Lenka Husáková

Analytical capabilities of inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (ICP-oa-TOF-MS) for multi-element analysis of food and beverages

Analytical capabilities of ICP-oa-TOF-MS for rapid, simultaneous and reliable determination of more than 50 major, trace and ultra-trace elements in different food and beverages samples (milk and dairy based products, cereals, meat, offal, sugar and sugar products, potatoes, fats, baby food samples, fruit juices, alcoholic beverages), following microwave closed vessel digestion of samples, were described. Under optimum instrumental conditions, and by using Rh as an internal standard and an external calibration method, ICP-oa-TOF-MS enables an accurate analysis, taking about one minute per a sample for all elements and isotopes of interest even for some elements such Zn, Ni, Cu, As or Co whose assay is more difficult when using conventional quadrupole instruments. In order to verify the accuracy and precision of the proposed method, 8 commercially available reference materials representing 3 major groups of food (milk and dairy based products, meat, cereals) were analysed, yielding results in agreement with certified values and the precision bellow 15%. In addition, accuracy was confirmed by spiked analytical recoveries study and accurate isotopic ratio determinations with the precision typically better than 5% with 5s data acquisition period, also for other elements of interest whose content was not certified and different sample matrices. Limits of detection (3σ) have varied from 0.04ngg(-1) for Th to 1630ngg(-1) for Ca.

Multi-element analysis of milk by ICP-oa-TOF-MS after precipitation of calcium and proteins by oxalic and nitric acid.

In this work a simple technique employing oxalic and nitric acid to cows milk samples prior to analysis by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (ICP-oa-TOF-MS) was introduced. After the precipitation of calcium and proteins via oxalic and nitric acid, respectively, the resulting liquid phase was aspirated with a concentric glass nebulizer for ICP-TOF-MS determination of trace elements. Precipitation of proteins is essential for better separation of solid and liquid phase of modified samples. Separation of calcium as a precipitated non-soluble oxalate enables the elimination of spectral interferences originating from different calcium containing species like (40)Ca(35)Cl(+), (40)Ca(37)Cl(+), (43)Ca(16)O(+), (40)Ca(18)O(+), (44)Ca(16)O(+), (43)Ca(16)O(1)H(+) onto the determination of As, Se, Co and Ni whose assay is more difficult when using conventional quadrupole instruments. High detection capability is further an advantage as the approach enables the analysis without dilution. The methodology may serve, in addition, for a fast and sensitive determination of some other elements. After that, direct, reliable and simultaneous determination of 16 elements (Li, Be, B, V, Cr, Mn, Ni, Co, Ga, As, Se, Mo, Sn, Sb, Cs, Tl) at trace and ultra-trace levels in milk can be performed under optimum instrumental conditions and by using Rh as an internal standard. Accuracy and precision was assessed by measuring NCS ZC73015 milk powder control standard, yielding results in agreement with certified values and RSD <10%. The accuracy was also checked by comparison of the results of the proposed method with those found by a method based on a microwave-assisted digestion of real samples.

Characterization of industrial explosives based on the determination of metal oxides in the identification particles by microwave digestion and atomic absorption spectrometry method

Identification particles used for the purpose of the post-blast identification of explosives have a coding system based on the combination of metal oxides and their various concentrations. These materials are composed of the polymeric matrix, iron powder (ferromagnetic properties), UV light active dyestuff and various metal oxides in a various ratios. A suitable analytical method has to be used for an accurate characterization of these metal components in the particles in order to find the required information, i.e. to determine the place and the year of production and as the case may be, also the production batch of misused explosives. In this work, the method of microwave digestion and flame atomic absorption spectrometry (F-AAS) was developed for an accurate determination of Zn, Mg, Cu and Pb in a few novel types of identification particles and applied to their characterization. When using specific sample treatment (digestion with a mixture of nitric acid with hydrochloric or hydrofluoric acid), the 3 sigma limits of detection (LODs) for the determination of Zn, Mg, Cu and Pb in 5mg original samples were 1.9, 0.2, 1.3 and 2.4 mg g(-1), respectively. The signal suppression due to the presence of HNO3+HCl or HNO3+HF was observed for Zn; therefore, the calibration solutions had to be prepared exactly with the same acids as those used for the sample mineralization. The determination of Mg, Cu and Pb was free of interferences; hence a simple calibration curve method could be adopted for attaining accurate results. The accuracy was checked by comparison of the results with those obtained by means of independent inductively coupled plasma optical emission spectrometry (ICP-OES). Good precision values, as relative standard deviation, in the range of 1-5% were obtained. A total number of 71 samples was analysed and classified by multivariate methods to prove the suitability of the procedure proposed for the purpose of the identification of explosives.

