Analysis of acrylamide in coffee and dietary exposure to acrylamide from coffee

An analytical method for analysing acrylamide in coffee was validated. The analysis of prepared coffee includes a comprehensive clean-up using multimode solid-phase extraction (SPE) by automatic SPE equipment and detection by liquid chromatography tandem mass spectrometry using electrospray in the positive mode. The recoveries of acrylamide in ready-to-drink coffee spiked with 5 and 10 μg l⁻¹ were 96±14% and 100±8%, respectively. Within laboratory reproducibility for the same spiking levels were 14% and 9%, respectively. Coffee samples (n = 25) prepared twice by coffee machines and twice by a French Press Cafetière coffee maker contained 8±3 μg l⁻¹ and 9±3 μg l⁻¹ acrylamide. Five ready-to-drink instant coffee prepared twice contained 8±2 μg l⁻¹. Hence, the results do not show significant differences in the acrylamide contents in ready-to-drink coffee prepared by coffee machine, French Press or from instant coffee. Medium roasted coffee contained more acrylamide (10 μg l⁻¹) than dark roasted coffee (5 μg l⁻¹). Males aged 35–45 years, drinking on average 1.1 l coffee per day are exposed to the highest doses of acrylamide from coffee. The dietary intake of acrylamide from coffee comprises, on an average, 10 μg day⁻¹ for males and 9 μg day⁻¹ for females aged 35–45 years. Probabilistic modelling of the exposure of Danish consumers (all adults) to acrylamide from coffee shows a mean exposure of 6.5 μg day⁻¹ and a 95 percentile of 18 μg day⁻¹.     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

Biosorption of heavy metals on Aspergillus fumigatus immobilized Diaion HP-2MG resin for their atomic absorption spectrometric determinations

A solid phase extraction procedure based on biosorption of copper(II), lead(II), zinc(II), iron(III), nickel(II) and cobalt(II) ions on Aspergillus fumigatus immobilized Diaion HP-2MG has been investigated. The analytical conditions including amounts of A. fumigatus, eluent type, flow rates of sample and eluent solutions were examined. Good recoveries were obtained to the spiked natural waters. The influences of the concomitant ions on the retentions of the analytes were also examined. The detection limits (3sigma, N = 11) were 0.30 μg l⁻¹ for copper, 0.32 μg l⁻¹ for iron, 0.41 μg l⁻¹ for zinc, 0.52 μg l⁻¹ for lead, 0.59 μg l⁻¹ for nickel and 0.72 μg l⁻¹ for cobalt. The relative standard deviations of the procedure were below 7%. The validation of the presented procedure is performed by the analysis of three standard reference materials (NRCC-SLRS 4 Riverine Water, SRM 1515 Apple leaves and GBW 07605 Tea). The procedure was successfully applied for the determination of analyte ions in natural waters microwave digested samples including street dust, tomato paste, black tea, etc.     

Speciation of chromium in mineral waters and salinas by solid-phase extraction and graphite furnace atomic absorption spectrometry

A simple GF-AAS method for speciation analysis of chromium in mineral waters and salinas was developed. Cr(VI) species were separated from Cr(III) by solid-phase extraction with APDC (ammonium pyrrolidinedithiocarbamate). The APDC complexes were formed in the sample solution under proper conditions, adsorbed on Diaion HP-2MG resin and the resin was separated from the sample. After elution with concentrated nitric acid Cr(VI) was determined by GF-AAS. Total chromium was determined by GF-AAS directly in the sample and Cr(III) concentration was calculated as the difference between those results.

The detection limit of the method defined as 3 s of background variation was 0.03 μg l⁻¹ for Cr(VI) and 0.3 μg l⁻¹ for total chromium. RSD for Cr(VI) determination at the concentration of 0.14 μg l⁻¹ was 9%, and for total chromium at the concentration of 5.6 μg l⁻¹ was 5%. The recovery of Cr(VI) was in the range of 94–100%, dependently on type of the sample.

The investigation of recovery of the spiked Cr(VI) showed that at concentration levels near 1 μg l⁻¹ and lower recovery may be reduced significantly even by pure reagents that seem to be free from any reductants.     

