Solid-phase extraction and simultaneous spectrophotometric determination of trace amounts of Co, Ni and Cu using partial least squares regression

A novel sensitive and simple method for rapid extraction, preconcentration and determination of cobalt, nickel and copper as their 1-(2-pyridilazo)-2-naphthol (PAN) complexes using polytetrafluoroethylene filter as solid phase and multivariate calibration of spectrophotometric data is presented. The analytical wavelengths of 400-700 nm were chosen and the experimental calibration matrix for partial least squares (PLS) was designed with 21 samples of 5.90-41.25, 0.30-29.35 and 0.64-41.30 ng ml⁻¹ for cobalt, nickel and copper, respectively. The cross-validation method was used for selecting the number of components. The root-mean-square errors of predictions (RMSEPs) were between 0.48 and 1.37 ng ml⁻¹. In this work we could reach preconcentration factors of 100 or even higher by using polytetrafluoroethylene as solid phase which is cheap and can be used in a wide range of pH, flow rates and for many times. The proposed method was successfully applied to the simultaneous determination of Co, Ni and Cu in tap and pit water samples.     

Solid-phase extraction and spectrophotometric determination of trace amounts of copper in water samples

A simple method for rapid and selective extraction, preconcentration and determination of copper as it's neocuproine complex by using octadecylsilica membrane disks and spectrophotometry is presented. Extraction efficiency and the influence of flow rates of sample solution and eluent, pH, amount of neocuproine and hydroxylamine hydrochloride, type and least amount of eluent for elution of copper complex from disks, break through volume and limit of detection were evaluated. Also the effects of various cationic interferences on percent recovery of copper were studied. Extraction efficiencies >99% were obtained by elution of the disks with minimal amount of solvent. The limit of detection of the proposed method is 0.12 ppb. The method was applied to the recovery and determination of copper in different water samples.     

Multisyringe chromatography (MSC) using a monolithic column for the determination of sulphonated azo dyes

A methodology based on multisyringe chromatography with a monolithic column was developed to determine three sulphonated azo textile dyes: Acid Yellow 23, Acid Yellow 9 and Acid Red 97. An ion pair reagent was needed because of the low affinity between the monolithic column and the anionic dyes. The proposed analytical system is simple, versatile and low-cost and has great flexibility in manifold configuration.The method was optimized through experimentation based on experimental design methodology. For this purpose two blocks of full factorial 2³ were done sequentially. In the first experimental plan, the factors studied were: the % of acetonitrile in organic phase, the % of H₂O in the mobile phase and the kind of ion pair reagent. In this stage, a simple configuration was used which has only one syringe for the mobile phase.After the first experimentation, we added a second syringe with a second mobile phase to the multisyringe module and performed a second full factorial 2³. The factors studied in this case were: the % of acetonitrile in the second mobile phase, the pH and the concentration of ion pair reagent in both mobile phases. After this design, the optimal conditions were selected for obtaining a good resolution between the peaks of yellow dyes (1.47) and the elution of red dye in less than 8 min.The methodology was validated by spiking different amounts of each dye in real water samples, specifically, tap water, well water and water from a biological wastewater lagoon.     

Electrochemical determination of trace amounts of environmentally important dyes

A number of dyes exhibit genotoxic or ecotoxic properties leading to the need for sensitive and selective methods for their determination. Because of the easy reducibility of dyes, modern polarographic and voltammetric methods (differential pulse polarography on classical dropping mercury electrode, differential pulse voltammetry on hanging mercury drop electrode or adsorptive stripping voltammetry) are suitable for the determination of trace amounts of these substances in the general environment in the vicinity of production plants. The scope and limitations of these methods is reviewed and optimum conditions for recently developed methods are summarized. It is shown that the sensitivity of newly developed polarographic and voltammetric methods is sufficient even for the most demanding applications and their selectivity can be increased by their combination with preliminary separation using thin layer chromatography or liquid extraction.     

Electrochemical determination of trace amounts of environmentally important dyes

A number of dyes exhibit genotoxic or ecotoxic properties leading to the need for sensitive and selective methods for their determination. Because of the easy reducibility of dyes, modern polarographic and voltammetric methods (differential pulse polarography on classical dropping mercury electrode, differential pulse voltammetry on hanging mercury drop electrode or adsorptive stripping voltammetry) are suitable for the determination of trace amounts of these substances in the general environment in the vicinity of production plants. The scope and limitations of these methods is reviewed and optimum conditions for recently developed methods are summarized. It is shown that the sensitivity of newly developed polarographic and voltammetric methods is sufficient even for the most demanding applications and their selectivity can be increased by their combination with preliminary separation using thin layer chromatography or liquid extraction.     