Ammonium fluoride as a novel chemical modifier for the elimination of magnesium chloride interference on the determination of lead by graphite furnace atomic absorption spectrometry

Ammonium fluoride was found to be very efficient modifier for the elimination of MgCl(2) interference on Pb determination. Ammonium fluoride probably converts strongly interfering volatile MgCl(2) to less volatile MgF(2) matrix that makes possible the release of Pb analyte at lower temperature, before the matrix starts to vaporize. It was observed likewise that NH(4)F removes the interferences mentioned, i.e. caused by MgCl(2) presence, much more effectively as compared with some modifiers, before now recommended for this purpose. The application of this modifier to the determination of Pb in 2% (m/v) MgCl(2) has ensured the characteristic mass and LOD value in the original sample of 12pg and 60ngg(-1), respectively (10mul aliquots of sample). Applying the modifier to standards and samples enables the use of matrix-free standard solutions for attaining accurate analysis as verified by recovery studies.

Evaluation of ammonium fluoride for quantitative microwave-assisted extraction of silicon and boron from different solid samples

A novel, simple, efficient and environmentally friendly closed-microwave-assisted extraction (MAE) method of silicon and boron from a variety of industrial and environmental samples using ammonium fluoride as an extractant was developed. This method avoids handling the corrosive and toxic HF and prevents the potential risk of analyte loss due to the creation of volatile SiF4 and BF3 in the presence of HF. Atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry were employed for the subsequent analysis of the resulting supernatant for determination of Si and B, respectively. Certified reference material BCR®-032 Natural Moroccan Phosphate Rock (phosphate fertiliser) was taken to optimise the extraction parameters such as the sample amount, extraction temperature and time and the volume of the extractant. The optimum extraction parameters evaluated using a fractional factorial design were as follows: 50 mg of the sample extracted with 5 mL of 100 g L−1 NH4 F for 15 min at 180°C. The optimised MAE procedure was successfully applied to nine different matrix reference materials intended primarily for validation of methods for determination of components in fertilisers, sludge, plants and fly ash. The obtained results were in a good agreement with the certified or comparative values with an overall precision better than 10% in all cases. The proposed method is recommended for fast and reliable preparation of samples with silicon content <8.2% (w/w). However, further decreasing the sample mass to 10 mg enabled the quantitative extraction of silicon from fly ashes at levels of 23% (w/w).

Multi-elemental analysis of sulfuric acid by oaTOF-ICP-MS after matrix modification with barium bromide

