Determination of ultratrace amounts of copper (II) by its catalytic effect on the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline

Boosting the oxidase-like activity of platinum nanozyme in MBTH-TOOS chromogenic system for detection of trypsin and its inhibitor

Nanozymes, as a new type of artificial enzyme, have recently become a research hotspot in the field of catalysis and biomedicine. However, the application of nanozyme is limited by catalytic activity changes of different substrates and low specificity. This work shows that citrate-capped platinum nanoparticles (Cit-PtNPs) exhibit stronger oxidase-like activity than other platinum nanozymes at different pH when 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and n-ethyl-n- (2-hydroxy-3-sulfopropyl)-m-toluidine sodium salt (TOOS) were used as chromogenic substrates. This phenomenon has important reference value for different nanozymes to choose chromogenic substrates in catalysis. In MBTH-TOOS chromogenic system, MBTH (-NH) radical is first produced during the reaction through catalytic oxidation of Cit-PtNPs, which reacts with TOOS to produce a colorless compound. The blue-purple quinoid dye was produced through the dismutation of the colorless compound. The catalytic mechanism of the oxidase-like activity of Cit-PtNPs is that two-electron reduction process and four-electron reduction process are simultaneously carried out in the catalytic process. Furthermore, to solve the problem of low specificity of metal nanozymes, protamine is designed as aggregation promoter of Cit-PtNPs and the specifichydrolysis substrate of trypsin. In this work, it can achieve one-step detection of trypsin by the boosting oxidase activity of Cit-PtNPs at pH8. The catalytic activity of Cit-PtNPs is proportional to the concentration of trypsin. The linear range for trypsin is 1.0-70.0 ngmL^-1 and the limit of detection is measured to be 0.6 ngmL^-1. This novel method has also been successfully applied to the detection of inhibitors and trypsin in urine samples.

Flow injection determination of hydrogen peroxide using catalytic effect of cobalt(II) ion on a dye formation reaction

A novel flow injection photometric method was developed for the determination of hydrogen peroxide in rainwater. This method is based on a cobalt(II)-catalyzed oxidative coupling of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N-ethyl-N-(2-hydroxy-3-sulfopropyl)-3,5-dimethoxyaniline (DAOS) as a modified Trinder's reagent to produce intensely colored dye (λ(max)=530nm) in the presence of hydrogen peroxide at pH 8.4. In this method, 1,2-dihydroxy-3,5-benzenedisulfonic acid (Tiron) acted as an activator for the cobalt(II)-catalyzed reaction and effectively increased the peak height for hydrogen peroxide. The linear calibration graphs were obtained in the hydrogen peroxide concentration range 5×10(-8) to 2.2×10(-6)mol dm(-3) at a sampling rate of 20h(-1). The relative standard deviations for ten determinations of 2.2×10(-6) and 2×10(-7)mol dm(-3) hydrogen peroxide were 1.1% and 3.7%, respectively. The proposed method was successfully applied to the determination of hydrogen peroxide in rainwater samples and the analytical results agreed fairly well with the results obtained by different two reference methods; peroxidase method and hydrogen peroxide electrode method.

Novel catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine with 1,3-phenylenediamine and its applications to the determination of copper and iron at trace levels by flow injection technique

A new catalytic oxidative coupling reaction of N,N-dimethyl-p-phenylenediamine (DPD) with 1,3-phenylenediamine (mPD) in the presence of hydrogen peroxide has been developed for trace metals analysis. The rate of the oxidation/coupling reaction can be enhanced significantly by iron, copper and cobalt. These metal ions can catalyze the oxidation reaction of DPD to form an oxidized product; the oxidized DPD was then coupled with mPD to give a blue-colored product which was measured spectrophotometrically at 650 nm. On the basis of such a reaction scheme, two simple flow injection analysis methods for the determination of copper and iron have been developed. Detailed studies on chemical and FIA variables affecting the sensitivity of the detection were carried out. Interferences from several ionic species were examined for the determination of copper: the interference effect by Fe(III) and Fe(II) up to 1.5 mg L(-1) was successfully suppressed by pretreating sample with ammonium acetate buffer solution (pH 8.4). Good linearity of a standard calibration graph was obtained over the ranges of 0-8 and 0-2 microg L(-1) of copper and iron, respectively, and the detection limits were 0.05 and 0.02 microg L(-1) for copper and iron, respectively. The precision of the methods in terms of relative standard deviation were 1.4 and 1.5% of R.S.D. which were obtained from 10 injections of 2.0 and 1.0 microg L(-1) of standard copper and iron, respectively. The proposed methods were successfully applied to the determination of copper and iron in tap and river water samples. The accuracy of the proposed methods was assessed by the analysis of certified reference material of river water.

