Simultaneous Kinetic‐Potentiometric Determination of Hydrazine and Thiosemicarbazide by Partial Least Squares and Principle Component Regression Methods

Simultaneous determination of hydrazine (HZ) and thiosemicarbazide (TSC) by partial least squares (PLS) and principle component regression (PCR) was carried out based on kinetic data of novel potentiometry. The rate of chloride ion production in reaction of HZ and TSC with N‐chlorosuccinimide (NCS) was monitored by a chloride ion‐selective electrode. The experimental dada shows not only the good ability of ion‐selective electrodes (ISEs) as detectors for the direct determination of chloride ions but also for simultaneous kinetic‐potentiometric analysis using chemometrics methods. The methods are based on the difference observed in the production rate of chloride ions. The results show that simultaneous determination of HZ and TSC can be performed in their concentration ranges of 0.7‐20.0 and 0.5‐20.0 μg mL^?1, respectively. The total relative standard error for applying PLS and PCR methods to 9 synthetic samples in the concentration ranges of 0.8‐10 μg mL^?1 of TSC and 1.0‐12.0 μg mL^?1 of HZ was 4.62 and 4.98, respectively. The effects of certain foreign ions upon the reaction rate were determined for the assessment of the selectivity of the method. Both methods (PLS and PCR) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ and TSC in water samples.     

Simultaneous Kinetic‐Spectrophotometric Determination of Hydrazine and its Derivatives by Partial Least Squares and Principle Component Regression Methods

Simultaneous kinetic‐spectrophotometric determination of a ternary mixture of hydrazine (HZ) and its derivatives by principal component regression (PCR) and partial least squares (PLS) calibration is described. The methods were based on the difference observed in the reduction rate of iron(III) with HZ, thiosemicarbazide (TSCZ) and phenylhydrazine (PHZ) in the presence of 2,2′‐bipyridine (Bpy). The colored complex of [Fe(Bpy)₃]²⁺ was formed in sodium dodecyl sulfate (SDS) as micellar media, and then monitored at 520 nm. The results showed that simultaneous determination of HZ, TSCZ and PHZ could be performed in their concentration ranges of 1.0–70.0, 0.2–6.0 and 0.1–10.0 μg mL^?1, respectively. The root mean squares errors of prediction (RMSEP) of HZ, TSCZ and PHZ were 0.719, 0.164 and 0.105 (for PLS) 0.788, 0.166 and 0.993 (for PCR), respectively. Both methods (PCR and PLS) were validated using a set of synthetic sample mixtures and then applied for simultaneous determination of HZ, TSCZ and PHZ in water samples.     

Simultaneous spectrophotometric determination of iron and vanadium by H-point standard addition method and partial least squares regression in micellar medium

Simultaneous determination of total iron and vanadium by H-point standard addition method (HPSAM) and partial least squares (PLS) is described. Gallic acid (GA) in a cationic micellar solution of CTAB was used for determination of iron and vanadium in different oxidation states at pH 5. The presence of a micellar system enables total iron and vanadium to be determined with improved sensitivities. The total relative standard error for applying the PLS method to 15 synthetic samples in the ranges 0.20–15.00 μg ml⁻¹ iron and 0.20–8.00 μg ml⁻¹ vanadium was 2.2%. The results of applying the H-point standard addition method showed that iron and vanadium can be determined simultaneously with the concentration ratios of iron to vanadium from 10:1 to 1:20 in the mixed sample. Both HPSAM and PLS methods showed suitable abilities to resolve accurately overlapped absorption spectra of the compounds. Both proposed methods were successfully applied to the determination of Fe and V in several synthetic alloy solutions.     

Simultaneous determination of cobalt and palladium in micellar media using H-point standard addition method and partial least square regression

A simple, sensitive and selective spectrophotometric method for the simultaneous determination of Co(II) and Pd(II) using partial least square (PLS) calibration and H-point standard addition method is described. The method is based on the complex formation of Co(II) and Pd(II) with 4-(2-pyridylazo) resorcinol (PAR) in acidic media and in the presence of sodium dodecyl sulfate (SDS) as a micellizing agent. Acidic media and the presence of a micellar system improve selectivity and sensitivity, respectively. By applying PLS calibration, Co(II) and Pd(II) can be determined in the range of 0.20-2.0 and 0.40-4.0 microg ml(-1), respectively. The relative errors of prediction for the determination of Co(II) and Pd(II) in the 10 prediction samples were 1.69 and 1.72%, respectively. The results of applying H-point standard addition method show that Co(II) and Pd(II) can be determined simultaneously with concentration ratio of Co(II) to Pd(II) varying between 7:1 and 1:8 in the mixed samples. Both proposed methods (PLS and HPSAM) were applied to the determination of Co(II) and Pd(II) in several alloy solutions with satisfactory results.     