Monoclonal antibody-based ELISA for the quantification of nitrofuran metabolite 3-amino-2-oxazolidinone in tissues using a simplified sample preparation

A sensitive and specific monoclonal ELISA for the determination of tissue bound furazolidone metabolite 3-amino-2-oxazolidinone (AOZ) is described. The procedure enables the detection of AOZ in matrix supernatant after homogenisation, protease treatment, acid hydrolysis and derivatisation of AOZ released from the tissue by o-nitrobenzaldehyde. The formed p-nitrophenyl 3-amino-2-oxazolidinone (NPAOZ) is determined by ELISA calibrated with matrix-matched standards in the concentration range of 0.05–5.0 μg I⁻¹. The assay was validated according to criteria set down by Commission Decision 2002/657/EC for the performance and validation of analytical methods for chemical residues. Detection capability, set on the basis of acceptance of no false negative results, was 0.4 μg kg⁻¹ for shrimp, poultry, beef and pork muscle. This sensitivity approaches the established confirmatory LC–MS/MS able to quantify tissue-bound AOZ at levels as low as 0.3 μg kg⁻¹. An excellent correlation of results obtained by ELISA and LC/MS–MS within the concentration range 0–32.1 μg kg⁻¹ was found in the naturally contaminated shrimp samples (r = 0.999, n = 8). A similar correlation was found for the incurred poultry samples within the concentration range of 0–10.5 μg kg⁻¹ (r = 0.99, n = 8).     

Flow injection hydride generation electrothermal atomic absorption spectrometric determination of toxicologically relevant arsenic in urine

Analytical procedure for the determination of toxicologically relevant arsenic (the sum of arsenite, arsenate, monomethylarsonate and dimethylarsinate) in urine by flow injection hydride generation and collection of generated inorganic and methylated hydrides on an integrated platform of a transverse-heated graphite atomizer for electrothermal atomic absorption spectrometric determination (ETAAS) is elaborated. Platforms are pre-treated with 2.7 μmol of zirconium and then with 0.10 μmol of iridium which serve both as an efficient hydride sequestration medium and permanent chemical modifier. Arsine, monomethylarsine and dimethylarsine are generated from diluted urine samples (10–25-fold) in the presence of 50 mmol L⁻¹ hydrochloric acid and 70 mmol L⁻¹ l-cysteine. Collection, pyrolysis and atomization temperatures are 450, 500, 2100 and 2150 °C, respectively. The characteristic mass, characteristic concentration and limit of detection (3σ) are 39 pg, 0.078 μg L⁻¹ and 0.038 μg L⁻¹ As, respectively. The limits of detection in urine are ca. 0.4 and 1 μg L⁻¹ with 10- and 25-fold dilutions. The sample throughput rate is 25 h⁻¹. Applications to several urine CRMs are given.     

Mimic oil recovery with a SDBS–dodecane–silica gel system

The wettability of the solid powder of silica gel was determined via a modified Washburn equation expressed as contact angles. The interfacial tension (γ) between the dodecane and the dilute sodium dodecyl benzene sulfonate (SDBS) aqueous solution was obtained using the spinning drop (γ<10 mN m⁻¹) or drop volume methods (γ>10 mN m⁻¹). Contact angle changes for SDBS aqueous solutions on the surface of a silica gel powder were studied. The average aggregation number of SDBS micelles in aqueous solution was determined using the fluorescence quenching method. The relationship between the wettability of the powder surface, the critical micelle concentration (CMC) of SDBS and the mimic oil recovery of the resident oil on the powder surface has been explored. It has been found that good residual oil recovery was achieved by surface wettability changes at the interfacial tensions around 4–5 mN m⁻¹, which is far from the ‘ultra low’ condition (≤10⁻³ mN m⁻¹).     

Spectrophotometric determination of terfenadine in pharmaceutical preparations by charge-transfer reactions

A simple, rapid and accurate method for the spectrophotometric determination of terfenadine has been developed. The proposed method based on the charge-transfer reactions of terfenadine, as n-electron donor, with 7,7,8,8-tetracyanoquinodimethane (TCNQ), tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, p-CLA) as π-acceptors to give highly colored complexes. The experimental conditions such as reagent concentration, reaction solvent and time have been carefully optimized to achieve the highest sensitivity. Beer's law is obeyed over the concentration ranges of 3–72, 3–96, 12–168 and 24–240 μg mL⁻¹ terfenadine using TCNQ, TCNE, DDQ and p-CLA, respectively, with correlation coefficients 0.9999, 0.9974, 0.9997 and 0.9979 and detection limits 0.3, 0.4, 2.6 and 12.3 μg mL⁻¹, for the reagents in the same order. DDQ and p-CLA react spontaneously with terfenadine to give colored complexes that can be applied for the flow injection analysis of terfenadine in the concentration ranges 2.4–120 and 24–240 μg with correlation coefficients 0.9990 and 0.9985 and detection limits 0.8 and 2.7 μg for DDQ and p-CLA, respectively, in addition to the high sampling through output of 40 sample h⁻¹.     

