Influence of water on the dielectric behaviour of chitosan films

 The dielectric properties of chitosan films with a degree of deacetylation of 86% have been investigated in the frequency range of 10^3–10⁶ Hz covering a broad range of temperatures from −150 to 150 °C. The variation of the dielectric pro-perties with temperature has been associated with two dielectric processes: (a) a local relaxation attributed to the presence of hydrogen-bonded water appearing at low temperatures (b) a conduction process related to water molecules which becomes desorbed upon heating at T>80 °C. Isothermal dielectric experiments have been performed in order to follow, in real time, the occurrence of both, the water sorption and desorption processes. Received: 20 June 1996 Accepted: 19 November 1996     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Bromide/bromate speciation by NTI-IDMS and ICP-MS coupled with ion exchange chromatography

 Two different mass spectrometric methods, negative thermal ionization isotope dilution mass spectrometry (NTI-IDMS) and inductively coupled plasma mass spectrometry (ICP-MS), off-line and on-line coupled with anion exchange chromatography, have been developed for simultaneous bromide and bromate determinations in water samples. The detection limits of these methods are in the range of 0.03–0.09 μg/L using a 50 mL sample.The results are independent of the content of other anions, which could be demonstrated by the analyses of six mineral waters containing chloride and sulfate of up to 160 mg/L and 1500 mg/L, respectively. Bromide has been analyzed by the NTI-IDMS method in the range of 10–500 μg/L and bromate in the range of 1–50 μg/L with relative standard deviations of 0.3–1.2% and 0.4–6%. Quantification for the ICP-MS method was carried out by the standard addition technique, which resulted in relative standard deviations of 5.5% for bromide at the 500 μg/L level and of 13% for bromate at the level of about 3 μg/L. These results are compared with those described in the literature for ion chromatographic (IC) and other methods and those obtained in this work by IC using UV detection, which allows high concentrations of chloride in the bromate fraction. The detection limits of this IC method are 6 μg/L for bromide and 30 μg/L for bromate. NTI-IDMS and ICP-MS therefore fit the recommendations of the European Union (detection limit<2.5 μg/L; precision and accuracy better than 25% at the 10 μg/L level) for methods analyzing the carcinogenic bromate much better than IC and other methods applied up to now. As a definitive but time consuming method, NTI-IDMS is preferably applicable as a calibration technique, whereas ICP-MS, with relatively short analysis times, due to on-line coupling with chromatography, can be used as a sensitive and powerful routine method for trace bromide and bromate species in water samples. Received: 5 July 1996/Accepted: 7 August 1996     

Distillation, on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS as a new combination for the determination of methylmercury in sediments and fish tissue

 Distillation as a way of sample digestion has been combined with on-line RP C18 preconcentration and HPLC-UV-PCO-CVAAS (high performance liquid chromatography – ultra violet – post column oxidation – cold vapour atomic absorption spectrometry) for the determination of methylmercury at background levels in sediments, soils and fish tissue. To prove the accuracy of this method, it was applied to sediment and fish tissue reference materials. The results correspond with the reference values within their error ranges. Excellent recoveries (92–95%) were obtained for the sediment samples by means of the standard addition method. The standard deviations of the sediment samples were within an acceptable range (7.2–12.5%), those of the fish samples were substantially lower (3.4–5.0%). The detection limit is 0.04 ng/g for 1 g sample weight. Received: 23 November 1995/Revised: 16 April 1996/Accepted: 20 April 1996     

Spectrophotometric determination of nitrite in natural waters using diazotization-coupling method with column preconcentration on naphthalene supported with ion-pair of tetradecyldimethylbenzyl-ammonium and iodide

