Determination of trace elements in liquid aspartame sweeteners by ICP OES and ICP-MS following acid digestion

In order to determine inorganic constituents and contaminants in liquid aspartame sweeteners, different brands of this product were analyzed by ICP OES and ICP-MS. The samples were submitted to acid digestion and parameters such as internal standardization and wavelengths, in the case of ICP OES, and a recovery test were evaluated. The analytes studied were As, Ca, Cd, Co, Cu, K, Fe, Mg, Mn, Na, Ni, Pb, Se and Zn. Since there is not a certified reference material for sweeteners, the accuracy of the proposed method was evaluated by recovery tests and the values were in the range of 90–110% for the majority of the analytes. The detection limits for the elements determined by ICP OES were in the range 0.01 (Mn)– 2.0 (K) μg g⁻¹ while those determined by ICP-MS were 0.001 μg g⁻¹ for all the elements except Mn and As (0.002 μg g⁻¹). The relative standard deviations were below 12% for ICP OES and below 14% for ICP-MS determinations. The mean concentration of the elements detected by ICP OES (Ca, Fe, K, Mg, Na, and Zn) varied according to the brand. The other analytes, were determined by ICP-MS. For these elements, a significant variation in their concentrations was also found for different samples, except for Co and Ni. The use of both multielemental techniques allowed the evaluation of the inorganic composition and the rapid determination of several elements in aspartame sweeteners, with adequate accuracy.     

Evaluation of closed-vessel microwave digestion method for the determination of trace impurities in polymer-based photoresist by inductively coupled plasma mass spectrometry

A closed microwave digestion method followed by inductively coupled plasma spectrometric (ICP-MS) analysis was evaluated for the determination of trace impurities in photoresist. To optimize the digestion procedure, several digestion parameters such as acid, heating temperature and heating time were evaluated. Besides, the digestion efficiency of used photoresist material and the recovery of analyte elements obtained by the use of gravimetric method and ICP-MS measurement, individually, were also compared to clarify the completeness of digestion. According to our experiments, the gravimetric method was found to be not so relevant to the completeness of digestion, because the remaining sample matrix could cause suppression effect in the subsequent ICP-MS measurement. In view of minimizing blank value and working time, a simple single-step heating program was proposed to mineralize 0.25 ml of photoresist material with 5 ml of nitric acid at 180 °C for 10 min. Based on the comparative study of the analytical results obtained by instrumental neutron activation analysis (INAA) and proposed method, the reliability of proposed method for the determination of trace metallic impurities in photoresist material has been confirmed.     

Determination of metals in marine species by microwave digestion and inductively coupled plasma mass spectrometry analysis

A microwave digestion method suitable for determination of multiple elements in marine species was developed, with the use of cold vapor atomic spectrometry for the detection of Hg, and inductively coupled plasma mass spectrometry for all of the other elements. An optimized reagent mixture composed of 2 ml of HNO₃, 2 ml of H₂O₂ and 0.3 ml of HF used in microwave digestion of about 0.15 g (dry weight) of sample was found to give the best overall recoveries of metals in two standard reference materials. In the oyster tissue standard reference material (SRM 1566b), recoveries of Na, Al, K, V, Co, Zn, Se, Sr, Ag, Cd, Ni, and Pb were between 90% and 110%; Mg, Mn, Fe, Cu, As, and Ba recoveries were between 85% and 90%; Hg recovery was 81%; and Ca recovery was 64%. In a dogfish certified reference material (DORM-2), the recoveries of Al, Cr, Mn, Se, and Hg were between 90% and 110%; Ni, Cu, Zn, and As recoveries were about 85%; and Fe recovery was 112%. Method detection limits of the elements were established. Metal concentrations in flounder, scup, and blue crab samples collected from coastal locations around Long Island and in the Hudson River estuary were determined.     

