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.     

Flow-injection in-line complexation for ion-pair reversed phase high performance liquid chromatography of some metal-4-(2-pyridylazo) resorcinol chelates

Flow injection (FI) was coupled to ion-pair reversed phase high performance liquid chromatography (IP-RPHPLC) for the simultaneous analysis of some metal-4-(2-pyridylazo) resorcinol (PAR) chelates. A simple reverse flow injection (rFI) set-up was used for in-line complexation of metal-PAR chelates prior to their separation by IP-RPHPLC. The rFI conditions were: injection volume of PAR 85 μL, flow rate of metal stream 4.5 mL min⁻¹, concentration of PAR 1.8 × 10⁻⁴ mol L⁻¹ and the mixing coil length of 150 cm. IP-RPHPLC was carried out using a C₁₈ μBondapak column with the mobile phase containing 37% acetonitrile, 3.0 mmol L⁻¹ acetate buffer pH 6.0 and 6.2 mmol L⁻¹ tetrabutylammonium bromide (TBABr) at a flow rate of 1.0 mL min⁻¹ and visible detection at 530 and 440 nm. The analysis cycle including in-line complexation and separation by IP-RPHPLC was 16 min, which able to separate Cr(VI) and the PAR chelates of Co(II), Ni(II) and Cu(II).     

Investigation of on-line coupling electrothermal atomic absorption spectrometry with flow injection sorption preconcentration using a knotted reactor for totally automatic determination of lead in water samples

A flow injection on-line sorption preconcentration electrothermal atomic absorption spectrometric system for fully automatic determination of lead in water was investigated. The discrete non-flow-through nature of ETAAS, the limited capacity of the graphite tube and the relatively large volume of the knotted reactor (KR) are obstacles to overcome for the on-line coupling of the KR sorption preconcentration system with ETAAS. A new FI manifold has been developed with the aim of reducing the eluate volume and minimizing dispersion. The lead diethyldithiocarbamate complex was adsorbed on the inner walls of a knotted reactor made of PTFE tubing (100 cm long, 0.5 mm i.d.). After that, an air flow was introduced to remove the residual solution from the KR and the eluate delivery tube, then the adsorbed analyte chelate was quantitatively eluted into a delivery tube with 50 μl of ethanol. An air flow was used to propel the eluent from the eluent loop through the reactor and to introduce all the ethanolic eluate onto the platform of the transversely heated graphite tube atomizer, which was preheated to 80°C. With the use of the new FI manifold, the consumption of eluent was greatly reduced and dispersion was minimized. The adsorption efficiency was 58%, and the enhancement factor was 142 in the concentration range 0.01–0.05 μg l⁻¹ Pb at a sample loading rate of 6.8 ml min⁻¹ with 60 s preconcentration time. For the range 0.1–2.0 μg l⁻¹ of Pb a loading rate of 3.0 ml min⁻¹ and 30 s preconcentration time were chosen, resulting in an adsorption efficiency of 42% and an enhancement factor of 21, respectively. A detection limit (3σ) of 2.2 ng l⁻¹ of lead was obtained using a sample loading rate of 6.8 ml min⁻¹ and 60 s preconcentration. The relative standard deviation of the entire procedure was 4.9% at the 0.01 μg l⁻¹ Pb level with a loading rate of 6.8 ml min⁻¹ and 60 s preconcentration, and 2.9% at the 0.5 μg l⁻¹ Pb level with a 3.0 ml min⁻¹ loading rate and 30 s preconcentration. Efficient washing of the matrix from the reactor was critical, requiring the use of the standard addition method for seawater samples. The analytical results obtained for seawater and river water standard reference materials were in good agreement with the certified values.     

