Use of modified rice husks as a natural solid adsorbent of trace metals: characterisation and development of an on-line preconcentration system for cadmium and lead determination by FAAS

The use of rice husks as an alternative adsorbent in an on-line preconcentration system for Cd (II) and Pb (II) determination by flame atomic absorption spectrometry (FAAS) is described. The potential of rice husks as a natural adsorbent was evaluated as a material modified with 0.75 mol l⁻¹ NaOH solution and in the unmodified form. For this task, several techniques such as spectroscopy and thermogravimetry were used for elucidation of possible functional groups responsible for the uptake of Cd (II) and Pb (II). Furthermore, based on adsorption studies and adsorption isotherms applied to the Langmüir model, it was possible to verify that modified rice husks present a higher adsorption capacity for both metals. After establishing this material as a promising natural adsorbent, it was used for on-line preconcentration of Cd (II) and Pb (II) metals. The multivariate optimisation of chemical and flow variables was performed by using a full factorial design (2⁴) including the following factors: preconcentration time, preconcentration flow rate, concentration and volume of eluent. The optimum pH values used for on-line preconcentration were taken from prior univariate experiments. Under optimised conditions for Cd (II) determination (4 min of preconcentration at a 6 ml min⁻¹ preconcentration flow rate, in which comprises 24 ml of preconcentration volume, 200 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent), the system achieved a detection limit of 1.14 μg l⁻¹ and an enrichment factor of 72.4. Similar conditions were used for Pb (II) determination (4 min of preconcentration, 6 ml min⁻¹ preconcentration flow rate, 300 μl elution volume and 1.0 mol l⁻¹ HNO₃ solution as eluent) from which a detection limit of 14.1 μg l⁻¹ and enrichment factor of 46.0 were achieved. Also, rice husks have been shown to be a homogeneous and stable adsorbent in which more than 100 preconcentration/elution cycles provide a relative standard deviation (RSD) of less than 6.0% on the analytical signal. The satisfactory accuracy of the method developed was obtained by using spiked water samples (mineral water and lake water) and spiked red wine samples. These values were confirmed by electrothermal atomic absorption spectrometry (ETAAS). The certified reference material [pig kidney (CRM 186)] and the reference material [beech leaves (CRM 100)] were also used.     

Spectrophotometric determination of zinc, cadmium, and lead after extraction of their morpholine-4-carbodithioates into molten naphthalene and replacement by copper

Zinc, cadmium, and lead react quantitatively in the pH ranges of 3.9–9.2, 3.5–11.2, and 5.5–10.5, respectively, to form water insoluble and thermally stable complexes which are easily extracted into molten naphthalene. The solid naphthalene containing the colorless complex is dissolved in chloroform and then replaced by copper to develop a yellow color in the chloroform layer. The absorbance in each case is measured at 435 nm against reagent blank. Beer's law holds over the concentration ranges of 3.5–95.0, 3.0–105.0, and 8.5–125. 0 μg for zinc, cadmium, and lead, respectively, into 10 ml of the chloroform solution. The molar absorptivities are calculated to be Zn, 1.048 × 10⁴ liters mol⁻¹ cm⁻¹; Cd, 1.054 × 10⁴ liters mol⁻¹ cm⁻¹, and Pb, 1.014 × 10⁴ liters mol⁻¹ cm⁻¹ with sensitivities in terms of Sandell's definition of 0.0062 μg Zn/cm², 0.010 μg Cd/cm², and 0.020 μg Pb/cm², respectively. Ten replicate determinations of sample solutions containing 30 μg of zinc, 18.7 μg of cadmium, and 42.5 μg of lead give mean absorbances 0.480, 0.175, and 0.208 with standard deviations of 0.0017, 0.0013, and 0.0015 or relative standard deviations of 0.35, 0.74, and 0.72%, respectively. The interference of various ions has been studied and the method has been applied to the determination of cadmium in various synthetic mixtures and zinc and lead in some standard reference materials.     

