Total sulfur determination in gasoline,kerosene and diesel fuel using inductively coupled plasma optical emission spectrometry after direct sample introduction as detergent emulsions

Herein, we present the development of a procedure for the determination of total sulfur in petroleum-derived products (gasoline, kerosene and diesel fuel) employing inductively coupled plasma optical emission spectrometry (ICP OES). For this procedure, samples were prepared as emulsions that were made using concentrated nitric acid, Triton X-100, sample, and ultra pure water in proportions of 5/10/7/78% (v/v), respectively. Sample volumes were weighed because of the density differences, and oxygen was added to the sheat gas entrance of the ICP OES in order to decrease carbon deposition in the torch and to minimize background effects. A Doehlert design was applied as an experimental matrix to investigate the flow ratios of argon (sheat and plasma gas) and oxygen in relation to the signal-to-background ratio. A comparative study among the slopes of the analytical curves built in aqueous media, surfactant/HNO₃, and by spike addition for several sample emulsions indicates that a unique solution of surfactant in acidic media can be employed to perform the external calibration for analysis of the emulsions. The developed procedure allows for the determination of the total sulfur content in petroleum derivatives with a limit of detection (LOD) and limit of quantification (LOQ) of 0.72 and 2.4 μg g^− 1, respectively. Precision values, expressed as the relative standard deviations (% RSD, n = 10) for 12 and 400 μg g^− 1, were 2.2% and 1.3%, respectively. The proposed procedure was applied toward the determination of total sulfur in samples of gasoline, kerosene, and diesel fuel commercialized in the city of Niterói/RJ, Brazil. The accuracy of the proposed method was evaluated by the determination of the total sulfur in three different standard reference materials (SRM): NIST 2723a (sulfur in diesel fuel oil), NIST 1616b (sulfur in kerosene), and NIST 2298 (sulfur in gasoline). The data indicate that the methodology can be successfully applied to these types of samples. Spiking tests, conducted with the analyzed samples, indicate that recoveries are between 97 and 103%.     

Analysis of metals and phosphorus in biodiesel B100 from different feedstock using a Flow Blurring multinebulizer in inductively coupled plasma-optical emission spectrometry

A simple and fast method for determining the content of Na, K, Ca, Mg, P, and 20 heavy metals in biodiesel samples with inductively coupled plasma optical emission spectrometry (ICP OES) using a two-nozzle Flow Blurring^® multinebulizer prototype and on-line internal standard calibration, are proposed. The biodiesel samples were produced from different feedstock such as sunflower, corn, soybean and grape seed oils, via a base catalyst transesterification. The analysis was carried out without any sample pretreatment. The standards and samples were introduced through one of the multinebulizer nozzles, while the aqueous solution containing yttrium as an internal standard was introduced through the second nozzle. Thus, the spectral interferences were compensated and the formation of carbon deposits on the ICP torch was prevented. The determination coefficients (R²) were greater than 0.99 for the studied analytes, in the range 0.21–14.75 mg kg⁻¹. Short-term and long-term precisions were estimated as relative standard deviation. These were acceptable, their values being lower than 10%. The LOQ for major components such as Ca, K, Mg, Na, and P, were within a range between 4.9 ng g⁻¹ for Mg (279.553 nm) and 531.1 ng g⁻¹ for Na (588.995 nm), and for the other 20 minor components they were within a range between 1.1 ng g⁻¹ for Ba (455.403 nm) and 2913.9 ng g⁻¹ for Pb (220.353 nm). Recovery values ranged between 95% and 106%.     