Simultaneous determination of arsenic, antimony and selenium by gas-phase diode array molecular absorption spectrometry, after preconcentration in a cryogenic trap

This paper describes a method for the simultaneous determination of As(III), Sb(III) and Se(IV) by combining hydride generation and gas phase molecular absorption spectrometry. A system for continuous hydride generation has been designed and developed, based on the use of a double process of gas-liquid separation, and optimal compromise operation conditions for the three compounds have been found. After generation, the hydrides are collected in a liquid nitrogen cryogenic trap, and then evaporated and driven to the flow cell of a diode array spectrophotometer, in which the transient signals over the 190–250 nm wavelength interval are measured. Under the recommended conditions (sample flow: 35 ml min⁻¹, 0.5 M HCl; reductor flow: 4 ml min⁻¹ of 4% NaBH₄, solution) linear response ranges above 50 μg 1⁻¹ for As(III), 30 μg 1⁻¹ for Sb(III) and 200 μg 1⁻¹ for Se(IV) are obtained with detection limits of 22 μg 1⁻¹, 15 μg 1⁻¹ and 65 μg 1⁻¹, respectively. Multiwavelength linear regression equations were used for the simultaneous determination of the three elements in different synthetic samples, with good precision and accuracy and to study simultaneously the interference from different chemical species for the three compounds. Results were similar to those obtained by other techniques using hydride generation.     

Low-molecular-mass anion screening for forensic environmental analyses by capillary zone electrophoresis with indirect UV detection

A method for low-molecular-mass anion screening is described using a buffer composed of 5-sulfosalicylate (SS) as a visualizing ion, hexadimethrine bromide as an electroosmotic flow modifier and Tris as a pH buffer component, at pH 8.6. All ions with effective mobility higher than 2610⁻⁹ m² s⁻¹ V⁻¹ can be separated within 7.5 min under −30 kV. By using the moderately mobile SS (5410⁻⁹ m² s⁻¹ V⁻¹), not only the sensitivity of the detection is improved due to its high UV absorptivity, but also a smaller overall overloading effect is achieved. Meanwhile, the resolution of the high mobility ions, which is normally critical, remains almost the same as compared to a chromate buffer. With an electrokinetic injection, the limit of detection (LOD) of the common ions is 2–13 nM and the detection range is linear up to 0.5–3 μM. With a hydrostatic injection the LOD is 0.15–1 μM and the detection range is linear up to 25–200 μM. The identification of ions is performed by comparing the mobility of the ions with that of standards, taking the apparent and effective mobility of HCO₃⁻, which is normally present in the sample solution, as a reference.     

Supported liquid membranes for the determination of vanillin in food samples with amperometric detection

A supported liquid membrane system has been developed for the extraction of vanillin from food samples. A porous PTFE membrane is impregnated with an organic solvent, which forms a barrier between two aqueous phases. The analyte is extracted from a donor phase into the hydrophobic membrane and then back extracted into a second aqueous solution, the acceptor. The determination (100–1400 μg ml⁻¹ vanillin) was performed using a PVC-graphite composite electrode versus Ag/AgCl/3MKCl at +0.850 V placed in a wall-jet flow cell as amperometric detector. The solid sample is directly placed in the membrane unit without any treatment, and the analyte was extracted from the sample, passes through the membrane and conduced to the flow cell by the acceptor stream. The limit of detection (3σ) was 44 μg ml⁻¹. The method was applied to the determination of vanillin (9–606 μg g⁻¹) in food samples.     

Donnan dialysis preconcentration coupled with ion chromatography and electrocatalytic oxidation for the determination of cyanide

An electrocatalytic amperometric detector for the ion chromatographic determination of CN⁻ is described. A conducting composite that is based on a graphite-loaded sol–gel material comprises the working electrode. The composite is doped with a Ru^II metallodendrimer which is demonstrated to promote the electrochemical oxidation of CN⁻ at potentials positive of 0.5 V vs. Ag/AgCl. In 6 mM NaOH, 0.05 M NaCl flowed at 1.0 ml min⁻¹, a 5-point calibration curve with the following linear least squares parameters is obtained over the range, 1.0–30 M CN⁻: slope, 24.2±0.1 nA M⁻¹; intercept, −6±2 nA; and r, 0.9997. The detection limit, 0.7 μM CN⁻, compares favorably to that obtained by amperometry at a silver electrode, 0.5 μM CN⁻, under comparable experimental conditions. A 60-min preconcentration by Donnan dialysis increases the sensitivity by a factor of 23.6.     

