Molybdenum, Mo-Ir and Mo-Ru coatings as permanent chemical modifiers for the determination of cadmium and lead in sediments and soil samples by electrothermal atomic absorption spectrometry

Molybdenum, Ir, Ru, Mo-Ir, Mo-Ru thermally coated on to platforms inserted in pyrolytic graphite tubes as permanent modifiers and Pd + Mg(NO₃)₂ conventional modifier mixture have been employed for the determination of cadmium and lead in dissolved sediments and soil samples by electrothermal atomic absorption spectrometry (ETAAS). Optimum masses and mass ratios of permanent modifiers for the analysis of Cd and Pb in sample solutions have been investigated. The 280 μg of Mo, 200 μg of Ir, 200 μg of Ru, 280 μg of Mo + 200 μg of Ir or 280 μg of Mo + 200 μg of Ru has been found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ for increasing thermal stabilization of analytes and for decreasing the most serious interferences. Pyrolysis and atomization temperatures, atomization and background signal shapes, characteristic masses and detection limits of analytes in dissolved samples with or without permanent and conventional modifiers have been compared. The detection limits and characteristic masses obtained with Mo-Ir coated platform are 0.01 μg g⁻¹ and 1.1 pg for Cd and 0.09 μg g⁻¹ and 19 pg for Pb, respectively. Long-term stabilities for analytes in samples with Mo, Mo-Ir, Mo-Ru and Pd + Mg(NO₃)₂ have been studied. Cadmium and lead contents have been determined in certified and standard reference materials by using optimum conditions investigated and the results obtained with Mo-Ir or Mo-Ru were in agreement with the values of certified reference materials.     

Evaluation of V, Ir, Ru, V-Ir, V-Ru, and W-V as permanent chemical modifiers for the determination of cadmium, lead, and zinc in botanic and biological slurries by electrothermal atomic absorption spectrometry

Permanent modifiers (V, Ir, Ru, V-Ir, V-Ru, and W-V) thermally coated on to platforms of pyrolytic graphite tubes were employed for the determination of Cd, Pb, and Zn in botanic and biological slurries by electrothermal atomic absorption spectrometry (ETAAS). Conventional Pd + Mg(NO₃)₂ modifier mixture was also used for the determination of analytes in slurries and digested samples. Optimum masses and mass ratios of permanent modifiers for Cd, Pb, and Zn in slurry sample solutions were investigated. The 280 μg of V, 280 μg of V + 200 μg of Ir, 280 μg of V + 200 μg of Ru or 240 μg of W + 280 μg of V in 0.2% (v/v) Triton X-100 plus 0.5% (v/v) HNO₃ mixture was found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ modifier mixture for obtaining thermal stabilization, and for obtaining best recoveries. Optimization conditions of analytes, such as pyrolysis and atomization temperature, characteristic masses and detection limits, and atomization and background peak profiles were studied with permanent and 5 μg of Pd + 3 μg of Mg(NO₃)₂ conventional modifiers and compared with each other. The permanent V-Ir, V-Ru, and W-V modifiers remained stable for approximately 250-300 firings when 20 μl of slurries and digested samples were delivered into the atomizer. In addition, the mixed permanent modifiers increase the tube lifetime by 50-95% when compared with untreated platforms. The characteristic masses and detection limits of analytes (dilution factor of 125 ml g⁻¹) obtained with V-Ir based on integrated absorbance as example for 0.8% (m/v) slurries were 1.0 pg and 3 ng g⁻¹ for Cd, 18 pg and 17 ng g⁻¹ for Pb, and 0.7 pg and 4 ng g⁻¹ for Zn, respectively. The results of analytes obtained by employing V-Ir, V-Ru, and W-V permanent modifier mixtures in botanic and biological certified and standard reference materials were in agreement with the certified values of reference materials.     

