Simultaneous determination of pH, chloride and nickel in electroplating baths using sequential injection analysis

A sequential injection analysis system was developed to quantify pH, chloride and nickel in electrolytic baths, in the ranges 1-5 pH units, and 0.1-1.0 and 0.1-1.6 mol l⁻¹, respectively. To enable pH and chloride determination, potentiometric detection with two ion-selective electrodes in a tubular configuration was used. Nickel concentrations were assessed using colorimetric detection at 660 nm. pH was determined prior to nickel determination and just after sample injection (500 μl) into a 0.025 mol l⁻¹ phosphate buffer carrier stream at pH 6.3 and a 9.10 ml min⁻¹ flow rate. For chloride determination, on-line dialysis through a cellulose membrane was used to enable sample dilution and matrix separation. A 2⁵⁻¹ fractional factorial design based on the carrier solution composition and the levels of the hydrodynamic parameters was used for system optimization. At the optimized settings a sampling rate of 40 samples h⁻¹ was attained, with precision and accuracy statistically indistinguishable from those achieved with conventional procedures.     

Flow injection analysis: Part VIII. Determination of glucose in blood serum with glucose dehydrogenase

The flow injection principle is used for enzymatic determination of glucose in blood serum with glucose dehydrogenase. Methods based on single-point determination on deproteinized serum samples, single-point determination comprising continuous flow dialysis, and two-point kinetic assay, are described and discussed. Special consideration is given to optimizing the flow parameters in order to minimize reagent consumption, yet to maintain a high sampling rate. Thus, for the single-point determination, a sampling rate of 120 samples per h was achieved at an expenditure of 3.12 g-units of glucose dehydrogenase per sample.     

A novel flow-through microdialysis separation unit with integrated differential potentiometric detection for the determination of chloride in soil samples

In this paper, a novel and miniaturised flow-through dialysis-based potentiometric detector is proposed for the determination of chloride in soil samples. The outstanding feature of the designed unit is the integration of analyte isolation from matrix constituents via membrane separation with differential potentiometric detection. Two identical tubular all-solid-state Ag/AgCl ion selective electrodes (ISEs) were assembled respectively at the inlet and outlet of the acceptor channel. Thus, as a consequence of the continuous forward flow of solutions through the microdialyser the outlet tube becomes the indicator electrode for the analyte diffusate while the nested tube at the entrance serves as reference electrode. The effect of physical and chemical parameters on the mass transfer efficiency is discussed in detail and compared with conventional configurations involving downstream detection. The membrane morphology for optimum dialysis performance is also thoroughly evaluated in terms of thickness, porosity and molecular weight cut-off. Higher dialysis efficiency and reduction of dilution factors up to a value of 5 were attained by halting the recipient stream temporarily. Under the optimised conditions, a dynamic working range of 5-5000 mg l(-1) chloride with a linear interval between 10 and 5000 mg l(-1) (for 1 min stopped-flow and 200 microl sample volume), a repeatability better than 3.0% and a 3 sigma(blank) detection limit of 1.2 mg l(-1) chloride were the analytical figures of merit of the devised configuration. The potentiometric dialysis sensor features extreme tolerance to high molecular weight interfering matrix compounds (> 1000 mg l(-1) humic acid), which makes it specially suited for the interference-free potentiometric determination of chloride in soils containing high levels of organic matter. The miniature size, low-reagent consumption and high analytical throughput (25-40 h(-1)) also warrant its applicability to in-field monitoring or screening schemes. The accuracy of the measurements was assessed using ion-chromatography as an external reference method. A mean t-test showed no statistical differences between both methodologies at the 95% confidence level.     

Automated dilution in flow injection analysis with double on-line dialysis. A system for the determination of chloride in industrial effluents and plating bath solutions

Summary An automated on-line system for the determination of chloride in industrial effluents and plating bath solutions based on the concept of flow injection analysis is described. Samples with a very high chloride content up to 6 g/100 ml (60 g/l) are analysed by using an automated in-manifold double on-line dialysis technique. The sampling rate is 100 samples per hour. The method is suitable for the analysis of chloride with a relative standard deviation of better than 0.8%. The measurement is based on the red-coloured iron thiocyanate complex.     

Simultaneous flow-injection analysis of three components with on-line dialyzers in series. Determination of sodium, potassium and chloride in blood serum

A fast and reliable fully automated three-component flow-injection procedure for the simultaneous determination of sodium, potassium and chloride in blood serum is described. A single sample injection (100-mul blood serum) is directed to two different channels by using two dialyzers in series. To avoid interferences and blocking of the fine jet of the atomizer, sodium and potassium are dialyzed by the first dialyzer before measurement by AES with a flame photometer. A second dialyzer in series is used to eliminate interferences and for automated dilution before the dialyzed chloride is measured by UV/VIS spectrophotometry at 485 nm. The results obtained for the sodium, potassium and chloride in blood serum at a sampling rate of 106 samples per hour compared well with data obtained by standard methods.     