Flow-injection hydride generation atomic absorption spectrometric study of the automated on-line pre-reduction of arsenate, methylarsonate and dimethylarsinate and high-performance liquid chromatographic separation of their -cysteine complexes

An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of -cysteine and on the temperature in the following increasing order: inorganic As(V)<DMA<MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70–100°C compared to 1 h at room temperature, while MMA and DMA require 1.5–2 min at 70–100°C and up to 1–2 h at room temperature. The characteristic masses and concentrations for 100 μl injections are 0.01 ng and 0.1 μg l⁻¹ in integrated absorbance and 0.2 ng and 2 μg l⁻¹ in peak height measurements, and the limits of detection are ca. 0.5 ng and 5 μg l⁻¹, respectively. In a high-performance liquid chromatography (HPLC)–HGAAS system, the -cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120×4 mm (5 μm) with a mobile phase containing 12 mmol l⁻¹ phosphate buffer (KH₂PO₄/H₃PO₄)–2.5 mmol l⁻¹ -cysteine, pH 3.3–3.5. Upon dilution to -cysteine levels below 10 mmol l⁻¹, which are compatible with HPLC separations, the DMA–cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C₁₈ HPLC columns. The limits of detection with 50 μl injections in peak area mode are ca. 0.5 ng and 10 μg l⁻¹, respectively.     

Indirect atomic absorption spectrometry (IAAS) as a tool for the determination of iodide in infant formulas by precipitation of AgI and redissolution with cyanide

A method to determine iodide in infant formula samples by indirect atomic absorption spectrometry (IAAS) was developed. The iodide in solution resulting from an alkaline digestion (Na₂CO₃–NaOH) of the sample is precipitated with silver; the precipitate is redissolved by adding cyanide solution, and this solution is subjected to GF-AAS. Temperatures of 1000 and 2100°C were selected for the ashing and atomization steps, respectively, using a mixture of Pd and Mg(NO₃)₂ as a matrix modifier (at concentrations of 36 and 16 μg ml⁻¹, respectively). The sensitivity, LOD, LOQ and characteristic mass obtained were, respectively, 1.12×10⁻² l μg⁻¹, 3.1 μg g⁻¹ and 10.4 μg g⁻¹ and 7.3 pg, referred to sample. The linear interval of concentrations extends up to 10 μg l⁻¹ of iodide, with no need to use the standard addition method; the mean R.S.D. of data within this range is 3.4%, with 2.9% over the whole procedure. No interfering effects were observed among the foreign ions studied, and 100.0% was the mean analytical recovery achieved within the linear range of concentrations. The application of the method to seven real samples gave a mean content of 12.8 μg g⁻¹ of iodide, as well as less than 3.1 μg g⁻¹ in eight other samples.     

Amberlyst A-26 resin loaded with pyrocatechol violet—Preparation and applications as a preconcentrator in the atomic absorption spectrophotometric determination of lead and cadmium

Amberlyst A-26 loaded with pyrocatechol violet has been prepared and used for preconcentrating cadmium and lead before their flame atomic absorption Spectrophotometric determination. The optimum sorption pHs are 7.0–7.8 and 7.0–7.5 for Cd and Pb, respectively. The absorbance varies linearly in the concentration ranges of 0.1–1.0 and 1.5–7.5 μg cm⁻³, respectively, for the two metals. The sensitivity of the procedure for 1% absorption has been found to be 1.5 and 2.3 ng cm⁻³ of the solution to be analyzed, respectively, for Cd and Pb. The relative standard deviation is approximately 2.8%. The method has been used to determine Cd and Pb in the water of the Yamuna River (New Delhi, India) with a relative standard deviation between 4.3 and 5.1%.     

Electroanalytical and chromatographic determination of pentachlorophenol and related molecules in a contaminated soil: a real case example

Electroanalytical and chromatographic methodologies have been applied for the determination of pentachlorophenol (PCP) and some of its derivatives in real soil samples contaminated by industrial discharge. The analytes were extracted with hexane from soil samples collected at different points of the site and mixed to produce a representative sample. Square wave voltammetry (SWV) experiments were carried out on either a boron-doped diamond (BDD) electrode or a gold ultramicroelectrode (Au-UME) in an analyte composed by the Britton-Robinson (B-R) buffer at pH 5.5 with the direct addition of proper amounts of the extract. The voltammetric responses revealed an irreversible anodic peak at approximately 0.80 V vs. Ag/AgCl with a peak current showing a linear dependence on PCP concentration. This linear relationship yielded a detection limit (DL) of 2×10⁻⁸ mol l⁻¹ (or 5.5 μg l⁻¹) for the BDD electrode and 6.9×10⁻⁸ mol l⁻¹ (18.4 μg l⁻¹) for the Au-UME, while the independently measured HPLC detection limit was 1.1×10⁻⁸ mol l⁻¹ (3.0 μg l⁻¹). The application of electroanalytical and chromatographic methodologies in the analysis of soil extracts revealed, besides the PCP responses, signals for some related molecules such as o-tetrachlorobenzoquinone (o-chloranil), hexachlorobenzene and tetrachlorophenol. Recovering experiments for PCP showed a concentration of 27.5 mg kg⁻¹ for the electroanalytical determinations and 26.8 mg kg⁻¹ for the HPLC analysis, values exceedingly high if considering that the maximum residue limit established for natural waters by the Brazilian Environmental Agency is 10 μg l⁻¹.     