Simultaneous pre-concentration procedure for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry

In this paper is proposed a simultaneous pre-concentration procedure using cloud point extraction for the determination of cadmium and lead in drinking water employing sequential multi-element flame atomic absorption spectrometry. The ligand used is 2-(2-thiazolylazo)-p-cresol (TAC) and the micellar phase is obtained using non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114) and centrifugation.The optimization step was performed using two-level factorial design and Doehlert design. A multiple response function was established in order to get experimental conditions for simultaneous extraction of cadmium and lead.The method allows the determination of cadmium and lead with detection limits of 0.077 μg L^− 1 and 1.05 μg L^− 1 respectively, precision expressed as relative standard deviation (RSD) of 1.5 and 3.3% (n = 10) for cadmium concentrations of 30 μg L^− 1 and 50 μg L^− 1, respectively, and RSD of 1.8% and 2.7% for lead concentrations of 30 μg L^− 1 and 50 μg L^− 1, respectively. The accuracy was confirmed by analysis of a certified reference material of natural water.This method was applied for the determination of cadmium and lead in drinking water samples collected in Jaguaquara City, Brazil. Tests of addition/recovery were also performed for some samples and results varied from 95 to 104% for cadmium and 96 to 107% for lead. The cadmium and lead concentrations found in these samples were always lower than the permissible maximum levels stipulated by Brazilian Health Organization.     

Comparison of direct solid sampling and slurry sampling for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry

Two analytical methods for the determination of cadmium in wheat flour by electrothermal atomic absorption spectrometry without prior sample digestion have been compared: direct solid sampling analysis (SS) and slurry sampling (SlS). Besides the conventional modifier mixture of palladium and magnesium nitrates (10 μg Pd + 3 μg Mg), 0.05% (v/v) Triton X-100 has been added to improve the penetration of the modifier solution into the solid sample, and 0.1% H₂O₂ in order to promote an in situ digestion for SS. For SlS, 30 μg Pd, 12 μg Mg and 0.05% (v/v) Triton X-100 have been used as the modifier mixture. Under these conditions, and using a pyrolysis temperature of 800 °C, essentially no background absorption was observed with an atomization temperature of 1600 °C. About 2 mg of sample have been typically used for SS, although as much as 3-5 mg could have been introduced. In the case of SlS multiple injections had to be used to achieve the sensitivity required for this determination. Calibration against aqueous standards was feasible for both methods. The characteristic mass obtained with SS was 0.6 pg, and that with SlS was 1.0 pg. The limits of detection were 0.4 and 0.7 ng g⁻¹, the limits of quantification were 1.3 and 2.3 ng g⁻¹ and the relative standard deviation (n = 5) was 6-16% and 9-23% for SS and SlS, respectively. The accuracy was confirmed by the analysis of certified reference materials. The two methods were applied for the determination of cadmium in six wheat flour samples acquired in supermarkets of different Brazilian cities. The cadmium content varied between 8.9 ± 0.5 and 13 ± 2 ng g⁻¹ (n = 5). Direct SS gave results similar to those obtained with SlS using multi-injections; the values of both techniques showed no statistically significant difference at the 95% confidence level. Direct SS was finally adopted as the method of choice, due to its greater simplicity, the faster speed of analysis and the better figures of merit.     

Determination of cadmium in rice and water by tungsten coil electrothermal vaporization-atomic fluorescence spectrometry and tungsten coil electrothermal atomic absorption spectrometry after cloud point extraction

In this work, the microsampling nature of tungsten coil electrothermal vaporization Ar/H₂ flame atomic fluorescence spectrometry (W-coil ETV-AFS) as well as tungsten coil electrothermal atomic absorption spectrometry (W-coil ET-AAS) was used with cloud point extraction (CPE) for the ultrasensitive determination of cadmium in rice and water samples. When the temperature of the extraction system is higher than the cloud point temperature of the selected surfactant Triton X-114, the complex of cadmium with dithizone can be quantitatively extracted into the surfactant-rich phase and subsequently separated from the bulk aqueous phase by centrifugation. The main factors affecting the CPE, such as concentration of Triton X-114 and dithizone, pH, equilibration temperature and incubation time, were optimized for the best extract efficiency. Under the optimal conditions, the limits of detection for cadmium by W-coil ETV-AFS and W-coil ET-AAS were 0.01 and 0.03 μg L⁻¹, with sensitivity enhancement factors of 152 and 93, respectively. The proposed methods were applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with certified values.     

