Spectrophotometric Method for the Determination of Cobalt with N,N′-Bis(2-Aminobenzoyl)Ethylenediamine

 A simple and direct spectrophotometric method has been developed for the determination of cobalt(II) using N,N′-Bis(2-aminobenzoyl)ethylenediamine (Baben). The method is based on the colour reaction between Baben and cobalt(II) in borax buffer (pH 9.2). The studies are carried out at 470 nm at which the calculated value of molar absorptivity is found to be 1.102 × 10⁴ L mol⁻¹ cm⁻¹. The system obeys Beer’s law over a wide range of concentration (2–20 μg/ml). The effect of interfering ions has been studied and the method was applied to the determination of cobalt in water, industrial effluents and in alloys and the results were highly satisfactory. Received May 8, 2000. Revision January 30, 2001.     

Spectrophotometric determination of trimethoprim by oxidation in drug formulations

A spectrophotometric determination of trimethoprim is described based on the reaction of its amine group with persulfate which acts as a strong oxidizing agent in alkaline media. The reaction produces a stable yellow colored compound after heating in a boiling water bath for 30 min. At λ_max 355 nm, Beer’s law is obeyed in the concentration range 10–60 μg ml^–1 with a molar absorptivity of 2.7 × 10³ l mol^–1cm^–1. The method is applied to formulations with sulfamethoxazole. Received: 30 July 1996 / Revised: 16 October 1996 / Accepted: 22 October 1996     

Organic solvent-soluble membrane filters for the preconcentration and spectrophotometric determination of iron(II) traces in water with Ferrozine

An organic solvent-soluble membrane filter (MF) is proposed for the simple and rapid reconcentration with subsequent spectrophotometric determination of trace levels of iron (II) in water. Iron (II) is collected on a nitrocellulose membrane filter as ion associate of an anionic complex, which is formed by iron (II) and Ferrozine and a cation-surfactant. The ion-pair compound and the MF can be dissolved in small volumes of 2-ethoxyethanol and the absorbance of the resulting solution is measured at 560 nm against a reagent blank with molar absorptivity of 4.01 × 10⁴ L mol^–1 cm^–1. Beer’s law is obeyed over the concentration range 0–10 μg L^–1 of iron (II) in water and the detection limit is 0.03 μg L^–1 with a 50-fold enrichment factor. The proposed method can satisfactorily be applied to the determination of iron (II) in natural water and sea water. Received: 23 June 1998 / Revised: 21 July 1998 / Accepted: 25 August 1998     

Quantitation of Some Recently Introduced Antibacterial Drugs Using Sudan III as Chromogenic Reagent

 A simple, rapid, accurate and sensitive spectrophotometric method for the determination of norfloxacin (NRF), ofloxacin (OFL) and ciprofloxacin (CPF) is described. This method is based on the formation of an ion pair with sudan III in aqueous-acetone medium [40% (v/v) acetone]. The coloured products are measured at 567, 565 and 566 nm for NRF, OFL and CPF, respectively. The optimization of various experimental conditions is described. Beer’s law is obeyed in the range 0.4–12.0, 0.4–8.8 and 0.4–10.4  ;μg mL⁻¹ of NRF, OFL and CPF, respectively. For more accurate results, Ringbom optimum concentration ranges were 0.8–11.2, 0.6–8.5 and 0.8–10.0 μg mL⁻¹, respectively. The results obtained showed good recoveries of ±1.2, ±1.5 and ±1.7% with relative standard deviations of 0.67, 0.83 and 1.08% for NRF, OFL, and CPF, respectively. The molar absorptivity and Sandell sensitivity were also calculated. Applications of the proposed method to representative pharmaceutical formulations are successfully presented. Received April 30, 1999. Revision November 25, 1999.     

Extraction-spectrophotometric study of the system manganese(VII)-methyl violett-water-chloroform and its application

The system manganese(VII)-methyl violet(MV)-water-chloroform has been studied. The composition of the complex is established as MV: MnO₄⁻=1:1. The molar absorptivity of the complex is (2.67 ± 0.09) × 10⁴ l mol⁻¹ cm⁻¹ at 300 nm, limit of detection is 0.027 μg ml⁻¹ and the system obeys Beer’s law in the range 0.22–1.6 μg ml⁻¹ Mn(VII). The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase was determined. The influence of foreign ions on the accuracy of the results is investigated. Extraction investigations of the system discussed were carried out. A new rapid, selective, simple and sensitive extractive-spectrophotometric method for the determination of trace amounts of manganese(VII) in plants, soils and steels were developed.     

