was sensitive, accurate, reproducible and suitable for the determination of microamount of (I) in water.

Conjugation reaction of methazolamide with glutathione and its subsequent reactions were studied in vitro. Glutathione, cysteinylglycine, and cysteine conjugates of methazolamide were chemically synthesized. All of the three compounds showed absorbance below 330 nm, with maximal absorbance at approximately 300 nm. At the wavelengths below 220 nm, absorbance was proportional to the number of the amino acids each compound had. Amino acid analysis of the glutathione conjugate showed that the conjugation reaction involved the cysteine residue of glutathione. In order to identify the chemical structure of the reaction product, cysteine conjugate was subjected to infrared, proton nuclear magnetic resonance, and mass spectral analyses. These studies indicated that the cysteine conjugate was S-(5-acetylimino-4-methyl-delta 2-1,3,4-thiadiazolinyl)cysteine. The reaction with glutathione was not catalyzed by glutathione S-transferases, but proceeded in the absence of the enzyme. The glutathione conjugate was degraded by bovine ciliary body homogenate to the cysteinylglycine conjugate and then to the cysteine conjugate.

A rapid, sensitive, and accurate method for the quantitative analysis of 2-mercapto-5-methyl-1,3,4-thiadiazole in cefazolin is presented. The method utilizes NMR spectroscopy and is based on the difference in the chemical shift of the methyl protons on free thiadiazole and the thiadiazole moiety of cefazolin.

The spectra of 22 drug substances with chromophores and auxochromes in the aliphatic chain, in the saturated heterocyclus and in heterocyclic compounds (furan, imidazole, thiazole, thiadiazole and oxadiazole) underwent a systematic investigation and the results obtained were evaluated. Influences of substituents and solvents on shifts of the E, K, B and R bands were discussed.

The Autoturb System, a semiautomated system for photometric bioassay, was used to determine cefazolin content. Suitable conditions for the assay using Streptococcus faecalis ATCC 10541 as the indicator organism included a medium pH of 6.0 to 7.0 and an incubation time of 3 to 3.5 h at 36 C. Multiple independent assays of samples from a common batch showed the test to be highly reproducible. Accuracy of the turbidimetric assay was evaluated by comparing data obtained from a chemical (hydroxylamine) and a biological (disk diffusion) assay. The available data show the turbidimetric assay to be a rapid, accurate, and reproducible method for determining the biological activity of cefazolin samples.

Procedures are described for the analysis of Oryzalin, Tebuthiuron, and several other selected dinitroaniline herbicides by high-pressure liquid chromatography (HPLC). Quantitation of Oryzalin and small concentrations of chemical impurities from the production process can be performed rapidly. Linearity and reproducibility are discussed and comparisons to other methods are made.

A GLC procedure was developed for measuring nanogram quantities of timolol in plasma and urine. The unchanged drug was extracted into heptane-4% isoamyl alcohol from alkalinized plasma or urine, together with a homolog of timolol which served as the internal standard. The compounds were subsequently back-extracted into 0.1 N HC1 and then into chloroform following adjustment of the acid phase to an alkaline pH. The compounds in the chloroform extract were derivatized with heptafluorobutyrylimidazole to form the diheptafluorobutyryl derivatives; these were quantitated by electron-capture GLC. Recovery of timolol added to normal plasma and urine was quantitative and reproducible, and no interfering substances were observed in normal biological samples. The method is capable of measuring concentrations as low as 2 ng/ml in plasma or 20 ng/ml in urine. After a 10-mg oral dose of 14C-timolol, peak plasma levels of approximately 30 ng/ml were ovserved in 1-2 hr.