Tomáš Černohorský

Determination of metals in lubricating oils by X-ray fluorescence spectrometry

The determination of common wear metals, namely iron, chromium, copper, zinc and lead, in a wide range of lubricating oil samples was investigated for the use of a low-cost, wavelength-dispersive X-ray fluorescence spectrometer. The procedure provided results in satisfactory agreement with inductively coupled plasma spectrometry used as reference method after microwave digestion of the samples in concentrated nitric acid. Statistical tests following extensive regression analyses of the data indicated that interelement effects were not statistically significant and that a simple linear regression was adequate for the calibration of individual metals.

LIBS analysis of crop plants

A fast and cheap method for the analysis of macronutrients (K, P, Mg and Ca) in leaves of crop plants (wheat, poppy, barley and rape) using double pulse laser induced breakdown spectrometry (LIBS) is suggested. A commercially available LIBS spectrometer was calibrated with the aid of authentic plant samples previously analysed by AAS and ICP-OES after microwave digestion. The concentration ranges of K, P, Mg and Ca in the calibration standards were 30–66; 2.8–6.6; 1.0–5.6 and 6–24 g kg−1, respectively. Cryogenic grinding and powder pressing to pellets were used as sample preparation steps. Obtained LIBS/ICP-OES recovery values for authentic crop plant samples were 93–109% (K); 93–114% (P); 89–109% (Mg) and 94–110% (Ca). Six certified reference materials (CRMs) of plant tissues were used for the LIBS method validation. Recovery values of 96–101% were obtained for K and P, when the certified concentration of the element in the CRM was inside the concentration range of the used calibration standards. Substantial matrix differences of the CRMs and LIBS calibration standards seem to be a probable reason for the worse recovery results (58–99%) obtained for Mg and Ca.

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.

Quantitative LIBS analysis of vanadium in samples of hexagonal mesoporous silica catalysts.

The method for the analysis of vanadium in hexagonal mesoporous silica (V-HMS) catalysts using Laser Induced Breakdown Spectrometry (LIBS) was suggested. Commercially available LIBS spectrometer was calibrated with the aid of authentic V-HMS samples previously analyzed by ICP OES after microwave digestion. Deposition of the sample on the surface of adhesive tape was adopted as a sample preparation method. Strong matrix effect connected with the catalyst preparation technique (1st vanadium added in the process of HMS synthesis, 2nd already synthesised silica matrix was impregnated by vanadium) was observed. The concentration range of V in the set of nine calibration standards was 1.3-4.5% (w/w). Limit of detection was 0.13% (w/w) and it was calculated as a triple standard deviation from five replicated determinations of vanadium in the real sample with a very low vanadium concentration. Comparable results of LIBS and ED XRF were obtained if the same set of standards was used for calibration of both methods and vanadium was measured in the same type of real samples. LIBS calibration constructed using V-HMS-impregnated samples failed for measuring of V-HMS-synthesized samples. LIBS measurements seem to be strongly influenced with different chemical forms of vanadium in impregnated and synthesised samples. The combination of LIBS and ED XRF is able to provide new information about measured samples (in our case for example about procedure of catalyst preparation).

Determination of beryllium in drinking and waste water by tungsten furnace atomic absorption spectrometry

The optimum conditions for the determination of Be with the use of a tungsten furnace were investigated. A high rate of heating, which can be achieved with a tungsten atomizer, and the reductive action of hydrogen in the protective atmosphere both contribute to the higher sensitivity obtained at 234.9 nm in comparison with the use of a graphite furnace. The addition of Al(NO3)3 as a chemical modifier eliminated the interference of Mg and Ca at concentration levels typical for natural waters. For the peak height absorbance, a linear calibration between 0.5 and 30 pg of Be, a 3s detection limit of 0.16 pg and a characteristic mass of 0.2 pg of Be were obtained. The method is suitable for rapid assays in prospecting for water sources and in the control of drinking water but can also be applied successfully to the determination of Be in samples of contaminated water by using the standard additions technique.

An elemental analysis of conventionally, organically and self-grown carrots

Conventionally-, organically- and self-grown carrots available across the Czech market were characterised based on their elemental, nitrate and dry matter content (218 samples, 20 parameters) in order to assess the quality of the carrots and address the question whether organic also means better. The results were compared with information describing the elemental composition of carrots published previously, recommended daily intakes, and legislative limits for contaminants in food. Significant differences in the amounts of Na, K, S, Al, Mn, Ni, As and Cd were observed between conventional and organic carrots. From the perspective of inter-element interactions, and the origin of these, a principal components analysis of the datasets found no significant differences between conventionally- and organically-grown carrots. For the consumer, it is valuable to know there are no differences between conventionally- and organically-grown carrots, and no potential harm arising from heavy metal contamination. Based on our data, carrots are an excellent source of potassium.

LIBS analysis of chromium in samples of dyed wool fabric

A method for the analysis of chromium in wool fabric samples was developed. It is fast and cheap with no sample preparation. This method involved the use of double pulse Laser Induced Breakdown Spectrometry (LIBS) for the wool fabric samples dyed by two types of metal complex dyes (C.I. Acid Orange 173 and C.I. Acid Black 60). A commercially available LIBS spectrometer was calibrated with the aid of authentic wool fabric samples previously analysed by F-AAS after microwave digestion. Comparable results can be obtained using this unique procedure if the same set of standards is used for XRF and LIBS calibration. Limits of detection for chromium achieved by suggested LIBS methods (from 5 to 10 mg kg−1) are comparable with the WD XRF ones (from 4 to 5 mg kg−1).

The cryogenic grinding as the important homogenization step in analysis of inconsistent food samples

Some homogenisation approaches have been investigated to make easier and overcome troublesome preparation of inconsistent food samples. Contents of Na, Ca, Mg, P, Fe, Mn and Zn in muesli, seed and instant food samples were determined by inductively coupled plasma optical emission spectrometry after their grinding with an agate mortar, a kitchen coffee grinder and a cryogenic mill. The efficiency of a grinding step was evaluated using RSDs and homogeneity factors (H-factor). For cryogenically grinded samples, RSDs were detected about 4% and H-factors on 10, what is acceptable for the analytical purpose. The results for grinding with an agate mortar as well as a coffee grinder were quite unsatisfactory (RSDs in tens percent). Differences between RSDs and H-factors for the procedures tested were detected to be statistically significant. Different element contents were observed in differently treated samples which is probably a result of an unevenly element distribution in inhomogeneous components forming sample.

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.

Fast determination of the surface density of titanium in ultrathin layers using LIBS spectrometry

This work deals with the use of laser-induced breakdown spectroscopy (LIBS) for determining the surface density of titanium in ultrathin layers, particularly in ultrathin layers on a steel sheet. The results obtained by LIBS spectroscopy were compared with those obtained by wavelength dispersive X-ray fluorescence spectroscopy (WDXRF), X-ray photoelectron spectroscopy (XPS) and laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOF-MS). A simple, cheap and efficient method for the determination of the surface density of titanium in thin layers has been developed.