Determination of Proteins in a Mesofluidic Lab-on-Valve System

The application of a mesofluidic lab-on-valve system to the spectrophotometric determination of protein was investigated. Protein species in the sample solution reacts rapidly with Congo red at pH 4.1, which forms a complex with a maximum absorption at 496 nm. A univariant approach was used for the optimization of the experimental parameters. A sample volume of 20 μl was used along with 4.0 μl of Congo red solution of 0.9 g l⁻¹, and a flow rate for the detection process of 20 μl s⁻¹ was used. Under optimal conditions, a linear calibration curve was obtained in the range of 12.5–200 μg ml⁻¹ of bovine serum album, along with a detection limit (3σ) of 5.6 μg ml⁻¹ and a sampling frequency of 60 per hour. Protein concentrations in human serums, urine, milk, and yoghourt were determined using this procedure, and satisfactory agreements were obtained with that achieved using the Coomassie brilliant blue method.     

Inductively coupled plasma-mass (ICP-MS) and atomic emission spectrometry (ICP-AES): Versatile analytical techniques to identify the archived elemental information in human teeth

Human dental enamel is composed of sequentially calcifying growth layers that can provide an archival record of temporal changes such as past pollution events and changes in elemental nutrition. Human teeth and bones alike are mainly made out of calcium and a phosphorous rich crystalline building block called hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂]. Divalent cations such as Zn²⁺, Pb²⁺, Sr²⁺, and Mg²⁺ can replace isovalent calcium sites, and phosphate and hydroxyl sites can substitute with anions, such as carbonate and fluoride, respectively. In this investigation inductively coupled plasma-atomic emission (ICP-AES) and mass spectrometry (ICP-MS) was used to determine lead, zinc, and strontium concentrations in deciduous teeth from contemporary populations from Solís, Mexico and Kalama, Egypt and permanent teeth from Bronze age Tell Abraq, United Arab Emirates and the 18th century New York African Burial Ground (NYABG) from Lower Manhattan. The concentration of lead in children's teeth from a semi-urban village in Egypt (ranged from 162 to 2.6 μg g^{− 1}; n = 10) and NYABG individuals (range 112–1.2 μg g^{− 1}; n = 6) showed the elevated lead levels while the ancient population from Tell Abraq had the lowest level (1.34 to 0.03 μg g^{− 1}; n = 10). Lead isotope ratios (i.e., ²⁰⁸Pb/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb) of above individuals' teeth were measured using ICP-MS to discern their domicile. Zinc and Sr concentrations of teeth reflect the diet, nutritional and environmental history of individuals. The versatility of ICP-AES and ICP-MS as trace metal analytical techniques in unraveling elemental information embedded in hard tissue, like teeth, is demonstrated.     

The rapid separation of trace metals from neutron-activated saline matrices by chelation on a poly-5-vinyl-8-hydroxyquinoline column

Instrumental neutron activation analysis of biological and environmental samples suffers from interferences caused by high salt concentrations. Poly-5-vinyl-8-hydroxy-quinoline coated on controlled pore diameter glass beads is suggested as a chelating column for the rapid removal of aluminum, vanadium, copper and manganese from neutron-activated sea-water samples. Separation from bulk elements is satisfactory at flow rates of 20 ml min⁻¹. With addition of carriers and with chemical yield determinations, relative standard deviations of 2–10% can be achieved for spike concentrations of 0.1 μg Mn ml⁻¹, 0.3 μg V ml⁻¹, 20 μg Al ml⁻¹ and 1.0 μg Cu ml⁻¹.     