Development of a luminol-based chemiluminescence flow-injection method for the determination of dichlorvos pesticide

A simple, fast chemiluminescence (CL) flow-injection method based on the reaction of luminol with H₂O₂ in the presence of a cationic surfactant (cyltrimethylammonium bromide, CTMAB) has been described for the direct determination of dichlorvos pesticide (DDVP). Under the optimal conditions, the CL intensity was linear to the DDVP concentration in the range of 0.02–3.1 μg ml⁻¹ (r=0.9998, n=10). The relative standard deviation was 3.4% at 0.35 μg ml⁻¹ (n=10), with a detection limit (3σ) of 0.008 μg ml⁻¹ DDVP. The possible reaction mechanism was also discussed. This method has been successfully applied to the determination of trace DDVP residue in vegetable sample and results have been compared with that of the UV method.     

Enhancement of the chemiluminescence of penicillamine and ephedrine after derivatization with aldehydes using tris(bipyridyl)ruthenium(II) peroxydisulfate system and its analytical application

A novel sequential injection (SI) method was developed for the determination of penicillamine (PA) and ephedrine (EP) based on the reaction of these drugs with tris(bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) and peroxydisulfate (S₂O₈²⁻) in the presence of light. Derivatization of PA and EP with aldehydes has resulted in a significant enhancement of the chemiluminescence emission signal by at least 25 times for PA and 12 times for EP, leading to better sensitivities and lower detection limits for both drugs. The instrumental setup utilized a syringe pump and a multiposition valve to aspirate the reagents, (Ru(bpy)₃²⁺ and S₂O₈²⁻), and a peristaltic pump to propel the sample. The experimental conditions affecting the derivatization reaction and the chemiluminescence reaction were systematically optimized using the univariate approach. Under the optimum conditions linear calibration curves between 0.2–24 μg mL⁻¹ for PA and 0.2–20 μg mL⁻¹ for EP were obtained. The detection limits were 0.1 μg mL⁻¹ for PA and 0.03 μg mL⁻¹ for EP. The procedure was applied to the analysis of PA and EP in pharmaceutical products and was found to be free from interferences from concomitants usually present in these preparations.     

A new immune resonance scattering spectral assay for trace fibrinogen with gold nanoparticle label

An on-line stacking method based on moving reaction boundary (MRB) was developed for the sensitive determination of barbital and phenobarbital in human urine via capillary electrophoresis (CE). The optimized conditions for the method are: 60 mmol L⁻¹ pH 11.0 Gly–NaOH as the background electrolyte, 10 mmol L⁻¹ pH 5.5 Gly–HCl as sample buffer, secobarbital as the internal standard (IS), 12.5 kV, 1.4 psi 10 s sample injection, 75 μm ID 60.2 cm total length (50 cm effective length) capillary and 214 nm detect wavelength. Under the optimized conditions, the method can well stack and separate barbital and phenobarbital in urine samples and result in 20.5-fold and 22.6-fold improvement in concentration sensitivity for barbital and phenobarbital, respectively. Furthermore, the method holds: (1) good linear calibration functions for the two target compounds (correlation coefficients r > 0.999), (2) low limits of detection (0.27 μg mL⁻¹ for barbital and 0.26 μg mL⁻¹ for phenobarbital), (3) low limits of quantification (0.92 μg mL⁻¹ for barbital and 0.87 μg mL⁻¹ for phenobarbital), (4) good precision (R.S.D. of intra-day and inter-day less than 5.38% for barbital and 1.67% for phenobarbital, respectively) and (5) high recoveries at three concentration levels (90.27–106.36% for barbital and 93.05–113.60% for phenobarbital in urine). The method is simple, sensitive and efficient, and can fit to the need of clinical and forensic toxicology.     