Sequential cloud point extraction for the speciation of mercury in seafood by inductively coupled plasma optical emission spectrometry

A novel nonchromatographic speciation technique for the speciation of mercury by sequential cloud point extraction (CPE) combined with inductively coupled plasma optical emission spectrometry (ICP-OES) was developed. The method based on Hg²⁺ was complexed with I⁻ to form HgI₄²⁻, and the HgI₄²⁻ reacted with the methyl green (MG) cation to form hydrophobic ion-associated complex, and the ion-associated complex was then extracted into the surfactant-rich phase of the non-ionic surfactant octylphenoxypolyethoxyethanol (Triton X-114), which are subsequently separated from methylmercury (MeHg⁺) in the initial solution by centrifugation. The surfactant-rich phase containing Hg(II) was diluted with 0.5 mol L^− 1 HNO₃ for ICP-OES determination. The supernatant is also subjected to the similar CPE procedure for the preconcentration of MeHg⁺ by the addition of a chelating agent, ammonium pyrrolidine dithiocarbamate (APDC), in order to form water-insolvable complex with MeHg⁺. The MeHg⁺ in the micelles was directly analyzed after disposal as describe above. Under the optimized conditions, the extraction efficiency was 93.5% for Hg(II) and 51.5% for MeHg⁺ with the enrichment factor of 18.7 for Hg(II) and 10.3 for MeHg⁺, respectively. The limits of detection (LODs) were 56.3 ng L^− 1 for Hg(II) and 94.6 ng L^− 1 for MeHg⁺ (as Hg) with the relative standard deviations (RSDs) of 3.6% for Hg(II) and 4.5% for MeHg⁺ (C = 10 μg L⁻¹, n = 7), respectively. The developed technique was applied to the speciation of mercury in real seafood samples and the recoveries for spiked samples were found to be in the range of 93.2–108.7%. For validation, a certified reference material of DORM-2 (dogfish muscle) was analyzed and the determined values are in good agreement with the certified values.     

Feasibility of using in situ fusion for the determination of Co,Cr and Mn in Portland cement by direct solid sampling graphite furnace atomic absorption spectrometry

In situ fusion on the boat-type graphite platform has been used as a sample pretreatment for the direct determination of Co, Cr and Mn in Portland cement by solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS). The 3-field Zeeman technique was adopted for background correction to decrease the sensitivity during measurements. This strategy allowed working with up to 200 µg of sample. The in situ fusion was accomplished using 10 µL of a flux mixture 4.0% m/v Na₂CO₃ + 4.0% m/v ZnO + 0.1% m/v Triton® X-100 added over the cement sample and heated at 800 °C for 20 s. The resulting mould was completely dissolved with 10 µL of 0.1% m/v HNO₃. Limits of detection were 0.11 µg g^− 1 for Co, 1.1 µg g^− 1 for Cr and 1.9 µg g^− 1 for Mn. The accuracy of the proposed method has been evaluated by the analysis of certified reference materials. The values found presented no statistically significant differences compared to the certified values (Student's t-test, p < 0.05). In general, the relative standard deviation was lower than 12% (n = 5).     

Comparison of direct sampling and emulsion analysis using a filter furnace for the determination of lead in crude oil by graphite furnace atomic absorption spectrometry

The determination of trace elements in crude oil is difficult due to the complex nature of the sample and the various different chemical forms in which the metals can occur. The advantage of graphite furnace atomic absorption spectrometry is that only a minimum of sample pretreatment is required. In this work two techniques have been compared to establish a fast and reliable method for lead determination in crude oil. In the first one the crude oil samples were weighed directly onto solid sampling (SS) platforms and introduced into the graphite tube for analysis. In the second one the samples were prepared as oil-in-water emulsions and analyzed in a filter furnace (FF). Twenty μL of a mixture of 0.5 mg L^− 1 Pd + 0.3 mg L^− 1 Mg + Triton X-100 has been used as the modifier, and calibration against aqueous solutions has been used for both methods. The sensitivity obtained with the FF was more than a factor of two better than that with SS; however, as a larger sample mass could be introduced in the latter case, so that the limits of detection for both techniques were 0.004 mg kg^− 1. Seven crude oil samples were analyzed using the two procedures, and all results were in agreement at a 95% confidence level using a paired Student's t-test. For validation purposes, three crude oil samples have been mineralized using an open-vessel acid digestion, and the results were in agreement with those found with direct sampling and with emulsion sampling using FF according to ANOVA test. Both methods are simple, fast and reliable, being appropriated for routine analysis; however, the direct method using SS technology should be preferred because of its simplicity, speed and commercial availability.     

