Derivative spectrophotometric determination of nickel using Br-PADAP

A major problem with spectrophotometric methods for nickel is cobalt interference, because many of the reagents for nickel also react with cobalt. In this work, the interference of cobalt in the determination of nickel using 2-(5-bromo-2-pyridylaxo)-5-diethylaminophenol (Br-PADAP) was eliminated by the use of derivative spectrophotometry, using the zero-crossing method for evaluation of the derivative signal. Br-PADAP reacts with nickel(II) in the presence of Triton X-100 to form a red complex with absorption maxima at 530 and 562 nm. The reactions parameters and the conditions for the measurements of the first-derivative signal were studied and the results demonstrated that using the derivative technique, Br-PADAP can be used for nickel determination with a selectivity higher than that of ordinary spectrophotometry and with a limit of detection of 0.2 ng ml(-1). The pH should be in the range 5.0-6.0 using an acetate buffer. The determination of nickel in the presence of cobalt was performed with conventional and derivative procedures, and the results demonstrated that only the derivative method should be used and, of the methods used for evaluation of the derivative signal, the zero-crossing method is the best. The proposed procedure was used for nickel determination in steels standards. The results demonstrated that the procedure has satisfactory accuracy and precision. Cobalt interference can be also eliminated by using dual-wave-length spectroscopy.     

Derivative spectrophotometric determination of nitrate in plant tissue

A derivative spectrophotometric method was developed to determine NO3(-)-N in plant tissues. The method is based on measurement of the first-derivative spectrum of nitrosalicylic acid in basic solution. The nitrosalicylic acid was obtained by reaction of samples with salicylic acid in concentrated sulfuric acid and was used by Cataldo et al. in nonderivative spectrophotometry. The main strength of this technique is the lack of matrix background interference, typical of plant extracts in traditional spectrophotometric methods. This method is fast, inexpensive, easy-to-apply, and highly selective. The calibration graph was linear in the range of 0.1 and 1.0 mg/L N as NO3(-). Average recovery in real matrixes (lettuce and spinach) was 102.6%; average standard deviation was 3.3. This method has been applied to leaves of 4 types of lettuce.     

Flow-injection spectrophotometric determination of arylamines and sulphonamides by diazotization and coupling in a micellar medium

In a sodium dodecyl sulphate (SDS) micellar solution, the rate of coupling of a diazonium ion with N-(1- naphthyl)ethylenediamine (NED) increases greatly, the protonation of the resulting azo dyes takes place at higher pH values and the dyes are more soluble. These favourable features were applied to the development of a simple flow-injection spectrophotometric procedure for the determination of diazotizable substances of pharmaceutical interest. Limits of detection in the range 0.2–0.5 μg ml^?1 (signal-to-noise ratio=3), with relative standard deviation of 0.7–3% (n=3) for 5 μg ml^?1 standards, were obtained.     

Derivative spectrophotometric determination of praseodymium in rare earth mixtures with lomefloxacin

Praseodymium forms a Pr(LMFX)(3) complex with lomefloxacin. In this paper, the absorption spectra of the complex has been investigated by applying conventional and derivative spectrophotometric methods. It was found that lomefloxacin could form a stable complex with praseodymium in the pH 6.5-8.5 media. The absorption intensity of the complex is 4.5-fold more than PrCl(3). Using the second derivative spectra, the sensitivity is 7.4 times higher for Pr than in the normal method (zero derivative spectra). The second derivative spectrophotometry for determination of praseodymium in the presence of other rare earths has been developed. The calibration curves were linear in the range of 3.5-65 mug ml(-1) for Pr. The detection limit is 0.85 mug ml(-1). The method is satisfactory for the determination of praseodymium in mixed rare earths.     

Sensitive spectrophotometric kinetic determination of osmium by catalysis of the pyrogallol red-bromate reaction

Osmium(VIII) is determined by means of its catalytic effect on the oxidation of pyrogallol red (PGR) by potassium bromate at pH 6.0, 30°C and 545 nm. The decrease in absorbance of PGR (2.5 × 10^?5 M) in the presence of KBrO₃ (0.20 M) over a period of 0–150 s is proportional to the concentration of osmium(VIII) over the range 0–1400 ng ml^?1. The limit of detection of osmium was 0.65 ng ml^?1. The precision and accuracy of the method are described. The effects of the presence of 45 cations and anions on osmium determination were studied. The effects of probable interferences were completely removed by a single extraction of osmium as osmium tetraoxide into isobutyl methyl ketone and back-extraction into sodium hydroxide solution.     

Micellar modified spectrophotometric determination of nitrobenzenes based upon reduction with tin(II), diazotisation and coupling with the Bratton-Marshall reagent

Nitrobenzenes, such as the antibiotic chloramphenicol, the vasodilator nicardipine, and the herbicides dinitramin, dinobuton, fenitrothion, methylparathion, oxyfluorfen, parathion, pendimethalin, quintozene, and trifluralin, were determined by using a spectrophotometric method in the visible region (540 nm). The method was based on the reduction of the nitrobenzenes to arylamines with tin(II) chloride, diazotisation of the arylamines and coupling of the diazonium ions with the Bratton-Marshall reagent. The two latter reactions were performed in a micellar medium of sodium dodecyl sulphate. The linear calibration range was 2x10(-6) to 7x10(-5) M (r>0.999), with limits of detection in the 10(-7) M level, which is 2-6 fold lower with respect to the corresponding spectrophotometric procedure in non-micellar medium. The procedure was applied to the analysis of the compounds in commercial preparations (pharmaceuticals and herbicide formulations) and in water samples, with good recoveries.     

