Catalytic Kinetic Spectrophotometry Research Articles

Determination of trace amounts of selenium in natural spring waters and tea samples by catalytic kinetic spectrophotometry

In this work, a new kinetic method is described for the determination of trace Se(IV) in natural spring waters and commercial tea samples. The method is based on the activation of Se(IV) onto the indicator reaction in acidic medium. The reaction was monitored using a fixed time approach of 20 min at 680 nm. The variables affecting the reaction rate were evaluated and optimized. The method allows the determination of Se(IV) in the range of 0.0125-1.0 mg L-1 with a detection limit of 3.6 µg L-1. The precision was in range of 0.63-3.15% (as RSD %) with a higher recovery than 98.6%. The method has been found to be selective against matrix effect. The method was applied to the speciation analysis of inorganic Se species present in the selected samples. The method was statistically validated by analysis of two certified samples and comparing the obtained results to those of HG-AAS analysis. Also, the total Se levels of the samples were determined by using both methods after conversion of Se(VI) into Se(IV) in ultrasonic bath in acidic medium for 30 min at 85-90 °C. The results were in good agreement with those of HG-AAS. The Se(VI) level of the samples was calculated from the difference between amounts of total Se and Se(IV).

Determination of Trace Levels of Nitrite in Beverages Samples Through Micellar Improved Catalytic Kinetic Spectrophotometry

In this study, a simple and sensitive catalytic kinetic spectrophotometry method for determination of nitrite has been described. The method is based on the oxidation of chlorpromazine by nitrite in presence of mixed surfactants in acidic medium, which results in the decrease in absorbance at 520 nm. Various chemical (such as the effect of acidity, reagents concentrations) and instrumental parameters (time, sample volume and temperature) were optimized. The interfering effects of various chemical species were studied. At the optimum conditions, linear calibration graph was linear in the nitrite concentration ranges of 2.5-125 µg L –1 . The detection limit is 0.71 µg L –1 for nitrite. The relative standard deviation for determination of 25 and 75 µg L –1 were 3.40 and 2.35%, for ten replicate measurements, respectively. The micellar improved catalytic kinetic spectrophotometry showed good analytical performance including good sensitivity, reproducibility, stability and selectivity to nitrite. The method has been applied to determine nitrite in beverages samples with a satisfactory recovery in the range of 97.3–103.8%, showing its promising application for food safety monitoring.

Determination of Trace Amounts of Total Fe as Fe(II) in Environmental Samples by Catalytic Kinetic Spectrophotometry

The method is based on the selective catalytic effect of iron (II) ions in the presence of 1,10-phenanthroline as an activator, on the oxidation of Coomassie Brillant Blue 2R by bromate. The catalytic reaction was monitored spectrophotometrically at 520 nm by fixed time approach of 3 min. The optimization of the operating conditions are investigated. Obtained optimum conditions: 1.5 mL of Coomassie Brillant Blue 2R (1.0 x 10 -4 mol L -1 ), 0.6 mL of bromate (0.01 mol L -1 ), 1.5 mL of 1,10-phenanthroline (1.0 x 10 -3 mol L -1 ), reaction temperature 25 o C and time 3 min in pH 2.0 at 520 nm. The proposed method allows quantitatively determination of iron (II) in the range of 0.05-5 mg L -1 with a selectivity and quantification limit of 0.0141 and 0.047 mg L -1 . The relative standard deviations for five replicate determinations of 0.2 and 3 mg L -1 iron (II) are 3.8% and 2.3%, respectively. The method was applied to determination of total iron in some environmental surface waters such as lake, river and well water including pharmaceutical samples used in the treatment of iron deficiency (such as ferrosolanol and maltose) after pre-reduction of iron (III) to iron (II) with sulfite at 40 o C at pH 4.0, and quantitative percentages of retinas ranging from 98.7-102.7% were obtained by standard attachment-based analysis after wet acid dissolution for possible matrix effect.

Micellar sensitized catalytic kinetic spectrophotometry for highly accurate and reproducible determination of V(IV) and V(V)

A highly accurate and reproducible micellar sensitized kinetic method was proposed for determination of V(VI). The method is based on its catalytic effect on the oxidation of Coomassie brilliant blue R 250 (CBB+) by bromate at pH 2.0. The reaction was monitored spectrophotometrically by measuring absorbance change with a fixed-time method of 5 min at 594 and 552 nm with and without surfactant. The variables influencing the calibration sensitivity were extensively investigated, and the optimal conditions were established. The linear calibration range was 10–1,600 μg·L−1 with a relative SD ranging from 0.35 % to 3.35 % (for five replicate measurements of 75, 500, 1,000, and 1,500 μg·L−1) and a detection limit of 3.8 μg·L−1. The selectivity was also investigated, and greatly enhanced by suitable masking agents. The method was successfully applied to the analysis of V(IV) in presence of excess V(V) up to 25 fold in environmental waters with the recoveries of 100.0 %–102.8 % for V(IV) and 95.7 %–99.7 % for total V. Its accuracy was validated by analysis of certified reference material via the present kinetic method and standard flame atomic absorption spectrometric method after extractive preconcentration with good agreement between certified and found values.

