Ion-chromatographic measurements of ammonium,fluoride, acetate,formate and methanesulphonate ions at very low levels in antarctic ice

Ion chromatography is used to determine the concentrations of organic (formate, acetate and methanesulphonate) and inorganic (fluoride and ammonium) ions present in Antarctic ice at less than 10⁻⁹ g g⁻¹ levels. With suitable columns, the simultaneous measurement of these ions requires only 6 min. A sample volume of 5 ml is sufficient to reach the 10⁻¹⁰ g g⁻¹ level. The determination of such low concentrations requires stringent contamination-free techniques. For formate and acetate, the samples should never come into contact with plastics. Except for methanesulphonate, all the ions studied can be produced by dissolution of the various gaseous compounds present in a polluted atmosphere. Therefore a glass device with pure nitrogen circulation was designed for air-free melting of samples. To prevent possible biological activity on organic matter, samples were analysed immediately after melting. Measurements of ammonium ion in these Antarctic ice samples demonstrate that the problem of contamination by surrounding ammonia was not completely eliminated in previous studies. The serious contamination problems encountered, particularly for carboxylic acids, cast doubt on some earlier results for remote areas.     

Speciation analysis of iodine and bromine at picogram-per-gram levels in polar ice

Iodine and bromine species participate in key atmospheric reactions including the formation of cloud condensation nuclei and ozone depletion. We present a novel method coupling a high-performance liquid chromatography with ion chromatography and inductively coupled plasma mass spectrometry, which allows the determination of iodine (I) and bromine (Br) species (IO ₃ ^? , I^?, Br^?, BrO ₃ ^? ) at the picogram-per-gram levels presents in Antarctic ice. Chromatographic separation was achieved using an IONPAC® AS16 Analytical Column with NaOH as eluent. Detection limits for I and Br species were 5 to 9 pg g^?1 with an uncertainty of less than 2.5% for all considered species. Inorganic iodine and bromine species have been determined in Antarctic ice core samples, with concentrations close to the detection limits for iodine species, and approximately 150 pg g^?1 for Br^?. Although iodate (IO ₃ ^? ) is the most abundant iodine species in the atmosphere, only the much rarer iodide (I^?) species was present in Antarctic Holocene ice. Bromine was found to be present in Antarctic ice as Br^?.     

An evaluation of differential pulse anodic stripping voltammetry at a rotating glassy carbon electrode for the determination of cadmium,copper, lead and zinc in antarctic snow samples

A procedure is described for the determination without preconcentration of Cd, Cu, Pb and Zn in Antarctic snow, based on differential pulse anodic stripping voltammetry at a rotating glassy carbon electrode with in situ mercury plating. Thirty four surface snow samples from Adelaide Island in the Antarctic Peninsula demonstrate the scope of this method, and allow an assessment of local heavy metal sources such as the rock, the sea, and a manned base. The zinc data are affected by container contamination, but concentrations as low as 0.005, <0.02 and 0.05 ng g^-1 were measured for Cd, Cu and Pb, respectively.     

Ion chromatographic determination of selected ions in antarctic ice

Ion chromatography is used to measure the concentrations of chloride, nitrate, sulphate, ammonium and sodium ions at the μg l^?1 level in Antarctic ice and to investigate the occurrence of methanesulphonate, fluoride, formate, acetate and nitrite. Of the latter group of ions, only methanesulphonate was found in measurable concentrations.     

Clean conditions for the determination of ultra-low levels of mercury in ice and snow samples

Laboratory facilities and methods are presented for the determination of ultra-low levels of mercury (Hg) in ice and snow samples originating from polar ice caps or temperate regions. Special emphasis will be given to the presentation of the clean laboratory and the cleaning procedures. The laboratory is pressurized with air filtered through high efficiency particle filters. This first filtration is not enough to get rid of contamination by Hg in air. Experiments are conducted in a clean bench, especially built for Hg analysis, equipped with both particle filter and activated charcoal filter. It allows to obtain very low levels of atmospheric Hg contamination. Ultrapure water is produced for cleaning all the plastic containers that will be used for ice and snow samples and also for the dilution of the standards. Hg content in laboratory water is about ¶0.08 ± 0.02 pg/g. A Teflon system has been developed for the determination of Hg in ice and snow samples based on Hg(II) reduction to Hg(0) with a SnCl₂/HNO₃ solution followed by the measurement of gaseous Hg(0) with a Hg analyzer GARDIS 1A+ based on the Cold Vapor Atomic Absorption Spectroscopy method. Blank determination is discussed.     

