Catalytic spectrophotometric methods

There are very sensitive catalytic spectrophotometric methods for the determination of manganese, in which traces of Mn(II) catalyse the oxidation of various organic substances by another oxidant (e.g., KIO4), with the formation of coloured reaction products. In these methods, the amount of colour depends on the reaction time. The catalytic effect of Mn on oxidation of Malachite Green by periodate has been utilised in determination of manganese by the FI A method [54—57]. 

A low-cost assay of iodine in foods and urine can be performed using catalytic spectrophotometric methods, namely those based on the Sandell—Kolthoff reaction. These methods, however, are not optimal for determination of the lower range of iodine levels occurring in foodstuffs, because of possible interference. 

While the main advantage of catalytic spectrophotometric methods is low cost of the needed equipment, chromatography is arguably the most widely used separation technique in the... 

Walash et al. [14] described a kinetic spectrophotometric method for determination of several sulfur containing compounds including penicillamine. The method is based on the catalytic effect on the reaction between sodium azide and iodine in aqueous solution, and entails measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. Regression analysis of the Beer s law plot showed a linear graph over the range of 0.01 0.1 pg/mL for penicillamine with a detection limit of 0.0094 pg/mL. 

Photometric measurements performed in clinical laboratories use advanced chemical and biochemical methods and diverse instrumentation. Most analyses performed in clinical laboratories are based on spectrophotometric methods using photometric systems, such as absorption photometers, atomic absorption spectrophotometers and flame photometers. Typically, the result is expressed as mass concentration of analyte in solution (mg/dl), molar concentration (mmol/1), or catalytic concentration of enzyme activities in solution (U/l) [6],... 

A number of spectrophotometric methods for determining Rh has been based on its catalytic effect on redox reactions, such as the oxidation of Methyl Red [66], Methyl Orange [67], or copper [68] with periodate. The catalytic reactions have been the basis for Rh determinations in technological samples [67] and in copper and nickel alloys [68]. 

Ruthenium can be determined by spectrophotometric methods, based on its catalytic effect on various redox reactions, e.g., ferrozine with KIO4 [74], Ce(IV) with As(lll) [75,76], haematoxylin with H2O2 [77], or Thymol Blue with BrO [78]. 

Some spectrophotometric methods for Se determination are based on its catalytic effect on the redox reactions of various organic compounds [59-65]. 

I.Y. Kolotyrkina, L.K. Shpigun, Y.A. Zolotov, G.I. Tsysin, Shipboard flow injection method for the determination of manganese in sea-water using in-valve preconcentration and catalytic spectrophotometric detection, Analyst 116 (1991) 707. 

An alternative flow injection spectrophotometric method for the determination of h in the ground and surface water was reported by Kamavisdar and Patel (Kamavisdar Patel, 2002). The method was based on the catalytic destruction of the colour of the Fe(lll)-SCN"-CF -nBPy quarternary complex. The detection limit of the method was reported to be 0.1 ng ml"i of iodide. Another redox reaction between chloramine-T and N,N -tetramethyldiaminodiphenylmethane (Feigl s Catalytic Reaction) was applied for the determination of traces of iodine in drinking water (Jimgreis Gedalia, 1%0). 

Another modification of the catalytic kinetic spectrophotometric method has been established for the determination of iodine using the principle that potassium periodate oxidize rhodamine B (RhB) to discolor and 1 has a catalytic effect on the reaction. The absorbance difference (AA) is linearly related with the concentration of iodine in the range of 0 - 2.6 pg/mL and fits the equation AA = 0.1578 C(C pg/mL) + 0.0052, with a regression coefficient of 0.9965. The detection limit of the method is 7.10 ng/mL. The method was used to determine iodine in kelp, potato, tap water, and rain water samples. The relative standard deviation of 13 replicate determinations was 1.81-2.10%. The recovery of the standard addition of the method was 96.2-99.2% (Zhaiet al., 2010). 

Today, spectrophotometric methods are almost solely used for determination of the catalytic activities of enzymes in physiological samples in both manual and automated techniques because of their ease, simplicity, and sensitivity. No sampling is required, no reagents are necessary other than the actual reactants, and the result can be obtained with one small sample. 

Nitrite Nitrite is an important indicator of fecal pollution in natural waters as well as a potential precursor of carcinogenic species. A rush of flow and sequential injection spectrophotometric method based on Griess-type reactions has been proposed, also coupled to online sorbent enrichment schemes. The catalytic effect of nitrite on the oxidation of various organic species constitutes the basis of fairly sensitive spectrophotometric methods. Fluorometric methods based on the formation of aromatic azoic acid salts, quenching of Rhodamine 6G fluorescence, and direct reaction with substituted tetramine or naphthalene species have been also reported. Indirect CL methods usually involve conversion into nitric oxide and gas-phase detection as mentioned in the foregoing section. The redox reaction between nitrite and iodide in acidic media is the fundamental of a plethora of flow injection methodologies with spectrophotometric, CL, or biamperometric detection. New electrochemical sensors with chemically modified carbon paste electrodes containing ruthenium sites, or platinum electrodes with cellulose or naphthalene films, have recently attracted special attention for amperometric detection. 