In this work a novel method for the simultaneous multi-elemental analysis of sulfuric acid by inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometry (oaTOF-ICP-MS) after matrix modification with barium bromide was introduced. For this purpose sample aliquots consisting of 10% (w/w) sulfuric acid were mixed with barium bromide and after the precipitation of sulfates, the resulting liquid phase was aspirated with a concentric glass nebulizer for TOF-ICP-MS determination. The separation of sulfur as a precipitated non-soluble barium sulfate enables the elimination of spectral interferences originating from different sulfur containing species like SN+, SNH+, SO+, SOH+, SOH2+, SCO+, SNOH+, SO2+, S2+, SO2H+, or S2H+ on the determination of e.g. Ti, Zn, Ge, and Cu. After that, direct, reliable, and simultaneous determination of 15 elements (Be, Ti, V, Cr, Mn, Ni, Co, Cu, Zn, Ga, Ge, As, Sn, Sb, and Te) at trace and ultra-trace levels in sulfuric acid were performed under optimum instrumental conditions and by using Rh as an internal standard. Accuracy and precision were assessed by analysing sulfuric acid and by comparison of the results of the proposed method with those obtained by the high resolution ICP-MS method. The results of both methods were in good agreement for Ti, V, Cr, Mn, Ni, Co, Cu, Zn, Ga, Ge, and As. The accuracy for all of the 15 elements was also checked by an analytical recovery study. The reported method has a precision greater than 12.5%.

Interference-free determination of thallium in aqua regia leaches from rocks, soils and sediments by D2-ETAAS method using mixed palladium-citric acid-lithium chemical modifier

The mixture of palladium (chloride) with citric acid and lithium is proposed as a new chemical modifier for the elimination of interference occurred during the determination of Tl in aqua regia extracts from rocks, soils and sediments by electrothermal atomic absorption spectrometry using instrumentation with deuterium-lamp background correction (D2-ETAAS). Palladium was preferred to rhodium and platinum as to analyte stabilization, citric acid served as an effective reducing agent facilitating formation of Pd–Tl stable covalent bonds playing an important role in the analyte stabilization. Citric acid in addition helps to remove most of interfering chloride at low temperature. The further addition of Li increased significantly the robustness of chemical modifier against strongly interfering ZnCl2 matrix by binding free chlorine into a more stable LiCl molecule. In the presence of the proposed chemical modifier the temperature for the final step of pyrolysis was adjustable up to 1000 ◦ C, without any noticeable loss of volatile Tl species and the interference of the rest chloride matrix was significantly reduced. The application of the modifier to direct determination of Tl in aqua regia extracts from rocks, soils and sediments has ensured the characteristic mass and LOD value for the original sample 13 pg and 0.043 gg −1 , respectively (10-L aliquots of sample) and has enabled the use of matrix-free standard solutions for attaining accurate analysis. The accuracy was verified by the analysis of certified reference samples and by the comparison of results with those found by an inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometer (ICP-oa-TOFMS) method.The mixture of palladium (chloride) with citric acid and lithium is proposed as a new chemical modifier for the elimination of interference occurred during the determination of Tl in aqua regia extracts from rocks, soils and sediments by electrothermal atomic absorption spectrometry using instrumentation with deuterium-lamp background correction (D(2)-ETAAS). Palladium was preferred to rhodium and platinum as to analyte stabilization, citric acid served as an effective reducing agent facilitating formation of Pd-Tl stable covalent bonds playing an important role in the analyte stabilization. Citric acid in addition helps to remove most of interfering chloride at low temperature. The further addition of Li increased significantly the robustness of chemical modifier against strongly interfering ZnCl2 matrix by binding free chlorine into a more stable LiCl molecule. In the presence of the proposed chemical modifier the temperature for the final step of pyrolysis was adjustable up to 1000 degrees C, without any noticeable loss of volatile Tl species and the interference of the rest chloride matrix was significantly reduced. The application of the modifier to direct determination of Tl in aqua regia extracts from rocks, soils and sediments has ensured the characteristic mass and LOD value for the original sample 13 pg and 0.043 microg g(-1), respectively (10-microL aliquots of sample) and has enabled the use of matrix-free standard solutions for attaining accurate analysis. The accuracy was verified by the analysis of certified reference samples and by the comparison of results with those found by an inductively coupled plasma orthogonal acceleration time-of-flight mass spectrometer (ICP-oa-TOFMS) method.