 A column preconcentration method has been established for the spectrophotometric determination of traces of nitrite using diazotization and coupling on an naphthalene-tetradecyldimethylbenzylammonium (TDBA)-iodide (I) adsorbent. Nitrite ion reacts with sulfanilic acid (SA) in the pH range 1.8–3.0 for the SA-1-naphthol system and in the pH range 2.3–3.2 for the SA-1-naphthylamine-4-sulfonate system (SA-NAS system) in hydrochloric acid medium to form water-soluble colourless diazonium cations. These cations were coupled with 1-naphthol in the pH range 1.6–4.6 and with NAS in the pH range 2.6–5.0 to be retained on naphthalene-TDBA-I packed in a column. The solid mass was dissolved from the column with 5 mL of dimethylformamide (DMF) and the absorbance measured at 418 nm for the SA-1-naphthol system and at 485 nm for the SA-NAS system. The calibration curve was linear over the concentration range 0.02–0.87 mg/L for SA-1-naphthol and 0.02–0.80 mg/L in the sample for SA-NAS. The molar absorptivity was calculated to be 1.70×10⁴ L mol^-1 cm^-1 for SA-1-naphthol and 1.66×10⁴ L mol^-1 cm^-1 for SA-NAS. The detection limits were found to be 0.014 and 0.016 mg/L for SA-1-naphthol and SA-NAS, respectively. The preconcentration factors were 8 and 6 for SA-1-naphthol and SA-NAS, respectively. Replicate determinations of seven sample solutions containing 6.6 μg of nitrite for SA-1-naphthol and 5.3 μg of nitrite for SA-NAS gave mean absorbances of 0.486 and 0.382 with relative standard deviations of 0.49 and 0.58%, respectively. Interferences due to various foreign ions have been studied and the method has been applied to the determination of 27–65 μg/L levels of nitrite in natural waters. The recovery and relative standard deviation for water samples were 98–102% and 0.49–0.58% for both systems. Received: 1 December 1995/Revised: 22 April 1996/Accepted: 22 April 1996     

On-line dilution with sequential injection analysis: a system for monitoring sulphate in industrial effluents

 On-line dilution with sequential injection analysis has been evaluated for sulphate monitoring in industrial effluents using a dilution coil in the conduits of the manifold system and a dilution step as part of the timing sequence. The manifold of the SIA system with the dilution coil is more complex than the system including the dilution step. The former method needs more complicated programming as well. Shorter analysis time favoured the dilution with the dilution step, but the limited linear range of this method is a large drawback. The large linear range of the SIA system with dilution coil makes it very suitable to be used as a process analyser. The proposed SIA system is suitable to monitor sulphate in industrial effluents in the range 50–5000 mg/L with a dilution coil, in the range 50–1000 mg/L with a timing sequence of 6.5 s and in the range 750–5000 mg/L with a timing sequence of 15 s using a dilution step; all three ranges with a RSD <4.5%. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

On-line dilution with sequential injection analysis: a system for monitoring sulphate in industrial effluents

 On-line dilution with sequential injection analysis has been evaluated for sulphate monitoring in industrial effluents using a dilution coil in the conduits of the manifold system and a dilution step as part of the timing sequence. The manifold of the SIA system with the dilution coil is more complex than the system including the dilution step. The former method needs more complicated programming as well. Shorter analysis time favoured the dilution with the dilution step, but the limited linear range of this method is a large drawback. The large linear range of the SIA system with dilution coil makes it very suitable to be used as a process analyser. The proposed SIA system is suitable to monitor sulphate in industrial effluents in the range 50–5000 mg/L with a dilution coil, in the range 50–1000 mg/L with a timing sequence of 6.5 s and in the range 750–5000 mg/L with a timing sequence of 15 s using a dilution step; all three ranges with a RSD <4.5%. Received: 11 March 1996/Revised: 1 July 1996/Accepted: 4 July 1996     

Thermal Analysis of Adsorbed Poly(methyl methacrylate) on Silica

Modulated differential scanning calorimetry has been used to quantify the glass transitions of small adsorbed amounts of poly(methyl methacrylate) (PMMA) on silica. While a relatively narrow, single glass transition was found for bulk PMMA, broader two-component transitions were found for the adsorbed polymer. A two-state model based on loosely bound polymer (glass transition similar to bulk) and more tightly bound polymer (glass transition centered around 156 degrees C) was used to interpret the thermograms. On the basis of this model, the amount of tightly bound polymer was found to be approximately 1.3 mg/m2, corresponding to a 1.1 nm thick layer. The change in heat capacity for the tightly bound polymer at the glass transition temperature was estimated to be about 16% of that of the bulk polymer.     