Simultaneous spectrophotometric determination of minoxidil and tretinoin by the H-point standard addition method and partial least squares

A simple, sensitive and selective spectrophotometric method for simultaneous determination of tretinoin and minoxidil using partial least square (PLS) calibration and H-point standard addition method (HPSAM) is described. The results of the H-point standard addition method show that minoxidil and tretinoin can be determined simultaneously with the concentration ratio of tretinoin to minoxidil varying from 2: 1 to 1: 33 in mixed samples. A partial least squares multivariate calibration method for the analysis of binary mixtures of tretinoin and minoxidil was also developed. The total relative standard error for applying the PLS method to eleven synthetic samples in the concentration range of 0–10 μg mL⁻¹ tretinoin and 0–32 μg mL⁻¹ minoxidil was 2.59 %. Both proposed methods (PLS and HPSAM) were also successfully applied in the determination of tretinoin and minoxidil in several synthetic pharmaceutical solutions.     

Application of H-Point standard addition method and multivariate calibration methods to the simultaneous kinetic-potentiometric determination of permanganate and dichromate

Simultaneous kinetic-potentiometric determination of binary mixture of permanganate (MnO₄ ^?) and dichromate (Cr₂O₇ ^2?) by H-point standard addition method (HPSAM), partial least squares (PLS) and principal component regression (PCR) is described. In this work, the difference between the rate of the oxidation reaction of Fe(II) to Fe(III) in the presence of MnO₄ ^? and Cr₂O₇ ^2? formed the basis of the method. The rate of the consumed fluoride ion for making the complex was detected by a fluoride ion selective electrode (FISE). The results show that the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? could be conducted in their concentration ranges of 0.5?C10.0 and 0.1?C20.0 ??g ml^?1, respectively. The total relative standard error (RSE) for applying the PLS and PCR methods to 9 synthetic samples was 5.30 and 3.17, respectively in the concentration range of MnO₄ ^?, and 3.30 and 2.04, respectively, in the concentration range of Cr₂O₇ ^2?. In order for the selectivity of the method to be assessed, we evaluated the effects of certain foreign ions upon the reaction rate. The proposed methods (HPSAM, PLS and PCR) were evaluated using a set of synthetic sample mixtures and then applied to the simultaneous determination of MnO₄ ^? and Cr₂O₇ ^2? in different water samples.     

Simultaneous Spectrophotometric Determination of Uranium and Thorium Using Arsenazo III by H‐Point Standard Addition Method and Partial Least Squares Regression

Simultaneous determination of uranium and thorium using arsenazo III as a chromogenic reagent at pH 1.70 by H‐point standard addition method (HPSAM) and partial least squares (PLS) calibration is described. Under optimum conditions, the simultaneous determinations of uranium and thorium by HPSAM were performed. The absorbencies at one pair of wavelengths, 649 and 669 nm, were monitored with the addition of standard solutions of uranium. The results of applying the HPSAM showed that uranium and thorium can be determined simultaneously with weight concentration ratios of uranium to thorium varying from 20:1 to 1:15 in the mixed sample. By multivariate calibration methods such as PLS, it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. In this study, the calibration model is based on absorption spectra in the 600–750 nm range for 25 different mixtures of uranium and thorium. Calibration matrices contained 0.10–21.00 and 0.25–18.5 μg mL^?1 of uranium and thorium, respectively. The RMSEP for uranium and thorium were 0.7400 and 0.7276, respectively. Both proposed methods (HPSAM and PLS) were also successfully applied to the determination of uranium and thorium in several synthetic and real matrix samples.     