Sub-picomole high-performance liquid chromatographic/mass spectrometric determination of glutathione in the maize (Zea mays L.) kernels exposed to cadmium

Changes in fresh weight, total protein amounts (Bradford’s method), cadmium concentration (DPASV) and glutathione content (HPLC/MS) were studied in maize kernels cultivated for 5 days at three different cadmium concentrations (0, 10 and 100 μmol l⁻¹ CdCl₂). A highly sensitive HPLC/MS method was used for the determination of glutathione on a reversed-phase Atlantis dC₁₈ chromatographic column (150 mm×2.1 mm, 3 μm particle size). An isocratic mode with acetonitrile–0.01% TFA (5:95, flow rate 0.1 ml min⁻¹ and 30 °C) was applied. The m/z spectra and the data for the selected ion monitoring (SIM) mode were recorded at m/z for glutathione 308→179. Cadmium concentration was measured by a differential pulse adsorptive stripping voltammetry (DPASV) after deposition on a hanging mercury drop electrode (HMDE) at potential −0.7 V (accumulation time 180 s, acetate buffer of pH 3.6, 22 °C). An AUTOLAB with a VA-Stand 663 and a three-electrode system consisting of the HMDE as a working electrode with area 0.4 mm², an Ag/AgCl/3 mol l⁻¹ KCl as a reference electrode and a Pt-wire as an auxiliary electrode was employed. The maize kernels exposed to the highest cadmium concentration (100 μmol l⁻¹) germinated formerly and much better. A rapid increase of the fresh weight probably relates with more intensive uptake of water in order to decrease cadmium concentration. An intensive preservation of homeostasis of Cd²⁺ ions in the germinating plants by defending mechanisms might explain differences of uptake rate of cadmium. The linear increase of GSH content with the exposure time at all studied concentration suggests the defending mechanisms might be triggered by concentrations of a heavy metal.     

Sequential injection sample introduction microfluidic-chip based capillary electrophoresis system

A sequential injection micro-sample introduction system was coupled to a microfluidic-chip based capillary electrophoresis system through a split–flow sampling interface integrated on the micro-chip. The microfluidic system measured 20×70×3 mm in dimension, and was produced using a non-lithographic approach with components readily available in the analytical laboratory. In the H-configuration channel design the horizontal separation channel was a 75 μm I.D.×60 mm quartz capillary, with two vertical side arms produced from plastic tubing. The conduits were embedded in silicon elastomer with a planar glass base. Sequential introduction of a series of samples with about 2.5% carryover was achieved at 48 h⁻¹ throughput with samples containing a mixture of fluorescein isothiocyanate (FITC)-labeled amino acids using SI sample volumes of 3.3 μl and carrier flow-rate of 2.0 ml min⁻¹. Baseline separation was achieved for FITC-labeled arginine, phenylalanine, glycine and FITC (laser induced fluorescence detection) in sodium tetraborate buffer (pH 9.2) within 8–80 s, at separation lengths of 25–35 mm and electrical field strengths of 250–1500 V cm⁻¹, with plate heights in the 0.7–3 μm range.     

Tuning the parameters for fast respirometry

The aerobic bacterial respiration rate is an indicator of microbial growth and metabolism, essential for monitoring the oxidation process and organic load content of samples in a diverse field of application from influent streams in wastewater treatment facilities to industrial fermentations. This paper looks at the influence of parameters, such as culture concentration and volume, sample surface area/volume ratio and headspace volume to achieve optimisation of respirometry measurement and thus design a bench-top respirometric device, based on the monitoring of the pressure changes in a closed chamber where a bacterial culture is allowed to respire in contact with a sample. Contrary to traditional respirometry, the goal is detection of bacterial respiration within 5 min in a minimal sample volume. Both qualitative and quantitative data could be derived using a simple equation and fine-tuning of the micro-manometric parameters of the device, with a most important finding being that minimal headspace volume in combination with elevated bacterial populations maximised absolute pressure change response and favoured high sensitivity at short response time, even though the conditions indicated oxygen-limitation. Furthermore, in comparison with a commercially available respirometer the typical respiration rate of stationary phase P. putida M10 gave oxygen uptake rate (OUR) and specific oxygen uptake rate (SOUR) of 38 μmol l⁻¹ min⁻¹ and 5 μmol g⁻¹ min⁻¹, respectively with the ‘classical’ system, while the μ-Warburg device designed here showed a typical response, for the culture with the same dry cell concentration, of 66 μmol l⁻¹ min⁻¹ for the OUR and 9 μmol g⁻¹ min⁻¹ for the SOUR. The remarkable outcome from this data, therefore, is that it appears that the high surface area/volume geometry of the μ-Warburg device design has achieved less respiration limitation, even though the sample is unstirred. This presents important insight regarding future respirometer design.     

Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent

A fully automated procedure for the determination of ng l⁻¹ amounts of lead has been developed using flow injection (FI) online column preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. The interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn (50 μl) packed with Pb-02, and after washing the column with dilute nitric acid, air is introduced to remove all solution from the column and connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100°C, with 36 μl of ETDA solution (0.035 mol l⁻¹, pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and with a sample loading flow rate of 3 ml min⁻¹ and a 60 s preconcentration time, the enhancement factor was 77 and the throughput was 17 samples per hour. The relative standard deviation (n = 10) at the 300 ng l⁻¹ level was 2.7%, and the detection limit (3σ) was 0.4 ng l⁻¹. No interference from heavy metals was observed, but ions of Ba²⁺, Sr²⁺ and K⁺ were found to interfere when the concentration ratios of interferent to lead exceeded values of 2000, 20 000 and 200 000, respectively. Quantitative recovery of lead was achieved from sodium, magnesium, aluminum, lanthanum and heavy metal salt solutions. The high selectivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of high-purity reagents, semiconductors and other high-purity materials. Results are presented for the determination of lead in some high-purity reagents.     

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.     

Optimisation of sample treatment for arsenic speciation in alga samples by focussed sonication and ultrafiltration

A procedure for arsenic species fractionation in alga samples (Sargassum fulvellum, Chlorella vulgaris, Hizikia fusiformis and Laminaria digitata) by extraction is described. Several parameters were tested in order to evaluate the extraction efficiency of the process: extraction medium, nature and concentration (tris(hydroxymethyl)aminomethane, phosphoric acid, deionised water and water/methanol mixtures), extraction time and physical treatment (magnetic stirring, ultrasonic bath and ultrasonic focussed probe). The extraction yield of arsenic under the different conditions was evaluated by determining the total arsenic content in the extracts by ICP-AES. Arsenic compounds were extracted in 5 mL of water by focussed sonication for 30 s and subsequent centrifugation at 14,000 × g for 10 min. The process was repeated three times. Extraction studies show that soluble arsenic compounds account for about 65% of total arsenic.

An ultrafiltration process was used as a clean-up method for chromatographic analysis, and also allowed us to determine the extracted arsenic fraction with a molecular weight lower than 10 kDa, which accounts for about 100% for all samples analysed.

Speciation studies were carried out by HPLC–ICP-AES. Arsenic species were separated on a Hamilton PRP-X100 column with 17 mM phosphate buffer at pH 5.5 and 1.0 mL min⁻¹ flow rate. The chromatographic method allowed us to separate the species As(III), As(V), MMA and DMA in less than 13 min, with detection limits of about 20 ng of arsenic per species, for a sample injection volume of 100 μL. The chromatographic analysis allowed us to identify As(V) in Hizikia (46 ± 2 μg g⁻¹), Sargassum (38 ± 2 μg g⁻¹) and Chlorella (9 ± 1 μg g⁻¹) samples. The species DMA was also found in Chlorella alga (13 ± 1 μg g⁻¹). However, in Laminaria alga only an unknown arsenic species was detected, which eluted in the dead volume.     