Solid-phase extraction, separation, and visible spectrophotometric determination of trace amounts of iron in water samples.

A simple and reliable method is presented for the rapid extraction, separation, preconcentration, and determination of iron as its bathophenanthroline complex by the use of octadecylsilica membrane disks and spectrophotometry. We evaluted extraction efficiency, the influence of sample matrix, type and optimum amount of extractant, flow rates of sample solution and eluent, pH, amounts of bathophenanthroline and hydroxylamine hydrochloride, breakthrough volume, and limit of detection. We also studied the effects of various cationic interferences on percent recovery of iron. Complete elution of the complex from disks was obtained with a minimal amount of solvent. The limit of detection of the proposed method is 0.080 ppb. The method was applied to the recovery and determination of iron in natural waters.     

Solid-phase spectrofluorimetric determination of acetylsalicylic acid and caffeine in pharmaceutical preparations using partial least-squares multivariate calibration

PLS-1, a variant of the partial least-squares algorithm was used for the solid-phase spectrofluorimetric determination of acetylsalicylic acid (ASA) and caffeine (CF) in pharmaceutical formulations. The method allows the simultaneous quantification of the analytes, as the closely overlapping spectral bands are efficiently solved. Sample preparation prior to analysis is not required. The calibration set consisted of 83 samples with 50-170 mg g⁻¹ ASA plus 5-20 mg g⁻¹ CF; another set of 25 samples was used for external validation. Agreement between predicted and experimental concentrations was fair (r = 0.987 and 0.974 for ASA and CF models). For both models, the prediction performance was evaluated in terms of the coefficient of variability (CV), relative predictive determination (RPD), and ratio error range (RER). The final PLS-1 models were used for the determination of ASA and CF in pharmaceutical formulations.     

Simultaneous determination of five commercial cationic dyes in stream waters using diatomite solid-phase extractant and multivariate calibration

A simple spectrophotometric method was developed for the simultaneous determination of five commercial cationic dyes at 2.0?8.5 μg L^?1 level after using diatomite as solid-phase extractant. The method is based on preconcentration of the five dyes on natural diatomite solid-phase extractant and on multivariate calibration using partial least squares method (PLS-1). Compared with commonly used chromatographic or electrophoretic methods the developed method is simple and sensitive. With enrichment factors between 89 and 96, diatomite outperformed zeolite and activated carbon for dyes preconcentration. Before preconcentration and using PLS-1 method, the cationic dyes were simultaneously analyzed with linear ranges of 0.18–4.5, 0.32–5.0, 0.23–4.5, 0.45–8.0 and 0.82–12.0 mg L^?1 for crystal violet, malachite green, methylene blue, safranine O, and thioflavin T, respectively. The detection limits of dyes were estimated using Lorber’s method and found to be within the range 43–245 μg L^?1. The proposed SPE/PLS-1 method was applied to spiked stream water samples with good accuracy (79–91%) and precision (RSD 1.8–7.3%) but with slightly lower enrichment factors (80–92).     

Solid-phase extraction using multiwalled carbon nanotubes and quinalizarin for preconcentration and determination of trace amounts of some heavy metals in food,water and environmental samples

A solid phase extraction procedure has been developed using multiwalled carbon nanotubes (MWCNTs) as a solid sorbent and quinalizarin [1,2,5,8-tetrahydroxyanthracene-9,10-dione] as a chelating agent for separation and preconcentration of trace amounts of some heavy metal ions, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) before their determination by flame atomic absorption spectroscopy (FAAS). The influences of the analytical parameters, including pH, amounts of quinalizarin and adsorbent, sample volume, elution conditions such as volume and concentration of eluent, flow rates of solution and matrix ions, were investigated for the optimum recoveries of the analyte ions. No interference effects were observed from the foreign metal ions. The preconcentration factor was 100. The detection limit (LOD) for the investigated metals at the optimal conditions were observed in the range of 0.30–0.65 μg L^?1. The relative standard deviation (RSDs), and the recoveries of standard addition for this method were lower than 5.0% and 96–102%, respectively. The new procedure was successfully applied to the determination of analytes in food, water and environmental samples with satisfactory results.     