Application of multivariate techniques in the optimization of a procedure for the determination of bioavailable concentrations of Se and As in estuarine sediments by ICP OES using a concomitant metals analyzer as a hydride generator

A procedure has been developed for the determination of bioavailable concentrations of selenium and arsenic in estuarine sediments employing inductively coupled plasma optical emission spectrometry (ICP OES) using a concomitant metals analyzer device to perform hydride generation. The optimization of hydride generation was done in two steps: using a two-level factorial design for preliminary evaluation of studied factors and a Doehlert design to assess the optimal experimental conditions for analysis. Interferences of transition metallic ions (Cd²⁺, Co²⁺, Cu²⁺, Fe³⁺ and Ni²⁺) to selenium and arsenic signals were minimized by using higher hydrochloric acid concentrations. In this way, the procedure allowed the determination of selenium and arsenic in sediments with a detection limit of 25 and 30 μg kg⁻¹, respectively, assuming a 50-fold sample dilution (0.5 g sample extraction to 25 mL sample final volume). The precision, expressed as a relative standard deviation (% RSD, n = 10), was 0.2% for both selenium and arsenic in 200 μg L⁻¹ solutions, which corresponds to 10 μg g⁻¹ in sediment samples after acid extraction. Applying the proposed procedure, a linear range of 0.08-10 and 0.10-10 μg g⁻¹ was obtained for selenium and arsenic, respectively. The developed procedure was validated by the analysis of two certified reference materials: industrial sludge (NIST 2782) and river sediment (NIST 8704). The results were in agreement with the certified values. The developed procedure was applied to evaluate the bioavailability of both elements in four sediment certified reference materials, in which there are not certified values for bioavailable fractions, and also in estuarine sediment samples collected in several sites of Guanabara Bay, an impacted environment in Rio de Janeiro, Brazil.     

Determination of water-soluble and insoluble compounds in size classified airborne particulate matter

The elemental composition of water soluble and acid soluble size-fractionated airborne particulate matter (APM) was investigated. PM2.5 and PM2.5-10 samples were collected every three days from October 2006 to October 2007 in Buenos Aires, Argentina. The collection was performed on Nucleopore® filters using a GENT sampler. Samples containing fine and coarse particles were subjected to an aqueous leaching to obtain information on the dissolution behaviors of ions, metal and metalloids. Key elements namely, Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Pb, Se, Ti and Zn were determined in each fraction by inductively coupled plasma optical emission spectrometry (ICP OES). In the aqueous fractions, Cl⁻, SO₄²⁻, Na⁺ and NH₄⁺ were determined by high performance liquid chromatography (HPLC). A (6:2:5) mixture of nitric, hydrochloric and perchloric acids was used for leaching metals from the residual filters. For validation of the extraction procedure, the ICP OES measurements the Standard Reference Material NIST 1648 (Urban particulate matter) was subjected to the same analytical procedure that the samples loaded with APM. Total analyte concentration varied from 333.2 μg g^− 1 (equivalent to 3.7 ng m^− 3) for Ti to 692 mg g^− 1 (equivalent to 2.47 μg m^− 3) for Ca.     

Automatic flow procedure based on multicommutation exploiting liquid-liquid extraction for spectrophotometric lead determination in plant material

A not expensive automatic flow system based on multicommutation and exploiting the liquid-liquid extraction methodology for the determination of lead in plant material is described. The spectrophotometric procedure for lead determination was based on the reaction with dithizone followed by extraction using an organic solvent. The facilities afforded by the multicommutation approach allowed the use of an air stream as carrier, thus contributing to reduce the overall waste generation. The results obtained analysing plant materials compare very well with those obtained employing inductive coupled plasma optical emission spectrometry (ICP OES) at 90% confidence level. Others profitable features such as a linear response range between 50 and 200 μg l⁻¹ Pb (r = 0.999); a sampling rate of 15 determination per hour; a relative standard deviation of 1.8% (n = 12) for a typical sample containing 163 μg l⁻¹ Pb; a detection limit of 12 μg l⁻¹; a reagent consumption of 4.5 mg dithizone; and a waste generation of 225 μl organic solvent per determination were also achieved.     