Kinetic spectrophotometric methods have also been used. The catalytic effect of manganese(II) on the oxidation of diphenylamine-4-azo-benzen-4 -sul-fonic acid potassium salt with potassium periodate in the presence of 1,10-phenanthroline in weak media has been reported, with an LOD of 0.017ng mH A sensitive flow injection procedure is based on the catalytic effect of manganese on the oxidation of 2-2 -azinobis(3-thylbenzothiazoline-6-sulfonic acid) with periodate (415 nm). 

Molybdenum can be determined using a kinetic spectrophotometric method based on the catalytic effect of molybdenum on the reduction of thionine by hydrazine monochloride in an acid medium. The reaction is monitored at 605 nm due to the decrease in absorbance of thionine. 

Several kinetic spectrophotometric methods have been developed for selenium determination. The catalytic effect of Se(IV) on the reduction of thionine by sulfide ions has been explored. The reaction is monitored spectrophotometrically by following the decrease in absorbance at 598 nm, and the method has an LOD of 5ngml . Another method is based on the catalytic effect of selenium on the oxidation of methyl yellow by hydrogen peroxide in a nitric acid medium. It is monitored by the loss of the red color of methyl yellow. The method is extremely sensitive, with the possibility of measuring concentrations of 0.2ngml . Selenium can be also determined based on its effect on the oxidation reaction of methyl orange with bromate in acidic media. 

One of the reviews cited earlier enumerates spectrophotometric methods for the determination of cyanide up to 1962 [8]. Also, instrumental methods such as colorimetric and spectrophotometric methods, electroanalytical methods, catalytic methods, gas chromatography methods, radiochemical methods, and miscellaneous methods for determination of cyanide up to 1977 have been summarized by Williams [7]. The instrumental methods developed since 1977 are considered here. 

Finally, and in the framework of this kind of methods, the use of catalytic spectrophotometric techniques (CST) must be considered. In this sense, the ability of traces of the... 

A. A. Ensafi and M. Keyvanfard, Kinetic spectrophotometric method for the determination of rhodium by its catalytic effect on the oxidation of o-toluidine blue by periodate in micellar media, Journal of Analytical Chemistry, vol. 58, no. 11, pp. 1060-1064, 2003. 

The two variables change their role with respect to their dependent versus independent, intensive versus extensive nature. This is also true of e.g. calorimetric, conductometric and spectrophotometric titrations using UV-, IR- or NMR-spectrosco-py We additionally have to consider that in the titration of the catalytic process only the external dynamics are measured a direct comparison with the actual metal fraction of the related intermediate complexes is generally not possible We call this analysis of homogeneous catalytic systems by a metal-ligand titration the method of inverse titration and for the resulting diagrams we use the term li nd-concentration control maps ([L]-control maps) . 

A method for determination of sodium isoascorbate (see 2) in boiler feed water, where it is used for deoxygenation, consists of following the reaction kinetics of Rhodamine B (13) in the presence of KBrOs, measuring at 555 nm. A linear correlation exists between the catalytic effect of the analyte on the reaction rate and its concentration Fe(III), Ca(II) and Mg(II) in the 5-200 ppm range interfere with the analysis . The effects of solvents, pH, surfactants, metal ions and other food additives on the absorbance were studied for the micelle-enhanced UV spectrophotometric determination of the food preservative sodium D-isoascorbate. The optimal conditions were using water at pH 7-8 as solvent and polyvinyl alcohol as surfactant, which causes an up to 3-fold increase of the UV absorbance. ... 

The catalytic effect of Cu on the oxidation of organic compounds by H2O2 [87-92] and K2S2O8 [93] has become the basis for a number of spectrophotometric determination methods. 

Kinetic spectrophotometric determination methods for Ag(I) were proposed, based on the strong catalytic effect of this ion on the controlled oxidation of various dyes, by measuring the rate of change of absorbance. Some recently published examples are Ag(I)-catalyzed peroxodisulfate oxidation of brilliant cresyl blue (33)104 or gallocyanine (34)105, both in the presence of 1,10-phenanthroline (35) and hexacyanoferrate (36) oxidation of indigo carmine (37)106. 

We recognized the need for methodology to measure SOD activity directly that would be more accessible to the bench-top scientist than is the method of pulse radiolysis, another direct measure. Consequently, we developed methodology to measure the catalytic dismutation of superoxide by stopped-flow kinetic analysis.By this technique, we directly monitor the decay of superoxide spectrophotometrically in the presence or absence of a putative SOD mimic at a given pH. Kinetic analysis of this decay can determine whether the complex is a SOD mimic (decay of superoxide becomes first-order in superoxide and first-order in complex see equations 1 and 2), or is inactive (decay of superoxide remains second-order for its self-dismutation see equation 3). At least a tenfold excess of superoxide over the putative SOD mimic is used in the stopped-flow assay, to eliminate contributions due to a stoichiometric reaction of the complex with superoxide. A catalytic rate constant for the dismutation of superoxide by the complex can be determined from the observed rate constants of superoxide decay as a function of catalyst concentration. ... 

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