Dual-wavelength dual-indicator catalytic kinetic spectrophotometry for determination of trace Ru(III)

A new dual-wavelength dual-indicator catalytic kinetic spectrophotometric method for the determination of trace Ru(III) was studied. This method was based on Ru(III)-catalyzing oxidation of Arsenazo I and indigo carmine by potassium bromate in sulfuric acid. The absorbances of the catalytic and noncatalytic systems were measured at 510 and 610 nm, respectively. Under the optimum conditions, the linear range of determination is 0–0.12 μg·ml−1 and the detection limit is 1.21 × 10−4 μg·ml−1. The method was applied for the determination of trace Ru(III) in ore samples with satisfactory results.

Simultaneous determination of dissolved inorganic chromium species in wastewater/natural waters by surfactant sensitized catalytic kinetic spectrophotometry

A simple, rapid, highly accurate and sensitive kinetic method is proposed for determining chromium(VI). The method is based on its catalytic effect on the oxidation of Celestine blue (CB+) by H2O2 in the presence of 2,2′-bipyridyl (Bipyr) and cetylpyridinium chloride (CPC) at pH 6.50. The reaction was monitored spectrophotometrically by measuring the absorbance of indicator dye at 645nm. The analytical variables, which have influences on the sensitivity, were investigated and the optimum conditions were established. The optimized conditions made it possible to determine and speciate chromium in a linear range of 5–200μgL−1 with a detection limit of 0.65μgL−1. The recoveries and relative standard deviations (RSDs) for the determination of 10, 25, 75 and 150μgL−1 Cr(VI) (n: 5) were in the range of 99.0–99.8% and 0.2–3.5%, respectively. The selectivity was also studied and greatly enhanced by adding a suitable masking mixture. The method was successfully applied to the simultaneous analysis of Cr(III) and Cr(VI) in natural water and waste water samples with a recovery changing in the range of 95–103% for Cr(III) and 100–104% for Cr(VI). Its accuracy was validated by the analysis of certified reference materials with good agreement between certified and found values.

CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE AMOUNTS OF ETHYLENEDIAMINETETRAACETIC ACID BASED ON ITS CATALYTIC EFFECT ON THE REACTION OF RHODAMINE B AND POTASSIUM DICHROMATE

A new method for the determination of trace ethylenediaminetetraacetic acid (EDTA) was developed using catalytic kinetic spectrophotometry based on the principle that in the medium of 0.10 mol/L sulfuric acid, trace EDTA has a catalytic effect on the oxidation of rhodamine B by potassium dichromate, and a suitable amount of 6.0 mol/L NaOH solution can inhibit the catalytic reaction. At the maximum absorption wavelength of 546 nm, the linear range for the determination of EDTA was shown over the concentration range 5.0 × 10−5–7.0 × 10−4 mol/L and the detection limit of this method for EDTA was 0.0501 mmol/L. The linear regression equation for the determination of EDTA and regression coefficient were ΔA = 512C (C: mol/L) + 0.0966, γ = 0.9993, respectively. The apparent activation energy of the catalytic reaction was 81.57 KJ/mol. The proposed method has been successfully applied to the determination of trace ethylenediaminetetraacetic acid in water and apple tinned foodstuff samples with satisfactory results. The relative standard deviation of 13 replicate determinations of EDTA was 1.15–2.37% and the recovery of the method was 99.90–102.7%, respectively. The determined results were in good agreement with that of established method Fe(III)-H2O2-bromothymol blue system inhibitory-kinetic spectrophotometry.

Determination of trace titanium with titanium(IV)-(DBC-arsenazo)-potassium bromate system by catalytic-kinetic spectrophotometry

In a 0.080 M sulphuric acid medium, trace titanium(IV) catalyzes the discoloring reaction of DBC-arsenazo oxidized by potassium bromate and the discoloring degree is proportional to the concentration of titanium(IV) in the solution. A new catalytic-kinetic spectrophotometric method for the determination of trace titanium(IV) was developed based on this principle. At a wavelength of 516 nm, the linear range of determination of titanium(IV) is 0–2.2 μg/25 mL. The detection limit for the determination of titanium is 2.04 ng/mL. The present method has been satisfactorily applied to the determination of titanium in fish samples.