Determination of lead traces in water and liqueurs by derivative atom trapping flame atomic absorption spectrometry

 A new method for the direct determination of lead traces using derivative atom trapping flame atomic absorption spectrometry (DAT-FAAS) with an improved water-cooled stainless steel trapping equipment in an air-acetylene flame was investigated. The optimum conditions concerning the sensitivity were studied. For a 1 min collection, the characteristic concentration (given as derivative absorbance of 0.0044) and the detection limit (3s) were 1.4 ng/mL and 0.27 ng/mL, respectively. This is 361 and 74-fold better than those of the conventional flame atomic absorption spectrometry (FAAS) and comparable to those of graphite furnace atomic absorption spectrometry (GFAAS). The detection limit and sensitivity of DAT-FAAS for a 3 min collection time were 2 and 3 orders of magnitude higher than those of conventional FAAS. The present method was applied to the determination of lead in water and liqueur samples with a recovery range of 94–108% and a relative standard deviation of 3.5–5.6%. Received: 10 January 1996/Revised: 9 December 1996/Accepted: 20 December 1996     

HPLC determination of collectors used for the flotation of heavy metal minerals

 A reversed-phase HPLC-method for the separation of mixtures of collectors for the flotation of heavy metal minerals is described. It is based on a Nucleosil 5C18 column, isocratic elution and UV-detection at 238 nm. The mobile phase is methanol-water-5% phosphoric acid (40:60:4, v/v). The method is applied to the determination of six collectors in aqueous solutions from flotation processes. The relative standard deviations are 1.6–3.2% in the concentration range 2–10 mg/L. The detection limits are 1 μg/L for 8-hydroxyquinoline, dimethylglyoxime and salicylic acid, 2 μg/L for salicylhydroxamic acid and 5 μg/L for benzenetriazol and salicylaldoxime, respectively. Received: 19 April 1996/Revised: 14 August 1996/Accepted: 23 August 1996     

An effective cross-linking of polymer layer on monodisperse, poly(maleic anhydride-styrene)-modified colloidal silica particles and properties of the composite

Summary  The cross-linkings of the surface polymer layer on mono disperse, poly(maleic anhydride-styrene)-modified silica particles by the reaction with diisocyanate were studied. The extent of cross-linking was estimated by the weight decrease by immersing the particles in the buffer solution of pH 2.0, 4.0 and 9.0 at a room temperature for 24 h. The reaction of the polymer-modified silica with 1,6-diisocyanatohexane afforded relatively stable composite particles which lost less than 5 wt% of the polymer in aqueous solution in the pH range 2.0–9.0. The diisocyanate was a preferable cross-linker to 2,4-diisocyanatotoluene in terms of stability in acidic or basic aqueous solution. The flexibility of the cross-linker molecule possibly plays an important role in the cross-linking reaction. The carboxyl and amino groups were formed by treating the cross-linked composite particles with diluted HCl solution; 5–6 and 0.5–1.1 μmol g^-1, respectively. The cross-linked composite particles exhibited the characteristic property of ζ-potential, −44 to −47 mV and −102 to −107 mV in a neutral aqueous solution and ethanol, respectively. Received: 26 May 1997 Accepted: 4 August 1997     

Results of collaborative trials concerning the analysis of benzo-a-pyrene in creosote

