Bulk Acoustic Wave Sensor for Non-suppressed Ion Chromatographic Determination of Nitrate and Other Inorganic Anions in Vegetables

Abstract

A new type of bulk acoustic wave sensing device based on a conductivity-bulk acoustic wave frequency response is applied in ion chromatography to determine nitrate and other inorganic ions in vegetables. The present method has the advantages in its rapidity, simplicity, sensitivity and accuracy. Detection limits (peak=3[sgrave]) are obtained for NO₃ ^?, Cl^?, NO₂ ^?, H₂PO₄ ^? and SO₄ ^2? at concentrations of 1, 0.6, 1, 7 and 3 ng (on column), respectively. Neither derivatization nor a clean-up step is necessary besides filtration. For the IC analysis, the analytical column is a Shim-pack IC AI column, and the eluent is 2.0 mM phthalic acid solution with pH 4.0. A comparison of IC-SBAW with conventional IC is made. The method allows the simultaneous determination of nitrate and other inorganic ion levels in vegetables.     

Novel Flow Injection/Potentiometric Measurement of Slightly Soluble Salts in Small Volumes: Determination of Solubility Product Constants of Some Silver Salts

Abstract

The flow injection technique is shown to provide fast, reliable and sensitive determination of solubility product constants of silver acetate, silver sulfate, silver oxide, silver bromate and silver chloride in microliter volume samples. Potentiometric detection using electrodes of the first kind and second kind was used for measuring silver ions and chloride ions, respectively. The solubilities were determined from measurement of the silver ion concentration in the saturated solutions. In the case of silver chloride, the solubility product constant was calculated from the concentrations corresponding to the intersection of the silver ion calibration curve and the chloride ion calibration curve, i.e., where the potentials of the two electrodes are equal. Tenth-molar sodium nitrate was used for all solutions to maintain constant ionic strength. At a concentration range of 1.00 × 10^?2 ? 1.00 × 10^?5 M silver, and 1.00 × 10^?2 ? 1.00 × 10^?4 M chloride, a Nernstian response of 60 m V per decade was obtained. At a sampling rate of 50–70 samples per hour, with 50 μl sample injections, high reproducibility of measurements was achieved, with a -pL 2% relative standard deviation in measured concentrations. The scope and applications of this system are discussed.     

Interference of Humic Substances in the Spectrophotometric Determination of Bromate by Phenothiazines in Natural Waters

Abstract

The spectrophotometric method of bromate (BrO₃ ^?) determination by phenothiazines was applied to natural water samples and the interferences due to the presence of inorganic and humic substances were investigated. Common ions present in natural waters did not interfere and only the less abundant NO₂ ^? and Fe²⁺ exhibited strong interferences. Interferences of the two latter ions, if they existed, could be controlled and the method proved to be accurate and with a low detection limit. However, it was found that the presence of soluble humic substances resulted in positive interference, rendering the method unsuitable for bromate determination in natural waters and restricted its use in pure bromate solutions. This interference can be attributed to the electron acceptor groups invariably existing in the humic molecules. Since humic substances can remain in the water even after its ozonation, they will also contribute to a positive interference in bromate determination in potable waters.     

Flow Injection Determination of Humic Acid with Chemiluminescence Detection

Abstract

A very sensitive and fast flow injection chemiluminescence method, based on the oxidation of humic acid (HA) by 1,3‐dibromine‐5,5‐dimethylhydantion in the presence of glycine in alkaline medium, was developed for the determination of trace humic acids in water. A wide calibration range from 0.001 to 1.0 µg mL^?1 was obtained at the optimized conditions and the detection limit was as low as 0.5 ng mL^?1 of humic acids. Most of the foreign substances tested showed relatively high tolerance levels and the proposed method was successfully applied to the determination of humic acid in river water and tap water.     

Separation and determination of traces of heavy metals complexed with humic substances in fresh waters by sorption on diethylaminoethyl-sephadex a-25

Copper(II), lead and cadmium complexed with humic and fulvic acids in filtered 1-l samples of fresh water are sorbed on a column containing 0.5 ml of the macroreticular weak-base anion exchanger, diethylaminoethyl-Sephadex A-25 at a flow rate of 20 ml min^?1. Simple metal cations are not sorbed at all. The sorbed trace metals are quantitatively desorbed with 4 M nitric acid batchwise and determined by graphite-furnace atomic absorption spectrometry. For synthetic aqueous solutions containing traces of heavy metals and humic acid, the results are in conformity with those obtained by cationexchange separation. About 80% of the sorbed humic substances are eluted with 0.5 M sodium hydroxide solution from the A-25 column and its quantity is estimated spectrophotometrically at 400 nm.     

Determination of nitrate in natural waters by voltammetry at a stationary mercury drop electrode

Nitrate can be determined by second-sweep cyclic voltammetry at a stationary mercury drop electrode utilizing the autocatalytic effect of the hydroxyl ions formed at the surface of the electrode during the reduction of nitrate in the presence of an excess of trivalent cations. The reduction current in the second sweep with the same drop is proportional to the nitrate concentration in the range 1–1500 μmol l^?1 in natural waters. The humic substances present in natural waters have a favourable effect on the determination of nitrate. The method is applied to the determination of nitrate in drinking and river waters.     