Simultaneous determination of nickel and copper by H-point standard addition method-first-order derivative spectrophotometry in plant samples after separation and preconcentration on modified natural clinoptilolite as a new sorbent

For the simultaneous determination of nickel(ll) and copper(ll) in plant samples, a rapid and accurate method was developed. In this method, solid-phase extraction (SPE) and first-order derivative spectrophotometry (FDS) are combined, and the result is coupled with the H-point standard addition method (HPSAM). Compared with normal spectrophotometry, derivative spectrophotometry offers the advantages of increased selectivity and sensitivity. As there is no need for carrying out any pretreatment of the sample, the spectrophotometry method is easy, but because of a high detection limit, it is not so practical. In order to decrease the detection limit, it is suggested to combine spectrophotometry with a preconcentration method such as SPE. In the present work, after separation and preconcentration of Ni(ll) and Cu(ll) on modified clinoptilolite zeolite that is loaded with 2-[1-(2-hydroxy-5-sulforphenyl)-3-phenyl-5-formaza-no]-benzoic acid monosodium salt (zincon) as a selective chromogenic reagent, FDS-HPSAM, which is a simple and selective spectrophotometric method, has been applied for simultaneous determination of these ions. With optimum conditions, the detection limit in original solutions is 0.7 and 0.5 ng/mL, respectively, for nickel and copper. The linear concentration ranges in the proposed method for nickel and copper ions in original solutions are 1.1 to 3.0 x 10(3) and 0.9 to 2.0 x 10(3) ng/mL, respectively. The recommended procedure is applied to successful determination of Cu(ll) and Ni(ll) in standard and real samples.     

Spectrophotometric determination of ternary mixtures of thiamin, riboflavin and pyridoxal in pharmaceutical and human plasma by least-squares support vector machines.

Ternary mixtures of thiamin, riboflavin and pyridoxal have been simultaneously determined in synthetic and real samples by applications of spectrophotometric and least-squares support vector machines. The calibration graphs were linear in the ranges of 1.0 - 20.0, 1.0 - 10.0 and 1.0 - 20.0 microg ml(-1) with detection limits of 0.6, 0.5 and 0.7 microg ml(-1) for thiamin, riboflavin and pyridoxal, respectively. The experimental calibration matrix was designed with 21 mixtures of these chemicals. The concentrations were varied between calibration graph concentrations of vitamins. The simultaneous determination of these vitamin mixtures by using spectrophotometric methods is a difficult problem, due to spectral interferences. The partial least squares (PLS) modeling and least-squares support vector machines were used for the multivariate calibration of the spectrophotometric data. An excellent model was built using LS-SVM, with low prediction errors and superior performance in relation to PLS. The root mean square errors of prediction (RMSEP) for thiamin, riboflavin and pyridoxal with PLS and LS-SVM were 0.6926, 0.3755, 0.4322 and 0.0421, 0.0318, 0.0457, respectively. The proposed method was satisfactorily applied to the rapid simultaneous determination of thiamin, riboflavin and pyridoxal in commercial pharmaceutical preparations and human plasma samples.     

Simultaneous kinetic determination of beryllium and aluminium by spectrophotometric H-point standard addition method.

The H-point standard addition method (HPSAM), based on spectrophotometric measurements for simultaneous determination of beryllium and aluminium, is described. This method is based on the difference between their rates of reactions with Chrome Azurol S (CAS) in cetyltrimethylammonium bromide (CTAB) micellar media. The results showed that beryllium and aluminium could be determined simultaneously in the ranges of 10-200 and 10-300 ng mL(-1), respectively. Under working conditions, the proposed method was successfully applied to the simultaneous determination of beryllium and aluminium in environmental, geochemical and alloy samples.     

H-point standard addition method for the selective simultaneous determination of nickel and copper using 1-(2-pyridylazo)-2-naphthol in Tween 80 micellar media.

The H-point standard addition method (HPSAM) has been applied for the simultaneous determination of nickel and copper in trace levels, using 1-(2-pyridylazo)-2-naphthol (PAN) as a chromogenic reagent in aqueous Tween 80 micellar media. Under the optimum condition, the simultaneous determinations of nickel and copper by HPSAM were performed. The absorbances at one pair of wavelengths, 548 and 579 nm, were monitored with the addition of standard solutions of copper. The method is able to accurately determine copper-to-nickel ratios of 15:1 to 1:10 (Wt/Wt). The effects of diverse ions on the determination of nickel and copper to investigate the selectivity of the method were also studied. The recommended procedure was successfully applied to some water and alloy samples.     

Simultaneous Determination of Tyrosine and Histidine by Differential Pulse Cathodic Stripping Voltammetry Using H‐point Standard Addition Method in Tap and Seawater

H‐point standard addition method (HPSAM) has been applied for simultaneous determination of tyrosine and histidine in trace levels using copper ions by adsorptive cathodic stripping voltammetry. The amino acids‐Cu(II) complexes were accumulated onto the surface of a hanging mercury drop electrode for 40 s. The reduction peaks of preconcentrated complexes were used for simultaneous determination of amino acids in the range 8.0–180 and 30–1100 nM for tyrosine and histidine respectively. The effect of various parameters such as pH, concentration of copper, accumulation time and scan rate on the selectivity were studied. Under the optimized conditions the method was successfully applied for determination of tyrosine and histidine in synthetic and real samples.     