 The results of five collaborative studies concerning the analysis of benzo-a-pyrene (BaP) in creosote by high-performance liquid chromatography (HPLC) are presented. Six to twelve laboratories participated in these studies over a time period of three years. These studies were carried out in order to evaluate the method which is described in the CEN standard ENV 1014-3. The concentrations of BaP in creosote samples analysed were in the range of 20 ppm to 550 ppm. Whereas the values for repeatability (5–10%) were acceptable in nearly all collaborative trials, those for reproducibility have improved significantly in the last study (23–33%). For the previous four collaborative trials the reasons for the relatively poor reproducibility values, especially for analytes containing low concentrations of BaP, could be detected. They were mainly based on problems with chromatographic separation and with integration. The method described in ENV 1014-3 has been proven to be suitable for the determination of the BaP content in creosote. Received: 21 June 1996/Revised: 21 August 1996/Accepted: 25 August 1996     

Results of collaborative trials concerning the analysis of benzo-a-pyrene in creosote

 The results of five collaborative studies concerning the analysis of benzo-a-pyrene (BaP) in creosote by high-performance liquid chromatography (HPLC) are presented. Six to twelve laboratories participated in these studies over a time period of three years. These studies were carried out in order to evaluate the method which is described in the CEN standard ENV 1014-3. The concentrations of BaP in creosote samples analysed were in the range of 20 ppm to 550 ppm. Whereas the values for repeatability (5–10%) were acceptable in nearly all collaborative trials, those for reproducibility have improved significantly in the last study (23–33%). For the previous four collaborative trials the reasons for the relatively poor reproducibility values, especially for analytes containing low concentrations of BaP, could be detected. They were mainly based on problems with chromatographic separation and with integration. The method described in ENV 1014-3 has been proven to be suitable for the determination of the BaP content in creosote. Received: 21 June 1996/Revised: 21 August 1996/Accepted: 25 August 1996     

Preparation of micron-sized monodispersed highly monomer- “adsorbed” polymer particles having snow-man shape by utilizing the dynamic swelling method with tightly cross- linked seed particles

Micron-sized, monodispersed highly styrene-“adsorbed” particles having snow-man shape were prepared by the dynamic swelling method (DSM) with tightly cross-linked polymer seed particles as follows. First, 3.8 μm-sized monodispersed polystyrene (PS)/ poly(divinylbenzene) (PDVB) (PS/PDVB = 1/10 wt. ratio) composite particles produced by seeded polymerization utilizing DSM were dispersed in an ethanol/water (6/4, w/w) solution dissolving styrene monomer, and poly(vinyl alcohol) as a stabilizer. Second, water was subsequently added to the dispersion with a micro-feeder at a rate of 2.88 ml/h at room temperature. The cross-linked seed particles adsorbed a large amount of styrene onto the surfaces and resulted in mono-dispersed highly styrene-“adsorbed” snow-man shape particles having about 10 μm in diameter. Received: 16 April 1998 Accepted: 9 June 1998     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

Determination of As, Cd, and Pb in epicuticular waxes of pine and spruce needles by ETAAS

 Waxes were separated from needles by chloroform washing, drying and dissolving the residue in tetrahydrofuran (THF). Both a THF solution of the wax and an aqueous solution of the Pd-Mg matrix modifier were sampled directly into the graphite tube. The reaction conditions were optimised for the wax concentration of 45 mg ml^-1 in THF and the Pd:Mg ratio of 1:1 in the matrix modifier. The atomisation and charring temperatures for As, Cd and Pb were the same as those recommended for analysis of aqueous solutions except the charring temperature of Cd takes 200 °C lower. The characteristic masses for As (26 pg), Cd (0.5 pg) and pb (9 pg) are also comparable to published data. The parameters of calibration curves were identical for all three elements dissolved either in clear THF or in the wax solution. Elemental concentrations were found to range from 0.1 to 1.0 mg g^-1, increasing with needle age for As, Pb but not Cd. Received: 20 September 1996 / Revised: 14 November 1996 / Accepted: 13 December 1996     

