Rapid determination of lead and cadmium in sewage sludge samples using electrothermal atomic absorption spectrometry with slurry sample introduction

Lead and cadmium concentrations in sewage sludge samples are determined by suspending the ground samples in a solution containing 10% (v/v) concentrated hydrofluoric acid, 1% (v/v) concentrated nitric acid, 0.5% (m/v) dihydrogen ammonium phosphate and 0.1% (m/v) sodium hexametaphosphate. Aliquots of 20 μL of these suspensions (4 mg/mL) are diluted to 1000 μL with the same solution and then injected into the electrothermal atomizer. The drying stage is performed by programming a 400?°C temperature, a ramp time of 20 s and a hold time of 15 s on the power supply of the atomizer. No ashing step is used. Platform atomization is carried out at 1600 and 1800?°C for Pb and Cd, respectively. Calibration is performed using aqueous standards in the 5–75 and 0.2– 5 μg/L Pb and Cd ranges, respectively. Results obtained for three certified reference materials and four samples demonstrate the reliability of the procedures described.     

Rapid determination of lead, cadmium and thallium in cements using electrothermal atomic absorption spectrometry with slurry sample introduction

 A method is proposed for the determination of Pb, Cd and Tl in cements by ETAAS. The samples are suspended in a medium containing 10% v/v ethanol and 1% v/v both conc. nitric and hydrofluoric acids and are directly introduced into the electrothermal atomizer. The drying stage is performed by programming a 400 °C temperature, a ramp time of 5 s and a hold time of 30 s on the power supply to the atomizer. No ashing step is used. Atomization is carried out at 2100, 1800 and 1700 °C for Pb, Cd and Tl, respectively. For Cd determination, ammonium dihydrogen phosphate is added to the suspension medium. No modifier other than hydrofluoric acid is required for the Pb and Tl determination. It is shown that the results obtained by using direct calibration with aqueous standards for five commercial samples agree with those found by means of the standard additions method. Received: 29 March 1996/Revised: 24 May 1996/Accepted: 30 May 1996     

Chemical analysis of manganese nodules. Part I. Determination of seven main and trace constituents after anion-exchange separation

A method is described for the determination of Mn, Cu, Co, Zn, Cd, Pb and U in samples of manganese nodules. After dissolution of the sample in concentrated hydrochloric acid, the elements are adsorbed on a column of the strongly basic anion-exchange resin Dowex 1 from a medium consisting of 50 % (v/v) hexone, 40 % (v/v) isopropanol and 10 % (v/v) 12 M hydrochloric acid. After removal of iron by washing the resin bed with a mixture of the same composition, 6 M hydrochloric acid is passed through the column to elute Mn, Cu, Co, and Pb, and then 1 M hydrochloric acid and 2 M nitric acid to elute Zn, Cd and U. In the eluates the elements are determined by atomic-absorption spectrometry except for uranium which is determined by fluorimetry. The method was used successfully for the determination of mg and p.p.m. quantities of Mn, Cu, Co, Zn, Cd, Pb and U in 17 samples of manganese nodules from the Pacific Ocean.     

Determination of Cd and Pb in food slurries by GFAAS using cryogenic grinding for sample preparation

A simple method combining slurry sampling after cryogenic grinding and the use of a permanent modification of the integrated platform inside the transversely heated graphite atomizer (THGA) was proposed for the determination of Cd and Pb in foods. Potentialities of the cryogenic grinding were evaluated for grinding different materials of difficult homogenization such as high fat and high fiber tissues. Animal and vegetal samples were cut into small pieces and ground in liquid nitrogen for 2 min. Slurries were prepared directly in the autosampler cup after cryogenic grinding by transferring an exact amount of homogeneous powdered material (5-20 mg) to the cup, followed by 1.00 mL of 0.2% (v/v) HNO3 containing 0.04% (v/v) Triton X-100 and sonication for 30 s, before transferring into the platform previously coated with 250 microg W and 200 microg Rh. Use of a tungsten carbide-rhodium permanent modifier combined with NH4H2PO4 conventional modifier improves tube lifetime and increases the pyrolysis temperature for Cd. Homogeneity tests, carried out by comparing the between- and within-batch precision for each kind of sample, showed no significant differences at the 95% confidence level, indicating good homogeneity for 5-20 mg masses. Detection limits were 3.3 ng g(-1) Cd and 75 ng g(-1) Pb for 1% m/v slurries. Results for determination of Cd and Pb in foods slurries were in agreement with those obtained with digested samples, since no statistical differences were found by the paired t-test at the 95% level.     