Determination of trace sulfur in biodiesel and diesel standard reference materials by isotope dilution sector field inductively coupled plasma mass spectrometry

A method is described for quantification of sulfur at low concentrations on the order of mg kg⁻¹ in biodiesel and diesel fuels using isotope dilution and sector field inductively coupled plasma mass spectrometry (ID-SF-ICP-MS). Closed vessel microwave-assisted digestion was employed using a diluted nitric acid and hydrogen peroxide decomposition medium to reduce sample dilution volumes. Medium resolution mode was employed to eliminate isobaric interferences at ³²S and ³⁴S related to polyatomic phosphorus and oxygen species, and sulfur hydride species. The method outlined yielded respective limits of detection (LOD) and limits of quantification (LOQ) of 0.7 mg kg⁻¹ S and 2.5 mg kg⁻¹ S (in the sample). The LOD was constrained by instrument background counts at ³²S but was sufficient to facilitate value assignment of total S mass fraction in NIST SRM 2723b Sulfur in Diesel Fuel Oil at 9.06 ± 0.13 mg kg⁻¹. No statistically significant difference at a 95% confidence level was observed between the measured and certified values for certified reference materials NIST SRM 2773 B100 Biodiesel (Animal-Based), CENAM DRM 272b and NIST SRM 2723a Sulfur in Diesel Fuel Oil, validating method accuracy.     

Determination of metals and metalloids in light and heavy crude oil by ICP-MS after digestion by microwave-induced combustion

A method for light and heavy crude oil digestion using microwave-induced combustion (MIC) in closed vessels is described for further determination of Ag, As, Ba, Bi, Ca, Cd, Cr, Fe, K, Mg, Li, Mn, Mo, Ni, Pb, Rb, Se, Sr, Tl, V, and Zn by inductively coupled plasma mass spectrometry (ICP-MS). Conventional microwave-assisted acid digestion (MW-AD) in pressurized vessels and analyte determination by inductively coupled plasma optical emission spectrometry (ICP OES) were also used for results comparison. For MIC procedure, samples were wrapped in polyethylene films and combusted using 20 bar of oxygen and 50 µl of 6 mol l^− 1 ammonium nitrate as aid for ignition. The concentration of nitric acid used as absorbing solution was evaluated (1, 2, 4, 7, 10 and 14 mol l^− 1) using an additional reflux step after combustion. Accuracy was evaluated for As, Ba, Ni, Se V, and Zn using certified reference material (CRM) with similar matrix composition and for Cr, Fe, K, Mg, Mn, and Mo by neutron activation analysis (NAA). Recovery tests were also performed for all the analytes by MIC and they were better than 97% using 2 mol l^− 1 nitric acid as absorbing solution (with reflux step). Agreement with certified values and NAA results was better than 95%. Using MIC it was possible to obtain lower limits of detection (LODs) by ICP-MS and also by ICP OES in comparison with those obtained by MW-AD. In spite of both sample preparation techniques were apparently suitable for crude oil digestion, MIC was preferable in view of the possibility of using diluted nitric acid as absorbing solution that is an important aspect to minimize interferences by ICP-MS and ICP OES. In order to avoid polyatomic interferences on ⁵²Cr and ⁵⁶Fe determinations by ICP-MS, a dynamic reaction cell with ammonia gas was used. Residual carbon content in digests obtained by MW-AD and MIC was 15% and < 1%, respectively. Using MIC the simultaneous digestion of 8 samples was possible in less than 30 min.     

Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm^− 2. An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg^− 1 B, 3.0 mg kg^− 1 Cu, 3.6 mg kg^− 1 Fe, 1.8 mg kg^− 1 Mn and 1.2 mg kg^− 1 Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition.     