Sequential injection lab-on-valve simultaneous spectrophotometric determination of trace amounts of copper and iron

A sequential injection (SI) method in a lab-on-valve (LOV) format for simultaneous spectrophotometric determination of copper and iron has been devised. The detection chemistry is based on the complex formation of 2-(5-bromo-2-pyridylazo)-5-[N-n-propyl-N-(3-sulfopropyl)amino]aniline (5-Br-PSAA) with copper(II) and/or iron(II) at pH 4.6. Copper(II) reacts with 5-Br-PSAA to form the complex which has an absorption maximum at 580 nm but iron(III) does not react. In the presence of a reducing agent only iron(II)-5-Br-PSAA complex is formed and detected at 558 nm. Under the optimum experimental conditions, the determinable ranges are 0.1-2 mg l⁻¹ for copper and 0.1-5 mg l⁻¹ for iron, respectively, with a sampling rate of 18 h⁻¹. The limits of detection are 50 μg l⁻¹ for copper and 25 μg l⁻¹ for iron. The relative standard deviations (n = 15) are 2% for 0.5 mg l⁻¹ copper and 1.8% for 0.5 mg l⁻¹ iron when determined in standard solutions. The recoveries range between 96 and 105% when determining 0.25-2 mg l⁻¹ of copper and 0.2-5 mg l⁻¹ of iron in artificial mixtures at copper/iron ratios of 1:10 to 5:1. The proposed SI-LOV method is successfully applied to the simultaneous determination of copper and iron in multi-element standard solution and in industrial wastewater samples.     

Analysis of electrochemical degradation products of sulphonated azo dyes using high-performance liquid chromatography/tandem mass spectrometry

Electrochemical treatment of wastewaters containing azo dyes in the textile industry is a promising approach for their degradation. The monitoring of the course of the decomposition of azo dyes in wastewaters is essential due to the environmental impact of their degradation products. In this work, aqueous solutions of a simple azo dye with a low molecular weight (C.I. Acid Yellow 9) and more complex commercial dye (C.I. Reactive Black 5) were electrochemically treated in a laboratory-scale electrolytic cell in sodium chloride or ammonium acetate as supporting electrolytes. Ion-pairing reversed-phase high-performance liquid chromatography coupled with negative-ion electrospray ionization mass spectrometry is applied for the identification of electrochemical degradation products. In addition to simple inorganic salts, the formation of aromatic degradation products obtained due to the cleavage of azo bonds and further degradation reactions is shown, as well as chlorination where sodium chloride is the supporting electrolyte. Degradation mechanisms are suggested for the treatment with sodium chloride as the supporting electrolyte.     

Solid-phase spectrophotometric determination of trace amounts of vanadium using 2,3-dichloro-6(3-carboxy-2- hydroxynaphthylazo)quinoxaline

Solid-phase spectrophotometry (SPS) has been applied to analysis for trace amounts of vanadium in several environmental water (potable and polluted), biological samples (human blood and urine), and soil samples. Vanadium was sorbed in a styrene-divinylbenzene-type anion-exchanger Dowex 1-X8 as a vanadium--2,3-dichloro-6(3-carboxy-2-hydroxynaphthylazo)quinoxaline. Resin phase absorbances at 606 and 800 nm were measured directly which allowed the determination of vanadium in the range 0.03-2.2 ng ml(-1) with a relative standard deviation (R.S.D.) of 1.4%. The comparison of the SPS method and the gallic acid persulphate method shows that the linearity, analytical sensitivity, and precision were better for the SPS method, and that the latter method has lower detection and quantification limits compared with the gallic acid persulphate method.     

Solid-phase extraction and determination of trace aroma and flavour components in cider by GC-MS

Summary Minor volatile compounds are responsible for the aromas of cider. A simple technique for the analysis of these components is described based on solid-liquid phase extraction followed by quantitation by gas chromatography-mass spectrometry (GC-MS). The method is quantitative for analysis of alcohols, esters, lactones, phenols, and medium and long chain-length fatty acid.     

Atomic absorption spectrometric determination of trace amounts of copper and zinc after simultaneous solid-phase extraction and preconcentration onto modified natrolite zeolite.

This work assesses the use of modified natural natrolite zeolite as an adsorptive material for the separation and preconcentration of trace amounts of ions. In this work we investigated the potential of modified natural natrolite zeolite for the simultaneous separation and preconcentration of trace amounts of copper and zinc ions. We have developed a simple, rapid, selective, sensitive and economical method for the simultaneous separation and preconcentration of trace amounts of copper and zinc in an aqueous medium using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) as an analytical reagent. The sorption was quantitative in the pH range 7.5 - 9.5, whereas quantitative desorption occurred instantaneously with 5.0 mL of 2 mol L(-1) nitric acid. Linearity was maintained between 0.05 - 6.0 microg mL(-1) for copper and 0.02 - 1.5 microg mL(-1) for zinc in the final solution. Ten replicate determinations of 1.0 microg mL(-1) copper and 0.5 microg mL(-1) zinc in a mixture gave mean absorbances of 0.1687 and 0.2788 with relative standard deviations of +/-1.2% and +/-1.3%, respectively. The detection limits were 0.03 ng mL(-1) for Cu(II) and 0.006 ng mL(-1) for Zn(II) in the original solution (3 sigma(bl)/m). Different parameters, such as the effect of the pH, flow rate, breakthrough volume and interference of a large number of anions and cations, were studied and the proposed method was used for the determination of these metal ions in water as well as standard samples (e.g. Nippon Keikinzoku Kogyo (NKK) CRM, No. 916 and No. 920 aluminum alloy, National Institute for Environment Studies (NIES) No. 1 pepperbush and NIES No. 2 pond sediment). The determination of these metal ions in standard samples showed that the proposed method has good accuracy (recovery > 97%).     