Direct sample introduction of wines in graphite furnace atomic absorption spectrometry for the simultaneous determination of arsenic, cadmium, copper and lead content

A multi-element graphite furnace atomic absorption spectrometry (GFAAS) method was elaborated for the simultaneous determination of As, Cd, Cu, and Pb in wine samples of various sugar contents using the transversally heated graphite atomizer (THGA) with end-capped tubes and integrated graphite platforms (IGPs). For comparative GFAAS analyses, direct injection (i.e., dispensing the sample onto the IGP) and digestion-based (i.e., adding oxidizing agents, such as HNO(3) and/or H(2)O(2) to the sample solutions) methods were optimized with the application of chemical modifiers. The mixture of 5 microg Pd (applied as nitrate) plus 3 microg Mg(NO(3))(2) chemical modifier was proven to be optimal for the present set of analytes and matrix, it allowing the optimal 600 degrees C pyrolysis and 2200 degrees C atomization temperatures, respectively. The IGP of the THGA was pre-heated at 70 degrees C to prevent the sputtering and/or foaming of sample solutions with a high organic content, dispensed together with the modifier solution, which method also improved the reproducibility of the determinations. With the digestion-based method, the recovery ranged between 87 and 122%, while with the direct injection method it was between 96 and 102% for Cd, Cu, and Pb, whereas a lower, compromise recovery of 45-85% was realized for As. The detection limits (LODs) were found to be 5.0, 0.03, 1.2, and 0.8 microg l(-1) for As, Cd, Cu, and Pb, respectively. The characteristic mass (m(0)) data were 24 pg As, 1.3 pg Cd, 13 pg Cu, and 35 pg Pb. The upper limits of the linear calibration range were 100, 2, 100, and 200 microg l(-1) for As, Cd, Cu, and Pb, respectively. The precisions were not worse than 4.8, 3.1, 3.7, and 2.3% for As, Cd, Cu, and Pb, respectively. For arsenic, a higher amount of the modifier (e.g., 20 microg Pd plus 12 microg Mg(NO(3))(2)) could be recommended to overcome the interference from the presence of sulphate and phosphate in wines. Although this method increased the sensitivity for As (m(0)=20 pg), it also enhanced the background noise, thus only a slight improvement in the LOD of As (3.9 microg l(-1)) was realized. For the 35 red and white wine samples studied, the highest metal contents were observed for Cu ranging from 20 to 640 microg l(-1) (average: 148 microg l(-1)), followed by Pb from 6 to 90 microg l(-1) (average: 32.3 microg l(-1)), and Cd from 0.05 to 16.5 microg l(-1) (average: 1.06 microg l(-1)), whereas the As content was below the LOD. This wide fluctuation in the trace metal content could be associated with the origin of wines from various regions (i.e., different trace metal level and/or quality of soil, and/or anthropogenic impact), and with diverse materials (e.g., additives and containers) involved in the wine production processes. The Cu content of wine samples was significantly correlated with Pb, whereas its weak anti-correlation was found with Cd. Interestingly, the level of Pb was anti-correlated with the year of production of the wines. This is likely due to the gradual decrease in the Pb content of soils of vineyards by time, which certainly causes less Pb-uptake of the grape plant, thus a decrease in the Pb content of wines as well.     