A Catalytic Method for Determining Cadmium(II), Nickel(II), and Zinc(II) Inhibitor Metals

The inhibitory effect of Cd(II), Ni(II), and Zn(II) on the oxidation of 3,3′,5,5′ -tetramethylbenzidine with periodate was detected. The optimum reaction conditions were found, and the procedures were developed for determining 1 × 10⁻² to 10 μg/mL Cd(II), Ni(II), and Zn(II) in solution. The indicator reaction was performed on a number of supports. The maximum inhibitory effect was observed on silica gel-based plates for TLC. Procedures for determining 6 × 10⁻³ to 0.4 μg of these metals were developed. Silica gel plates with the immobilized reagent for cadmium (bromobenzothiazo) were used to preconcentrate cadmium. A selective test procedure was developed for determining 1 × 10⁻⁴ −3 × 10⁻³ μg/mL cadmium with the visual detection of the process rate. Upon the introduction of dimethylglyoxime into the indicator reaction, the inhibitory effect of nickel changed to its promoting effect and the detection limit for nickel was lowered. A procedure was developed for determining 3 × 10⁻⁴ −3 × 10⁻³ μg/mL nickel in solution and 7 × 10⁻³−4 × 10⁻¹ μg nickel on the surface of Sorbfil plates. An assumption was made about the reasons for the inhibitory effect of metal ions on the oxidation of aryl diamines with periodate.__________Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 6, 2005, pp. 662–669.Original Russian Text Copyright © 2005 by Beklemishev, Kiryushchenkov, Stoyan, Dolmanova.     

Speciation Stabilities of Iodine in underground Water by High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometry

Specific determination for IO₃⁻ and I⁻ in ground water using high performance liquid chromatography-inductively coupled plasma mass spectrometry (HPLC-ICPMS) is described. Chromatographic separations were carried out using an ICS-A23 column. Iodine species were quantitatively eluted with 0.03 M ammonium carbonate. Under the Shield Torch high sensitive mode, the method detection limits for IO₃⁻ and I⁻ with injection of 1 ml were 0.035 μg l⁻¹ and 0.025 μg l⁻¹, respectively. The method was applied to the determination of iodide and iodate in ground water. However, the signal response difference between iodate and iodide was observed by both the HPLC-ICP-MS system and the ICP-MS system. Also, the same signal response difference was also observed in other laboratories. It was reported that the signal response and stability of iodine species vary with their solution medium. The instability of IO3 – and I – was controlled by using KOH as their solution storing media. The IO₃⁻ and I⁻ peak area ratios by HPLC-ICP-MS measurement were still close to 1:1 when the mixed standard solution was stored in the 0.01% KOH medium for 5 days.     

Multivariate optimization and validation studies in on-line pre-concentration system for lead determination in drinking water and saline waste from oil refinery

The present paper proposes an on-line pre-concentration procedure for lead determination in drinking water and saline waste from oil refinery by flame atomic absorption spectrometry (FAAS). It is based on the sorption of lead (II) ions in a minicolumn of polyurethane foam loaded with 4-(2-pyridylazo)-resorcinol (PAR) reagent. The optimization step was performed using Doehlert matrix involving the variables: sampling flow rate (SR), buffer concentration (BC), pH and eluent concentration (EC). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line system, precision, robustness, effect of other ions in the pre-concentration system and accuracy. Using the established experimental conditions, the procedure allows lead determination with detection limit (3δ/S) of 0.4 μg l⁻¹, quantification limit (10δ/S) of 1.4 μg l⁻¹, and a precision, calculated as relative standard deviation (RSD) of 5.7 (n=8) and 2.1% (n=8) for lead concentration of 5 and 50 μg l⁻¹, respectively. The pre-concentration factor (PF) considering the ratio among the slopes of the analytical curves with and without pre-concentration is 51. The achieved recovery for lead determination in presence of several cations demonstrated that this procedure could be applied for analysis of water samples. The accuracy was confirmed by analysis of the standard reference material NIST 1640 Trace elements in natural water. The sorption process was characterized by the Langmuir isotherm. The method was applied for lead determination in drinking water collected in Salvador City, Brazil and in saline effluent samples from oil refinery. The lead content for 16 samples of drinking water analyzed varied from 0.77 to 6.98 μg l⁻¹.     

阳离子表面活性剂对电化学法测试牛奶中氯霉素残留量的影响

为探索用电化学方法检测生物样品中氯霉素残留的高灵敏度技术,本实验研究了阳离子表面活性剂十六烷基三甲基溴化铵(CTMAB)对氯霉素在玻碳电极上伏安行为的影响,实验结果表明,以0.02 mol/L高氯酸为支持电解质,在0.40~-0.60 V的范围内进行伏安扫描时,2×10-5mol/L CTMAB能显著提高氯霉素在-0.41 V处的还原峰电流。利用这种改进的电化学方法检测氯霉素的线性范围为0.0026~8 mg/L,检出限达到0.83μg/L。研究了缓冲液种类及其酸碱度及其它表面离子活性剂等对测试氯霉素的影响。     