Tandem on-line dialysis with a double and single dialyser in flow injection dialysis — Simultaneous determination of calcium and high chloride in industrial effluents

The on-line double membrane dialyser described previously was coupled in series to a single dialyser in the manifold of a flow injection system to include the determination of samples with a high chloride content simultaneously with calcium in industrial effluents from a single sample injection. 50 μl of industrial effluent samples are injected into a carrier stream and are simultaneously dialysed in the double on-line dialyser for chloride and calcium. The dialysed chloride sample zones are further directed to a second dialyser that is incorporated in series with the first dialyser. This enables laboratories to determine samples with a very high chloride content up to 60 g/l simultaneously with calcium by using an automated tandem on-line dialysis technique. The fast and reliable fully automated two-component flow injection procedure operated at a sampling frequency of 90 samples per hour and the results obtained for chloride and calcium in industrial effluents compared well with those obtained by standard methods.     

Determination of chloride, sulfate and nitrate in groundwater samples by ion chromatography

Groundwater is a significant source of water for both domestic and agricultural use in some regions of the Maracaibo lake basin in Venezuela. Chemically suppressed ion chromatography with a Dionex Model 2000i/sp, lonpac AS11, ASRS-I system was used for the analysis of major inorganic anions in groundwater samples. About 50 samples of groundwater, taken over several months in three different locations, were analyzed after filtration and sometimes dilution. In all the samples, the separation between the peaks of chloride, nitrate and sulfate showed good resolution (symmetrical peaks, not broadened), even when the chloride concentration was as high as 850 mg l(-1) and reproducibility (RSD) was -2%. No other peaks (i.e. fluoride, nitrite and phosphate) were observed at selected experimental conditions. With the chosen parameters, the method is well-suited for the routine determination of these anions in groundwater samples, giving results in less than 10 min (including column clean-up). With an appropriate combination of detector output ranges (300 and 1,000 microS), only one set of calibration solutions was needed for all samples. In the Sierra Maestra location, the groundwater samples, were significantly different in total anion levels. Mean total chloride plus sulfate concentrations (approximately 525 mg l(-1)) were about 100 times higher than in the other sites. Some water quality implications of these groundwater samples are also discussed.     

Ion chromatographic determination of some organic acids, chloride and phosphate in coffee and tea

An ion chromatographic method for the simultaneous determination of organic acids and inorganic ions is described. Acetic, malic, ascorbic, citric, malic and succinic acids, chloride and phosphate were determined in coffee and tea samples. The separation is performed on an anion-exchange column operated at 40 °C within 25 min by an isocratic elution with 0.6 mM aqueous potassium hydrogenphthalate (pH 4.0) solution containing 4% (v/v) acetonitrile as eluent and determination by conductivity detection. The method does not need a special sample treatment and was successfully applied to the analysis of black, green and oolong tea samples. Also, green and roasted coffee samples from the varieties arabica and robusta were analyzed.     

Precise method for the measurement of catalase activity in honey

An improved method is reported for the determination of catalase activity in honey. We tested different dialysis membranes, dialysis fluid compositions and amounts, dialysis temperatures, sample amounts, and dialysis times. The best results were obtained by dialysis of 7.50 g sample in a cellulose dialysis sack, using two 3 L portions of 0.015 M sodium phosphate buffer (pH 7.0) as the dialysis fluid at 4 degrees C for 22 h. As in previous methods, catalase activity was determined on the basis of the rate of disappearance of the substrate, H202, with the H202 determined spectrophotometrically at 400 nm in an assay system containing o-dianisidine and peroxidase. Trials indicated that the best solvent for the o-dianisidine was 0.2 M sodium phosphate buffer, pH 6.1; the best starting H202 concentration was 3 mM; the best HCl concentration for stopping the reaction was 6 N; and the best sample volume for catalase measurement was 7.0 mL. Precision values (relative standard deviations for analyses of 10 subsamples of each of 3 samples) were high, ranging from 0.48% for samples with high catalase activity to 1.98% for samples with low catalase activity.     

