A simple spectrophotometric method for the determination of methyldopa using p-chloranil in the presence of hydrogen peroxide

A simple, rapid and sensitive spectrophotometric method has been developed for the determination of methyldopa in pharmaceutical formulations. The method is based on the reaction between tetrachloro-p-benzoquinone (p-chloranil) and methyldopa, accelerated by hydrogen peroxide (H2O2), producing a violet-red compound (λmax = 535 nm) at ambient temperature (25.0 ± 0.2 ºC). Experimental design methodologies were used to optimize the measurement conditions. Beer's law is obeyed in a concentration range from 2.10 x 10-4 to 2.48 x 10-3 mol L-1 (r = 0.9997). The limit of detection was 7.55 x 10-6 mol L-1 and the limit of quantification was 2.52 x 10-5 mol L-1. The intraday precision and interday precision were studied for 10 replicate analyses of 1.59 x 10-3 mol L-1 methyldopa solution and the respective coefficients of variation were 0.7 and 1.1 %. The proposed method was successfully applied to the determination of methyldopa in commercial brands of pharmaceuticals. No interferences were observed from the common excipients in the formulations. The results obtained by the proposed method were favorably compared with those given by the Brazilian Pharmacopoeia procedure at 95 % confidence level.

Spectrophotometric determination of arsenic in soil samples using 2-(5-bromo-2-pyridylazo)-5-di-ethylaminophenol (Br-PADAP)

In this paper, a new, simple and sensitive method for arsenic determination in soil is proposed. This is based on the reduction of silver (I) and iron (III) ions by arsine followed by a complexation reaction of iron (II) with the spectrophotometric reagent Br-PADAP 2-(5-bromo-2-pyridylazo)-5-di-ethylaminophenol. Arsenic determination with a Sandell's sensitivity of 3.1 10-4 cm-2, linear range from 0.1 µg ml-1 to 2.0 µg ml-1 (r560 = 0.9995), molar absorptivity of 2.45 10(5) l mol-1 cm-1 and a concentration detection limit of 1.4 ng ml-1 (3s) were obtained using a 10 ml sample volume. Selectivity was increased with the use of EDTA as a masking agent. The proposed method was applied for arsenic determination in the presence of several ions amounts in digested soil samples. The results revealed that antimony (III), mercury (II), germanium (IV), platinum (IV) interferes at all analyzed proportions. The interferences can be easily removed by the use of EDTA. Precision and accuracy obtained were satisfactory with a R.S.D. < 5 %. Recovery of arsenic in soil samples varied from 95.55 to 102.70 % with a mean of 99.63 %. These results demonstrated that the proposed method is applicable for arsenic analysis in different soil samples.

Highly sensitive spectrophotometric methods for the determination of olanzapine

Highly sensitive and selective spectrophotometric methods (A and B) were developed for the determination of micro amounts of olanzapine (OLZ). Method A (direct method) is based on the oxidation of olanzapine with a known excess of iodine monochloride (ICl) in an acidic medium. Under the same condition, thymol blue was iodinated by unreacted ICl, and the absorbance of uniodinated thymol blue was measured at 536 nm. The decrease in ICl concentration is a measure of drug concentration. In method B (indirect method), oxidation of OLZ by a known excess of Ce(IV) in sulfuric acid medium followed by the reaction of unreacted Ce(IV) with leuco crystal violet (LCV) to crystal violet (CV), which is measured in an acetate buffer medium ( pH 4.9) at 580 nm. These methods obey the Beer's law in the concentration range of 0.2-1.6 µg mL-1 (method A) and 0.1-1.4 µg mL-1 (method B). The developed procedures have been successfully applied to the determination of OLZ in pure and in dosage forms. The results exhibit no interference from the presence of excipients. The reliability of the methods was established by parallel determination of OLZ against the reference method.