Slurry sampling graphite furnace atomic absorption spectrometry: determination of trace metals in mineral coal

A procedure for lead, cadmium and copper determination in coal samples based on slurry sampling using an atomic absorption spectrometer equipped with a transversely heated graphite tube atomizer is proposed. The slurries were prepared by weighing the samples directly into autosampler cups (5-30 mg) and adding a 1.5 ml aliquot of a diluent mixture of 5% v/v HNO(3), 0.05% Triton X-100 and 10% ethanol. The slurry was homogenized by manual stirring before measurement. Slurry homogenization using ultrasonic agitation was also investigated for comparison. The effect of particle size and the use of different diluent compositions on the slurry preparation were investigated. The temperature programmes were optimized on the basis of pyrolysis and atomization curves. Absorbance characteristics with and without the addition of a palladium-magnesium modifier were compared. The use of 0.05% m/v Pd and 0.03% m/v Mg was found satisfactory for stabilizing Cd and Pb. The calibration was performed with aqueous standards. In addition, a conventional acid digestion procedure was applied to verify the efficiency of the slurry sampling. Better recoveries of the analytes were obtained when the particle size was reduced to <37 mum. Several certified coal reference materials (BCR Nos. 40, 180, and 181) were analyzed, and good agreement was obtained between the results from the proposed slurry sampling method and the certificate values.     

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Comparison of stir bar sorptive extraction and membrane-assisted solvent extraction for the ultra-performance liquid chromatographic determination of oxazole fungicide residues in wines and juices

The present study compares two new sample preparation methods, stir bar sorptive extraction (SBSE) and membrane-assisted solvent extraction (MASE) coupled to the novel technique of ultra-performance liquid chromatography (UPLC) for the sensitive, selective and solvent-free determination of six oxazole fungicide residues (hymexazol, drazoxolon, vinclozolin, chlozolinate, oxadixyl and famoxadone) in wine and juices. The analytes were separated on a rapid resolution C(18) column (50 mm x 4.6 mm, I.D., 1.8 microm) thermostated at 50 degrees C with isocratic elution using a 50/50 (v/v) water/acetonitrile (ACN) mobile phase at a flow-rate of 1 mL min(-1) and detected by diode-array detection (DAD). The UPLC method rapidly separates the fungicides (7 min). The best results as regards sensitivity, repeatability and analyte recovery were obtained using SBSE with a polydimethylsiloxane (PDMS) twister, at 60 degrees C for 30 min with stirring at 1700 rpm in the presence of a 0.1M acetate/acetic acid buffer (pH 5) and 20% (m/v) sodium chloride. Liquid desorption was performed with 100 microL of a 80/20 (v/v) ACN/water solution in a desorption time of 15 min. With the PDMS polymer, an apolar phase, hymexazol and oxadixyl were not extracted. Consequently, the SBSE procedure can only be applied to the other four fungicides. Detection limits ranged from 0.05 to 2.5 microgL(-1) at a signal to noise ratio of 3, depending on the compound. Recoveries obtained for spiked samples were satisfactory (83-113%) for all compounds. The proposed method was successfully applied to the analysis of different samples, residues of chlozolinate and drazoxolon being found in samples of red wine and grape juice, respectively.     

Determination of cadmium,mercury and lead in seawater by electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry

Electrothermal vaporization isotope dilution inductively coupled plasma mass spectrometry (ETV-ID-ICP-MS) has been applied to the determination of Cd, Hg and Pb in seawater samples. The isotope ratios of the elements studied in each analytical run were calculated from the peak areas of each isotope. Various modifiers were tested for the best signal of these elements. After preliminary studies, 0.15% m/v TAC and 4% v/v HCl were added to the sample solution to work as the modifier. The ETV-ID-ICP-MS method has been applied to the determination of Cd, Hg and Pb in NASS-4 and CASS-3 reference seawater samples and seawater samples collected from Kaohsiung area. The results for reference sample NASS-4 and CASS-3 agreed satisfactorily with the reference values. Results for other samples determined by isotope dilution and method of standard additions agreed satisfactorily. Detection limits were approximately 0.002, 0.005 and 0.001 ng ml⁻¹ for Cd, Hg and Pb in seawater, respectively, with the ETV-ICP-MS method. Precision between sample replicates was better than 20% for most of the determinations.     