Spectrophotometric determination of total inorganic arsenic with hexamethylene ammonium-hexamethylenedithiocarbamate in nonionic triton X-100 micellar media

We have developed a cost-effective and sensitive spectrophotometric method for the determination of arsenic at trace level using a new reagent, hexamethylene ammonium-hexamethylenedithiocarbamate (HMA-HMDTC). Here we show that arsenic reacts with HMA-HMDTC in acidic conditions to yield the As(HMDTC)₃ complex. We studied the Beer’s law at 256 nm, which showed linearity over the concentration range 0.2–1.0 μg/mL of arsenic. We have shown that molar absorptivity, Sandell’s sensitivity and the detection limit of the method are 6.06 × 10⁴ L/mol cm, 0.0012 μg/cm² and 0.060 μg/mL, respectively. We have applied this new method to the determination of arsenic in drinking water.     

Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO₂) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO₂ in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO₂ for phenol is 2.4 mg g⁻¹ with distribution coefficients up to 3.4 × 10⁴ mL g⁻¹; corresponding data for 1-naphthol are 1.5 mg g⁻¹ and 3 × 10³ mL g⁻¹. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than 0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A ₅₄₀) and phenol concentration (C) in water was found according to the equation A ₅₄₀ = (6 ± 1) × 10⁻² + (0.9 ± 0.1)C (μmol L⁻¹) with a detection range from 1 × 10⁻⁸ mol L⁻¹ (0.9 μL g⁻¹) to 2 × 10⁻⁷ mol L⁻¹ (19 μL g⁻¹), a limit of quantification of 1 μL g⁻¹ (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 μL g⁻¹ while the quantification limit is 20 μL g⁻¹. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g⁻¹.     

Colorimetric Procedure for the Microdetermination of the Antibilharzial Drug Praziquantel and its Applications to Pharmaceutical Formulations

 A procedure for the colorimetric assay of praziquantel has been developed. The method is based on the formation of charge-transfer complexes with p-chloranil (I), dichloronitrophenol (II), 2,3-dichloro-5,6 dicyano-p-benzoquinone (III), 7,7,8,8-tetracyanoquinodimethane (IV) and tetracyanoethylene (V) as π-acceptors to give highly coloured species. The coloured products are measured spectrophotometrically at 550, 425, 460, 844 and 393 nm for I, II, III, IV and V, respectively. Optimization of the different reaction conditions is described. The colour system obeyed Beer’s law in non-aqueous media in the concentration range 2.0–48 μg ml⁻¹. It was stable for at least 4.0 h. The detection limit was found to be 0.6 μg ml⁻¹. Applications of the procedure to the analysis of various pharmaceutical samples gave reproducible and accurate results. Further, the validity of the procedure was confirmed by applying the standard addition technique. The total average recovery was 100.2%. Received June 10, 2000. Revision December 23, 2000.     

Derivative Spectrophotometric Determination of Nd, Ho and Er in Rare Earth Mixtures with 1-Ethyl-6,8-difluoro-7-(3-methyl-1-piperazinyl)-4-oxo-1,4-dihydro-3-quinoline carboxylic acid

 The second derivative spectrophotometric method has been developed as a procedure for the determination of neodymium, holmium and erbium in mixed rare earths. It was found that the 1-ethyl-6, 8-difluoro-7-(3-methyl-1-piperazinyl)-4-oxo-1,4- dihydro-3-quinoline carboxylic acid forms stable complexes with neodymium, holmium and erbium ions in the pH 9.2–10.5 range. In the second derivative spectra the optimum analytical signals for neodymium, holmium and erbium are at 576.2 (+)−574.5 (−)nm, 444.2 (+) −447.8 (−)nm and 516.0 (+) −517.2(−)nm, respectively. Beer’s law is obeyed from 5.0×10⁻⁵ M to 2.5×10⁻⁴ M of neodymium, holmium and erbium. The quantification limits (10 Sb) were 1.2×10⁻⁵ M for Nd, 9.7×10⁻⁵ M for Ho and 3.0×10⁻⁶ M for Er. Received April 22, 1998. Revision March 8, 1999.     