Continuous flow system for lead determination by faas in spirituous beverages with solid phase extraction and on-line copper removal

A continuous flow system for the determination of lead in home made spirituous beverages was developed. The determination was based on the formation of a neutral chelate of the element with ammonium pyrrolidine dithiocarbamate, its adsorption onto a minicolumn packed with sodium faujasite type Y synthetic zeolite, followed by elution with methyl isobutyl ketone and determination by flame atomic absorption spectrometry. Ethanol and copper interfere strongly in the determination and therefore, must be separated prior to the analysis. Copper is removed by precipitation with rubeanic acid, while ethanol is eliminated by rotaevaporation. Sample solutions containing Pb²⁺ in the concentration range from 5 to 120 μg l⁻¹ at pH 2.5 could be analyzed, by using a preconcentration time of 3 min. Preconcentration factors from 80 to 140 were achieved for a sample volume of 6 ml and the detection limit varied from 1.4 to 3.5 μg l⁻¹, depending on the matrix composition. The relative standard deviations for 60 μg l⁻¹ Pb was 3.2% (n = 10) and the recovery of spikes (20, 40, 60 and 80 μg l⁻¹) added to the samples was estimated within 92–105% range, suggesting that lead can be quantitatively determined in such samples. Determining lead in several samples by an alternative technique further checked the accuracy. Finally, the concentrations of Pb²⁺ determined in 28 samples of Venezuelan spirituous beverages were in 12.6–370.0 μg l⁻¹ range, depending on the fermenting material based on different mixtures of agave, raw sugar cane and white sugar.     

Cyclic-AMP levels in the lichen Evernia prunastri are modulated by light quantity and quality

Changes in the accumulation of cAMP levels were measured by the isotope dilution assay using protein kinase A in the lichen Evernia prunastri at varying light conditions. cAMP levels decreased following exposure to low irradiance (20 μmol quanta m⁻² s⁻¹, and below the compensation point for photosynthesis) of red light (600–710-nm wave length) and increased by 50% after far-red light illumination (15 μmol quanta m⁻² s⁻¹, 710–800-nm wavelength). Far-red partially reverted the effect of red light when the former was supplied after the latter. cAMP increased to its maximum level under high irradiance supplied by a non-photomorphogenic yellow light source (400 μmol quanta m⁻² s⁻¹, reaching photosynthetic saturation). The addition of small quantities of red and far-red light, however, had profound restricting effects on cAMP accumulation. The addition of inhibitors of electron transport chains did not promote any significant change in cAMP levels in any of the treatments, indicating that cAMP accumulation could not depend on ATP synthesis. We propose that the response of cAMP accumulation at low irradiance comprises the activation of a morphogenic pathway through a red/far-red photoreceptor. In addition, at high irradiance the response would occur most likely through photosystems II and I acting as sensors of light quantity, that can be strongly modified by the red/far-red photomorphogenic system. Thus, cAMP would be involved in sensing the overall light environment.     

Effect of pH on interface composition and on quality of oil-in-water emulsions made with hen egg yolk

Constituents of egg yolk are key ingredients of many food emulsions. They contribute to create an interfacial film between oil and water, which determines largely the characteristics of the emulsions. Food emulsions prepared with yolk are made at various pHs. However, the effect of pH on the adsorption of yolk constituents and on the composition of the interfacial film is not known. The present study deals with the influence of pH (3, 6 and 9), on protein interface concentration and composition, change in interfacial tension, and oil droplet diameter, of emulsions made with yolk. Emulsions were prepared as follows: 0.5% w/v of yolk; oil volume fraction: 0.375, homogenisation rate: 20 000 rpm/2 min. pH 6 provided the best conditions to prepare emulsion with yolk. The average diameter of oil droplets was lower at pH 6 (8.5 μm) than at pH 3 (11.8 μm) and pH 9 (13.5 μm). The interfacial protein concentration was higher at pH 6 (1.7 mg m⁻²) than at pH 3 and pH 9 (0.5 mg m⁻²). At pH 6, all the proteins of yolk, except phosvitin, were adsorbed at the interface and the interfacial tension at steady-state was lower (10 mN m⁻¹) than at pH 3 (15 mN m⁻¹) and pH 9 (30 mN m⁻¹). At pH 3, proteins at the interface are mainly phosvitin, and, at pH 9, some apoproteins of LDL and HDL. The pH modulates the composition of yolk proteins at the interface, mainly by modifying the net charge of the proteins causing their repulsion or dimerisation.     