反相高效液相色谱法同时测定镉、铅、铜和锌

 研究了meso-四（对羟基苯基）卟啉为柱前衍生化试剂与Cd2+,Pb2+,Cu2+和Zn2+离子的配合反应条件及配合物在C18色谱柱上的分离条件,建立了反相高效液相色谱快速分离光度检测Cd2+,Pb2+,Cu2+和Zn2+的新方法。配合物和试剂在15 min内出峰完毕。4种离子的检出限为: Cd2+0.02 ng,Pb2+0.02 ng, Cu2+0.02 ng,Zn2+0.12 ng;线性范围为:Cd2+0.8 μg/L～150 μg/L,Pb2+0.8 μg/L～300 μg/L,Cu2+0.8 μg/L～500 μg/L,Zn2+5.0 μg/L～1 000 μg/L;方法的日内相对标准偏差为:2.8%～4.8%,测定低、中、高3个浓度的日间相对标准偏差为3.7%～9.7%。     

Use of sodium tungstate as a permanent chemical modifier for slurry sampling electrothermal atomic absorption spectrometric determination of indium in soils

A number of chemical modifiers have been assessed for the direct determination of indium in soils using electrothermal atomic absorption spectrometry and slurry sampling. The best results were obtained when the graphite atomizer was impregnated with sodium tungstate, which acts as a permanent chemical modifier. Slurries were prepared by suspending 100 mg sample in a solution containing 1% (v/v) concentrated nitric acid and 10% (v/v) concentrated hydrofluoric acid and then 15-microL aliquots were directly introduced into the atomizer. Standard indium solutions prepared in the suspension medium in the range 4-80 microg L(-1) indium were used for calibration. The relative standard deviation for ten consecutive measurements of a 40 microg L(-1) indium solution was 2.8%. The limit of detection in soils was 0.1 microg g(-1). The reliability of the procedures was confirmed by analysing two standard reference materials and by using an alternative procedure.     

Analysis of phospholipids by NACE with on-line ESI-MS

A hyphenated method of nonaqueous capillary electrophoresis coupled to electrospray ionization mass spectrometry (NACE-ESI-MS) is described for the simultaneous analysis of phospholipids. The best results were obtained with a mixed solution of methanol/ACN (40:60 v/v) containing 20 mM ammonium acetate and 0.5% acetic acid, under the applied voltage of 30 kV and capillary temperature of 25 degrees C. ESI-MS measurements were performed in the negative mode with methanol/ACN (40:60 v/v) containing 50 mM ammonium acetate as sheath liquid at a flow rate of 2 microL/min. Different phospholipid classes have been successfully separated within 16 min, and the molecular species of every single class have been identified by using MS(2) or MS(3), which generates characteristic fragments through CID. The developed method has been applied to analyze the phospholipids extracted from rat peritoneal surface and the molecular species of phospholipid classes are presented.     

Determination of pharmaceutical compounds in aqueous dimethyl sulfoxide by electrospray ionization mass spectrometry

