Vítězslav Otruba

Preconcentration of platinum group metals on modified silicagel and their determination by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry in airborne particulates

Modified silicagel (C18) was studied for separation and preconcentration of platinum group metals (Ru, Rh, Pd, Os, Ir and Pt) as ion associates of their chlorocomplexes with cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide. Sample containing HCl and the onium salt was pumped through the column. After elution with ethanol the eluate was evaporated in the presence of HCl. Resulting aqueous solutions were analysed with inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). Recovery values of 1-20 mug Pt and Pd from 50 ml of synthetic pure solution were 100+/-3 and 100+/-1%, respectively, however, they diminished with increasing sample volume and in the presence of the real sample matrix or nitrate ions. Samples of engine soot (NIES No. 8), decomposed by low pressure oxygen high-frequency plasma, and airborne particulates from dust filters of meteorological stations, leached with HNO(3) and H(2)O(2), were analysed. A reasonable agreement was found between ICP-MS and ICP-AES results for airborne dust samples and the values comparable with those in literature were determined in NIES No. 8.

Vapour generation inductively coupled plasma optical emission spectrometry in determination of total iodine in milk

Vapour generation inductively coupled plasma optical emission spectrometry (VG-ICP-OES) was used for the determination of the iodine content in milk samples. Modified alkaline ashing of the milk sample was employed for the total digestion of organic matrix constituents. A mixture of potassium hydroxide (2 mL, 2 mol L−1 in ethanol) and calcium nitrate (2 mL, 0.4 mol L−1 in ethanol) was used in the digestion step as an ashing aid for 2 ml of milk sample (or 200 mg of milk powder). Sample ash was then treated with hydrochloric acid (1.5 mL, 5 mol L−1) and sodium sulfite (1.25 mL, 1 mol L−1) for the elimination of carbonates, which would otherwise cause spectral interference. The vapour of elemental iodine was generated by means of oxidation of iodide by hydrogen peroxide (1 mol L−1) in sulfuric acid (5 mol L−1). Using a gas phase separator, matrix elements were completely eliminated; thus the spectral interference of phosphorus (178.222 nm) was removed and the most intense analytical line of iodine (178.218 nm) could be used for determination. The accuracy of the method was verified by analysis of CRM Non-Fat Milk Powder 1549 from NIST, as well as by the comparative study of VG-ICP-OES and ICP-MS results after alkaline solubilization (TMAH 2.5 mL, 10%). The limit of detection for the VG-ICP-OES method is 20 μg L−1 for original milk samples (based on 3σ of blank value). The concentration of iodine in real milk samples was found in the range 0.2–0.8 mg L−1 with a precision of determination from 0.5 to 3.5% (3 replicates).

Determination of platinum in plants by emission spectrometry after preconcentration on modified silicagel

Silicagel Separon SGX C18 (particle size 7 microm) was suitable for the preconcentration of 2-20 microg of Pt from 0.1M hydrochloric acid in the presence of cationic surfactants especially dimethyllaurylbenzylammonium bromide, with subsequent elution with 96% ethanol. The recovery was 86-110% for 2 microg of Pt. The sample matrix corresponding to 2.5 g of average plant ash does not interfere. The final emission spectrometry of platinum was carried out in 15 A dc-arc at Pt I 265.942 nm in the presence of Au as internal standard (Au I 267.595 nm). RSD was 6.3% in average.

Comparison of some analytical performance characteristics in inductively coupled plasma spectrometry of platinum group metals and gold.

The limits of detection, precision and matrix effects in the inductively coupled plasma spectrometry of platinum group metals (PGMs) and gold were measured and evaluated for four ICP-AES and one ICP-MS instrument. The sample matrix was a cationic surfactant used for the PGMs and gold preconcentration on a modified silica gel (C18). A sorption of ion associates of PGMs and gold chlorocomplexes with the cation of onium salt N(1-carbaethoxypentadecyl)-trimethyl ammonium bromide was considered. The calibration curves, limits of detection and matrix effects were evaluated in the presence of 0.003 mol dm(-3) of onium salt (1.3 mg cm(-3)) and 0.1 mol dm(-3) HCl. The values of limits of detection (3 sigma(bl)) of PGMs for all axial ICP instruments were mostly below 10 ng cm(-3). Lateral observation on dual view ICP instrument yielded only 3 times higher detection limits in comparison to the axial mode of the same spectrometer and the detection limits for ICP-MS instrument were on the levels of units or tens of pg cm(-3). These limits of detection did not significantly differ from values obtained with pure solutions. Matrix effects in the presence of onium salt did not exceed 12% depression in the analytical signals. Besides the coefficients of correlation, the uncertainties on centroids of concentrations were calculated for calibration graphs obtained by linear regression.

Selective preconcentration of thallium on modified silica gel for its determination by flame emission and absorption spectrometry.