Passive sampling of ambient ozone by solid phase microextraction with on-fiber derivatization

The solid phase microextraction (SPME) device with the polydimethylsiloxane/divinylbenzene (PDMS/DVB) fiber was used as a passive sampler for ambient ozone. Both O-2,3,4,5,6-(pentafluorobenzyl)hydroxylamine hydrochloride (PFBHA) and 1,2-di-(4-pyridyl)ethylene (DPE) were loaded onto the fiber before sampling. The SPME fiber assembly was then inserted into a PTFE tubing as a passive sampler. Known concentrations of ozone around the ambient ground level were generated by a calibrated ozone generator. Laboratory validations of the SPME passive sampler with the direct-reading ozone monitor were performed side-by-side in an exposure chamber at 25 °C. After exposures, pyriden-4-aldehyde was formed due to the reaction between DPE and ozone. Further on-fiber derivatizations between pyriden-4-aldehyde and PFBHA were followed and the derivatives, oximes, were then determined by portable gas chromatography with electron capture detector. The experimental sampling rate of the SPME ozone passive sampler was found to be 1.10 × 10⁻⁴ cm³ s⁻¹ with detection limit of 58.8 μg m⁻³ h⁻¹. Field validations with both SPME device and the direct-reading ozone monitor were also performed. The correlations between the results from both methods were found to be consistent with r = 0.9837. Compared with other methods, the current designed sampler provides a convenient and sensitive tool for the exposure assessments of ozone.     

Flow injection determination of bismuth in urine by successive retention of Bi(III) and tetrahydroborate(III) on an anion-exchange resin and hydride generation atomic absorption spectrometry

Bismuth as BiCl₄⁻ and BH₄⁻ ware successively retained in a column (150 mm × 4 mm, length × i.d.) packed with Amberlite IRA-410 (strong anion-exchange resin). This was followed by passage of an injected slug of hydrochloric acid resulting in bismuthine generation (BiH₃). BiH₃ was stripped from the eluent solution by the addition of a nitrogen flow and the bulk phases were separated in a gas–liquid separator. Finally, bismutine was atomized in a quartz tube for the subsequent detection of bismuth by atomic absorption spectrometry. Different halide complexes of bismuth (namely, BiBr₄⁻, BiI₄⁻ and BiCl₄⁻) were tested for its pre-concentration, being the chloride complexes which produced the best results. Therefore, a concentration of 0.3 mol l⁻¹ of HCl was added to the samples and calibration solutions. A linear response was obtained between the detection limit (3σ) of 0.225 and 80 μg l⁻¹. The R.S.D.% (n = 10) for a solution containing 50 μg l⁻¹ of Bi was 0.85%. The tolerance of the system to interferences was evaluated by investigating the effect of the following ions: Cu²⁺, Co²⁺, Ni²⁺, Fe³⁺, Cd²⁺, Pb²⁺, Hg²⁺, Zn²⁺, and Mg²⁺. The most severe depression was caused by Hg²⁺, which at 60 mg l⁻¹ caused a 5% depression on the signal. For the other cations, concentrations between 1000 and 10,000 mg l⁻¹ could be tolerated. The system was applied to the determination of Bi in urine of patients under therapy with bismuth subcitrate. The recovery of spikes of 5 and 50 μg l⁻¹ of Bi added to the samples prior to digestion with HNO₃ and H₂O₂ was in satisfactory ranges from 95.0 to 101.0%. The concentrations of bismuth found in six selected samples using this procedure were in good agreement with those obtained by an alternative technique (ETAAS). Finally, the concentration of Bi determined in urine before and after 3 days of treatment were 1.94 ± 1.26 and 9.02 ± 5.82 μg l⁻¹, respectively.     

Determination of arsenic by pervaporation-flow injection hydride generation and permanganate spectrophotometric detection

A novel pervaporation-flow injection (PFI) system for the determination of As(III) in aqueous samples at μg l⁻¹ level is described. The analytical procedure involved stopping the acceptor stream and injecting acidified As(III) samples into a 0.3 M HCl stream which was mixed with a 0.14 M sodium borohydride in 0.025 M NaOH stream. The arsine generated was transported in the pervaporation unit across a semi-permeable membrane (1.5 mm thickness) into the static acceptor solution containing 1.0×10⁻⁴ M KMnO₄ in 0.1 M H₂SO₄ where it was oxidised. The acceptor stream was restarted after 6.5 min, and the decrease in permanganate absorbance at 528 nm was monitored to determine the initial concentration of As(III) in the samples. The method is characterised by a linear calibration range from 0.25 to 2000 μg l⁻¹, a detection limit of 0.18 μg l⁻¹ and a sampling frequency of 7 h⁻¹. Samples containing As(V) were pre-treated with KI and HCl prior to injection to reduce As(V) to As(III). The effects of common anionic and cationic interferences, and the elimination of some metallic interferences using -cysteine are discussed. The method was applied to the analysis of environmental waters and the results were in good agreement with hydride generation atomic absorption spectrometric data.     