Standard solutions of reserpine, dextromethorphan, imipramine and amitriptyline in dimethyl sulfoxide (DMSO), DMSO containing 0.1% formic acid, and DMSO/H(2)O (1:1, v/v) containing 0.1% formic acid were analyzed by positive electrospray ionization mass spectrometry (ESI-MS). A triple-quadrupole mass spectrometer equipped with a TurboIonspray (TIS) interface was used for the ESI-MS analyses. The samples dissolved in the respective DMSO solution were infused directly into the mass spectrometer at 10 microL/min using an infusion pump. The positive Q1 full-scan (m/z 50-650) mass spectrum of DMSO (MW = 78) showed three main peaks at m/z 79, 101 and 179, corresponding to the protonated molecule [DMSO+H](+), and the sodiated adducts [DMSO+Na](+) and [2DMSO+Na](+), respectively. The ESI of the compounds in DMSO and DMSO containing 0.1% formic acid was promoted by using the TIS gas (GS2) combined with the nebulizer gas (GS1), and TIS source temperature set to 250 degrees C. In contrast, samples dissolved in DMSO/H(2)O (1:1, v/v) containing 0.1% formic were sprayed at a lower temperature (100 degrees C) using only the nebulizer gas. The TIS voltage (V) was optimized in order to establish the lowest voltage necessary to achieve optimum ESI of each pharmaceutical compound with the voltage maintained below the onset potential required to produce a corona discharge at the TIS probe (sprayer). Detection limits of 10 ng/mL were achieved for reserpine, dextromethorphan, imipramine and amitriptyline in each solvent composition.     

Direct determination of lead in sweet fruit-flavored powder drinks by electrothermal atomic absorption spectrometry

A simplified method for direct determination of lead in sweet fruit-flavored powder drinks, syrups and honeys by electrothermal atomic absorption spectrometry without sample digestion is proposed. Samples were dissolved in water, acidified to 0.2% (v/v) HNO₃, and directly injected into an end-capped transversely heated graphite atomizer (THGA). Building up of carbonaceous residue inside the atomizer was effectively precluded for sugar solutions not exceeding 8.0% (m/v) when a heating program with two pyrolysis steps (600 and 1000°C) was carried out without air-ashing. Under these conditions one atomizer supported about 250 firings. Among various chemical modifiers tested, better recovery and repeatability results were obtained with a 5 μg Pd + 3 μg Mg(NO₃)₂ mixture. Tests carried out with individual concomitants containing up to 1.0 μg Na, K, Ca or Cl, and up to 10.0 μg phosphate or sulphate, and several mixtures of these six concomitants, did not reveal significant interferences on lead atomization. Characteristic mass and detection limit based on integrated absorbance were 15 and 11 pg Pb, respectively. The relative standard deviation based on 10 measurements for typical samples (20–60 ng g⁻¹ Pb) was always lower than 5.5%. The detection limit of 7.0 ng g⁻¹ Pb attained the Codex recommendation for the maximum allowed lead contents in the sugar samples. Application of t-test to the results obtained by the proposed direct analysis, and the official method adopted by Food Chemical Codex, demonstrated that there were no significant differences at the 5% probability level.     

Development of multi-elemental method for quality control of parenteral component solutions using ICP-MS

An inductively coupled plasma mass spectrometry (ICP-MS) method for elemental impurities determination in components used for parenteral nutrition solutions is proposed. Solutions of amino acids (10% m/v), glucose (50% m/v) and lipids (20% m/v) were analyzed. Arsenic, Cd, Cu, Pb and Mo were determined by ICP-MS operated at standard mode, whilst pneumatic nebulization was used for introducing the sample solution into the ICP. Mercury was determined using cold vapor generation (CVG) coupled to ICP-MS. Chromium, Mn, Ni and V were determined by means of dynamic reaction cell-inductively coupled plasma mass spectrometry (DRC-ICP-MS), while ammonia was used as reaction gas. The operational conditions of each technique were optimized in order to achieve better sensitivity, precision and accuracy. The influence of the sample matrix, mainly carbon, on all investigated elements was evaluated. The use of DRC was effective to reduce interferences on Cr, Mn, Ni and V determination. The other investigated elements (As, Cd, Cu, Pb, Mo and Hg) were determined directly in the samples, which were properly diluted. Results obtained were in good agreement (between 96 and 103%) with certified values (certified reference materials of water were analyzed), at the same time as the relative standard deviation was lower than 5%. Sample throughput was relatively high (up to 30 samples of components used for parenteral nutrition solution could be analyzed per hour). In this way, the proposed method can be recommended for routine analysis.     