Thallium (0.02-20 mug) was successfully preconcentrated on silica gel C18 from 0.1M hydrochloric acid in the presence of various cationic surfactants as ion pairs with tetrachlorothallate(III), and subsequently eluted with 96% ethanol. Of various atomic spectrometric procedures considered, emission spectrometry in a nitrous oxide-acetylene flame is suitable for the final determination of thallium in plants, this is more sensitive for thallium than flame atomic absorption spectrometry.

Contribution to vapor generation-inductively coupled plasma spectrometric techniques for determination of sulfide in water samples

Vapor generation-inductively coupled plasma-optical emission spectrometry was used for the determination of sulfide in water samples preserved by the addition of a zinc acetate and sodium hydroxide solution. Hydrogen sulfide and acid-volatile sulfides were transformed, by acidification, to a gaseous phase in a vapor generator and subsequently detected by inductively coupled plasma optical emission spectrometry. Compounds interfering with iodometric titration and spectrophotometric determination were examined as potential chemical interferents. The proposed method provides results comparable to iodometric titration in the tested concentration range 0.06-22.0 mg L(-1). Limit of detection for the determination of hydrogen sulfide by this method is 0.03 mg L(-1).

Analysis of tungsten carbide coatings by UV laser ablation inductively coupled plasma atomic emission spectrometry

Tungsten carbide coatings (thickness 0.1–0.2 mm) containing 8.0, 12.2, 17.2 and 22.9% Co were studied with laser ablation inductively coupled plasma atomic emission spectrometry (LA-ICP-AES). Composition of these plasma sprayed deposits on steel disks was determined using X-ray fluorescence spectrometry and electron microprobe energy/wavelength dispersive X-ray spectrometry. The coatings were ablated by means of a Q-switched Nd:YAG laser at 266 nm (10 Hz, 10 mJ per shot) coupled to an ICP echelle-based spectrometer equipped with a segmented charge-coupled device detector. Non-linear dependences of cobalt lines intensities on the Co percentage were observed both at a single spot ablation and at a sample translation. This behaviour could be attributed to a complex phase composition of the system W–C–Co. However, employing tungsten as internal standard the linear calibration was obtained for studied analytical lines Co II 228.616 nm, Co II 230.786 nm, Co II 236.379 nm and Co II 238.892 nm.

Development of a remote laser-induced breakdown spectroscopy system for investigation of calcified tissue samples

The development of a remote laser-induced breakdown spectroscopy (LIBS) setup with an off-axis Newtonian collection optics, Galilean-based focusing telescope, and a 532 nm flattop laser beam source is presented. The device was tested at a 6 m distance on a slice of bone to simulate its possible use in the field, e.g., during archaeological excavations. It is shown that this setup is sufficiently sensitive to both major (P, Mg) and minor elements (Na, Zn, Sr). The measured quantities of Mg, Zn, and Sr correspond to the values obtained by reference laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) measurements within an approximately 20% range of uncertainty. A single point calibration was performed by use of a bone meal standard . The radial element distribution is almost invariable by use of LA-ICP-MS, whereas the LIBS measurement showed a strong dependence on the sample porosity. Based on these results, this remote LIBS setup with a relatively large (350 mm) collecting mirror is capable of semiquantitative analysis at the level of units of mg kg−1.

Determination of trace lanthanides in their pure oxides by liquid chromatography-emission spectrometry

Traces of lanthanides can be separated effectively from major lanthanide oxides by liquid chromatography on a column of Separon SGX-C-18 silica gel modified by sorption of ammonium dodecylsulphate, and determined by flame - or inductively coupled plasma-atomic emission spectrometry. Spectral interferences from the major component at concentration ratios up to 10(4)-10(6) can be eliminated by isocratic or stepwise pH-gradient elution with ammonium 2-hydroxyisobutyrate. Methods of determining europium, ytterbium and holmium in yttrium, lanthanum and lutetium oxides are described. The flame method is shown to have some advantages.

Plasma pencil as an excitation source for atomic emission spectrometry

A 13.56 MHz plasma jet discharge, called a plasma pencil, was investigated. Rotational and excitation temperatures, and electron number densities for the pencil under and without sample load were calculated using OH band spectra, Ar lines and Hβ line, respectively. The rotational temperatures were found to be relatively low at about 800 K, however, excitation temperatures exceeded 4000 K. The plasma was found to be strongly non-isothermal. Some atomic lines of elements were easily observed. Aqueous solution-based aerosols were incorporated into the plasma without desolvation. Standard water solutions of the elements were nebulized into the plasma. The Ar carrier gas and Ar plasma gas flow rates were 0.3 and 4.0 l min−1, respectively. The forwarded power was 140 W. Intensities of the atomic lines, temperatures and electron number densities along the discharge tube were acquired in different positions from the aerosol entrance and an optimal position providing the best signal-to-noise ratio for each line intensity was established. Calibration dependencies for Ca, Cu, Mg, Zn, Li, Na were measured in the rage of 1–100 mg l−1. 3-sigma detection limits in the best observation axial position were (μg l−1): 27 (Ca), 49 (Cu), 58 (Mg), 40 (Li), 13 (Na) and 180 (Zn).