Determination of copper,iron and vanadium in petroleum by direct sampling electrothermal atomic absorption spectrometry

A procedure for the direct determination of Cu, Fe and V in petroleum samples by electrothermal atomic absorption spectrometry using a solid sampling accessory, without any sample pre-treatment or dilution, is proposed. A Pd + Triton X-100 solution was used as chemical modifier. The pyrolysis and atomization temperatures, as well as the Pd mass were defined by multivariate optimization. The other parameters of the temperature programs were defined by univariate optimization. The limits of detection at the optimized conditions were 10, 200 and 800 pg for Cu, Fe and V, respectively, for typical sample masses ranging from 0.10 to 3.00 mg. Method accuracy was confirmed by the analysis of oil certified reference materials as well as by comparison with independent methods. Aqueous calibration solutions were used and no statistically significant difference (analysis of variance) was observed between obtained and expected values.     

Direct determination of arsenic in petroleum derivatives by graphite furnace atomic absorption spectrometry: A comparison between filter and platform atomizers

In the present work a direct method for the determination of arsenic in petroleum derivatives has been developed, comparing the performance of a commercial transversely heated platform atomizer (THPA) with that of a transversely heated filter atomizer (THFA). The THFA results in a reduction of background absorption and an improved sensitivity as has been reported earlier for this atomizer. The mixture of 0.1% (m/v) Pd + 0.03% (m/v) Mg + 0.05% (v/v) Triton X-100 was used as the chemical modifier for both atomizers. The samples (naphtha, gasoline and petroleum condensate) were stabilized in the form of a three-component solution (detergentless microemulsion) with the sample, propan-1-ol and 0.1% (v/v) HNO₃ in a ratio of 3.0:6.4:0.6. The characteristic mass of 13 pg found in the THFA was about a factor of two better than that of 28 pg obtained with the THPA; however, the limits of detection (LOD) and quantification (LOQ) were essentially the same for both atomizers (1.9 and 6.2 μg L⁻¹, respectively, for THPA, and 1.8 and 5.9 μg L⁻¹, respectively, for THFA) due to the increased noise observed with the THFA. A possible explanation for that is a partial blockage of the radiation from the hollow cathode lamp by the narrow inner diameter of this tube and the associated loss of radiation energy. Due to the lack of an appropriate certified reference material, recovery tests were carried out with inorganic and organic arsenic standards and the results were between 89% and 111%. The only advantage of the THFA found in this work was a reduction of the total analysis time by about 20% due to the ‘hot injection’ that could be realized with this furnace. The arsenic concentrations varied from < LOQ to 43.3 μg L⁻¹ in the samples analyzed in this work.     

Cloud point extraction of iron(III) and vanadium(V) using 8-quinolinol derivatives and Triton X-100 and determination of 10(-7)moldm(-3) level iron(III) in riverine water reference by a graphite furnace atomic absorption spectroscopy

The cloud point extraction behavior of iron(III) and vanadium(V) using 8-quinolinol derivatives (HA) such as 8-quinolinol (HQ), 2-methyl-8-quinolinol (HMQ), 5-butyloxymethyl-8-quinolinol (HO₄Q), 5-hexyloxymethyl-8-quinolinol (HO₆Q), and 2-methyl-5-octyloxymethyl-8-quinolinol (HMO₈Q) and Triton X-100 solution was investigated. Iron(III) was extracted with HA and 4% (v/v) Triton X-100 in the pH range of 1.70-5.44. Above pH 4.0, more than 95% of iron(III) was extracted with HQ, HMQ, and HMO₈Q. Vanadium(V) was also extracted with HA and 4% (v/v) Triton X-100 in the pH range of 2.07-5.00, and the extractability increased in the following order of HMQ < HQ < HO₄Q < HO₆Q. The cloud point extraction was applied to the determination of iron(III) in the riverine water reference by a graphite furnace atomic absorption spectroscopy. When 1.25 × 10⁻³ M HMQ and 1% (v/v) Triton X-100 were used, the found values showed a good agreement with the certified ones within the 2% of the R.S.D. Moreover, the effect of an alkyl group on the solubility of 5-alkyloxymethyl-8-quinolinol and 2-methyl-5-alkyloxymethyl-8-quinolinol in 4% (v/v) Triton X-100 at 25 °C was also investigated.     