A chemometric study of the simultaneous determination of calcium and magnesium in natural waters

A method for the simultaneous spectrophotometric determination of calcium and magnesium in mineral waters with an FIA system is tested. The method is based on the reaction between the analytes and arsenazo(III) at pH 8.5. The calculations of the amounts of both analytes in the samples are carried out with the H-point standard addition method (HPSAM) for ternary mixtures, and with a partial least squares (PLS) model after a proper variable selection. The results obtained for the determination of calcium were comparable using both methods. The employment of the HPSAM brings to our attention the influence of the calcium concentration in the sample to the development of the reaction between magnesium and arsenazo(III). HPSAM also permits to estimate the concentration of magnesium in the samples.     

Simultaneous derivative spectrophotometric determination of zinc and cadmium with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in the presence of cetylpyridinium chloride.

A selective and sensitive derivative photometric method has been developed for the determination of trace amounts of Zn2+ with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol in the presence of cetylpyridinium chloride, a cationic surfactant. The molar-absorption coefficient and analytical sensitivity of the 1:2 complex at 554 nm are 1.19 x 10(5) L mol(-1) cm(-1) and 0.56 ng mL(-1), respectively. The detection limit is 1.96 x 10(-2) ng mL(-1) and Beer's law is valid in the 0.02-0.66 microg mL(-1) range of Zn2+. The developed derivative procedure, using the zero-crossing measurement approach, is applied for the rapid and selective simultaneous determination of Zn2+ and Cd2+ in the range of 0.06-0.66 and 0.20-1.60 microg mL(-1), respectively. Complex matrices, including reference materials, environmental and biological samples and synthetic mixtures, have been successfully analyzed for trace amounts of the two metal ions.     

Simultaneous spectrophotometric determination of levodopa and carbidopa in pharmaceutical formulations and water samples by using mean centering of ratio spectra and H-point standard addition methods

Two spectrophotometric methods are described for the simultaneous determination of binary mixtures of carbidopa and levodopa in pharmaceutical formulations, without prior separation steps, using the mean centering of ratio spectra and H-point standard addition methods (HPSAM). The methods are based on the difference in the absorption spectra for the products of the reaction of carbidopa and levodopa with 4-aminobenzoic acid in the presence of periodate ion at pH 4.0. The methods allow rapid and accurate determination of carbidopa and levodopa. The results showed that the methods were capable to simultaneous determination of 0.30-10.00 microg ml(-1) and 0.50-10.00 microg ml(-1) each of carbidopa and levodopa. The proposed methods were successfully applied to the simultaneous determination of carbidopa and levodopa in pharmaceutical samples.     

Simultaneous spectrophotometric determination of mercury and palladium with Thio-Michler's Ketone using partial least squares regression and orthogonal signal correction

A simple, novel and sensitive spectrophotometric method was described for simultaneous determination of mercury and palladium. The method is based on the complex formation of mercury and palladium with Thio-Michler's Ketone (TMK) at pH 3.5. All factors affecting on the sensitivity were optimized and the linear dynamic range for determination of mercury and palladium found. The simultaneous determination of mercury and palladium mixtures by using spectrophotometric method is a difficult problem, due to spectral interferences. By multivariate calibration methods such as partial least squares (PLS), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration range. Orthogonal signal correction (OSC) is a preprocessing technique used for removing the information unrelated to the target variables based on constrained principal component analysis. OSC is a suitable preprocessing method for PLS calibration of mixtures without loss of prediction capacity using spectrophotometric method. In this study, the calibration model is based on absorption spectra in the 360-660 nm range for 25 different mixtures of mercury and palladium. Calibration matrices were containing 0.025-1.60 and 0.05-0.50 microg mL(-1) of mercury and palladium, respectively. The RMSEP for mercury and palladium with OSC and without OSC were 0.013, 0.006 and 0.048, 0.030, respectively. This procedure allows the simultaneous determination of mercury and palladium in synthetic and real matrix samples good reliability of the determination.     

