Kinetic determination of organosulphur ligands by inhibition: Trace determination of cysteine and maleonitriledithiolate (MNDT)

Kinetic determination of ethyl carbamate in sugarcane spirits exploiting digital videos

Kinetic methods are useful analytical methods, whose widespread application is often hindered by the need for strict time control. In this study, digital videos obtained using a smartphone camera were exploited for the first time for a kinetic enzymatic method. The inhibition of the acetylcholinesterase activity on the hydrolysis of acetylthiocholine to thiocholine was exploited for ethyl carbamate determination. This toxic and potentially carcinogenic contaminant must be controlled in beverages with a threshold limit of 210 μg L-1 for sugarcane spirits. Ethyl carbamate binds to the active site of acetylcholinesterase in an alkaline medium (pH 8), thus diminishing the hydrolysis rate. Digital videos were recorded for 25 min, and analytical information (channel B, RGB color system) was extracted from frames taken every 10 s. The time required to achieve a reaction plateau, which is proportional to the analyte concentration, was used as the analytical parameter. Under the optimized conditions a linear response was observed for ethyl carbamate concentrations from 50 to 500 μg L-1 (r2 > 0.99) with a limit of detection of 15 μg L-1 and a coefficient of variation of 3.2 % (n = 10). The proposed kinetic method is a cost-effective alternative for the determination of ethyl carbamate in sugarcane spirits, which compares favorably with other methods reported in the literature with regard to detectability and greenness (AGREE score of 0.77), while yielding results in agreement with the gas chromatography-mass spectrometry reference method.

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0x10(-6)M and the progress of reaction was followed spectrophotometrically at 525nm (lambda(max) of purple-red complex [Ru(CN)(5)NRS](3-), epsilon=3.1x10(3)M(-1)s(-1)) under the optimized reaction conditions; 8.75x10(-5)M [Ru(CN)(6)(4-)], 3.50x10(-4)M [nitroso-R-salt], pH 7.00+/-0.02, ionic strength, I=0.1M (KCl), temp 45.0+/-0.1 degrees C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t=15, 20 and 25min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0x10(-7)M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.

Application of ruthenium catalyzed oxidation of [tris(2-aminoethyl)amine] in trace determination of ruthenium in environmental water samples

The ruthenium catalyzed oxidation of tris(2-aminoethyl)amine (TREN) by hexacyanoferrate(III) has been utilized for the development of a new and sensitive catalytic kinetic method (CKM) for the determination of ruthenium(III). The reaction was followed spectrophotometrically by the decrease in absorbance at 420 nm (lambda(max) of [Fe(CN)6]3-). The CKM developed utilizes fixed time procedure under optimum reaction conditions where the change in absorbance (DeltaAt) versus ruthenium(III) concentrations is plotted. The calibration curve recommended for the method is linear in the concentration range 10.11-252.67 ng ml(-1) with very good accuracy and reproducibility and a maximum error 2.20%. The detection limits of the method for ruthenium(III) corresponding to 10, 15 and 20 min are 8.02, 5.03 and 3.15 ng ml(-1), respectively. The ruthenium(III) has also been determined in the presence of several other interfering and non-interfering cations and anions and no foreign ions interfered in the determination of ruthenium(III) up to five-fold higher concentration of the foreign ions tested. The method is highly sensitive, selective and stable. It has successfully been applied for the determination of trace ruthenium(III) in some synthetic and environmental water samples. A review of most of the published catalytic kinetic and some other important methods for the determination of ruthenium has also been presented.

Highly sensitive catalytic spectrophotometric determination of ruthenium

A new and highly sensitive catalytic kinetic method (CKM) for the determination of ruthenium(III) has been established based on its catalytic effect on the oxidation of l-phenylalanine (l-Pheala) by KMnO(4) in highly alkaline medium. The reaction has been followed spectrophotometrically by measuring the decrease in the absorbance at 526nm. The proposed CKM is based on the fixed time procedure under optimum reaction conditions. It relies on the linear relationship where the change in the absorbance (DeltaA(t)) versus added Ru(III) amounts in the range of 0.101-2.526ngml(-1) is plotted. Under the optimum conditions, the sensitivity of the proposed method, i.e. the limit of detection corresponding to 5min is 0.08ngml(-1), and decreases with increased time of analysis. The method is featured with good accuracy and reproducibility for ruthenium(III) determination. The ruthenium(III) has also been determined in presence of several interfering and non-interfering cations, anions and polyaminocarboxylates. No foreign ions interfered in the determination ruthenium(III) up to 20-fold higher concentration of foreign ions. In addition to standard solutions analysis, this method was successfully applied for the quantitative determination of ruthenium(III) in drinking water samples. The method is highly sensitive, selective and very stable. A review of recently published catalytic spectrophotometric methods for the determination of ruthenium(III) has also been presented for comparison.