MIR and NIR spectroscopy of sol–gel hydrotalcites with various trivalent cations

Three different hydrotalcites were synthesized from magnesium ethoxide, and aluminium, gallium and indium acetylacetonate, using the sol–gel technique. The colloid suspensions initially obtained were gelled and separated by centrifugation. XRD diffraction patterns confirmed that all solids thus obtained possessed a hydrotalcite structure. The resulting hydrotalcites were characterized by mid-infrared (MIR) and near-infrared (NIR) spectroscopies. The two types of spectra were found not to depend on the synthetic medium or trivalent metal used and were thus quite similar. The MIR spectra for the three solids included a strong band at 3500–3000 cm⁻¹ due to stretching vibrations of the different types of O–H groups in them. The signal at about 1370 cm⁻¹ observed for all solids indicates that the sole interlayer anion present was carbonate. The NIR spectra exhibited the bands for the first and second overtone of the O–H stretching vibration in addition to various combination bands.     

Analytical characterization of manganese in rainwater and snow samples

 Seven rain and 2 snow samples collected in October and November 1993 were analyzed by GFAAS. Manganese concentrations ranging from 0.3 to 11.3 μg/L were found. pH-values (4.04–4.89, mean 4.52) and redox potentials (528–665 mV, mean 581 mV) were additionally determined. This is important with respect to a qualified specification of Mn in atmospheric samples. A 0.45 μm-filtration of the samples prior to GFAAS-analysis showed the same manganese concentrations in the filtrate as in the unfiltered samples. Hence, the amount of solid Mn species in the investigated samples is negligible. For an examination of the oxidation state of Mn some investigations concerning the stability of Mn(III) were carried out. They indicated that Mn(III) is unstable under atmospheric conditions. For checking whether all the manganese in rainwater exists as Mn(II), a sensitive IC method for the detection of Mn(II) was developed. By adapting a photometric procedure based on the oxidation of Leucomalachite Green (LMG) to Malachite Green (MG) by permanganate (MnO^- ₄) to the IC-flow-through-system, a limit of determination of 1 μg/L Mn(II) could be achieved. A comparison of the IC measurements with GFAAS-results of the filtered samples showed agreeing results. Thus, manganese in rainwater and snow exists entirely as soluble Mn(II). Received: 24 May 1996/Revised: 7 July 1996/Accepted: 14 July 1996     

Anionic cartridge preconcentrators for inorganic arsenic, monomethylarsonate and dimethylarsinate determination by on-line HPLC-HG-AAS

 Preconcentration anionic cartridges in combination with hyphenated FI-HG-AAS and HPLC-HG-AAS have been evaluated for the preconcentration and quantification of total toxic arsenic and of inorganic arsenic, monomethylarsonate and dimethylarsinate species, respectively. Optimum retention and elution parameters of the species on the anionic cartridges are evaluated and the quality parameters of the analysis are reported. The detection limits for the arsenic species under study range from 0.1 μg L^-1 to 0.6 μg L^-1. The proposed method was successfully applied to the determination of arsenic species in spiked fresh water. Received: 2 April 1996/Revised: 22 July 1996/Accepted: 25 July 1996     

Dielectric behaviour of Gelatin solutions and Gels

 Sol and Gel state properties of aqueous gelatin solutions of concentrations 4%, 6%, 8% and 10% (w/v) have been investigated through dielectric relaxation studies done at various temperatures in the range T=20–60 °C carried out over a frequency range f=20 Hz–10 MHz and no relaxation of any nature was observed. The sharp transition observed at the gelation temperature T _gel provided an excellent matching with the same measured through differential scanning calorimetry (DSC). The capacitance (C _p) values above f=100 kHz became increasingly negative as the gel was melted to the sol state. However, in the gel state C _p was found to be almost independent of temperature for frequencies above 100 kHz. At frequencies lower than 10 kHz, C _p measured was ∼10⁵ F, implying pronounced interfacial polarization either due to electro-chemical reaction or because of ions getting trapped at some interface within the bulk. Received: 10 February 1997 Accepted: 2 September 1997