H-Point Standard Addition Method for Simultaneous Determination of Palladium and Cobalt

The H-point standard addition method (HPSAM) has been applied to simultaneous determination of palladium and cobalt at trace levels, using 1-(2-pyridylazo)-2-naphthol (PAN) as a chromogenic reagent. Palladium and cobalt at neutral pH levels form green colored neutral complexes with PAN which are soluble in aqueous sodium dodecylsulfate (SDS) micellar media and can be monitored spectrophotometrically. Simultaneous determination of cobalt and palladium by HPSAM were performed spectrophotometrically and under optimum conditions. Absorbances at the two pairs of wavelengths, 597 and 650 nm or 566 and 612nm, were monitored while adding standard solutions of cobalt or palladium, respectively. The method is able to accurately determine a cobalt/palladium ratio of between 5:1 and 1:30 (wt/wt). The accuracy and reproducibility of the determination method for various known amounts of cobalt and palladium in their binary mixtures were evaluated. The effects of diverse ions on the determination of cobalt and palladium to investigate the selectivity of the method were also studied. The recommended procedure was applied to real water samples and synthetic sample solutions.     

Simultaneous determination of potassium clavulanate and cefixime in synthetic mixtures by high-performance liquid chromatography

A simple, precise, and sensitive high-performance liquid chromatographic method was developed and validated for the simultaneous determination of potassium clavulanate and cefixime in synthetic mixture form. The analytes were separated on a C18 column by using 0.03 M disodium hydrogen phosphate buffer (pH 6.5)-methanol (84 + 16, v/v) as the mobile phase with detection at 220 nm. The method exhibited high sensitivity and good linearity in the concentration ranges of 12.5-62.5 and 20-100 microg/mL for potassium clavulanate and cefixime, respectively. The total run time for the 2 components was <8 min, and the average recovery was >101.5% with a relative standard deviation of <1.0%. The proposed method was validated according to guidelines of the International Conference on Harmonization by evaluation of linearity, recovery, selectivity, robustness, limits of detection and quantitation, and within- and between-day precision. The results obtained for the synthetic mixture show that the method is highly precise and accurate for the simultaneous determination of potassium clavulanate and cefixime.     

Liquid chromatographic and spectrophotometric determination of diflucortolone valerate and isoconazole nitrate in creams

A new RP-LC method and two new spectrophotometric methods, principal component regression (PCR) and first derivative spectrophotometry, are proposed for simultaneous determination of diflucortolone valerate (DIF) and isoconazole nitrate (ISO) in cream formulations. An isocratic system consisting of an ACE C18 column and a mobile phase composed of methanol-water (95 + 5, v/v) was used for the optimal chromatographic separation. In PCR, the concentration data matrix was prepared by using synthetic mixtures containing these drugs in methanol-water (3 + 1, v/v). The absorbance data matrix corresponding to the concentration data matrix was obtained by measuring the absorbances at 29 wavelengths in the range of 242-298 nm for DIF and ISO in the zero-order spectra of their combinations. In first derivative spectrophotometry, dA/dlambda values were measured at 247.8 nm for DIF and at 240.2 nm for ISO in first derivative spectra of the solution of DIF and ISO in methanol-water (3 + 1, v/v). The linear ranges were 4.00-48.0 microg/mL for DIF and 50.0-400 microg/mL for ISO in the LC method, and 2.40-40.0 microg/mL for DIF and 60.0-260 microg/mL for ISO in the PCR and first derivative spectrophotometric methods. These methods were validated by analyzing synthetic mixtures. These three methods were successfully applied to two pharmaceutical cream preparations.     

Liquid chromatographic method for the simultaneous determination of eprosartan and hydrochlorothiazide in tablets and human plasma

A new, specific, and sensitive RP-HPLC method was developed for the simultaneous determination of eprosartan (EPR) and hydrochlorothiazide (HCT). Good chromatographic separation was achieved using a 250 x 4.6 mm id, 5 microm particle size Symmetry C18 column. The mobile phase acetonitrile-0.1 M phosphate buffer (35+65, v/v), pH 4.5, was pumped at a flow rate of 1 mL/min, with UV detection at 275 nm. The method showed good linearity in the ranges of 0.5-50 and 0.1-10 microg/mL, with LOD of 0.06 and 0.02 microg/mL and LOQ of 0.20 and 0.08 microg/mL for EPR and HCT, respectively. The proposed method was successfully applied for the analysis of the studied drugs in their synthetic mixture and co-formulated tablets. The method was further extended to the in vitro and in vivo determination of the two drugs in spiked and real human plasma. Interference likely to be encountered from the co-administered drugs was studied.