Investigations for the determination of tin by flow injection hydride generation atomic-absorption spectrometry

It could be shown that the pre- or double peaks which are frequently observed in the determination of tin by hydride generation atomic-absorption spectrometry are not due to reagent contamination or memory effects. Rather they originate from the silica material used to make the quartz tube atomizer. At elevated temperatures the tin diffuses to the surface and it can be volatilized and atomized only in the presence of hydrogen. The height of the pre-peak depends, among other things, on the time for which the quartz tube atomizer has been at a high temperature without hydrogen. The pre-peaks disappear when argon with 10% (v/v) hydrogen is used as the purge gas. In flow injection the pre-peaks can be separated in time from the analytical signal by using a program in which hydrogen is generated by reaction of sodium tetrahydroborate reluctant solution with the acid carrier prior to the injection of the sample. Also investigated was the influence of the acid and sodium tetrahydroborate concentration on sensitivity and freedom from interferences. Best results were obtained when a saturated boric acid solution containing 0.1M hydrochloric acid was used for standards, samples and carrier solution, and a 0.4% (m/v) sodium tetrahydroborate solution with 0.05% (m/v) sodium hydroxide as the reluctant. Under these conditions tin could be determined accurately in the range 0.008-0.1% in low alloy steel standard reference materials, with matrix-free standard solutions for calibration.     

Temperature optimization for improved determination of phosphatidylserine species by micro liquid chromatography with electrospray tandem mass spectrometric detection

A sensitive method for determination of disaturated phosphatidylserine species in the presence of their monounsaturated analogs has been developed, using micro liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The hydrophobic nature of the phosphatidylserine species required a combination of low-eluting sample solvents and sub-ambient temperatures in order to focus large sample volumes up to 20 microL. The samples were dissolved in 2-propanol:hexane:water (20:10:4, v/v/v) prior to 1:9 dilution with ammonium formate buffer:2-propanol:tetrahydrofuran (30:55:15, v/v/v) and final 1:4 dilution with ammonium formate buffer (10 mM):2-propanol: tetrahydrofuran (55:37.5:7.5, v/v/v). The analytical column was a 0.5 x 150 mm stainless steel column packed with 5 microm C30 particles, while the mobile phase contained ammonium formate buffer (10 mM): 2-propanol:tetrahydrofuran (30:55:15, v/v/v). A temperature program from 5 degrees C (hold for 3 minutes) to 75 degrees C at 8 K/min provided separation of the disaturated phosphatidylserine species from their monounsaturated analogs, making available a sensitive determination of the isobaric species. The mass limit of detection for dipalmitoyl phosphatidylserine was 100 pg, corresponding to a concentration limit of detection of 5 pg/microL when using an injection volume of 20 microL. This is an improvement by a factor of 20 as compared to previously reported numbers obtained with conventional LC columns. The within-assay precision of dipalmitoyl phosphatidylserine was 11.9% RSD (n = 3), while the retention time precision was 4.1% RSD (n = 6).     

Use of iridium plus rhodium as permanent modifier to determine As, Cd and Pb in acids and ethanol by electrothermal atomic absorption spectrometry

The most severe interferences in atomic absorption spectrometry are caused by the presence of anions when they are in different concentrations in the samples and in the calibration solutions. The analyte addition technique or matrix matching calibration can be employed to minimize or compensate the non-spectral interferences, but they are time consuming or difficult to be carried out. The use of chemical modifiers usually allows higher pyrolysis temperatures and consequently the removal of components of the sample matrix, equalizing the analyte signal in the sample and in the calibration solution. In this work, a mixture of Ir and Rh is proposed as permanent modifier to determine As, Cd and Pb in diluted hydrochloric, sulfuric and phosphoric acids and in ethanol and methanol by electrothermal atomic absorption spectrometry (ET AAS) with calibration against 1% v/v nitric acid aqueous solutions. The performance of the proposed permanent modifier was compared to that of Pd plus Mg nitrates in solution. Better recoveries, low background levels and faster analysis were obtained with the permanent modifier. The permanent modifier was also successfully employed for the determination of As, Cd and Pb in different concentrations of sulfuric and hydrochloric acids. For the phosphoric acid, the proposed modifier was only efficient for acid concentrations up to 2% v/v for As and up to 5% v/v for Cd and Pb. The precision, expressed as the relative standard deviation (n=3), was lower than 10%, for all samples, including ethanol and methanol.     