Liquid—liquid distribution of ion associates of tetraiodopalladate(II) with quaternary ammonium counter ions

The distribution behaviour of ion association of Pdl^2?₄ with ten quaternary ammonium cations between chloroform and an aqueous phase was examined and extraction constants (log K_ex) were determined. Linear relationships between log K_ex and the number of methylene groups in the quaternary ammonium ions were observed. Quantitative extraction of palladium was achieved with Zeph⁺ or TBA⁺; the molar absorptivity was 2.5 × 10⁴ l mol^?1 cm^?1 at 344 nm. The effect of other ions on the spectrophotometric determination of palladium, based on their extraction, is reported.     

The electrochemical determination of ammonium based on the selective inhibition of the low-spin iron(II)/(III) system of Prussian blue

A new method is described for the determination of ammonium in aqueous solutions with electrodes modified by Prussian blue (PB). The specific voltammetric response of PB-modified electrodes to ammonium ions is used for their analytical determination. In the presence of ammonium ions, a concentration-dependent inhibition of the low-spin iron(II/III) system of PB occurs. Only thallium and rubidium ions cause similar inhibition. A useful electrochemical determination method is thus available for detecting ammonium ions in the presence of frequently interfering potassium and sodium ions. Paraffin-impregnated graphite electrodes modified with a mechanically transferred PB layer and bulk-modified PB-composite electrodes are studied. The method is applicable within a concentration range which extends from 4 × 10⁻⁵ mol/l to 10⁻² mol/l NH₄ ⁺. The composite electrode is used in an electrochemical flow-through system in conjunction with the Kjeldahl method. Received: 21 April 1997 / Accepted: 28 May 1997     

Processing of signals from an ion-elective electrode array by a neural network

Neural network software is described for processing the signals of arrays of ion-selective electrodes. The performance of the software was tested in the simultaneous determination of calcium and copper(II) ions in binary mixtures of copper(II) nitrate and calcium chloride and the simultaneous determination of potassium, calcium, nitrate and chloride in mixtures of potassium and calcium chlorides and ammonium nitrate. The measurements for the Ca²⁺/Cu²⁺ determinations were done with a pH-glass electrode and calcium and copper ion-selective electrodes; results were accurate to ±8%. For the K⁺/Ca²⁺NO^?₃/Cl^? determinations, the measurements were made with the relevant ion-selective electrodes and a glass electrode; the mean relative error was ±6%, and for the worst cases the error did not exceed 20%.     

Flow-through pH-ISFET as detector in the determination of ammonia

A simple flow-injection metod for the determination of ammonium ions in water, based on a flow-through pH-ISFET, is described. Ammonium is converted to ammonia, which diffuses through a microporous hydrophic membrane into an ammonium chloride recipient stream, forming a pH buffer which is monitored by the semiconductor detector. The linear working range extends from 0.1 to 10 mmol l^?1 with a relative standard deviation of ca. 1% at the 0.7 mmol l^?1 level.     

Effects of solvent and counterion on ion pairing and observed charge states of diquaternary ammonium salts in electrospray ionization mass spectrometry

Two diquaternary ammonium chloride salts have been used to examine the roles of solvent and counterion in determination of the degree of ion pairing in solution and the resultant charge state distributions in electrospray ionization mass spectrometry (ESI-MS). Three series of solvents, that is, alcohol, polar aprotic, and chlorinated solvents, have been employed to test the influence of solvent polarity and other parameters on the desorption behavior of diquaternary ammonium ions observed in ESI-MS. Solvents of higher polarity were found to yield gas-phase ions of higher charge states, in accordance with their reduced tendency toward ion pairing in solution. Counterion effects were investigated via the following approaches: (1) increase the diquaternary ammonium salt concentration; (2) increase the concentration of an external electrolyte that contained the common counterion Cl^?; (3) replace Cl^? with trifluoroacetate (TFA_c ^?); (4) increase the concentration of an external electrolyte that contained TFAc^?. These experiments indicate that variation of the specific counterion employed alters the degree of influence that the counterion exerts (via ion pairing) on electrospray ionization mass spectra. Increasing amounts of trifluoroacetate ions in a variety of solvent systems invariably led to a progressive shift of the observed ESI-MS charge states of diquaternary ammonium ions toward lower values.     