Fast flow-injection fluorimetric determination of amiloride by using a solid sensing zone

A rapid and simple flow-through solid phase spectrofluorimetric system is described in this paper for the determination of the diuretic amiloride in physiological fluid (serum) and pharmaceuticals. The sensor was developed in conjunction with a monochannel flow-injection analysis system with fluorimetric transduction. Amiloride was transitorily retained on cationic exchanger gel Sephadex SP-C25 placed in the detection area into the cell. The determination is carried out without any derivatization reaction, by measuring directly the intrinsic fluorescence of the analyte and using the peak height as analytical signal. The wavelengths of excitation and emission were 291 and 419 nm, respectively. Amiloride could be determined in the concentration ranges of 10–600 and 4–250 μg l⁻¹ at a sampling rate of 24 and 30 h⁻¹, respectively with detection limits of 0.92 and 0.33 μg l⁻¹ for 100, and 600 μl of sample volume injected, respectively. The relative standard deviations for ten independent determinations were better than 0.65%. The method was satisfactorily applied to the determination of amiloride in spiked biological fluids (serum) and pharmaceutical preparations without any pretreatment of the samples.     

Reverse flow injection spectrophotometric determination of iron(III) using chlortetracycline reagent

A simple reversed flow injection colourimetric procedure for determining iron(III) was proposed. It is based on the reaction between iron(III) with chlortetracycline, resulting in an intense yellow complex with a suitable absorption at 435 nm. A 200 μl chlortetracycline reagent solution was injected into the phosphate buffer stream (flow rate 2.0 ml min⁻¹) which was then merged with iron(III) standard or sample in dilute nitric acid stream (flow rate 1.5 ml min⁻¹). Optimum conditions for determining iron(III) were investigated by univariate method. Under the optimum conditions, a linear calibration graph was obtained over the range 0.5–20.0 μg ml⁻¹. The detection limit (3σ) and the quantification limit (10σ) were 0.10 and 0.82 μg ml⁻¹, respectively. The relatives standard deviation of the proposed method calculated from 12 replicate injections of 2.0 and 10.0 μg ml⁻¹ iron(III) were 0.43 and 0.59%, respectively. The sample throughput was 60 h⁻¹. The proposed method has been satisfactorily applied to the determination of iron(III) in natural waters.     

Selective determination of airborne hexavalent chromium using inductively coupled plasma mass spectrometry

A new method for determining ultra-trace levels of hexavalent chromium in ambient air has been developed. The method involves a 24-h sampling of air into potassium hydroxide solution, followed by silica gel column separation of chromium (VI), then preconcentration by complexation and solvent extraction. The chromium (VI) complex was dissolved in nitric acid. The resultant chromium ions were determined by inductively coupled plasma mass spectrometry (ICP–MS) using a dynamic reaction cell (DRC) with ammonia as the reactive gas to reduce polyatomic interferences. The interconversion of chromium in potassium hydroxide solution and air sample matrix were investigated under ambient conditions. It was found that there was no conversion of chromium (VI) into chromium (III) species. However, it was observed that some chromium (III) species were converted into chromium (VI) species. For a KOH solution containing 100 μg l⁻¹ of chromium (III) species, the rate of conversion was found to be 3% after 24 h exposure, 8% after 48 h, 10% after 72 h and no further conversion was observed thereafter. However, in a solution containing air sample matrix, 9.3% of chromium (III) converted to chromium (VI) within 6 h, and during the course of a 11-day exposure period, 13% (range 8–17%) of chromium (III) converted to chromium (VI). The method detection limit (MDL) for chromium (VI) in potassium hydroxide solution (0.025 M) was found to be 2×10⁻² μg l⁻¹. This is equivalent to 0.2 ng m⁻³ (for 23 m³ air sampled into 200 ml of KOH solution over a 24-h period). The recovery of spiked chromium (VI) from solutions containing air sample matrix was 95±9% (n=8). Matrix related interferences were estimated to be less than 10% based on recovery studies. The concentration of airborne chromium (VI) in Sydney residential areas was found to be less than 0.2 ng m⁻³, however, in industrial areas the concentrations ranged from 0.2 to 1.3 ng m⁻³ using this analytical procedure.