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     

Spectrophotometric determination of zirconium with 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate

The characteristics of the ternary complex formed between zirconium(IV) and 5,7-dibromo-8-hydroxyquinoline in presence of thiocyanate have been studied with an analytical point of view. The resulting colored species is extractable into chloroform with absorption maximum at 416 nm, which leads to the determination of the trace amounts of the metal ion. The method obeys Beer’s law in the range 0.2–9.0 μg Zr/mL having molar absorbitivity and Sandell’s sensitivity values of 1.05 × 10⁴ L/mol cm and 0.0087 μg Zr/cm², respectively. The ratio of zirconium(IV), 5,7-dibromo-8-hydroxyquinoline and thiocyanate in the extracted species is found to be 1: 2: 2. A large number of foreign ions do not interfere in the proposed method. The applicability of the procedure is tested by carrying out satisfactorily the analysis of a wide variety of samples.     

Determination of neodymium, holmium and erbium in mixed rare earths by norfloxacin

Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second derivative spectrum, Beer’s Law is obeyed from 5.0 × 10^–5∼ 2.5 × 10^–4 mol dm^–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10^–5 mol dm^–3 of neodymium, 6.1 × 10^–5 mol dm^–3 of holmium and 6.0 × 10^–5 mol dm^–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth elements with good accuracy and selectivity, is described. Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998     

Determination of neodymium, holmium and erbium in mixed rare earths by norfloxacin

Norfloxacin (NFX) is proposed as reagent for the derivative spectrophotometric determination of neodymium, holmium and erbium in mixed rare earths. The absorption spectra of 4f electron transitions of the systems of neodymium, holmium and erbium complexes with norfloxacin in presence of cetylpyridinium chloride were studied by normal and derivative spectra. The absorption bands found normally at 575 nm for neodymium, 450 nm for holmium and 523 nm for erbium were enhanced markedly. Using the second derivative spectrum, Beer’s Law is obeyed from 5.0 × 10^–5∼ 2.5 × 10^–4 mol dm^–3 for neodymium, holmium and erbium. The relative standard deviations are 1.0, 1.4 and 1.1% for 6.9 × 10^–5 mol dm^–3 of neodymium, 6.1 × 10^–5 mol dm^–3 of holmium and 6.0 × 10^–5 mol dm^–3 of erbium, respectively. A method for the direct determination of neodymium, holmium and erbium in mixtures of rare earth elements with good accuracy and selectivity, is described. Received: 18 December 1997 / Revised: 23 February 1998 / Accepted: 26 February 1998     

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     

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     

Use of a diazocoupling reaction for sensitive and selective spectrophotometeric determination of furosemide in spiked human urine and pharmaceuticals

Two simple, sensitive, and selective spectrophotometric methods for the determination of 5-(aminosulfonyl)-4-chloro-2-((2-furanylmethyl)amino)benzoic acid (furosemide, FUR) are described. The methods are based on acid hydrolysis of FUR to free primary aromatic amine and diazotization followed by coupling with N-1-napthylethylene diamine (NEDA) (method A) or 4,5-dihydroxynaphthalene-2,7-disulfonic acid (chromotropic acid, CTA) (method B). The colored reaction product can be measured spectrophotometrically at 520 nm (method A) or 500 nm (method B). Beer’s law is obeyed over the ranges of 1.75–21.0 μg mL⁻¹ and 2.5–30.0 μg mL⁻¹, for method A and method B, respectively. Apparent molar absorptivities and Sandell’s sensitivities (in L mol⁻¹ cm⁻¹ and μg cm⁻² per 0.001 absorbance unit, respectively) were 1.34 × 10⁴ and 0.0253 using NEDA as the coupling agent, and 8.5 × 10³ and 0.0389 using CTA for the same purpose. Analysis of solutions containing seven different concentrations of FUR gave a correlation coefficient of 0.9979 using NEDA and 0.9984 using CTA, while the slope and the correlation coefficient of the regression equation were calculated. The reaction stoichiometry in both methods was evaluated by the limiting logarithmic method and was found to be 1: 1 (diazotized FUR: NEDA or diazotized FUR: CTA). The methods were successfully applied to the determination of FUR in spiked human urine and in pharmaceutical formulations. The recovery of FUR from spiked urine was satisfactory resulting in the values of (109.4 ± 4.37) % using NEDA and (113.0 ± 4.74) % using CTA. Results of the analysis of pharmaceuticals demonstrated that the proposed procedures are at least as accurate and precise as the official method while a statistical analysis indicated that there was no significant difference between the results obtained by the proposed methods and those of the official method.     