Investigation into Photocatalytic Degradation of Gaseous Ammonia in CPCR

Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution because of continuous transformation and emission of urea to gaseous ammonia on indoor concrete walls. To control ammonia pollution from indoor concrete walls, a circulated photocatalytic reactor (CPCR) was designed to intensify the performance for the decomposition of gaseous ammonia in the present study and TiO2 film photocatalysts were prepared by the sol−gel method and coating onto the inner wall of this reactor using a bonder of polyacrylic ester emulsion, which was characterized by FTIR, TEM, and SEM. In particular, the influences of initial concentration of ammonia on the degradation conversion (Dp), apparent reaction rate constants (kr), initial degradation rate (r), deactivation, and regeneration of catalyst in CPCR were investigated. Furthermore, a designed equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in CPCR. The total number of adsorption sites available for the gas molecules NT and the adsorption equilibrium constant Kads values were determined through a linear-fitting method. Finally, undesirable NO2− and NO3− were detected as the intermediates in the process of photodegradation at different initial concentration of ammonia, which was detected by catalytic kinetic spectrophotometry. The results indicated that the degradation conversion (Dp), initial degradation rate (r), degraded products, and half-life (t1/2) were closely correlated to the initial concentration of ammonia. It was found that the reaction kinetics fixed the pseudofirst-order kinetic equation of photocatalytic degradation of gaseous ammonia in CPCR, and the kinetic results are discussed in terms of adsorption of ammonia and products degraded.

Heterogeneous Photocatalytic Degradation Kinetic of Gaseous Ammonia Over Nano-TiO 2 Supported on Latex Paint Film

To investigate the photocatalytic degradation of gaseous ammonia in static state by using nano-TiO2 as photocatalyst supported on latex paint film under UV-irradiation. Experiments were conducted to study the relationship between the initial concentration of ammonia and the degradation products competing to be adsorbed on catalyst surface. Degradation of ammonia and its products were detected by spectrophotometry and catalytic kinetic spectrophotometry, respectively. On the one hand, TiO2 catalyst was excellent for degradation of ammonia, and the crystal phase of TiO2, anatase or rutile, had little effect on degradation of ammonia, but the conversion of ammonia grew with the increase of catalyst content. On the other hand, apparent rate constant and conversion of ammonia decreased with the increase of initial concentration of ammonia, and the photocatalytic degradation reaction followed a pseudo-first-order expression due to the evidence of linear correlation between -lnC/C0 vs. irradiation time t, but the relationship between initial concentration and the degradation products was not linear in low initial concentration. Whether the photocatalytic degradation of ammonia in static state follows a first-order reaction depends on the initial ammonia concentration due to competition in adsorption between reactant and the degradation products.

<b>CATALYTIC KINETIC SPECTROPHOTOMETRIC DETERMINATION OF TRACE TITANIUM BASED ON TITANIUM(IV)-(DBS-ARSENAZO)-POTASSIUM BROMATE SYSTEM</b>

Based on the property that in 0.12 M sulfuric acid medium titanium(IV) catalyzes the discoloring reaction of DBS-arsenazo oxidized by potassium bromate, a new catalytic kinetic spectrophotometric method for the determination of trace titanium (IV) was developed. The linear range of the determination of titanium is 0-2.4 μg/25 mL. The detection limit of the method is 0.47 ng/mL. The effects of fifty coexisting substances were studied and most of common substances do not interfere with the determination of titanium. The method has good selectivity. The present method was used in the determination of trace amount of titanium in cabbage and potato samples with satisfactory results. The relative standard deviations of ten replicate determinations of the method are 1.4-1.5 % and the recoveries of standard addition are 97.6-98.0 %, respectively. KEY WORDS: Titanium(IV), Catalytic kinetic spectrophotometry, DBS-Arsenazo, Potassium bromate, Cabbage, Potato Bull. Chem. Soc. Ethiop. 2007, 21(3), 451-456.

Catalytic kinetic spectrophotometry for the determination of trace amount of oxalic acid in biological samples with oxalic acid–rhodamine B–potassium dichromate system

A new catalytic kinetic spectrophotometric method was proposed for determining trace oxalic acid based on the catalytic effect of oxalate on the oxidation of potassium dichromate with rhodamin B in 0.10 M of sulfuric acid. Good linearity is obtained over the concentration range 0.40–6.0 μg/mL of oxalic acid. After the reactions of the catalytic and non-catalytic systems were terminated by using 2.00 mL of 4 M sodium hydroxide solution, they can be stable for 3 h at room temperature. The apparent activation energy of the catalytic reaction is 12.44 kJ/mol. The effect of 50 coexisting substances was observed. The method was used to determine trace oxalic acid in tea, spinach and urine samples with satisfactory results.

Determination of trace amounts of manganese in natural waters by flow injection stopped-flow catalytic kinetic spectrophotometry

Trace amounts of manganese were analyzed by flow injection catalytic kinetic spectrophotometry, based upon the catalytic effects of Mn(II) on the redox reaction between sodium periodate and 4,4′-bis(dimethylamino)-diphenylmethane. The reaction could occur rapidly at room temperature in the presence of nitriloacetic acid at pH 5.4. The measurements were conducted at 602 nm of an unstable intermediate blue product of the reaction, which greatly increased the sample throughput. Flow injection technique was utilized to precisely control the timing of merging and reaction of the sample and reagents. A stopped-flow approach was used to improve the sensitivity of the system. A detection limit (3 σ) of 0.073 μg l −1 was achieved at a sampling frequency of 60 h −1. The relative standard deviation was 0.5% for the determination of 10 μg l −1 Mn ( n = 11). The proposed method was validated by the analysis of an estuarine water reference material, SLEW-2 and successfully applied to the analyses of several natural waters.