Minimization of lead and copper interferences on spectrophotometric determination of cadmium using electrolytic deposition and ion-exchange in multi-commutation flow system

A new strategy for minimization of Cu(2+) and Pb(2+) interferences on the spectrophotometric determination of Cd(2+) by the Malachite green (MG)-iodide reaction using electrolytic deposition of interfering species and solid phase extraction of Cd(2+) in flow system is proposed. The electrolytic cell comprises two coiled Pt electrodes concentrically assembled. When the sample solution is electrolyzed in a mixed solution containing 5% (v/v) HNO(3), 0.1% (v/v) H(2)SO(4) and 0.5 M NaCl, Cu(2+) is deposited as Cu on the cathode, Pb(2+) is deposited as PbO(2) on the anode while Cd(2+) is kept in solution. After electrolysis, the remaining solution passes through an AG1-X8 resin (chloride form) packed minicolumn in which Cd(2+) is extracted as CdCl(4)(2-). Electrolyte compositions, flow rates, timing, applied current, and electrolysis time was investigated. With 60 s electrolysis time, 0.25 A applied current, Pb(2+) and Cu(2+) levels up to 50 and 250 mg l(-1), respectively, can be tolerated without interference. For 90 s resin loading time, a linear relationship between absorbance and analyte concentration in the 5.00-50.0 mug Cd l(-1) range (r(2)=0.9996) is obtained. A throughput of 20 samples per h is achieved, corresponding to about 0.7 mg MG and 500 mg KI and 5 ml sample consumed per determination. The detection limit is 0.23 mug Cd l(-1). The accuracy was checked for cadmium determination in standard reference materials, vegetables and tap water. Results were in agreement with certified values of standard reference materials and with those obtained by graphite furnace atomic absorption spectrometry at 95% confidence level. The R.S.D. for plant digests and water containing 13.0 mug Cd l(-1) was 3.85% (n=12). The recoveries of analyte spikes added to the water and vegetable samples ranged from 94 to 104%.     

Determination of bradykinin and arg-bradykinin in rat muscle tissue by microdialysis and capillary column-switching liquid chromatography with mass spectrometric detection

Quantification of bradykinin peptides in limited amounts of rat muscle tissue dialysate has been performed using a packed capillary LC-ESI-TOF-MS method. The micro dialysate samples (450 microL) with added internal standard were loaded onto a 1 mm x 5 mm loading column packed with 5 microm Kromasil C18 particles by a carrier solution of 0.1% formic acid in ACN/water (5:95, v/v) at a flow rate of 250 microL/min for online preconcentration of the analytes. Back-flushed elution onto a 150 mm x 0.5 mm Zorbax C18 column packed with 5 microm particles was conducted using a linear solvent ACN/H2O gradient containing 0.1% formic acid. (Tyr8)-bradykinin was used as an internal standard and was added to the dialysis sample prior to injection. Baseline separation of bradykinin, arg-bradykinin and (tyr8)-bradykinin was achieved within 10 min. Positive ESI was performed in the m/z range of 200-1300. The method was validated in the range 0.2-1.0 ng/mL dialysate, yielding correlation coefficients of 0.995 and 0.990 for bradykinin and arg-bradykinin, respectively. The within-assay and between-assay precisions were between 4.3-9.6% and 6.2-10.6%, respectively. Both arg-bradykinin and bradykinin were detected in dialysate from rat muscle tissue, at concentrations of 0.1 and 0.4 ng/mL for bradykinin and arg-bradykinin, respectively, confirming the presence of arg-bradykinin in rat muscles.