Overcoming interference from the alumina matrix on the determination of arsenic at 189 nanometers using electrothermal atomic absorption spectrometry

A method is described enabling to eliminate the spectral interference from alumina matrix onto As determination at the wavelength 189 nm by electrothermal atomic absorption spectrometry with deuterium background correction. Matrix modification was performed by the addition of ammonium fluoride to protect the formation of aluminium oxide implicated in causing spectral interference and to increase volatility of alumina matrix via the formation of AlF(3). Pre-treating of the pyrolytic graphite platform with a solution of rhodium and citric acid has enabled to stabilize the analyte up to temperature of 1300 degrees C at which most of AlF(3) could be removed from the graphite furnace. The application of 2 microg of Rh+20 microg of citric acid+200 microg of NH(4)F has enabled an accurate and interference-free determination of As up to 40 microg of Al in the form of AlCl(3) as verified by analytical recoveries study and resulted in characteristic mass and LOD value in the original sample 15 pg and 50 ngg(-1), respectively (10-microL aliquots of sample).

Slurry sampling high-resolution continuum source electrothermal atomic absorption spectrometry for direct beryllium determination in soil and sediment samples after elimination of SiO interference by least-squares background correction

In this work a simple, efficient, and environmentally-friendly method is proposed for determination of Be in soil and sediment samples employing slurry sampling and high-resolution continuum source electrothermal atomic absorption spectrometry (HR-CS-ETAAS). The spectral effects originating from SiO species were identified and successfully corrected by means of a mathematical correction algorithm. Fractional factorial design has been employed to assess the parameters affecting the analytical results and especially to help in the development of the slurry preparation and optimization of measuring conditions. The effects of seven analytical variables including particle size, concentration of glycerol and HNO3 for stabilization and analyte extraction, respectively, the effect of ultrasonic agitation for slurry homogenization, concentration of chemical modifier, pyrolysis and atomization temperature were investigated by a 27-3 replicate (n = 3) design. Using the optimized experimental conditions, the proposed method allowed the determination of Be with a detection limit being 0.016mgkg-1 and characteristic mass 1.3pg. Optimum results were obtained after preparing the slurries by weighing 100mg of a sample with particle size < 54µm and adding 25mL of 20% w/w glycerol. The use of 1μg Rh and 50μg citric acid was found satisfactory for the analyte stabilization. Accurate data were obtained with the use of matrix-free calibration. The accuracy of the method was confirmed by analysis of two certified reference materials (NIST SRM 2702 Inorganics in Marine Sediment and IGI BIL-1 Baikal Bottom Silt) and by comparison of the results obtained for ten real samples by slurry sampling with those determined after microwave-assisted extraction by inductively coupled plasma time of flight mass spectrometry (TOF-ICP-MS). The reported method has a precision better than 7%.

Palladium-citric acid-ammonium fluoride as a matrix modifier for overcoming of interferences occurring during the direct determination of Sn in aqua regia extracts from environmental samples by D2-ETAAS.

When tin is to be determined in such a complex matrix like aqua regia extracts of environmental samples by electrothermal atomic absorption spectrometry (ETAAS), spectral interferences occur when deuterium-lamp (D(2)) background correction is used, even using high pyrolysis temperature of 1400 degrees C achieved with palladium with citric acid chemical modifier. We have found that the further addition of NH(4)F to palladium with citric acid chemical modifier is essential for overcoming the above-mentioned problems for which aluminium oxide is most probably responsible. It is supposed, that NH(4)F enables volatilization of the alumina matrix formed by hydrolysis from the chloride salt and interfering in a gas phase via the formation of AlF(3) which could be, in contrast to aluminium oxide, removed from the graphite furnace during the pyrolysis stage. Using the proposed chemical modifier, the direct and accurate determination of Sn in aqua regia extracts from rocks, soils and sediments is possible even when using matrix free standard solutions. This presumption was confirmed by the analysis of certified reference samples and by the comparison with inductively coupled plasma time of flight mass spectrometry (ICP-TOFMS) method. Characteristic mass and LOD value for the original sample (10-microL aliquots of sample) was 17 pg and 0.055 microg g(-1), respectively.