Exploratory analysis and inductively coupled plasma optical emission spectrometry (ICP OES) applied in the determination of metals in soft drinks

A 2³ factorial design and a CCD (Central Composite Design) were employed to optimize the operational conditions for determining Al, Ba, Ca, Cd, Cr, Cu, K, Mg, Na, Ni, Pb, Sn and Zn in soft drink samples by inductively coupled plasma optical emission spectrometry (ICP OES). Satisfactory parameters of merit were obtained (Plasma stability, linearity, SBR, BEC, LOD and LOQ). The accuracy was evaluated by means of a recovery study. Thirty five soft drink samples were analyzed. The results obtained were used in an exploratory analysis, in which principal component analysis and cluster analysis were applied in order to differentiate the several soft drink classes. Adequate LOQ values were obtained for all elements (0.34 μg L^− 1 for Ca to 88.7 μg L^− 1 for Mg) and the recovery study results ranged between 80 and 100%. Cluster analysis revealed four sample classes characterized by flavor and other characteristics, such as being light, diet, low calorie or regular beverages. A model with 4 PCs was obtained by means of a principal component analysis, which explained 99.8% of the total variance.     

Hydrophilic interaction vs ion pair liquid chromatography for the determination of streptomycin and dihydrostreptomycin residues in milk based on mass spectrometric detection

Streptomycin (STR) and dihydrostreptomycin (DHSTR) are two of the most common aminoglycoside antibiotics used in veterinary medicine. The physicochemical properties of both substances, make their determination challenging. In the present study the development of methods based on ion-pair chromatography (IPC) and on hydrophilic interaction chromatography (HILIC), for the determination of the above mentioned aminoglycosides in the range of 100–1000 μg L⁻¹ is described. The two methods were validated according to EU requirements for residues in food. The recoveries for the IPC method were 69.3% and 56.5% of STR and DHSTR, respectively, and for HILIC method 85.5% and 72.3%, respectively. The intra- and inter-day precision, studied at 100, 200 and 300 μg kg⁻¹ levels in milk samples, gave %RSD ≤ 13 for both methods. LOQs for the HILIC method were 14 μg kg⁻¹ for both analytes and for the IPC method were 109 and 31 μg kg⁻¹, for STR and DHSTR, respectively. The sensitivity of the HILIC method is 80 and 210 times greater than that of the ICP method, for STR and DHSTR, respectively.     

Flow injection system for the on-line preconcentration of Pb by cloud point extraction coupled to USN–ICP OES

A novel method for the determination of Pb by on-line cloud point extraction coupled to inductively coupled plasma optical emission spectrometry with ultrasonic nebulization (USN–ICP OES) is presented. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono-p-nonylphenylether (PONPE 7.5) and was retained in a minicolumn filled with particles of PTFE. Since the micelles of PONPE were able to extract Pb from the solutions, the use of a complexing reagent was not necessary. Afterwards, the surfactant-rich phase containing the analyte was removed from the minicolumn with nitric acid and introduced into the ultrasonic nebulizer. A total enhancement factor of 150 was obtained for a preconcentration time of 3.3 min, with respect to the direct determination of Pb by conventional ICP OES. The values of the detection (3σ) and quantification (10σ) limits for the preconcentration of 10 mL of sample solution were 0.09 µg L^{− 1} and 0.2 µg L^{− 1} respectively. The precision, expressed as the relative standard deviation (RSD), for 10 replicate determinations at 5.0 µg L^{− 1} Pb level was 6.0%. Verification of the accuracy was carried out by analysis of two certified reference materials (NIST SRM 1640e and VKI QC Metal LL1). The method was successfully applied to the determination of Pb in drinking water samples.     

Determination of cadmium,copper and lead in alumina based catalysts by direct solid sampling graphite furnace atomic absorption spectrometry

Trace impurities of Cd, Cu and Pb were determined in alumina based catalysts using direct solid sampling graphite furnace atomic absorption spectrometry (DSS-GF AAS). The analyzed catalysts are widely used in petrochemical processes. The following analytical parameters were evaluated: pyrolysis and atomization temperatures, feasibility of calibration with aqueous solutions, the necessity for palladium as chemical modifier and the sample mass introduced into the atomizer. Test samples between 0.05 and 8.5 mg were used. Palladium was investigated as chemical modifier but no improvement in analytical performance was obtained and its use was considered unnecessary for all elements. The results obtained by DSS-GF AAS were compared with those of inductively coupled plasma optical emission spectrometry (ICP OES) and also with conventional solution analysis by GF AAS (Sol-GF AAS). Characteristic masses were 1.4, 9 and 20 pg, for Cd, Cu and Pb, respectively. Using DSS-GF AAS the relative standard deviation was always less than 10% and the results agreed with those obtained by Sol-GF AAS and ICP OES. Calibration using aqueous solutions showed good linearity within the working range (R² better than 0.99). Limits of detection (3σ, n = 10) for Cd, Cu and Pb using the proposed procedure were 0.2, 22, and 1.2 ng g^− 1, respectively.     