Continuous monitoring for cyanide in waste water with a galvanic hydrogen cyanide sensor using a purge system

A continuous monitoring system for cyanide with a galvanic hydrogen cyanide sensor and an aeration pump for purging was developed. Hydrogen cyanide evolved from cyanide solution using a purging pump was measured with the hydrogen cyanide sensor. The system showed good performance in terms of stability and selectivity. A linear calibration curve was obtained in the concentrating range from 0 to 15 mg dm³ of cyanide ion with a slope of −0.24 μA mg⁻¹ dm⁻³. The lower detection limit was 0.1 mg dm⁻³. The 90% response time of the sensor system was within 3.5 min for a 0.5 mg dm⁻³ cyanide solution, when the flow rate of the purging air was 1 dm³ min⁻¹. The system maintained the initial performance for 6 months in the field test. The developed galvanic sensor system was not subject to interference from sulfide and residual chlorine, compared with a potentiometric sensor system developed previously. The analytical results obtained by the present system were in good agreement with those obtained by the pyridine pyrazolone method. The correlation factor and regression line between both methods were 0.979 and Y=2.30×10⁻⁴+1.12X, respectively. This system was successfully applied for a continuous monitoring of cyanide ion in waste water.     

Coupling of flow injection wetting-film extraction without segmentation and phase separation to flame atomic absorption spectrometry for the determination of trace copper in water samples

A flow injection wetting-film extraction system without segmentor and phase separator has been coupled to flame atomic absorption spectrometry for the determination of trace copper. Isobutyl methyl ketone (MIBK) was selected as coating solvent and 8-hydroxyquinoline (oxine) as the chelating reagent. By switching of a 8-channel valve and alternative initiation of two peristaltic pumps, MIBK, sample solution containing copper chelate of oxine, and air-segment sandwiched eluting solution (1.0 mol l⁻¹ nitric acid) were sequentially aspirated into an extraction coil made of PTFE tubing of 360 cm length and 0.5 mm i.d. The formation of organic film in the wall of the extraction coil, extraction of the copper chelate into the organic film and back-extraction of the analyte into the eluting solution occurred consecutively when these zones aspirated into the extraction coil were propelled down the extraction coil by a carrier solution at a flow rate of 2 ml min⁻¹. After leaving the extraction coil, the concentrated zone was transported to the nebulizer at its free uptake rate for atomization. Under the optimized conditions, an enrichment factor of 43 and a detection limit of 0.2 μg l⁻¹ copper were achieved at a sample throughput rate of 30 h⁻¹. Eleven determinations of a standard copper solution of 60 μg l⁻¹ gave a relative standard deviation of 1.5%. Foreign ions possibly present in tap water and natural water did not interfere with the copper determination. The developed method has been successfully used to the determination of copper content of tap water and river water.     

Acid-rain monitoring in East Asia with a portable-type ion-exclusion–cation-exchange chromatographic analyzer

A monitoring system consisting of a portable-type conductimetric ion-exclusion–cation-exchange chromatographic (CEC) analyzer and a meteorological satellite data analyzer has been investigated for the evaluation of the effects of acid precipitation on natural and urban environments in East Asia. The portable ion-exclusion–CEC analyzer uses a polymethacrylate-based weakly acidic cation-exchange resin column in the H⁺-form and a weak-acid eluent (tartaric acid–methanol–water) and is applied for the simultaneous determination of anions (SO₄²⁻, NO₃⁻, and Cl⁻) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) in precipitation transported from mainland China to central Japan, as mapped by the meteorological satellite data analyzer. Linear calibration graphs of peak area versus concentration for anions and cations were observed in the concentration range 0–1.0 mM for the anions and 0–0.5 mM for the cations. Detection limits at a signal-to-noise ratio of 3 were in the range 5.18–12.1 ppb for the anions and 6.58–16.5 ppb for the cations. The practical utility of this monitoring system is presented.     

Determination of nanomolar concentrations of phosphate in freshwaters using flow injection with luminol chemiluminescence detection