Application of non-steroidal anti-inflammatory drugs for palladium determination

A highly sensitive spectrophotometric method for palladium determination using piroxicam and tenoxicam as new chromogenic reagents has been developed. In the presence of sodium lauryl sulfate (SLS), palladium reacts with piroxicam (PX) or tenoxicam (TX) to form stable yellow orange complexes in an acetate buffer solution of pH 5.0 at 424 nm and 426 nm with molar absorptivity of 7.16 × 10⁴ L mol⁻¹ cm⁻¹ and 1.20 × 10⁵ L mol⁻¹ cm⁻¹, respectively. Sandell sensitivity, detection, and quantitation limits were also calculated. Optimum conditions were evaluated considering pH, reagent concentration, time, temperature, and surfactant concentration. The complex system conforms to Beer’s law over the range of 0.07–1.28 μg mL⁻¹ palladium. The stoichiometric ratio and stability constant were also evaluated. Tolerance limits of many cations and anions were determined. Finally, the proposed method was applied successfully in the determination of palladium in jewellery, anode mud, synthetic mixtures, catalysts, and alloy samples.     

Utility of Certain σ and π-Acceptors for the Spectrophotometric Determination of Sildenafil Citrate (Viagra)

 The molecular interaction between sildenafil citrate as electron donor and each of iodine; 7,7,8,8-tetracyanoquinodimethane (TCNQ); 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ); tetracyanoethylene (TCNE); 2,4,7-trinitro-9-fluorenon (TNF); chloranilic acid (CLA); chloranil (CL) and bromanil (BL) as acceptors have been investigated spectrophotometrically. Different variables affecting the reaction were studied and optimized. Beer’s law was obeyed in a concentration limit of 10–260 μg/mL for sildenafil citrate. For more accurate analysis, Ringbom optimum concentration range was found to be between 20–240 μg/mL. The limits of detection and determination were calculated and found to be 1.5 and 5.2 μg/mL, respectively. The standard deviations were calculated for different concentrations of sildenafil citrate using various acceptors. A Job’s plot of the absorbance versus the molar ratio of the sildenafil citrate to each of acceptors under consideration indicated (1:1) ratio. The proposed methods were found to be rapid, accurate, precise and sensitive and could be applied for determination of sildenafil citrate in pharmaceutical dosage forms (Viagra) without interferences from common additives encountered. Received August 30, 2000. Revision January 5, 2001.     

Determination of Zirconium (IV) and Aluminium (III) in Waste Water

 Zirconium (IV) was determined spectrophotometrically by reaction with quercetin as primary ligand and oxalate as secondary ligand. Polyvinylpyrrolidone (PVP) was used as protective colloid to solubilize the formed zirconium quercetin oxalate ternary complex. The molar absorptivity of the 1:3:1 (zirconium–quercetin–oxalate) complex is 7.31 × 10⁴ L·mol⁻¹ cm⁻¹ at 430 nm with a stability constant of 8.2 × 10²⁰ and its detection limit is 0.16 mg/L. Beer’s law is rectilinear up to 1.46 mg/L of zirconium (IV). The sensitivity index is 1.25 ng cm⁻². The reaction of aluminium (III) with quercetin in presence of PVP as a surfactant has been studied spectrophotometrically. The molar absorptivity of the 1:3 (aluminium–quercetin) complex is 8.09 × 10⁴ × L·mol⁻¹·cm⁻¹ at 433 nm, its stability constant is 2.6 × 10¹³ with sensitivity index of 0.33 ng·cm⁻² and its detection limit is 0.08 mg/L. The optimal conditions for the quantitative determination of zirconium and aluminium were studied. The proposed methods are examined by statistical analysis of the experimental data. The methods are free from interference of most cations and anions. The proposed methods have been used to determine zirconium and aluminium in industrial waste water. Received May 30, 2001; accepted November 2, 2001; published online July 15, 2002     

Spectrophotometric determination of methimazole in pharmaceutical,serum and urine samples by reaction with potassium ferricyanide-Fe(III)

This paper describes a novel method to determine methimazole by spectrophotometry using a potassium ferricyanide-Fe(III) reaction. The study indicates that at pH 4.0 Fe(III) is reduced to Fe(II) by methimazole and in situ formed Fe(II) reacts with potassium ferricyanide to give soluble Prussian Blue which is characterized by means of XRD analysis. The absorbance of Prussian Blue is measured at the absorption maximum of 735 nm, and the amount of methimazole can be determined based on this absorbance. Beer’s law is obeyed in the range of methimazole concentrations of 0.02–6.00 μg/mL. The equation of the linear regression is A = −0.0058 + 0.49988c (μg/mL), with a correlation coefficient of 0.9998 and RSD of 0.80%. The detection limit (3σ/k) is 0.015 μg/mL, and the apparent molar absorption coefficient of indirect determination of methimazole is 5.7 ± 10⁴ L/mol cm. This method has been successfully applied to the determination of methimazole in pharmaceutical, serum and urine samples, and average recoveries are in the range of 98.6–102.4%. Analytical results obtained with this novel method are satisfactory.     