Determination of Nitrite in Aqueous Solutions using the Linear Sweep Voltammetry Technique

ABSTRACT

An electrochemical method using linear sweep voltammetry techniques was developed to determine nitrite ion in aqueous solution in the presence of nitrate. Nitrite solutions exhibited a well-defined oxidation wave at +1.0V vs SCE at vitreous carbon, while no oxidation process was observed for nitrate solutions. The pH of the nitrite solutions varied from 2.37 to 5.60 and no change was observed in the Ep values, except for the pH 5.60 solution, where little change was verified. The potential also did not vary with change in the nitrite concentration in the 5.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range. Very good straight lines for plots of current versus nitrite concentration in the 7.0 x 10^?5 to 7.0 x 10^?4 mol L^?1 range were obtained; the correlation coefficient was never worse than 0.990. The nitrite determination was also performed in the presence of 1.0 x 10^?3 mol L^?1 of NO₃ ^? ions. The addition of NO₃ ^? did not change significantly the current values even when it was added in one hundred times molar excess.     

Determination of Total Nitrogen in Environmental Samples: Validation by Comparison of Techniques and Intralaboratory Studies

Abstract

A rapid, microwave-based extraction method was employed to oxidize all forms of nitrogen to nitrate in environmental samples using persulfate. The digest was then analyzed spectrophotometrically after an offline reduction of nitrate to nitrite using a cadmium reductor column was completed. The precision of the method was tested at the 0.5 mg l^?1 level and was 5.2% (N = 10). The detection limit based on S/N = 3 was calculated to be 0.15 mg l^?1. The method was thoroughly validated by comparison of analytical techniques and intralaboratory comparison studies.     

Spectrophotometric Determination of Sulfate by Solvent Extraction with Nonionic Surfactant Span 20 and Crystal Violet

Abstract

The sulfate ion is extracted into toluene with nonionic surfactant span 20 and crystal violet. A linear calibration curve was obtained between the absorbance due to crystal violet in the extract and sulfate concentrations over the range 2.5 × 10^?5 to 2.5 × 10^?4 mol 1^?1 (2.4 to 24 ppm) in the aqueous phase.     

Kinetics of the sulfate radical‐mediated photo‐oxidation of humic substances

The kinetics of the aqueous phase reaction of sulfate radicals with commercial humic acids and with organic matter extracted from vermicompost (VC) was studied by flash‐photolysis. The results can be interpreted by a mechanism that in a first step considers the reversible binding of the sulfate radicals by the humic substances. Both the bound and free sulfate radicals decay to oxidized products. From experiments performed with Aldrich humic acids in the temperature range from 283 to 303 K, the enthalpy change associated with the binding process was estimated to be ?(36 ± 11) kJ mol^?1. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 19–24, 2008     

Rapid Analysis of Nitrate and Nitrite by Ion-Interaction Chromatography on a Monolithic Column

Ion-interaction chromatography with direct conductivity detection has been used for analysis of nitrate and nitrite. Chromatographic separation was performed on a monolithic silica-based C₁₈ column dynamically modified with tetrabutylammonium (TBA⁺). Using the optimized mobile phase, containing 2.0 mmol L^?1 TBA⁺ and 0.8 mmol L^?1 citrate (pH 6.0), delivered at a flow rate of 6.0 mL min^?1, separation of five anions (chloride, nitrite, bromide, nitrate, and sulfate) was achieved in only 40 s at a column temperature of 30 °C. The detection limits for nitrate and nitrite were 0.74 and 0.92 mg L^?1, respectively. The relative standard deviation (RSD, n = 5) of the retention times of nitrate and nitrite was 0.1% and RSD of chromatographic peak areas were 0.4 and 0.2%, respectively. The method was successfully used for analysis of the anions in groundwater. Recovery of nitrate and nitrite was 99.1 and 105%, respectively.     

Aqueous size-exclusion chromatography of humic acids on a sephadex gel column with diluted phosphate buffers as eluents

The elution behavior of humic acids on a Sephadex gel column is senstive to the composition, concentration, and pH of the eluent. the concentrations of the eluent in the literature are too high to obtain the correct molecular size distribution of humic acids. By reducing the concentration of phosphate buffer eluents to about a hundredth of conventional concentrations, the correct distribution is obtained. In the proposed method, 1 ml of 0.1% sample solution is introduced into a Sephadex G-50 column (2.2-cm diameter, 55 cm long) and humic acids are eluted with a 10^?3 M phosphate buffer solution (pH 7–9) at a flow rate of 1 ml min^?1.     

An Ion-Selective Electrode for Dibasic Phosphate Ion

Abstract

A phosphate-selective electrode is developed based on a silver coordination reaction. The electrode responds linearly toward HPO₄ ⁼ in the concentration range of 10^?4 to 10^?1 M (slope = 27 mV/dec.). The electrode also shows good selectivity over sulfate, nitrate, perchlorate and acetate.     