Derivative spectrophotometric determination of copper(II) in non-ionic micellar medium

A photometric method for trace analysis of Cu(II) with 1-(2-pyridylazo)-2-naphthol (PAN) in presence of a neutral surfactant, Triton X-100, has been reported in normal and derivative modes. The molar absorption coefficient () and Sandell's sensitivity (S) of PAN-Cu(II) complex at 555 nm is 5.21 x 10(4) l mol(-1) cm(-1) and 1.22 ng cm(-2) respectively. The detection limit of Cu(II) is 4.0 ng ml(-1) and Beer's law is obeyed in the range 0.08-4.00 mug ml(-1) of the analyte. Copper content of a number of commercially available alcoholic beverages, biological and standard alloy samples is reported. The results obtained are in excellent agreement with those obtained using AAS.     

Highly sensitive spectrophotometric kinetic determination of vanadium by catalysis of the gallic acid-bromate reaction

Conditions are described for improving the speed and sensitivity of this catalytic determination of vanadium. The reaction of 0.018 M gallic acid with 0.96 M sodium bromate at pH 3.8 and double-beam spectrophotometric measurement at 380 nm are recommended. The calibration curves are obtained by the tangent (2-point) and fixed-time (single-point) method. The highest practical sensitivity at 22–30°C was ca. 40 pg for an absorbance change of 0.0005, 50 times better than previously. The detection limit was ca. 0.5 ng of vanadium. Reaction at 50°C gave even better sensitivity.     

Derivative spectrophotometric determination of mercury(II) with pan in the aqueous phase

The Hg-PAN complex can be made soluble in water by addition of surfactant, and this can be made the basis of a spectrophotometric determination of Hg at ppm level. The selectivity and sensitivity can be improved by use of derivative spectrometry. The method has been applied to mercury-containing pesticides.     

Derivative spectrophotometric method for determination of acidity constants of single step acid-base equilibria

A general derivative spectrophotometric method for determination of acidity constants is developed. The method appears suitable in cases when classical spectrophotometry cannot be employed due to little differences in the absorption spectra of conjugated acid-base pairs. Based on theoretical considerations, seven variants of the method have been established and their validity was checked, determining acidity constants of lorazepam and flurazepam as model compounds.     

A simple spectrophotometric method for the determination of hydrazine salts by reaction with phosphomolybdic acid

Summary A Simple Spectrophotometric Method for the Determination of Hydrazine Salts by Reaction with Phosphomolybdic Acid A simple, rapid and sensitive Spectrophotometric procedure is described for ppm determination of hydrazine salts. It is based on reduction of phosphomolybdic acid and measurement of the molybdenum blue thus formed at 822 nm. When compared with other procedures, this method proved to be of comparable sensitivity and has less interferences. As low as 0.31 ppm was accurately determined; the relative error and the relative standard deviation did not exceed 0.94 and 1.73%, respectively.     

Flow-injection analysis with the iron-induced perbromate-iodide reaction: spectrophotometric determination of iron

Total iron is determined by a flow-injection spectrophotometric technique. The production of I(-)(3) from the iron(II)- or iron(III)-induced perbromate-iodide reaction is monitored at 353 nm. Calibration graphs are linear from 10 to 100 ng/ml with correlations up to 0.9998 and can be extended up to 10 microg/ml by appropriate adjustment of conditions. The average sampling rate is 30 samples/hr. Detection limits and relative standard deviations compare well with those of other FIA methods.     

Colorimetric determination of some sulphonamides with phenothiazine

Two simple and sensitive calorimetric procedures for determination of some sulphonamides with phenothiazine (thiodiphenylamine) are presented. One is based on reaction in aqueous alcohol solution in presence of hypochlorite, with direct measurement at 515 nm. The other is based on reaction in presence of copper(II) acetate at 70 degrees , extraction with chloroform and measurement at 515 nm. The method is applied to the determination of sulphonamides in pure and tablet form, with a coefficient of variation less than 2%.     

Methods for the determination of sulphonamides in meat.

Sulphonamides, due to their important antibacterial effects, are widely used in veterinary practice and animal husbandry. Residues arising from administration without observing withdrawal time sufficiently are normally the parent compounds and the N4-acetyl derivatives, the latter being hydrolyzed to the parent compounds only during extraction under acidic conditions. It is therefore quite conceivable that many authors concentrate on determining these metabolites. In the past decade, we have witnessed a considerable increase in new analytical techniques dealing with the determination of sulphonamides. Among these procedures, especially the so-called multimethods using high-performance liquid chromatography--though sometimes including toilsome clean-up steps--can be mentioned. However, current approaches also utilize gas chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, supercritical fluid chromatography-mass spectrometry, thin-layer chromatography and immunological methods. For most of these techniques, a strong trend towards lowering the level of detectability (down to the sub-ppb range) and improving accuracy and reproducibility can be established.     

Derivative spectrophotometric determination of neodymium in rare earth mixtures using bromopyrogallol red and TX-100

A fourth-derivative spectrophotometric procedure is described for the determination of neodymium in mixed rare earths. It is based on the absorption spectrum of the 4f electron transition of the neodymium complex with bromopyrogallol red (BPR) in the presence of TX-100. The influence of various instrumental parameters and reaction conditions on the colour development of the Nd-BPR-TX-100 complex has been investigated. The detection limit is 0.15 g/mL and the linear dynamic range extends to 3.6 g/mL. The relative standard deviation is 1.2% for 1.5 g/mL (n=7). Satisfactory results were obtained.