A cellulose-based carboxyl cotton chelator having citric acid as an anchored ligand: preparation and application as solid phase extractant for copper determination by flame atomic absorption spectrometry

Citric acid was thermochemically esterified onto defatted cotton fibre to produce a carboxyl cotton chelator (CCC), which had been used for extraction of copper prior to its determination by flame atomic absorption spectrometry. The extraction of copper has been studied under both batch and column methods. Quantitative extraction of copper was achieved in the pH range 4–7. The time needed to extract each sample was less than 30 min by the batch method. The copper extraction capacity of CCC was found to be 22.7 mg g⁻¹ at optimal pH value. The elution was quantitative with 1 mol L⁻¹ hydrochloric acid. The feasible flow rate of copper-containing solution for quantitative extraction onto the column packed with CCC was 0.5–4.0 mL min⁻¹, whereas for elution it was less than 1.5 mL min⁻¹. A 100-fold extraction factor could be achieved under the optimal column conditions. The tolerance limits for common metal ions on the extraction of copper and the time of column reuse were investigated. The proposed method has been successfully applied for extraction and determination of copper in industrial wastewater and natural water samples.     

Investigation of 2-[2-(4-Methoxy-phenylamino)-vinyl]-1,3,3-trimethyl-3H-indolium Chloride as a New Reagent for the Determination of Chromium(VI)

 The complex formation and extraction of chromium(VI) with 2-[2-(4-methoxy-phenylamino)-vinyl]-1,3,3-trimethyl-3H-indolium chloride reagent was studied by means of spectrophotometry. The influence of medium acidity, the concentration of chloride ions and dye reagent, the nature of the extractant and some other factors (time of extraction, stability of color, interference, etc.) on the absorbance of colored extracts were studied. The optimum conditions were found to be 0.02–0.1 M H₂SO₄, 1.0–1.5 M NaCl, (2.0–2.5) × 10⁻⁴ M of reagent. The absorbance of the colored extracts obeys Beer’s Law in the range of 0.26–7.28 mg L⁻¹. The procedure of Cr(VI) extraction and spectrophotometric determination was examined. Author for correspondence. E-mail: andruch@kosice.upjs.sk Received November 19, 2002; accepted March 10, 2003 Published online June 13, 2003     

Determination of nitrites by the formation of bisazo dye

A facile, sensitive and rapid spectrophotometric method for the determination of nitrite is presented. The method involves the reaction of nitrite with 4-aminoazobenzene under acidic conditions in the presence of a bromide ion allowing to complete the diazotization reaction almost instantaneously. The formed diazonium ion is then coupled with acetyl acetone to give bisazo dye in an aqueous alkaline medium having maximum absorption at 500 nm. The molar absorptivity and Sandell’s sensitivity of the method were found to be 4.2 × 10⁴ dm³ mol⁻¹ cm⁻¹ and 1.1 ng cm⁻², respectively. The system obeys the Beer’s law within the concentration range of 0.1–9 μg of nitrite in the final sample volume of 10 cm³. Optimum reaction conditions were evaluated and the influence of ionic interference on the determination of nitrite has been studied. The developed method has been applied in the determination of nitrite in water and soil samples, and the results were statistically evaluated.     

LC–MS–MS determination of ibuprofen, 2-hydroxyibuprofen enantiomers,and carboxyibuprofen stereoisomers for application in biotransformation studies employing endophytic fungi