Characteristics of subtractive anodic stripping voltammetry of Pb and Cd at silver and gold electrodes

Silver and gold electrodes are useful for the quantitative determination of lead and cadmium with subtractive anodic stripping voltammetry (SASV). The use of SASV is essential for achieving good separation between the two peaks, to eliminate the interference of nitrates when cadmium is present and to allow analysis at very low concentrations without the removal of oxygen. The deposition and dissolution of Pb²⁺ and Cd²⁺ proceed at underpotential (UPD) on both electrodes. The UPD properties of the deposits are the main factor determining the analytical characteristics of the ASV method and are strongly affected by the type and concentration of the electrolyte. The effects of anions (Cl⁻, Br⁻, SO₄²⁻, NO₃⁻) and acids (HNO₃, HClO₄, H₂SO₄, HCl) are shown. The two electrodes complement each other and, in addition, enable the qualitative identification of Pb²⁺ and Cd²⁺, since the peaks appear in opposite order on the two electrodes. Analysis of mixtures of the two analytes is restricted on gold but not on silver. At gold the two peaks overlap: (i) at concentrations of cadmium higher than 250 nM at deposition times greater than 30 s, (ii) in the presence of copper at concentrations higher than 1 μM, and (iii) in the presence of Triton X-100 at concentrations above 10 mg/l. The repeatability at 10 nM analyte is better than 2.5%. The detection limits for Pb²⁺ and Cd²⁺ at 120 s deposition time and 3500 rpm rotation rate are: dl_Pb/Ag=0.04 nM; dl_Cd/Ag=0.7 nM; dl_Pb/Au=0.1 nM; dl_Cd/Au=0.3 nM. The analysis of lead and cadmium in natural waters has been performed.     

Development of a cloud point extraction and preconcentration method for determination of trace aluminum in mineral waters by FAAS

A cloud point extraction (CPE) method has been developed for the preconcentration of trace aluminum prior to its determination by flame atomic absorption spectrometry (FAAS). The CPE method is based on the complex of Al(III) with Xylidyl Blue (XB) and then entrapped in non-ionic surfactant Triton X-114. The main factors affecting CPE efficiency, such as pH of sample solution, concentration of XB and Triton X-114, equilibration temperature and time, were investigated in detail. An enrichment factor of 50 was obtained for the preconcentration of Al(III) with 50 mL solution. Under the optimal conditions, the detection limit of this method for Al(III) is 1.43 μg L^− 1, and the relative standard deviation is 2.7% at determination of 100 μg L^− 1 Al(III). The proposed method has been applied for determination of trace amount of aluminum in mineral water samples with satisfactory results. Also, the proposed method was applied to the certified reference materials. The results obtained were in good agreement with certified values.     

Use of the molybdenum-thiocyanate-rhodamine 6G ternary complex for spectrophotometric molybdenum determination without extraction

A modified thiocyanate method without extraction by using rhodamine 6G as a secondary ligand was developed. Molybdenum in 1.0×10⁻² M HCl, after the addition of ascorbic acid, was heated for 10 min in a 90 °C water bath for reduction. Suitable amounts of glycerine, Triton X-100, rhodamine 6G solutions and 2+1 (v/v) 9 M H₂SO₄+3 M KHSO₄ were added in this order. This solution was allowed to cool to room temperature and the absorbance at 570 nm was measured against a reagent blank 45 min after the addition of thiocyanate solution and the second aliquot of Triton X-100 solution. The complex was stable for at least 4 h, the order of reagent addition was important, and thiocyanate should be in large excess. Beer’s law was obeyed over the range 0.9×10⁻⁶ to 1.1×10⁻⁵ M Mo with the molar absorptivity being 1.1×10⁵ l mol⁻¹ cm⁻¹. The R.S.D. for the determination of 0.7 mg Mo l⁻¹ was 1.83% (n=8). Possible interferences of various cations and anions on molybdenum determination were studied. The proposed method was applied to the determination of molybdenum in a dental alloy, Wiron 99.     