Characterization and determination of 28 elements in fly ashes collected in a thermal power plant in Argentina using different instrumental techniques

Different techniques were selected for comprehensive characterization of seven samples of fly ashes collected from the electrostatic precipitator of the San Nicolás thermal power plant (Buenos Aires, Argentina). Particle size was measured using laser based particle size analyzer. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the mineral phase present in the matrix consisting basically of aluminosilicates and large amounts of amorphous material. The predominant crystalline phases were mullite and quartz. Major and minors elements (Al, Ca, Cl, Fe, K, Mg, Na, S, Si and Ti) were detected by energy dispersive X-ray analysis (EDAX). Trace elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, V and Zn) content was quantified by inductively coupled plasma optical emission spectrometry (ICP OES). Different acid mixtures and digestion procedures were compared for subsequent ICP OES measurements of the dissolved samples. The digestion procedures used were: i) a mixture of FH + HNO₃ + HClO₄ (open system digestion); ii) a mixture of FH + HNO₃ (MW-assisted digestion); iii) a mixture of HF and aqua regia (MW-assisted digestion). Instrumental neutron activation analysis (INAA) was employed for the determination of As, Ba, Co, Cr, Ce, Cs, Eu, Fe, Gd, Hf, La, Lu, Rb, Sb, Sc, Sm, Ta, Tb, Th, U and Yb. The validation of the procedure was performed by the analysis of two certified materials namely, i) NIST 1633b, coal fly ash and ii) GBW07105, rock. Mean elements content spanned from 41870 μg g^− 1 for Fe to 1.14 μg g^− 1 for Lu. The study showed that Fe (41870 μg g^− 1) ? V (1137 μg g^− 1) > Ni (269 μg g^− 1) > Mn (169 μg g^− 1) are the main components. An enrichment, with respect to crustal average, in many elements was observed especially for As, V and Sb that deserve particular interest from the environmental and human health point of view.     

Characterization and screening of metals,metalloids and biomarkers in crude oil by ICP–MS/OES,and GC–MS techniques after digestion by microwave‐induced combustion

A method for digestion of light and medium Iraqi crude oils (Basrah and Khanaken oils) using microwave‐induced combustion (MIC) in closed vessels is described for the determination of Hg, Au, Cu, Al, Ca, Co, K, Mg, Si and Sr by inductively coupled plasma optical emission spectrometry (ICP–OES) and Mo, Ti, Mn, Li, Se^?1, Rb, Ag, Ba, Pb, As, Cd, Cr, Fe, Ni, V and Zn by inductively coupled plasma mass spectrometry (ICP–MS). Upon using MIC it was possible to obtain lower limits of detection by ICP–MS and also by ICP–OES compared with those obtained by microwave‐assisted digestion. The MIC was the best choice with regard to the possibility of using dilute nitric acid as an absorbing solution, which is important to minimize the interference encountered by ICP–MS and ICP–OES.The physicochemical parameters and some contaminants of crude oil samples were analyzed to classify and assess the quality of the crude oils. This study determines the viability of the use of Fourier transform infrared spectroscopy as an alternativee to traditional petroleum geochemical methods for crude oil characterization. The infrared fingerprints agree with the results obtained from GC–MS analysis.     