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     

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.     

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.     

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.     

Formation and Extraction of Niobium(V) Complex with Xylenol Orange in the Presence of a 4-Pyridone Derivative

Xylenol orange (XO) is a suitable reagent for the spectrophotometric determination of niobium in a weakly acidic medium. The present study shows that the addition of 3-hydroxy-2-methyl-1-phenyl-4-pyridone (HX) influences the complex formation as well as the spectroscopic properties of this colored system. To prevent formation of niobium(V) hydrolyzed species in water, tartaric acid was used when preparing the niobium stock solution. The red-violet colored complex formed by heating niobium(V) with xylenol orange (XO) in the presence of HX at pH=3 has a maximum absorption wavelength at 565 nm. The complex can be extracted by a chloroform solution of tetraphenylphosphonium (TPP) chloride. The optimum reaction conditions and other parameters for complex formation have been evaluated. The mechanism of extraction is probably based on the formation of the associated ion pair between the tetraphenylphosphonium cation and the mixed Nb(V)-XO-HX anion. The extracted complex in chloroform showed a maximum absorbance at 585 nm with the corresponding molar absorption coefficient being 3.72×10⁴ L⋅mol⁻¹⋅cm⁻¹, and obeys Beer’s law in the range 3×10⁻⁶ to 3×10⁻⁵ mol⋅L⁻¹.     

Analysis of fenvalerate in its formulations and environmental samples using spectrophotometry

Two rapid, simple, sensitive, and nonextractive spectrophotometric methods were described for the determination of fenvalerate (syntheitic pyrethroid) in its formulations, water and grain samples. The methods are based on the hydrolysis of fenvalerate with methanolic NaOH to form 3-phenoxybenzaldehyde. The resultant aldehyde group was condensed with 4-aminoantipyrine in the basic medium to form a red product having λ_max at 489 nm or condensed with4,4′-methylene-bis-m-nitroaniline to form a plae red product with an absorption maximum of 513 nm. Beer’s law was obeyed over the range 0.6–10 μg/mL (molar absorptivity 2.184 × 10⁴ L/mol cm) for 4-aminoantityrine and over the range of 1–12 μg/mL (molar absorptivity 4.162 × 10⁴ L/mol cm) for 4,4′-methylene-bis-m-nitroaniline. The formations of color derivatives with the reagents are instantaneous and stable for 40 and 32 h, respectively. The methods were rapid, simple, sensitive, and free from nontarget species. The proposed methods have been applied to the determination of fenvalerate in its formulations and environmental samples. The text was submitted by the authors in English.     

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.     

A sensitive and simple flotation-spectrophotometric method for the determination of microgram amounts of silver using Schiff base 2-[(2-mercaptophenyliminio)methyl]phenol

A simple and sensitive spectrophotometric procedure for the determination of microgram amounts of silver has been developed. The method is based on the flotation of the complex of Schiff base, 2-[(2-mercaptophenylimino)methyl]phenol (MPMP), and silver at the aqueous solution-chloroform interface. The complex was then separated and dissolved in 5 mL of methanol, and its absorbance was measured at 330 nm. The quantitative flotation of the complex was possible from 5–140 mL of the aqueous phase in the pH range of 1–5. For a 100-mL aliquot of the water sample, the Beer’s law was obeyed over the range from 1 × 10⁻⁷ to 5 × 10⁻⁶ M of silver. The Sandell’s sensitivity was 6.9 × 10⁻⁹ mol cm⁻² for a 0.001 absorbance unit. The method is simple, rapid, free from the interference of many cations and anions, and has a wide linear range. The procedure was successfully applied to the determination of trace amounts of silver in tap water, well water, waste water in the mining industries, and a lead-concentrate reference material. The accuracy was assessed using either a recovery experiment and independent analysis with standard additions, or the analysis of certified reference materials. The text was submitted by the authors in English.     

Triphenyltetrazolium chloride as a new analytical reagent for molybdenum(VI): Application to plant analysis

Solvent extraction of molybdenum(VI) ion associate with triphenyltetrazolium chloride (TTC) has been studied. TTC was proposed as reagent for the spectrophotometric determination of micro amounts of molybdenum(VI) at λ_max 250 nm. The optimum conditions for extraction of molybdenum(VI) as an ionassociation complex with TTC has been determined. Beer’s law is obeyed in the range of 0.5–10 μg/mL molybdenum(VI). The molar absorptivity of the ion-pair is 1 × 10⁶ L/mol cm. The sensitivity of the method is 9.6 × 10⁻⁵ μg/cm². The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase are: distribution constant K _D = 32.64, extraction constant K _ex = 2.19 × 10¹⁰ association constant β = 6.71 × 10⁸. The interferences of different cations, anions on molybdenum(VI) determination were also investigated. A sensitive and selective method for the determination of microquantities of molybdenum(VI) has been developed. The determination was carried out without preliminary separation of molybdenum. A novel procedure of molybdenum(VI) extraction and spectrophotometric determination in different plant samples was examined.     