Determination of radiocobalt in seawater by successive extractions with the reagents of tris/pyrrolidine dithiocarbamato/bismuth/III/ and ammonium pyrrolidin-dithiocarbamate and back-extraction with bismuth/III/

Method for the isolation and radioactive cobalt /including⁵⁸Co and⁶⁰Co/ from a large volume of seawater and concentration in a small volume of chloroform as tris/pyrrolidine dithiocarbamato/cobalt/III/, Co/PDC/₃, is described. The seawater was extracted first with Bi/PDC/₃ in chloroform for removing parts of foreign metals like Hg, Ag, etc., and then added with ammonium pyrrolidindithiocarbamate, APDC, to complex with Co and possibly other ions and extracted into the organic phase. The final separation of Co from foreign ions in the organic phase was achieved by stripping with a Bi/III/ solution. The overall recovery of radiocobalt activity was found to be about 96%. The established method can be applicable for rapid and reliable determination of radiocobalt in seawater and other aqueous systems for environmental contamination.     

Effect of ammonium formate as ionizing additive in thermospray liquid chromatography-mass spectrometry for the determination of triazine,phenylurea and chlorinated phenoxyacetic acid herbicides

A comparison between the use of ammonium acetate and ammonium formate in thermospray liquid chromatography-mass spectrometry with positive and negative ion modes using ‘filament-on’ mode has been applied for the determination of simazine, atrazine, propazine, monuron, diuron, linuron, 2,4,-D, 2,4,5-T and silvex. By using ammonium formate, the positive ion mode showed for triazine and phenylurea herbicides [M + H]⁺ and [M + NH₄]⁺, respectively, and the formation of other adduct ions different from ammonium acetate. In the negative ion mode, chlorinated phenoxyacetic acid herbicides exhibited [M + acetate]^? or [M + formate]^?, depending on the ionizing additive. Applications are reported for the determination of triazine and chlorinated phenoxyacetic acid herbicides in spiked soil and water samples, respectively.     

Infrared spectrum of D2O vibrationally decoupled in H2O ice Ic

The study of D₂O isolated in amorphous H₂O (ice Iv) has been extended to the determination of the bending mode frequency (1230 cm^?1) and to the measurement of the vibrational spectrum of the cubic ice phase (ice Ic). The vibrationally decoupled stretching frequencies (ν₁ = 2367 cm^?1 and ν₃ = 2444 cm^?1) for D₂O in the H₂O (Ic) have been obtained and an estimate of the exchange activation energy is given.     

Rapid determination of dissolved silica in natural waters

A method is described for the simple and rapid determination of soluble silica in natural waters, based on the well-known molybdenum blue complex. Soluble silica reacts with an excess of ammonium molybdate at pH 1.5–2 to form silicomolybdate. Citrate/tartrate addition reduces phosphate and arsenate interference, if present. An acid solution if iron(II) and fluoride ions is used as reductant. Absorbance is read at 828 nm. The solution is stable at least 2 hr. Traces of silica are determinable down to 10 μg SiO₂ liter^?1 with an error of ± 3%. The analysis time is about 10 min. The effect caused by several other ions has been determined.     

Heterogeneous Electrofreezing of Super‐Cooled Water on Surfaces of Pyroelectric Crystals is Triggered by Trigonal Planar Ions

Electrofreezing experiments of super‐cooled water (SCW) with different ions, performed directly on the charged hemihedral faces of pyroelectric LiTaO₃ and AgI crystals, in the presence and in the absence of pyroelectric charge are reported. It is demonstrated that bicarbonate (HCO₃^?) ions elevate the icing temperature near the positively charged faces. In contrast, the hydronium (H₃O⁺) slightly reduces the icing temperature. Molecular dynamics simulations suggest that the hydrated trigonal planar HCO₃^? ions self‐assemble with water molecules near the surface of the AgI crystal as clusters of slightly different configuration from those of the ice‐like hexagons. These clusters, however, have a tendency to serve as embryonic nuclei for ice crystallization. Consequently, we predicted and experimentally confirmed that the trigonal planar ions of NO₃^? and guanidinium (Gdm⁺), at appropriate concentrations, elevate the icing temperature near the positive and negative charged surfaces, respectively. On the other hand, the Cl^? and SO₄^2? ions of different configurations reduce the icing temperature.     