Spectrophotometric determination of organic dye mixtures by using multivariate calibration

The simultaneous determination of organic dye mixtures by using spectrophotometric methods is a difficult problem in analytical chemistry, due to spectral interferences. By using multivariate calibration methods such as partial least-squares regression (PLSR), it is possible to obtain a model adjusted to the concentration values of the mixtures used in the calibration stage. In this study, the calibration model is based on absorption spectra in the 350-650-nm range for a set of 16 different mixtures of reactive red 195, reactive yellow 145 and reactive orange 122 dyes, and made the determination of the dye concentrations possible in a validation set with significantly greater accuracy than the conventional univariate calibration method. By using the developed model it was possible to monitor the decolorization kinetic of one dye (reactive orange 122), when the mixture of the three dyes was previously submitted to an ozonation process.     

Simultaneous spectrophotometric determination of diuretics by using multivariate calibration methods

The wavelength range and number of factors used in partial least-squares (PLS) calibration for the resolution of the dihydralazine (DHZ)-hydrochlorothiazide (HCT) binary mixture and the dihydralazine-hydrochlorothiazide-reserpine ternary mixture were optimized in terms of the relative standard error (R.S.E.) and relative mean standard error (R.M.S.E.). Under the optimum conditions thus established, synthetic mixtures of the analytes can be resolved with errors and relative standard deviations (R.S.D) less than 4.5 and 1.0%, respectively. The ensuing method, which was validated by comparison with high performance liquid chromatography (HPLC), also gives good results with real samples (pharmaceutical preparations).     

Solid phase extraction and spectrophotometric determination of trace amounts of thiocyanate in real samples

A simple, selective and rapid method for solid phase extraction and spectrophotometric determination of thiocyanate using a manganese (III) tetrakis (p-sulfonatophenyl) porphyrin, [Mn (TPPS) OAC] bound to Amberlite IR-400 has been developed. The influence of pH, amount of solid phase, sample matrix, type and amount of eluting agent and flow rates i.e. variables affecting the efficiency of the extraction system were evaluated and conditions of the sample, eluting solution and active phase were optimized. The maximal capacity was found to be as 1.16 microg mL(-1) for 1200 mL. Thiocyanate ions can be eluted quantitatively with 8 mL 0.3 M ferric chloride. The enrichment factor was 150. The linear range of the determination is between 0.4-2.0 microg mL(-1) for preconcentration method with a limit of detection of 2.8 ng mL(-1). The method has been successfully applied for determination of trace amounts of thiocyanate in tap water, saliva sample and a synthetic mixture.     

Radiometric determination of trace amounts of zinc using liquid scintillation counting

A sensitive and selective radiometric method of substoichiometric isotope dilution analysis for the determination of trace amounts of zinc is described. The activity of (65)Zn used as a tracer in this method was measured by liquid scintillation counting and its counting efficiency was found to be 76+/-2.7%. The method is based on the extraction of the ion-association complex of zinc from thiocyanate medium at pH 7.9 using substoichiometric amount of Aliquat-336 in toluene. The method is sensitive to 20 ng of Zn(II) in an aqueous phase volume of up to 15 ml and its reliability was tested by applying it to a certified reference material-magnesium alloy and pharmaceutical samples.     

Spectrophotometric determination of some lanthanides using 3-hydroxy-2-naphthoic acid azo dyes

A comparative spectrophotometric study of the reaction of some substituted phenylazo-3-hydroxy-2-naphthoic acid derivatives with trivalent yttrium, lanthanum, praseodymium, neodymium, samarium, gadolinium, and erbium ions has shown that 1:1 and 1:2 complexes are formed at pH 7–8. Applications of these chelating agents for direct spectrophotometric determination of the lanthanons under investigation and also as indicators for spectrophotometric titration with EDTA were reported. Interference of various cations and anions in this method was also studied. Beer's law was obeyed for metal ions of up to 5–10 ppm.