Simple,fast, and low-contamination microwave-assisted digestion procedures for the determination of chemical elements in biological and environmental matrices by sector field ICP-MS

A simple and convenient method for the digestion of animal tissues, lichens, and plants for 33 metals measured by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS) was described. Microwave-assisted acid digestions were performed at atmospheric pressure by means of a multi-samples rotor designed for processing a large number of samples at once in screw-capped disposable polystyrene liners. The digested samples were filled up to final volume directly in the polystyrene liners ready for elemental quantification. Seven certified reference materials, namely BCR 184 (bovine muscle), BCR 186 (pig kidney), DORM-2 (dogfish muscle), BCR 422 (cod muscle), BCR 62 (olive leaves), BCR 100 (beech leaves), and BCR 482 (lichen) were analysed to verify the accuracy of the method. The linearity range, limit of quantification, precision, and recovery by addition of non-certified elements were also assessed. All elements, with the exception of Hg in BCR 184 and As in BCR 186, were above the quantification limit and blank concentrations, and good agreement existed between found and target values in bovine muscle, pig kidney, and cod muscle. Significant deviations were observed for Al, Co, Cr, Mn, and Ni in dogfish muscle and for Ca, Cr, Fe, and Hg in lichens and plants. The proposed digestion procedure offers a low contamination risk, simplicity, speed, low cost, and applicability in routine analysis, and the SF-ICP-MS method allowed metals from a fraction of ng?g^?1 to hundreds of µg?g^?1 to be quantified in one analytical run.     

Evaluation of microwave-assisted digestion condition for the determination of metals in fish samples by inductively coupled plasma mass spectrometry using experimental designs

This paper describes the development of a compromised single-stage microwave-assisted digestion condition for multi-element determination in fish samples by inductively coupled plasm: mass spectrometry using experimental designs. A Plackett–Burman design was carried out as a multivariate strategy to investigate the main effects of the following parameter on microwave-assisted nitric acid digestion: microwave irradiation time, ramp time, digestion temperature, microwave power limit and the addition of hydrogen peroxide or hydrochloric acid. The most significant microwave setting parameters (radiation time, ramp and temperature) were further evaluated by response surface methodology under Box–Behnken design, while others were kept constant. The influences of different parameters vary according to metal element, thus the working conditions were established as a compromise within optimum region found for each targeted element which ensures quantitative recoveries and time efficiency. The compromised conditions are: ramp to 185°C in 10.5?min then hold for 14.5?min with 1600W (50%) of microwave power, using reagent mixture composed of 2.5?mL nitric acid, 0.5?mL hydrochloric acid and 7.0?mL water. Good agreements were demonstrated between measured and certified values with respect to DORM-3, DOLT-4 and ECM-CE278 and this method was successfully applied for metals determination in tilapia tissues.     

A rapid microwave-assisted acid extraction method based on the use of diluted HNO3-H2O2 followed by ICP-MS analysis for simultaneous determination of trace elements in coal samples

Before coal processing such as pyrolysis, liquefaction, gasification and combustion, it is very crucial to monitor the trace element concentration levels as that determines the coal quality. Therefore, the current study describes the development of microwave-assisted acid extraction (MW-AAE) method for extraction of 15 trace elements in coal samples prior to their determination using inductively coupled plasma-mass spectrometry. Diluted HNO₃-H₂O₂ was used in order to reduce reagents amount used, eliminate matrix interferences caused by concentrated acids and to decrease waste produced in analytical laboratories. The optimisation of the proposed extraction method was carried out by using a full factorial design (2⁴) involving four factors; that is, temperature, extraction time, HNO₃ and H₂O₂ concentrations. The optimum conditions for the MW-AAE procedure were found to be 200°C, 5 min, 5 mol L^?1 and 2 mol L^?1 for temperature, extraction time, HNO₃ and H₂O₂ concentrations, respectively. Under optimum conditions, the accuracy of the MW-AAE method was examined by analysing three coal certified reference materials (SARM 18, 19 and 20) and recoveries of 80–115% were achieved for V, Mn, Co, Ni, Cu, Zn, Ga, Ge, As, Sr, Zr, Cs, Ba, Pb and U, except for Ti (10–25%) and Hf (27–70%). In addition, the precision of the proposed method, expressed in terms of relative standard deviation (SD) (n = 15), was within the accepted range (≤3.5%). The method detection limits of 0.001–0.57 µg g^?1 for all trace elements under the investigation were similar to the literature reported work, except for Ti (4.00 µg g^?1).     