A preliminary investigation of ionic adsorption at the mercury—hexamethyl phosphoric triamide interface

A reference electrode is described that is reversible and reproducible in hexamethyl phosphoric triamide; it was used to study the adsorption of 1 : 1 electrolytes at the mercury—solution interface. The differential capacity curves show features similar to those found for water and the degree of specific adsorption of the anions follows the same sequence: PF^?₆ < BF^?₄, ClO^?₄ < Br^?. There appears to be no specific adsorption of the alkali metal cations at negative charge values whereas the tetraalkyl ammonium ions are strongly adsorbed.     

Electrochemical behaviour and analytical detection of ammonium ions in alkali nitrate melts

The voltammetric behaviour of ammonium ions was investigated in the (Na, K)NO₃ equimolar melt at 518 K. The voltammograms recorded at platinum, gold and vitreous carbon rotating-disc electrodes under one atmosphere of anhydrous nitrogen are characterized by three consecutive cathodic waves. The rapid disappearance of ammonium ions from the solution can be ascribed mainly to the evaporation of the salt, which is a more rapid process than thermal decomposition under the given experimental conditions. In order to be able to neglect the effect of evaporation and decomposition, the voltammograms were recorded within a few minutes from the addition of NH₄NO₃ to the melt. The experimental ratios between the limiting currents of the three waves recorded at a vitreous carbon rotating-disc electrode, the most suitable for analytical purposes, were found to have a constant value within the explored ammonium concentration range, i.e 8×10^?5 mol kg^?1<[NH₄⁺]<5.0×10^?3 mol kg^?1. A simple mechanistic model is proposed which permits a reasonable interpretation of the experimental results and, in particular, explains the origin of the three waves and their limiting current ratios. The diffusion coefficient of ammonium ions was found to be D=(4.0±0.4) 10^?6 cm² s^?1 at 518 K.     

Determination of urea by ion chromatography with an immobilized urease reactor

An immobilized urease reactor can be used with ion chromatography for the simultaneous determination of urea, and sodium, potassium and ammonium ions. The conversion of urea to ammonium ion was found to be 76.5%. The calibration graph for urea was linear over the range 1 × 10^?5?1 × 10^?3 M (RSD 3%). The method was applied to human urine and a chemical fertilizer.     

Simultaneous Determination of Levoglucosan,Mannosan and Galactosan at Trace Levels in Snow Samples by GC/MS

A method for the simultaneous determination of levoglucosan, mannosan and galactosan at trace levels in snow samples is reported by using GC/MS. This method is an improvement on previous aerosol studies. The required sample volume for this method is a mere 5.00 mL of melt water. Discrimination of three isomers is analyzed on the basis of different retention time and fragmentation patterns. The limit of detection is 0.070, 0.058 and 0.046 ng mL^?1 ice melt water for three isomers. This method has the advantage of simultaneous determination of three monosaccharide anhydrides at trace concentration levels in small sample volumes. The relatively high extraction efficiency and low limit of detection will facilitate further studies on biomass burning recorded in snow and ice samples.     

Extraction Spectrophotometric Determination of Vanadium in Industrial Waste Water

A new and simple extraction spectrophotometric method for the determination of vanadium(V) with KIO₄, N‐phenylbenzohydroxamic acid (PBHA) and crystal violet (CV), in industrial waste water samples is described. It is based on the extraction of mixed‐ligand complex V(V)‐IO₄^? ‐PBHA‐CV⁺ into chloroform solution over 2‐7 MHC1. The molar absorptivity of the complex is (7.20) × 10³1 mol^?1 cm^?1 at λ_max 535 nm. The detection limit of the method is 44 μg 1^?1 V. The linearity of the calibration curve is followed up to 6 μgmL^?1 in the organic solution with slope, intercept and correlation coefficient of 1.34 × 10^?1, 6.7 × 10^?3 and +0.99, respectively. This method enhances the sensitivity of the conventional PBHA method for the determination of vanadium, and is free from interferences of other metal ions commonly associated with vanadium. The method has been successfully tested for the determination of V in the industrial waste water samples.