Optimization of sample preparation using statistical methods: spectrophotometric determination of Fe and Co in pharmaceutical samples

This work presents alternatives for Fe and Co determination in pharmaceutical samples using flow analysis. The first procedure describes Fe extraction in mineral/vitamin complexes. The best conditions were reached when HNO₃ concentration and volume, sample mass and shaking time were 1.0 mol l⁻¹, 5 ml, 25 mg and 10 min. Three mineral/vitamin complexes of known concentrations (ranging from 12 to 32 g kg⁻¹) were analyzed (10 authentic replicates for each) and recoveries of around 100% were obtained when compared with a well-established mineralization procedure employing concentrated HNO₃ and H₂O₂ (30% w/v). The second work part shows the employment of Tiron and H₂O₂ reaction for Co determination in a drug for inappetence. The results (352±18.7 mg kg⁻¹) were compared with those using Electrothermal Atomic Absorption Spectrometry—ETAAS (346±15.7 mg kg⁻¹). The proposed method showed detection and quantification limits of 0.20 and 0.70 μg l⁻¹, respectively. Both procedures for Fe and Co determination presented time, reagent and effort reduction.     

Mercury, zinc, manganese, and iron accumulation in leachate pond sediments from a refuse tip in Southeastern Brazil

This work evaluates Hg, Zn, Fe and Mn transfer from the leachate of a refuse tip based on their accumulation in a sediment core of 17 cm collected in a leachate pond of a small refuse tip ageing approximately 10 years. Sediment samples were digested with an acid mixture (50% acqua regia solution), heated at 70 °C during 1 h, in a thermal-kinetic reactor “cold finger”. The extract was analysed to obtain Hg content by cold vapour absorption atomic spectrometry (CVAAS). Fe, Mn and Zn contents were obtained by flame atomic absorption spectrometry (FAAS) after total decomposition of the samples. Concentration ranges along the core varied from 0.16 to 0.58 μg g^− 1; 7.3 to 145 μg g^− 1; 11.7 to 116 μg g^− 1 and 0.21% to 1.82% for Hg, Zn, Mn and Fe, respectively. All metals showed enrichment in the upper layers (above 6 cm) which probably correspond to the year 1996. Results indicated that Hg transfer is one order of magnitude higher than Zn and suggest that metals accumulation in sediments probably reduce their migration to groundwater.     

Sensitive spectrofluorimetric determination of ruthenium at nanotrace levels using 2-(α-pyridyl) thioquinaldinamide [PTQA]

A new spectrofluorimetric method for the determination of ruthenium with nonfluorescent 2-(α-pyridyl) thioquinaldinamide (PTQA) is described. The oxidative reaction of Ru(III) upon PTQA gives oxidised fluorescent product (λ_ex(max)=347 nm; λ_em(max)=486 nm). The sensitivity of the fluorescence reaction between ruthenium and PTQA is greatly increased in the presence of Fe (III). The reaction is carried out in the acidity range 0.01–0.075 M H₂SO₄. The influence of reaction variables is discussed. The range of linearity is 1–400 μg l⁻¹ Ru(III). The standard deviation and relative standard deviation of the developed method are ±1.210 μg l⁻¹ Ru (III) and 2.4%, respectively (for 11 replicate determinations of 50 μg l⁻¹ Ru (III)). The effect of interferences from other metal ions, anions and complexing agents was studied; the masking action is discussed. The developed method has been successfully tested over synthetic mixtures of various base metals and platinum group metals, synthetic mixtures corresponding to osmiridium, certified reference materials in spiked conditions and rock samples.     

Slurry-based procedures to determine chromium, nickel and vanadium in complex matrices by ETAAS

Two slurry-based ETAAS methodologies are compared to determine directly Cr, Ni and V in coal fly ash, soils and sediments: current slurry analysis (USS) and ‘slurry extraction’ (SE). Slurries for USS-ETAAS were prepared in 0.5% HNO₃. HF and HNO₃ were evaluated as chemical modifiers. HF was the extractant for the SE-ETAAS approach.A unique slurry-based procedure to measure Cr, Ni and V could not be established. Cr concentrations up to 100 μg g^{− 1} were accurately determined by USS (0.5% HNO₃; λ = 429.0 nm; LOD = 0.35 μg g^{− 1}) whereas higher contents required the SE procedure (sample grinding, 30% HF; LOD = 0.02 μg g^{− 1}). Both methods were appropriate to determine Ni (LOD = 0.11 and 0.08 μg g^{− 1}, for USS and SE, respectively). V was satisfactorily quantified only with the USS approach (LOD = 0.80 μg g^{− 1}).     