Determination of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy

A simple analytical method for quantification of atenolol in pharmaceutical formulations by diffuse reflectance spectroscopy is described. The method is based on the reaction, on the filter paper surface, between the drug and p-chloranil producing a colored compound. The best reaction conditions were obtained with 20 µL of atenolol solution and 20 µL of p-chloranil. All reflectance measurements were carried out at 550 nm and the linear range was from 1.13x10-2 to 7.88x10-2 mol L-1 (r = 0.9992). The limit of detection was 2.80 x 10-3 mol L-1. The proposed method was successfully applied to analysis of different commercial brands of pharmaceutical formulations and the results obtained by the proposed method were in good agreement with those obtained using the British Pharmacopoeia method.

Spectrophotometric determination of metronidazole through Schiff's base system using vanillin and PDAB reagents in pharmaceutical preparations

Two simple sensitive and reproducible spectrophotometric methods have been developed for the determination of metronidazole either in pure form or in their tablets. The proposed methods are based on the reduction of the nitro group to amino group of the drug. The reduction of metronidazole was carried out with zinc powder and 5 N hydrochloric acid at room temperature in methanol. The resulting amine was then subjected to a condensation reaction with aromatic aldehyde namely, vanillin and p-dimethyl amino benzaldehyde (PDAB) to yield yellow colored Schiff's bases. The formed Schiff's bases are quantified spectrophotometrically at their absorption maxima at 422 nm for vanillin and 494 nm for PDAB. Beer's law was obeyed in the concentration ranges 10 to 65 µg mL-1 and 5 to 40 µg mL-1 with a limit of detection (LOD) of 0.080 µg mL-1 and 0.090 µg mL-1 for vanillin and PDAB, respectively. The mean percentage recoveries were found to be 100.05 ± 0.37 and 99.01 ± 0.76 for the two methods respectively. The proposed methods were successfully applied to determine the metronidazole in their tablet formulations and the results compared favorably to that of reference methods. The proposed methods are recommended for quality control and routine analysis.

Determination of phenolic compounds and evaluation of antioxidant capacity of Campomanesia adamantium leaves

Five flavanones and three chalcones were isolated from Campomanesia adamantium Berg. (Myrtaceae) leaves. The contents of these compounds were determined by HPLC. The phenolic contents were also determined. The monitoring of the antioxidant activity was carried out by inhibition of peroxidation using the linoleic acid system and radical-scavenging (DPPH). The plants were collected from 4 distinct cities of the Mato Grosso do Sul State, Brazil. The different samples exhibited a range of 4.67-232.35 mg/g chalcones and 15.62-50.71 mg/g flavanones and phenolic contents of the 7.24-21.19 mg/g gallic acid. All extracts showed high antioxidant activity with a wide range of the radical-scavenging (DPPH) from 52.0 to 92.2 % and inhibition oxidation of linoleic acid from 14.6 to 94.2%.

Direct and simultaneous spectrophotometric determination of Ni (II) and Co (II) using diethanoldithiocarbamate as complexing agent

A direct spectrophotometric method for simultaneous determination of Co(II) and Ni(II), with diethanoldithiocarbamate (DEDC) as complexing agent, is proposed using the maximum absorption at 360 and 638 nm (Co(II)/DEDC) and 390 nm (Ni/DEDC). Adjusting the best metal/ligand ratio, supporting eletrolite, pH, and time of analysis, linear analytical curves from 1.0 10-6-4.0 10-4 for Co(II) in the presence of Ni 1.0 10-6-1.0 10-4 mol L-1 were observed. No further treatment or calculation processes have been necessary. Recoveries in different mixing ratios were of 99%. Interference of Fe(III), Cu(II), Zn(II) and Cd(II), and anions as NO3-, Cl-, ClO4-, citrate and phosphate has been evaluated. The method was applied to natural waters spiked with the cations.

Potentiometric determination of Minoxidil in topical use pharmaceutical samples

A potentiometric titration method for the determination of minoxidil based on its redox reaction with K2Cr2O7 is described. The best results were observed using 1.00 x 10-3 mol L-1 K2Cr2O7 and 1.00 x 10-2 mol L-1 minoxidil solutions, and the minoxidil as titrant in 2.00 mol L-1 H2SO4 medium. The method was applied to commercial samples and compared with the results from a chromatographic procedure. Recoveries from 97.4 to 98.7 % were observed depending on the sample. Comparison with the chromatographic procedure reveled agreement within 90% confidence level.