Quality Control of Industrial Fluorinated Inorganic Acids by Ion Chromatography

A simple ion chromatographic method has been applied to the determination of anionic impurities chloride, bromide, nitrate, and sulfate in hexafluorotitanic acid and hexafluorozirconic acid samples. Industrial samples analyzed may contain high levels of fluorinated species at pH values lower than 1.0, which represents a handicap for the instrumental analysis of these matrixes. Up to now, these samples have been analyzed by chemical methods, which have interferences, involving detection of the final point in chloride determination by volumetry and coprecipitation in sulfate determination by gravimetry. The optimization of the method was carried out using industrial samples. In order to obtain the best chromatographic resolution, the dilution factor of the samples, flow rate, and eluent concentration were studied using isocratic elution. The ion chromatographic method was suitable for the determination of anionic impurities in acidic matrixes, except for chloride in hexafluorozirconic acid. The analytes were separated in hexafluorotitanic acid and hexafluorozirconic acid, without using any sample treatment apart from dilution, with good linearity with correlation coefficients higher than 0.99 and inter- and intra-day repeatability lower than 15 percent, expressed in terms of the relative standard deviation.     

Evaluation of a reagent-injection flow injection technique for sample background absorption elimination: determination of chloride in cigarettes

The applicability of reagent-injection flow injection (FI) technique in elimination of background absorption was evaluated by using the FI determination of water-soluble chloride in cigarettes, based on the mercury thiocyanate method, as a model. Some parameters of the proposed reagent-injection FI method were optimized and the proposed procedure had a linear range of 0-7.5 mg l(-1) Cl, a detection limit of 0.02 mg l(-1) Cl, a sampling rate of 60 h(-1) and a relative standard deviation of 0.1% at 5 mg l(-1) Cl. Eight cigarette samples were analyzed by this proposed reagent-injection FI method and the referential membrane dialysis FI procedure. The relative errors were <4.3%, and paired t-test shows that there are no significant differences between these two methods. As no dialysis unit was needed, the reagent-injection FI method has much simpler flow system than the existed CFA and FI methods.     

A new microdialysis unit for flow injection analysis

Summary A new dialysis unit optimized for FIA is described. It contains both a dialysis cell and a manifold for reagent addition. Both parts are included in the same module. For test purposes, a colorimetric determination of chloride — both with and without dialysis — has been carried out. For the conditions given in the experimental setup, the dialyzing efficiency was ca. 11 %. The dilution loss factor, i.e., dilution caused by the dialysis cell, was ca. 9. The dispersion coefficient (D) for the manifold — excluding the dispersion caused by dialysis — was calculated to 2.2. The analytical performance expressed as repeatability is around 1.3% r.s.d., and the sample throughput is around 80 – 90 samples/h. Potential application areas cover a wide range of possibilities, e.g., foods and feeds, dairy products, soils and plants, water and waste water analysis and fermentation products.

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Neue Mikrodialyseeinheit für die Fließinjektionsanalyse

     

On-line flow injection solid sample introduction, leaching and potentiometric determination of fluoride in phosphate rock

A flow injection method with on-line solid sample dissolution was developed for the determination of fluoride in phosphate rock. The fluoride was selectively leached (98-102.4 % recovery) from a 50-mg powdered phosphate rock sample with 0.50 M citric acid. Using the zone sampling technique the fluoride in the buffered leachate was determined by injecting 87 μL into the carrier stream using a fluoride ion-selective electrode detector. The sensing element of the electrode was housed in a home-made sleeve-type flow-through cell. On-line solid sample digestion with 0.50 M citric acid at 55 °C resulted in minimum dissolution of interfering iron and aluminum ions with improved accuracy and calibration linearity. The incorporation of relatively high level of fluoride in the carrier stream (40 μg mL⁻¹) facilitated the determination of high levels of fluoride in phosphate rock (up to 4.1%) with out the need for excessive on-line dilution.The optimized flow system was applied for the determination of fluoride in phosphate rocks samples and a reference material at a rate of nine samples per hour with a relative standard deviation (n = 5) of 2.95-4.0 %. Comparison of the proposed flow injection method with the standard method, which involves steam distillation from sulfuric acid solution and manual titration with thorium nitrate, showed no evidence of bias at the 95% confidence level.     

Potential of CE for the determination of inorganic and acidic anions in cyanoacrylate adhesives

In this work, a CZE method with indirect UV detection was developed for the simultaneous determination of the inorganic and acidic anions, chloride, sulfate, nitrate, fluoride, formate, phosphate, diethylphosphate, methyl sulfonate, cyanoacetate, and methacrylate present in cyanoacrylate adhesives. Chromate was employed as the probe ion, and the EOF was reversed by incorporating CTAB into BGE. Detection limits of 0.7-4.6 microg/mL were obtained for all the anions studied. The CE method developed is a significant improvement on traditionally used chromatographic methods such as ion chromatography, as it resulted in shorter analysis times with enhanced separation efficiencies. This method was successfully employed for the analysis of inorganic and acidic anions in cyanoacrylate adhesive samples.     