Spectrometric studies on the cloud points of Triton X-405

The effect of various chemicals on the cloud point (CP) of nonionic surfactant Triton X-405 (TX-405) in aqueous solutions has been investigated. In the measurements of cloud point temperatures, UV–visible spectrophotometer was used instead of visual observation. The values of CP for Triton X-405 could not be measured directly because TX-405 had an average number of oxyethylene units per molecule, p ≈ 35 and a CP > 100 °C. To avoid additional measurements under pressure, TX-405 had their CP lowered below the normal boiling point of their solutions by adding the salting-out, CP-lowering salts at various concentrations, measuring the depressed CP values and extrapolating them to zero salt concentration. The CP values decrease linearly with increasing concentration of salts at studied concentrations. The results showed that the addition of the simple salts and nonionic surfactant Triton X-114 (TX-114) which are infinitely miscible with water decreased the cloud point of the TX-405. In this study, the real CP values of TX-405 which are merely listed as >100 °C in the literature was found as 116 ± 1 °C in various samples. In the lyotropic series, it is expected that the effect of F⁻ > Cl⁻ > Br⁻ will be on the decrease in CP, because the ionic sizes increase along the group consequently decreasing the formal charge density on anion, thus lowering the attraction on anion and thereby lowering the attraction of water. The order of CP depression for the other anions is as follows: PO₄³⁻ > SO₄²⁻ > NO₃⁻ > Br⁻. This means that electrolyte containing trivalent anions is more effective at salting-out the PEO chain than those containing divalent anions and monovalent anions. Cations effectiveness is present in the following order for change: Na⁺ > K⁺ > NH₄⁺ because of their effect on water structure and their hydrophilicity. Overall the electrolytes and nonelectrolytes have a large amount of effect on CP of nonionic surfactant, because of their effect on water structure and their hydrophilicity.     

Study of matrix effects and spectral interferences in the determination of lead in sediments, sludges and soils by SR-ETAAS using slurry sampling

An interference-free, fast, and simple method is proposed for Pb determination in environmental solid samples combining slurry sampling and electrothermal atomic absorption spectrometry. Samples were ground to an adequate particle size and slurries were prepared by weighing from 0.05 g to 0.20 g of dry sediment, adding nitric acid, and a solution containing 0.1% Triton X-100. Ultrasonic agitation was employed for slurries homogenization. Analytical variables including acid pre-treatment conditions, particle size, slurry stability, temperature program of the graphite furnace, and type and concentration of the chemical modifier were studied. The undesirable effects of potential non-specific and spectral interferences on Pb signal were also taken into account. Continuum source and self-reversal methods for background correction were evaluated and compared. For calibration, synthetic acid solutions of Pb were employed. Calibration was linear within the range 1-30 μg L⁻¹ and 5-30 μg L⁻¹ when the 217.0 nm and 283.3 nm analytical lines were used. Correlation coefficients of 0.9992 and 0.9997 were obtained. Using optimized conditions, limits of detection (3σ) of 0.025 μg g⁻¹ and 0.1 μg g⁻¹ were achieved for the 217.0 nm and 283.3 nm analytical lines, respectively. The method was successfully applied to the determination of lead in soil, contaminated soil, municipal sludge, and sediment samples. The accuracy was assessed by the analysis of two certified reference materials: municipal sludge (QC MUNICIPAL SLUDGE A) and lake sediment (TRAP-LRM from IJS).     

Cloud point extraction for ultra-trace Cd determination in microwave-digested biological samples by ETAAS

Cloud point extraction (CPE) has been used for the preconcentration of cadmium, after the formation of a complex with 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (5-Br-PADAP), and further determination by graphite furnace atomic absorption spectrometry (ETAAS) using polyethyleneglicolmono-p-nonyphenylether (PONPE 7.5) as surfactant. The chemical variables that affect the cloud point extraction were optimized. The separation of the two phases was easily accomplished by cooling the mixture in order to make more viscous the surfactant-rich phase. In order to establish the optimum conditions for the determination of Cd by ETAAS, Pd + Mg, Pt, Ir, Rh and Ru were studied as chemical modifiers. The best thermal stabilization was obtained with Pd + Mg, with a maximum pyrolysis temperature of 1100 °C. Under the optimum conditions i.e., pH 9.0, [5-Br-PADAP] = 2.0 × 10⁻⁵ mol L⁻¹, [PONPE 7.5] = 0.02% (w/v), an enhancement factor of 22-fold was reached. The lower limit of detection (LOD) obtained under the optimal conditions was 0.008 μg L⁻¹. The precision for 10 replicate determinations at 0.2 μg L⁻¹ Cd was 3.5% relative standard deviation (R.S.D.). The calibration graph using the preconcentration method was linear with a correlation coefficient of 0.9984 at levels close to the detection limit up to at least 1.0 μg L⁻¹. The method was successfully applied to the determination of cadmium in urine samples and in a water standard reference material.     