Spectrophotometric flow injection system for determination of Zn2+ in ophthalmic formulations using Alizarin red S

A spectrophotometric flow injection method for the determination of Zn(II) in ophthalmic formulations was developed. In this work, Zn(II) ion was complexed with Alizarin red S in borate buffer solution (pH 9.0) and the chromophore produced was monitored at 520 nm. The analytical curve was linear in the Zn(II) concentration range from 6.05 x 10-6 to 1.50 x 10-4 mol L-1 with a detection limit of 3.60 x 10-6 mol L-1. Recoveries ranged from 96.3 to 105 % and a relative standard deviation of 1.2 % (n = 10) for 5.5x10-5 mol L-1 Zn(II) reference solution were obtained. The sampling rate was 60 h-1 and the results obtained of Zn(II) in ophthalmic products using this procedure are in close agreement with those obtained using a comparative spectrophotometric procedure at 95 % confidence level.

A novel indicator reaction for the catalytic determination of V(V) at ppb levels by the kinetic spectrophotometric method

A novel sensitive and relatively selective kinetic method is presented for the determination of V(V), based on its catalytic effect on the oxidation reaction of Ponceau Xylydine by potassium bromate in presence of 5-sulfosalicylic acid (SSA) as activator. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of Ponceau Xylydine at 640 nm between 0.5 to 7 min (the fixed time method) in H3PO4 medium at 25ºC. The effect of various parameters such as concentrations of H3PO4, SSA, bromate and Ponceau Xylydine, temperature and ionic strength on the rate of net reaction were studied. The method is free from most interferences, especially from large amounts of V(IV). The decrease in absorbance is proportional to the concentration of V(V) over the entire concentration range tested (1-15 ng mL−1) with a detection limit of 0.46 ng mL-1 (according to statistical 3Sblank/k criterion) and a coefficient of variation (CV) of 1.8% (for ten replicate measurement at 95% confidence level). The proposed method suffers few interferences such as Cr(VI) and Hg(II) ions. The method was successfully applied to the determination of V(V) in tap water, drinking water, bottled mineral water samples and a certified standard reference material such as SRM-1640 with satisfactory results. The vanadium contents of water samples were also determined by FAAS for a comparison. The recovery of spiked vanadium(V) was found to be quantitative and the reproducibility was satisfactory. It was observed that the results of the SRM 1640 were in good agreement with the certified value.

Spectrophotometric determination of ofloxacin in pharmaceuticals and human urine

Three simple and sensitive spectrophotometric methods are described for the determination of ofloxacin (OFX) in pharmaceuticals and in spiked human urine. First and second methods are based on the measurement of absorbance of OFX in 0.1 M HCl at 293 nm (method A) and 0.1 M NaOH at 287 nm, respectively. The third method is based on the measurement of 2:1 complex formed between OFX 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 is obeyed over the ranges 0.63-12.5 using method A and method B, and 10-120 µg mL-1 using method C. The apparent molar absorptivity values are calculated to be 3.5 × 10(4), 2.76 × 10(4) and 2.51 × 10³ L mol-1cm-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 results obtained from human spiked urine are satisfactory and recovery values are in the range 95.5-106.6%.

Mathematical equation correction to spectral and transport interferences in high-resolution continuum source flame atomic absorption spectrometry: determination of lead in phosphoric acid