Occurrence and distribution of metals and porphyrins in Nigerian coal minerals

The metal contents of Nigerian coal minerals were analyzed using an atomic absorption spectrophotometer. Calcium, Na, and Fe occurred as the major elements with concentrations ranging from 9 782 μg/g for Ca to 432 μg/g for Na whereas K, Mg, Mn, Ni, Cr, Zn, Pb, and Cu, which occurred at trace levels ranged from 673.73 μg/g for Mg to 2.97 μg/g for Mn. The results of the quantitative analysis of porphyrins extracted from the coal minerals showed that Onyeama coal has the highest amount of porphyrins (ca～0.96 μg/g) while Okpara has the lowest (ca～0.30 μg/g). The porphyrins were qualitatively characterized by a combination of thin layer chromatography (TLC), infrared, and ultraviolet-visible spectrophotometers. The results of the mid infrared analysis (MIR) showed the presence of absorption bands at 3 440 cm～1～3 450 cm-1 and 1 640 cm-1～1 680 cm-1 , which are owing to the stretching vibrations of N - H and C = C of aromatics, with C- H out of plane (oop) bending vibrations at wavenumbers less than 900 cm-1, all of which are characteristic absorptions of porphyrin free base. The ultraviolet-visible data showed prominent peaks at ～400 nm(Soret band) and at wavelength ranges of 535 nm～550 nm(β-band) and 565 nm～ 600 nm (α-band) for the coal porphyrins analyzed. The geochemical significance of the metals and porphyrins in coal minerals are discussed.     

Determination of lead,cadmium and mercury in blood for assessment of environmental exposure: A comparison between inductively coupled plasma–mass spectrometry and atomic absorption spectrometry

A biomonitoring method for the determination of Pb, Cd, and Hg at background levels in whole blood by inductively coupled plasma-mass spectrometry is described. While this method was optimized for assessing Pb, Cd and Hg at environmental levels, it also proved suitable for assessing concentrations associated with occupational exposure. The method requires as little as 200 μl of blood that is diluted 1 + 49 for direct analysis in the inductively coupled plasma-mass spectrometer. Method performance is compared to well-established AAS methods. Initial method validation was accomplished using National Institute of Standards and Technology (NIST) Standard Reference Material 966, Toxic Metals in Bovine Blood. Method detection limits (3s) are 0.05 μg dl^− 1 for Pb, 0.09 μg l^− 1 for Cd; and 0.17 μg l^− 1 for Hg. Repeatability ranged from 1.4% to 2.8% for Pb; 3% to 10% for Cd; and 2.6% to 8.8% for Hg. In contrast, AAS method detection limits were 1 μg dl^− 1, 0.54 μg l^− 1, and 0.6 μg l^− 1, for Pb, Cd, and Hg, respectively. Further performance assessments were conducted over a 2-year period via participation in four international External Quality Assessment Schemes (EQAS) operated specifically for toxic metals in blood. This includes schemes operated by (a) the New York State Department of Health's Wadsworth Center, Albany, NY, USA (b) L′Institut National de Santé Publique du Québec, Centre de Toxicologie du Québec, Canada, (c) Friedrich-Alexander University, Erlangen, Germany, and (d) the University of Surrey, Guildford, UK Trace Elements scheme. The EQAS data reflect analytical performance for blind samples analyzed independently by both inductively coupled plasma-mass spectrometry and AAS methods.     

A multi-pumping flow system for chemiluminometric determination of ascorbic acid in powdered materials for preparation of fruit juices

A multi-pumping flow-based procedure with chemiluminescent detection is proposed for the determination of ascorbic acid, AA, in fruit juices (powdered form). The method relies on the inhibitory effect of AA on the oxidation of luminol by hydrogen peroxide in alkaline medium. The system comprises several discretely actuated solenoid pumps as the only active components. It handles 100 samples per hour, and requires 96 μl of sample, 42 μg of luminol and 105 μg of potassium hexacyanoferrate(III) per determination. The analytical curve is linear up to about 11 mmol l^− 1 AA, and detection limit is 0.17 mmol l^− 1 AA. The system yields precise measurements (r.s.d. < 1%; n = 11), and recovery ranges from 94% to 106%. Results are in agreement with the reference method (AOAC) at the 95% confidence level.