Direct determination of sodium,potassium, chromium and vanadium in biodiesel fuel by tungsten coil atomic emission spectrometry

High levels of sodium and potassium can be present in biodiesel fuel and contribute to corrosion, reduced performance and shorter engine lifetime. On the other hand, trace amounts of chromium and vanadium can increase the emission of pollutants during biodiesel combustion. Sample viscosity, immiscibility with aqueous solutions and high carbon content can compromise biodiesel analyzes. In this work, tungsten filaments extracted from microscope light bulbs are used to successively decompose biodiesel's organic matrix, and atomize and excite the analytes to determine sodium, potassium, chromium and vanadium by tungsten coil atomic emission spectrometry (WCAES). No sample preparation other than simple dilution in methanol or ethanol is required. Direct analysis of 10-μL sample aliquots using heating cycles with less than 150 s results in limits of detection (LOD) as low as 20, 70, 70 and 90 μg kg⁻¹ for Na, K, Cr and V, respectively. The procedure's accuracy is checked by determining Na and K in a biodiesel reference sample and carrying out spike experiments for Cr and V. No statistically significant differences were observed between reference and determined values for all analytes at a 95% confidence level. The procedure was applied to three different biodiesel samples and concentrations between 6.08 and 95.6 mg kg⁻¹ for Na and K, and between 0.22 and 0.43 mg kg⁻¹ for V were obtained. The procedure is simple, fast and environmentally friendly. Small volumes of reagents, samples and gases are used and no residues are generated. Powers of detection are comparable to other traditional methods.     

Ionic liquids extraction of Para Red and Sudan dyes from chilli powder, chilli oil and food additive combined with high performance liquid chromatography

A simple analytical method, based on the coupling of ionic liquid-based extraction with high performance liquid chromatography (HPLC), is developed for the determination of Sudan dyes (I, II, III and IV) and Para Red in chilli powder, chilli oil and food additive samples. Two ionic liquids (ILs), 1-butyl-3-methylimidazolium hexafluorophosphate ([C₄mim][PF₆]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([C₈mim][PF₆]), were compared as extraction solvents; experiments indicated that the latter possesses higher recoveries for each analyte. Parameters related to extraction of Sudan dyes and Para Red were also optimized. Under the optimal conditions, good reproducibility of extraction performance was obtained, with the relative standard deviation (RSD) values ranging from 2.0% to 3.5%. The detection limits of Sudan dyes and Para Red (LOD, S/N = 3) were in the range of 7.0-8.2 μg kg⁻¹ for chilli powder and 11.2-13.2 μg L⁻¹ for chilli oil and food additive. The recoveries were in the range of 76.8-109.5% for chilli powder samples and 70.7-107.8% for chilli oil and food additive samples.     

Application of a quick,easy, cheap,effective, rugged and safe-based method for the simultaneous extraction of chlorophenols,alkylphenols, nitrophenols and cresols in agricultural soils,analyzed by using gas chromatography–triple quadrupole-mass spectrometry/mass spectrometry

Due to the different physico-chemical properties of phenols, the development of a methodology for the simultaneous extraction and determination of phenolic compounds belonging to several families, such as chlorophenols (CPs), alkylphenols (APs), nitrophenols (NTPs) and cresols is difficult. This study shows the development and validation of a method for the analysis of 13 phenolic compounds (including CPs, APs, NTPs and cresols) in agricultural soils. For this purpose, a quick, easy, cheap, effective, rugged and safe (QuEChERS)-based procedure was developed, validated and applied to the analysis of real samples. A derivatization step prior to the final determination by gas chromatography (GC) coupled to a triple quadrupole analyzer operating in tandem mass spectrometry (QqQ-MS/MS) was performed by using acetic acid anhydride (AAA) and pyridine (Py). The optimized procedure was validated, obtaining average extraction recoveries in the range 69–103% (10 μg kg⁻¹), 65–98% (50 μg kg⁻¹), 76–112% (100 μg kg⁻¹) and 76–112% (300 μg kg⁻¹), with precision values (expressed as relative standard deviation, RSD) ≤ 22% (except for 4-chlorophenol) involving intra-day and inter-day studies. Furthermore, 15 real soil samples were analyzed by the proposed method in order to assess its applicability. Some phenolic compounds (e.g. 2,4,6-trichlorophenol or 4-tert-octylphenol) were found in the samples at trace levels (<10 μg kg⁻¹).     