Determination of tungstate in soils and sludges by using single-column ion chromatography

A procedure has been developed for the determination of tungstate at trace levels in aqueous extracts of soil and sludge by single-column ion chromatography (SCIC). Chromatographic parameters based on ion selectivity, time of determination and signal response were optimized for tungstate with the simultaneous detection of nitrate and sulfate. Chloride, phosphate, chromate, molybdate and vanadate were found not to interfere in the determination. A low-capacity resin-based column was used for the separation with p-hydroxybenzoic acid (5 mM) at pH 8.5 as the eluent. The limit of detection defined as three times the signal-to-noise ratio was 170 μg l^?1 (2-ml sample). The resolution between tungstate and sulfate was R_s=2.84. The results for aqueous extracts agree closely with those obtained by an accepted spectrophotometric method.     

Indirect Determination of Pyrrolizidine Alkaloids by Flame Atomic Absorption Spectrometry

Abstract

This paper studies the formation and extraction of ion pairs of some alkaloids derived from pyrrolizidine. The substances studied are Nemorensine, Platyphylline, Senecionine and Seneciphylline, and the ion pairs studied and extracted are formed with Bil₄. The method consists of extracting an ion pair between the organic base and the inorganic complex, the metal is measured in the organic phase (1,2 dichloroethane) by Flame AAS. The optimal experimental conditions, pH, concentration of BiI₄ ^?, shaking time, phase ratio, number of extractions, and the range of calibration are studied for these substances. The linear range in organic phase is 0.13–1.91 mg.mL^?1. The standard deviation of the method varies between 2.4–3.2%, depending on the substance analyzed. The interferences produced by various substances are studied.     

Multiparametric automated system for sulfate,nitrite and nitrate monitoring in drinking water and wastewater based on sequential injection analysis

An automated monitoring system for sulfate, nitrite and nitrate based on sequential injection analysis (SIA) was developed. For nitrite determination the modified Griess-Ilosvay method was used, whereas nitrate was previously reduced to nitrite using a cadmium column followed by nitrite determination. A turbidimetric method was carried out in order to determine sulfate. The results showed that the proposed SIA monitoring system constitutes an effective approach for nitrite, nitrate and sulfate determination since it is able to determine levels required by international agencies that regulate these parameters in water. Detection limits of 0.0207 mg N L^? 1, 0.0022 mg N L^? 1 and 3 mg SO₄^2? L^? 1 were obtained for nitrate, nitrite and sulfate, respectively. The developed method offers also typical characteristics of the multicommutated systems, as portability, low reagents consumption and the subsequently minimization of waste generation. The proposed system was successfully applied to drinking water and wastewater samples and validated with a certified river water sample (ION-96.3, LGC Standards).     

Determination of methylmercury in natural waters at the sub-nanograms per litre level by capillary gas chromatography after adsorbent preconcentration

Methylmercury was preconcentrated from water on to a sulph-hydryl cotton fibre adsorbent, using the column technique or the batch-column two-stage technique. A small volume of 2 M HCl was used to elute methylmercury and to separate it from inorganic mercury; 0.4–0.6 ml of benzene was used to extract methylmercury from the eluate. Analysis was performed by capillary gas chromatography with electron-capture detection. The detection limit for methylmercury was <0.05 ng l^?1 in a 4-l water sample. Four surface waters were analysed to test the agreement of methylmercury concentration between the two preconcentration methods, and to test the interference of humic substances on the filtered and unfiltered surface water. The methylmercury concentrations found in different surface water samples ranged from 0.08 to 0.48 ng l^?1.     

Spectrophotometric Determination of Metoclopramide and Oxybuprocaine Through Ion Pair Formation with Thiocyanate and Molybdenum(V) or Cobalt(II)

Abstract

Two spectrophotometric methods involve the formation of two different ion pairs between the drug and inorganic complexes, Mo(V) and Co(II) thiocyanates followed by their extraction with dichlor?methane and o-nitrotoluene, respectively. The optimum conditions for the ion pair formation are established. The methods permit the determination of metoclopramide and oxybuprocaine hydrochlorides over a concentration range of 1-20 μg ml^?1 and 20–240 μg ml^?1 using Mo(V) and Co(II) thiocyanates, respectively. Molar ratio of drug to Mo(V) or Co(II) indicates a 2:1 ratio for the two drugs studied in the presence of excess thiocyanate concentration. Results of the analysis of drug substances and their dosage forms by the proposed methods are in good agreement with those obtained by the official methods.     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Measurement of Chelating Agent Levels in Media with High Concentrations of Interfering Metal Ions

Abstract

An ion-exchange method for the measurement of levels of chelating agents in media with high levels of metal ions has been developed. The test solution is passed through a specially prepared ion-exchange column, which both removes metal ion interferences, and places the chelating agent in the copper form. The copper levels in the column effluent are then measured by flame atomic absorption methods, the copper levels corresponding in a 1:1 ratio to the levels of chelating agent in the sample. The detection limit for this method is on the order of 1 ppm copper equivalent chelating capacity, and is applicable in situations where the interfering metal ions are at concentrations in the range of 10^?2 M. The method is reproducible in the pH ranges of 4 to 9 Precision and