Spectrophotometric determination of <Emphasis Type="Italic">L</Emphasis>-ascorbic acid in pharmaceuticals

A simple and sensitive spectrophotometric method for the determination of L-ascorbic acid with leuco crystal violet is proposed. The determination is based on the oxidation of analyte by potassium iodate. The colourless oxidation products were formed in the quantity equivalent to iodide ions. The iodide ions react with the excess of iodate ions in acidic medium, to form free iodine which oxidized leuco crystal violet (LCV) to the liberated crystal violet (CV ⁺) dye, showing maximum absorption at 588 nm. The absorbance was measured at pH of 4.1–4.2 in 1 cm cuvettes. Beer’s law was obeyed in the concentration range 0.5–4.0 μg/mL. The molar absorptivity of the coloured compound is 4.14 × 10⁴ L/mol cm for L-ascorbic acid. The analytical parameters were optimized and the method was successfully applied to the determination of L-ascorbic acid in pharmaceuticals. The results were compared with those obtained by methods proposed in Polish Standard.     

Simple UV and visible spectrophotometric methods for the determination of doxycycline hyclate in pharmaceuticals

Doxycycline hyclate (DOX), a broad spectrum antibiotic with activity against a wide range of gram-positive and gram-negative bacteria, is widely used as a pharmacological agent and as an effector molecule in inducible gene expression system. Three simple, selective, rapid, accurate, precise and cost-effective spectrophotometric methods for the determination of DOX in bulk drug and in tablets have been developed and validated. First method (method A) is based on the measurement of absorbance of DOX in 0.1 M HCl at 240 nm. The second method (method B) is based on the measurement of yellow chromogen at 375 nm which is formed in 0.1 M NaOH. The third method is based on the measurement of 2: 1 complex formed between DOX and iron(III) in H₂SO₄ medium, the complex peaking at 420 nm (method C). The optimum conditions for all the three methods are optimized. Beer’s law was obeyed over the ranges 2.5–50.0, 1.50–30.0 and 10–100 g/mL for method A, method B and method C, respectively. The apparent molar absorptivity values are calculated to be 1.03 × 10⁴, 1.73 × 10⁴, and 5.21 × 10³ L mol⁻¹ cm⁻¹ for method A, method B, and method C, respectively. The Sandell sensitivity, limit of detection (LOD) and limit quantification (LOQ) values are also reported. All the methods were validated in accordance with current ICH guidelines. The developed methods were employed with high degree of precision and accuracy for the estimation of total drug content in commercial tablet formulations of DOX.     

The use of Chromazurol S in the presence of a mixture of cationic and non-ionic surfactants for the spectrophotometric determination of iron in cereals

Simple and sensitive methods for the spectrophotometric determination of iron(III) in food, based on the formation of coloured complexes of Fe(III) with Chromazurol S (CAS) in the presence of tetradecyltrimethylammonium bromide (TTA) or octadecyltrimethylammonium chloride (ODTA) and Triton X-100 (TX100), have been developed. Optimum pH and the concentrations of CAS, TTA, ODTA, and TX100 ensuring maximum absorbance have been determined. For the Fe-CAS-TTA-TX100 system the molar absorptivity is 1.12 × 10⁵ L/(mol cm) at 650 nm; for Fe-CAS-ODTA-TX100 it is 1.35 × 10⁵ L/(mol cm) at 659.5 nm. Beer’s law was obeyed for iron concentration in the range 0.08–0.56 μg/mL for the complex Fe-CAS-TTA-TX100 and 0.08–0.64 μg/mL for Fe-CAS-ODTA-TX100. The influence of several interfering ions has been discussed. The stoichiometry of the complexes was established by applying Job’s method. The more sensitive method, based on the Fe-CAS-ODTA-TX100 system, has been applied to the determination of iron in cereals. To evaluate the accuracy of the elaborated method, the determined content of Fe was compared to the declared value as well as to the result obtained by the reference ICP-OES method.