Simultaneous extraction and preconcentration of uranium and thorium in aqueous samples by new modified mesoporous silica prior to inductively coupled plasma optical emission spectrometry determination

A new synthesized modified mesoporous silica (MCM-41) using 5-nitro-2-furaldehyde (fural) was applied as an effective sorbent for the solid phase extraction of uranium(VI) and thorium(IV) ions from aqueous solution for the measurement by inductively coupled plasma optical emission spectrometry (ICP OES). The influences of some analytical parameters on the quantitative recoveries of the analyte ions were investigated in batch method. Under optimal conditions, the analyte ions were sorbed by the sorbent at pH 5.5 and then eluted with 1.0 mL of 1.0 mol L⁻¹ HNO₃. The preconcentration factor was 100 for a 100 mL sample volume. The limits of detection (LOD) obtained for uranium(VI) and thorium(IV) were 0.3 μg L⁻¹. The maximum sorption capacity of the modified MCM-41 was found to be 47 and 49 mg g⁻¹ for uranium(VI) and thorium(IV), respectively. The sorbent exhibited good stability, reusability, high adsorption capacity and fast rate of equilibrium for sorption/desorption of uranium and thorium ions. The applicability of the synthesized sorbent was examined using CRM and real water samples.     

A new electrolytic dissolution of aluminum alloys and determination of some constituents by inductively coupled plasma optical emission spectrometry

The new electrolytic dissolution in batch of aluminum alloys samples as grains or turns and the determination of Fe, Cu, Mn, Mg, Cr, Ni, Zn, Pb and Ti by ICP OES was investigated. In on-line electrodissolution procedures described in the literature, samples were restricted to be in the form of solid blocks or plates with one polished flat face. Here, the sample was loaded in the barrel of a modified disposable syringe (the anodic semi-cell) and pressed with a modified plunger fitted with a platinum disk to establish electrical contact with the analyte. This arrangement was introduced in a beaker containing the electrolyte (1 mol L⁻¹ HNO₃) and a platinum wire as the cathode. The resulting solution from electrodissolution (0.6 A) was used for the ICP OES determinations. The influence of the aluminum concentration increase on the determination of the elements was evaluated. Electrodissolution of certified reference materials and commercial samples revealed relative errors lower than 10% for the elements Fe, Cu, Mg, Ni, Cr, Zn and Ti (when their content is above 0.1%). Higher inaccuracies (>10%) were observed for Mn and for Fe in B.C.S. 268/1 reference material certified. The proposed method presented a relative standard deviations (R.S.D.) lower or circa 10% to all of the elements (except Pb). In comparison with traditional acid dissolution, the proposed electrodissolution method is relatively fast (about 30 min), it is clean (there is no projection of solution) and simple (heating and fumes exhaust system were not necessaries).     

Multivariate optimization of a spectrophotometric method for copper determination in Brazilian sugar-cane spirits using the Doehlert design

This present work reports a multivariate optimization of a spectrophotometric method for copper determination in sugar-cane spirits, exploring the reaction of Cu(II) with phenylfluorone (PF) in the presence of cetylpyridinium chloride (CPC) and Triton X-100. The optimization strategy was based on the application of a two-level full factorial design for the screening of significant variables followed by a Doehlert design to determine the optimum conditions. The highest sensitivity was achieved when the pH was 8.0 and the PF and TX-100 concentrations were 6.2 × 10^− 5 and 1.0 × 10^− 2 mol L^− 1, respectively. The optimized method presented a limit of detection of 3.4 μg L^− 1 and a limit of quantification of 11 μg L^− 1 and was applied in the determination of Cu in 17 samples. The obtained results were compared with those obtained by ICP OES and no statistical difference between the methods was observed.