Differential pulse anodic stripping voltammetric determination of ziram (a dithiocarbamate fungicide)

A d.c. polarographic technique has been used previously for the determination of the pesticide, ziram, in aqueous samples, this paper reports differential pulse anodic stripping voltammetric determination of ziram zinc in rice samples using a static mercury drop electrode. The procedure developed distinguishes inorganic zinc and ziram zinc in sodium acetate-sodium chloride media. The procedure developed is suitable for the determination of concentrations as low as 10 ppb of ziram with a precision of 2.1% for five successive determinations of 150 ppb of ziram.     

Flow injection dialysis for the determination of anions using ion chromatography

Flow injection dialysis (FID) coupling with ion chromatography (IC) is proposed for simultaneous determination of some anions (bromide, chloride, fluoride, nitrate, nitrite, phosphate and sulfate). A standard or sample containing the anions is injected into a donor stream of a mixture (0.022 M Na(2)CO(3) and 0.028 M NaHCO(3)) flowing into a dialysis cell. The bolus of the dialysate containing the anions, in the acceptor stream of water, flows to the IC injection valve where a portion of the bolus is injected into the IC and analysed under normal IC conditions, with a conductivity detector. FID provides on-line separation and dilution of the analytes from matrix especially from some species such as proteins, surfactant, particulates which may cause damage to the IC columns. Prolongation of life-time of the IC columns is an additional advantage to others which will be discussed. On-line dialysis-IC was also investigated.     

Determination of aflatoxins in Chinese medicinal herbs by high-performance liquid chromatography using immunoaffinity column cleanup Improvement of recovery

Although analytical methods are available for the determination of aflatoxins in medicinal herbs, none of them can be applied satisfactorily to all sample matrices. The difficulty arises from the complex chemical composition of the herbs. Recovery is generally low by using immunoaffinity column cleanup due to the acidity of the water extractive leading to a weakened binding affinity. As a solvent for dilution and neutralization, phosphate buffer saline is useful for certain herbs but not for others that have high acidity. The problem can be solved by using 0.1 M phosphate buffer, which has a higher buffering capacity and eliminates sodium chloride. The modified method was validated by the analysis of a certified reference material and shown to be useful for the determination of aflatoxins in herbal samples of high acidity.     

Flow injection analysis of high chloride levels in electroplating baths using on-line dialysis and potentiometric detection

A method for the flow injection analysis (FIA) of high concentrations of chloride in electroplating baths using potentiometric detection is proposed. The system includes a unit of dialysis to promote dilution of samples and a tubular electrode with an homogeneous crystalline membrane as detector. The system was optimized in order to analyse samples within a broad range of concentrations and at high levels of chloride, thereby making pretreatment of the samples unnecessary. It results in a simple manifold applicable over the 4.0×10^–2 and 3.0 mol L^–1 range with a throughput of about 30 samples/h. Seven different plating bath samples were analysed by the proposed method and the quality of the results compared with those obtained by the conventional procedure. Satisfactory agreement was observed.     

Determination of very low levels of dissolved mercury(II) and methylmercury in river waters by continuous flow with on-line UV decomposition and cold-vapor atomic fluorescence spectrometry after pre-concentration on a silica gel-2-mercaptobenzimidazol sorbent

A new, simple and sensitive method for the simultaneous determination of mercury(II) and methylmercury chloride at sub-ng l⁻¹ levels in river waters is described. Inorganic and organic mercury were preconcentrated from fresh water samples simultaneously on a laboratory-made column containing 2-mercaptobenzimidazol loaded on silica gel and then quantitatively eluted with 0.05 M KCN solution and 2.0 M HCl to desorp inorganic and methylmercury species, respectively. After irradiation with an intensive UV source, MeHg⁺ was decomposed and mercury vapours were generated from inorganic and organic mercury using an acidic SnCl₂ solution in a continuous flow system and were subsequently determined with a cold vapour atomic fluorescence (CV-AFS) spectrometer. Detection limits (3σ) were 0.07 and 0.05 ng l⁻¹ (as Hg) for mercury(II) chloride and methylmercury chloride, respectively. Relative standard deviations of method (%R.S.D.) were 8.8 and 10 for inorganic and organomercuric species in the river water, respectively. The analysis of real samples, taken from different rivers, showed that inorganic mercury levels ranged from 4.0±0.6 to 12±1 ng l⁻¹ (as Hg and 95% confidence limit) and methylmercury levels at 0.2±0.02 ng l⁻¹(as Hg).