A simple and rapid flow injection (FI) method is reported for the determination of phosphate (as molybdate reactive P) in freshwaters based on luminol chemiluminescence (CL) detection. The molybdophosphoric heteropoly acid formed by phosphate and ammonium molybdate in acidic conditions generated chemiluminescence emission via the oxidation of luminol. The detection limit (3× standard deviation of blank) was 0.03 μg P l⁻¹ (1.0 nM), with a sample throughput of 180 h⁻¹. The calibration graph was linear over the range 0.032–3.26 μg P l⁻¹ (r²=0.9880) with relative standard deviations (n=4) in the range 1.2–4.7%. Interfering cations (Ca(II), Mg(II), Ni(II), Zn(II), Cu(II), Co(II), Fe(II) and Fe(III)) were removed by passing the sample through an in-line iminodiacetate chelating column. Silicate interference (at 5 mg Si l⁻¹) was effectively masked by the addition of tartaric acid and other common anions (Cl⁻, SO₄²⁻, HCO₃⁻, NO₃⁻ and NO₂⁻) did not interfere at their maximum admissible concentrations in freshwaters. The method was applied to freshwater samples and the results (26.1±1.1–62.0±0.4 μg P l⁻¹) were not significantly different (P=0.05) from results obtained using a segmented flow analyser method with spectrophotometric detection (24.4±4.45–84.0±16.0 μg P l⁻¹).     

Unauthorised antibiotic treatments in beekeeping: Development and validation of a method to quantify and confirm tylosin residues in honey using liquid chromatography–tandem mass spectrometric detection

A liquid chromatographic–tandem mass spectrometric (HPLC-MS/MS) method is proposed for the identification and quantification of tylosin in honey. Sample treatment involves an extraction in a Tris buffer at pH 10.5, followed by a solid-phase clean up step on an Oasis HLB column. Roxithromycin was used as the internal standard. Chromatographic separation of tylosin and roxithromycin was performed on an XTerra MS C₁₈ column (100 mm × 2.1 mm i.d., 5 μm) using a gradient of aqueous 0.01 M ammonium acetate pH 3.5 and acetonitrile as the mobile phase, at a flow rate of 0.25 ml min⁻¹. The method was validated according to the guidelines laid down by the Commission Decision 2002/657/EC. Tylosin residues were confirmed by MS/MS experiments considering the appropriate identification points. All validation parameters such as Cc (lower than 3 ng g⁻¹), Ccβ (lower than 5 ng g⁻¹), recovery and precision were assessed on the basis of the “critical ion” (less intense ion permitting unambiguous identification of the analyte).     

Use of silica gel chemically modified with zirconium phosphate for preconcentration and determination of lead and copper by flame atomic absorption spectrometry

An analytical method using silica gel chemically modified with zirconium (IV) phosphate for preconcentration of lead and copper, in a column system, and their sequential determination by flame atomic absorption spectrometry (FAAS), was developed. Sample solutions are passed through a glass column packed with 100 mg of the sorbent material, at pH 4.5, and lead and copper are eluted with 1.0 mol l⁻¹ HNO₃ at a flow rate of 2.0 ml min⁻¹. The extraction of copper is affected by Fe(II), Mn(II), Zn(II), Ni(II) and Co(II) while only Fe(II) interferes in the lead determination. These interferences may be overcome with an appropriate addition of a KI or NaF solution. An enrichment factor of 30 was obtained for both metals. While the limits of detection (3σ) were 6.1 and 1.1 μg l⁻¹, for Pb and Cu, respectively, the limits of determination were 16.7 and 3.3 μg l⁻¹. The precision expressed as relative standard deviation (R.S.D.) obtained for 3.3 μg l⁻¹ of Cu and 16.7 μg l⁻¹ of Pb were 4.3 and 4.7%, respectively, calculated from ten measurements. The proposed method was evaluated with reference material and was applied for the determination of lead and copper in industrial and river waters.     

Silicon determination by inductively coupled plasma atomic emission spectrometry after generation of volatile silicon tetrafluoride

A method for the determination of silicon by inductively coupled plasma atomic emission spectrometry (ICP-AES) is described. The procedure is based on a discontinuous generation of volatile silicon tetrafluoride in concentrated sulphuric acid medium after injecting 125 μl of 0.1%, w/v sodium fluoride solution into 100 μl of the sample. The gaseous silicon tetrafluoride is fed directly into the ICP torch by a flow of 250 ml min⁻¹ Ar carrier gas. The calibration curve was linear up to at least 100 μg ml⁻¹ of Si(IV) and the absolute detection limit was 9.8 ng working with a solution volume of 100 μl. The relative standard deviation for six measurements of 10 μg ml⁻¹ of Si(IV) was 2.32%. The method was applied to the determination of silicon in water and iron ores.