Spectrophotometric flow-injection determination of zinc in plant digests based on a spot test

A spot test was implemented in a flow-injection system for the spectrophotometric determination of zinc in digests of plant materials. It is based on the influence of Zn²⁺ on the oxidation rate of 1-naphthylethylenediamine (NED) by hexacyanoferrate(III) under acidic conditions. In order to control the precipitate formation and to maintain the resulting suspension, a micellar medium was established by adding Triton X-100. The proposed system handles about 65 samples per hour, meaning 72 μg NED and 9.0 mg K₃[Fe(CN)₆] per determination. Baseline drift is usually <0.01 absorbance per hour and the analytical signals for 0.5-2.5 mg l⁻¹ Zn range within ca. 0.07-0.45 absorbance. Linearity of the analytical curve is fair (r>0.999, n=6) and detection limit was estimated as 0.2 mg l⁻¹ Zn. Results are precise (R.S.D.<1%, n=10) and in agreement with flame atomic absorption spectrometry and with certified values of standard reference materials.     

Determination of trace alpha-fetoprotein variant by affinity adsorption solid substrate-room temperature phosphorimetry and its application to the forecast of human diseases

In the presence of ion perturber LiAc, 4-generation polyamidoamine dendrimers (4G-D) could emit strong and stable room temperature phosphorescence (RTP) signal at on nitrocellulose membrane (NCM), and Triton X-100 could sharply enhance the RTP signal of 4G-D. Triton X-100-4G-D was used to label concanavalin agglutinin (Con A) to get the labeling product Triton X-100-4G-D-Con A. Quantitative specific affinity adsorption (AA) reaction between Triton X-100-4G-D-Con A and α-fetoprotein variant (AFP-V) could be carried out on the surface of NCM, whose product Triton X-100-4G-D-Con A-AFP-V could emit strong and stable RTP and its ΔI_p was proportional to the content of AFP-V. According to the facts above, a new affinity adsorption solid substrate-room temperature phosphorimetry (AA-SS-RTP) for the determination of trace AFP-V by Con A labeled with Triton X-100-4G-D was established. Detection limits of this method were 0.23 fg spot⁻¹ (direct method, corresponding concentration: 5.8 × 10⁻¹³ g mL⁻¹) and 0.13 fg spot⁻¹ (sandwich method, corresponding concentration: 3.2 × 10⁻¹³ g mL⁻¹). It has been successfully applied to determine the content of AFP-V in human serum and forecast human diseases, for its high sensitivity, long RTP lifetime, good repeatability, high accuracy and little background perturbation with at the long wavelength area. Meanwhile, the mechanism for the determination of trace AFP-V using AA-SS-RTP was also discussed.     

Spectrophtometric determination of malachite green in fish farming water samples after cloud point extraction using nonionic surfactant Triton X-100

A novel and sensitive cloud point extraction procedure for the determination of trace amounts of malachite green by spectrophotometry was developed. Malachite green was extracted at pH 2.5 mediated by micelles of nonionic surfactant Triton X-100. The extracted surfactant-rich phase was diluted with ethanol and its absorbance was measured at 630 nm. The effect of different variables such as pH, Triton X-100 concentration, cloud point temperature and time and diverse ions was investigated and optimum conditions were established. The calibration graph was linear in the range of 4-500 ng mL⁻¹ of malachite green in the initial solution with r = 0.9996 (n = 10). Detection limit based on three times the standard deviation of the blank (3S_b) was 1.2 ng mL⁻¹ and the relative standard deviation (R.S.D.) for 20 and 300 ng mL⁻¹ of malachite green was 1.48 and 1.13% (n = 8), respectively. The method was applied to the determination of malachite green in different fish farming and river water samples.