The purpose of this study was the development and validation of an LC–MS–MS method for simultaneous analysis of ibuprofen (IBP), 2-hydroxyibuprofen (2-OH-IBP) enantiomers, and carboxyibuprofen (COOH-IBP) stereoisomers in fungi culture medium, to investigate the ability of some endophytic fungi to biotransform the chiral drug IBP into its metabolites. Resolution of IBP and the stereoisomers of its main metabolites was achieved by use of a Chiralpak AS-H column (150 × 4.6 mm, 5 μm particle size), column temperature 8 °C, and the mobile phase hexane–isopropanol–trifluoroacetic acid (95: 5: 0.1, v/v) at a flow rate of 1.2 mL min⁻¹. Post-column infusion with 10 mmol L⁻¹ ammonium acetate in methanol at a flow rate of 0.3 mL min⁻¹ was performed to enhance MS detection (positive electrospray ionization). Liquid–liquid extraction was used for sample preparation with hexane–ethyl acetate (1:1, v/v) as extraction solvent. Linearity was obtained in the range 0.1–20 μg mL⁻¹ for IBP, 0.05–7.5 μg mL⁻¹ for each 2-OH-IBP enantiomer, and 0.025–5.0 μg mL⁻¹ for each COOH-IBP stereoisomer (r ≥ 0.99). The coefficients of variation and relative errors obtained in precision and accuracy studies (within-day and between-day) were below 15%. The stability studies showed that the samples were stable (p > 0.05) during freeze and thaw cycles, short-term exposure to room temperature, storage at −20 °C, and biotransformation conditions. Among the six fungi studied, only the strains Nigrospora sphaerica (SS67) and Chaetomium globosum (VR10) biotransformed IBP enantioselectively, with greater formation of the metabolite (+)-(S)-2-OH-IBP. Formation of the COOH-IBP stereoisomers, which involves hydroxylation at C3 and further oxidation to form the carboxyl group, was not observed.     

Sampling and determination of hydrogen cyanide in cigarette smoke

A method for sampling and determination of hydrogen cyanide in cigarette smoke is described. Cigarette smoke is filtered through a glass fiber filter paper, and only gaseous compounds, such as hydrogen cyanide, are collected in a dilute sodium hydroxide solution. The cyanide is determined spectrophotometrically at 550 nm by the isonicotinic acid–pyrazolone method. Maximum absorbance is achieved within 10 min at room temperature, and remains constant for about 20 min. Beer’s law is obeyed in the range 0.04∼0.80 μg mL^–1 cyanide, with a molar absorptivity of 3.48 × 10⁴ L mol^–1 cm^–1. Received: 30 November 1998 / Revised: 21 April 1999 / Accepted: 30 April 1999     

Sampling and determination of hydrogen cyanide in cigarette smoke

A method for sampling and determination of hydrogen cyanide in cigarette smoke is described. Cigarette smoke is filtered through a glass fiber filter paper, and only gaseous compounds, such as hydrogen cyanide, are collected in a dilute sodium hydroxide solution. The cyanide is determined spectrophotometrically at 550 nm by the isonicotinic acid–pyrazolone method. Maximum absorbance is achieved within 10 min at room temperature, and remains constant for about 20 min. Beer’s law is obeyed in the range 0.04∼0.80 μg mL^–1 cyanide, with a molar absorptivity of 3.48 × 10⁴ L mol^–1 cm^–1. Received: 30 November 1998 / Revised: 21 April 1999 / Accepted: 30 April 1999     

Simultaneous First Derivative Spectrophotometric Determination of Palladium and Nickel Using 2-(2-Thiazolylazo)-5-Dimethylaminobenzoic Acid as an Analytical Reagent

 A simple, rapid, selective, sensitive and economical method has been developed for the simultaneous determination of trace amounts of palladium and nickel in aqueous methanolic medium using 2-(2-thiazolylazo)-5-dimethylam inobenzoic acid as an analytical reagent by first derivative spectrophotometr y. Palladium is determined by measuring base to peak distance at λ=695.0 nm while nickel is estimated by zero crossing method in the mixture. The linearity is maintained between 0.12–1.75 μg mL⁻¹ for palladium and 0.07–1.60 μg mL⁻¹ for nickel in the pH range 2.8–7.2 and 3.4–8.8 respectively. Seven replicate determinations of 1.0 μ g mL⁻¹ of palladium and 0.8 μg mL⁻¹ of nickel in a mixture give a mean signal height of 0.391 for Pd and 0.541 for Ni with relative standard deviations of 0.9% and 1.2%, respectively. The sensitivity of the proposed method is 0.391 (dA/dλ)/(μg mL⁻¹) for palladium and 0.685 (dA/dλ)/(μg mL⁻¹) for nickel. Various parameters have been optimised for the simultaneous determination of palladium and nickel in various complex samples. Received March 30, 1999. Revision November 25, 1999.