A Kinetic Method for the Determination of Copper(II) by Its Catalytic Effect on the Oxidation of 3-Methyl-2-benzothiazolinone Hydrazone with Hydrogen Peroxide: A Mechanistic Study

A catalytic spectrophotometric method for the determination of traces of copper(II) is proposed. 3-Methyl-2-benzothiazolinone hydrazone (MBTH) is oxidized by hydrogen peroxide to form a yellowish-brown compound. The reaction is accelerated by trace amounts of copper(II), and can be followed by measuring the increase in the absorbance at 390 nm. Since the absorbance at 40 min from the reaction start increases with an increase in the copper(II) concentration, the absorbance value is used as a parameter for copper(II) determination. Under the optimum experimental conditions (8.4 x 10(-3) mol dm(-3) MBTH, 0.7 mol dm(-3) hydrogen peroxide, pH 5.2, 35 degrees C), copper(II) can be determined in the range 0-50 microg dm(-3). The relative standard deviations are 6.9, 3.5, 2.7% for 2, 20 and 40 microg dm(-3), respectively. The detection limit of this method (3sigma) is 0.27 microg dm(-3). It was successfully applied to a determination of copper(II) in river water, tap water and ground-water samples. According to the results of a kinetic study, a mechanism is proposed which leads to the following rate equation: R0(cat) = kK1K2[MBTH][H2O2][Cu(II)]0/{(1 + K2[H2O2])[H+]}.

Catalytic flow-injection determination of sub-ppb copper(II) using the redox reaction of cysteine with iron(III) in the presence of 2,4,6-tris(2-pyridyl)-1,3,5-triazine

A kinetic-catalytic spectrophotometric flow-injection method was developed for the rapid and sensitive determination of trace amounts of copper(II). The method is based on the catalytic effect of copper(II) on the redox reaction of cysteine with iron(III). Iron(II) produced by the catalytic reaction reacts with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (TPTZ) to form the iron(II)-TPTZ complex (lambda(max) = 593 nm). By measuring an absorbance of the complex, one could determine 0.05-8 ppb copper(II) with the relative standard deviations (n = 10) of 1.6%, 1.3%, and 0.8% for 0.5 ppb, 1 ppb, and 2 ppb copper(II), respectively. The limit of detection (S/N = 3) was 0.005 ppb. The sample throughput was 30 h(-1). The proposed method was successfully applied to the determination of copper in natural water and serum samples.

Copper(II)-catalysed oxidative coupling reaction of 3-hydroxyacetanilide with 3-methyl-2-benzothiazolinone hydrazone for the spectrophotometric determination of traces of copper(II)

A spectrophotometric method is developed for the determination of traces of copper(II), based on the catalytic oxidative coupling reaction of 3-hydroxyacetanilide with 3-methyl-2-benzothiazolinone hydrazone in the presence of ammonia and hydrochloric acid. Beer's law is obeyed in the copper(II) concentration range of 0.008-0.16 microg mL(-1), and the molar absorptivity at 530 nm is 2.5x10(5) L mol(-1) cm(-1). The Sandell's sensitivity of the product is 0.000254 microg cm(-2). The optimum reaction conditions and other important analytical parameters have been investigated. The proposed method is applied to the analysis of water and soil samples and the results are compared with the literature method.

Spectrophotometric determination of metronidazole and tinidazole in pharmaceutical preparations

Sensitive and simple spectrophotometric methods for the determination of metronidazole (MNZ) and tinidazole (TNZ) in either pure form or in its pharmaceutical formulations are described. The first method is based on the interaction of 3-methylbenzothiazolin-2-one hydrazone (MBTH) with MNZ/TNZ (reduced drug) in presence of copper sulphate and pyridine in acidic medium. The resulting yellowish orange products have lambda(max) of 500 and 490 nm, respectively, for MNZ and TNZ and are stable for about 4 h. The second method describes the reaction between reduced diazotised drugs with N-(1-naphthyl)ethylenediamine dihydrochloride (NEDA) in neutral medium to yield pink products which have lambda(max) of 520 and 505 nm, respectively, for MNZ and TNZ, respectively. The products are stable for more than 24 h. Common excipients used as additives in pharmaceutical preparations do not interfere in the proposed method. Both the methods are highly reproducible and have been applied to a wide variety of pharmaceutical preparations and the results compare favourably with those of official methods.