Determination of trace impurities in high-purity zirconium dioxide by inductively coupled plasma atomic emission spectrometry using microwave-assisted digestion and wavelet transform-based correction procedure

This paper describes a rapid, accurate and precise method for the determination of trace Fe, Hf, Mn, Na, Si and Ti in high-purity zirconium dioxide (ZrO₂) powders by inductively coupled plasma atomic emission spectrometry (ICP-AES). The samples were dissolved by a microwave-assisted digestion system. Four different digestion programs with various reagents were tested. It was found that using a mixture of sulfuric acid (H₂SO₄) and ammonium sulfate ((NH₄)₂SO₄), the total sample dissolution time was 30 min, much shorter than that required for conventional digestion in an opening system. The determination of almost all of the target analytes suffered from spectral interferences, since Zr shows a line-rich atomic emission spectrometry. The wavelet transform (WT), a recently developed mathematical technique was applied to the correction of spectral interference, and more accurate and precise results were obtained, compared with traditional off-peak background correction procedure. Experimental work revealed that a high Zr concentration would result in a significant decrease in peak height of the analyte lines, which was corrected by standard addition method. The performance of the developed method was evaluated by using synthetic samples. The recoveries were in the range of 87-112% and relative standard deviation was within 1.1-3.4%. The detection limits (3σ) for Fe, Hf, Mn, Na, Si and Ti were found to be 1.2, 13.3, 1.0, 4.5, 5.8 and 2.0 μg g⁻¹, respectively. The results showed that with the microwave-assisted digestion and the WT correction, the detection limits have improved by a factor of about 5 for Fe, 4 for Mn and Ti, 3 for Si, and 2 for Hf and Na, respectively, in comparison with conventional open-system digestion and off-peak correction. The proposed technique was applied to the analysis of trace elements above-mentioned in three types of ZrO₂ powders.     

Investigation of ICP-MS spectral interferences in the determination of Rh, Pd and Pt in road dust: Assessment of correction algorithms via uncertainty budget analysis and interference alleviation by preliminary acid leaching

A method for classification of the potential spectral interferences in inductively coupled plasma mass spectrometry (ICP-MS) was proposed based on statistical assessment of the interfering signals. The concept was applied to investigate the variety of spectral interferences over the isotopes of Rh, Pd and Pt concerning their analysis in road dust samples. For the significant interferences the applicability of mathematical corrections using two alternative algorithms were studied by uncertainty budget analysis and the approach resulting in lower combined uncertainty of the corrected signals was selected. Further the uncertainty evaluation was used for assessment of the most appropriate Pd isotope to be measured. The adequateness of the mathematical corrections for Rh and Pd was highly relevant to the number of elements causing spectral interferences and the relative analyte/interferent concentrations. This was overcome by preliminary road dust leaching with 0.35 mol l⁻¹ hydrochloric acid. Interferents present as easily soluble salts were substantially removed form the samples while the platinum group metals were not leached which allowed a relative analyte preconcentration to be obtained. For the leached samples the isotopes of Rh and Pd were still spectrally interfered from Sr, Y and Pb but at considerably lesser degree thus after mathematical correction the ICP-MS analysis of Rh, Pd and Pt was reliable and robust using the isotopes 103, 105 and 195, respectively. The method was validated via an alternative analysis based on selective separation of the platinum group metals by microwave-assisted cloud point extraction.