In this work, a new mathematical equation correction approach for overcoming spectral and transport interferences was proposed. The proposal was applied to eliminate spectral interference caused by PO molecules at the 217.0005 nm Pb line, and the transport interference caused by variations in phosphoric acid concentrations. Correction may be necessary at 217.0005 nm to account for the contribution of PO, since Atotal217.0005 nm = A Pb217.0005 nm + A PO217.0005 nm. This may be easily done by measuring other PO wavelengths (e.g. 217.0458 nm) and calculating the relative contribution of PO absorbance (A PO) to the total absorbance (Atotal) at 217.0005 nm: A Pb217.0005 nm = Atotal217.0005 nm - A PO217.0005 nm = Atotal217.0005 nm - k (A PO217.0458 nm). The correction factor k is calculated from slopes of calibration curves built up for phosphorous (P) standard solutions measured at 217.0005 and 217.0458 nm, i.e. k = (slope217.0005 nm/slope217.0458 nm). For wavelength integrated absorbance of 3 pixels, sample aspiration rate of 5.0 ml min-1, analytical curves in the 0.1 - 1.0 mg L-1 Pb range with linearity better than 0.9990 were consistently obtained. Calibration curves for P at 217.0005 and 217.0458 nm with linearity better than 0.998 were obtained. Relative standard deviations (RSD) of measurements (n = 12) in the range of 1.4 - 4.3% and 2.0 - 6.0% without and with mathematical equation correction approach were obtained respectively. The limit of detection calculated to analytical line at 217.0005 nm was 10 µg L-1 Pb. Recoveries for Pb spikes were in the 97.5 - 100% and 105 - 230% intervals with and without mathematical equation correction approach, respectively.

Sensitive spectrophotometric determination of lamotrigine in bulk drug and pharmaceutical formulations using bromocresol green

Two new, simple, rapid and reproducible spectrophotometric methods have been developed for the determination of lamotrigine (LMT) both in pure form and in its tablets. The first method (method A) is based on the formation of a colored ion-pair complex (1:1 drug/dye) of LMT with bromocresol green (BCG) at pH 5.02±0.01 and extraction of the complex into dichloromethane followed by the measurement of the yellow ion-pair complex at 410 nm. In the second (method B), the drug-dye ion-pair complex was dissolved in ethanolic potassium hydroxide and the resulting base form of the dye was measured at 620 nm. Beer's law was obeyed in the concentration range of 1.5-15 µg mL-1 and 0.5-5.0 µg mL-1 for method A and method B, respectively, and the corresponding molar absorptivity values are 1.6932 x 10(4) and 3.748 x 10(4) L mol-1cm-1. The Sandell sensitivity values are 0.0151 and 0.0068 µg cm-2 for method A and method B, respectively. The stoichiometry of the ion-pair complex formed between the dug and dye (1:1) was determined by Job's continuous variations method and the stability constant of the complex was also calculated. The proposed methods were applied successfully for the determination of drug in commercial tablets.

Determination of patulin in apple juice by HPLC using a simple and fast sample preparation method

The goal of this work was to develop a simple and rapid preparation method for patulin analysis in apple juice without previous clean-up. This method combined sonication and liquid extraction techniques and was used for determination of patulin in 37 commercial apple juices available on the market in the South of Brazil. The method performance characteristics were determined using a sample obtained in a local market fortified at five concentration levels of patulin and done in triplicates. The coefficient of variation for repeatability at the fortification level of 20.70µg.L-1 was 3.53 % and the recovery 94.63 %, respectively. The correlation coefficient was 0.9996 and agrees with the requirements for a linear analytical method value. The detection limit was 0.21µg.L-1 and the quantification limit 0.70 µg.L-1. Only three of the analyzed samples were upper the allowed level of 50.00 µg.L-1 recommended for the World Health Organization.

A pH optode based on thymol blue: application to determination of CO2 using flow injection analysis system

An optode based on thymol blue (TB), an acid-based indicator, has been constructed and evaluated as a detector in FIA system for CO2 determination. The dye was chemically immobilised on the surface of a bifurcated glass optical fibre bundle, using silanisation in organic media. In FIA system, hydrogen carbonate or carbonate samples are injected in a buffer carrier solution, and then are mixed with phosphoric acid solution to generate CO2, which diffuses through a PTFE membrane, in order to be collected in an acceptor carrier fluid, pumped towards to detection cell, in which the optode was adapted. The proposed system presents two linear response ranges, from 1.0 x 10-3 to 1.0 x 10-2 mol l-1, and from 2.0 x 10-2 to 0.10 mol l-1. The sampling frequency was 11 sample h-1, with good repeatability (R.S.D < 4 %, n = 10). In flow conditions the optode lifetime was 170 h. The system was applied in the analysis of commercial mineral water and the results obtained in the hydrogen carbonate determination did not differ significantly from those obtained by potentiometry, at a confidence level of 95 %.