Peter Barth

Multielement analysis of green coffee and its possible use for the determination of origin

Using instrumental neutron activation analysis (INAA), graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS) and combustion elemental analysis, green coffees of the Arabica species produced in crop year 1987/88 in Colombia, Costa Rica, Cuba, El Salvador, Mexico, Nicaragua, Panamá and Papua New Guinea were analysed for the elements Ba, Br, C, Ca, Co, Cr, Cu, Cs, Fe, H, K, La, Mg, Mn, N, Na, Rb, Sc, Sr and Zn. In accordance with the concentrations determined, the elements could be ranked into five groups: Sc (sub-ppb level); Br, Co, Cr, Cs and La (ppb level); Ba, Cu, Fe, Mn, Na, Rb, Sr and Zn (ppm level); Ca and Mg (%o level); and C, H, K and N (% level). On the basis of the results obtained, an attempt was made to establish the origin of the green coffee via its elemental composition. Among the investigated elements, manganese was found to be best suited as an indicator for this purpose. However, the elements C, Co, Cs, Na and Rb proved to be of interest too.

Analysis of Silicon Dioxide and Silicon Nitride Powders by Electrothermal Vaporization Inductively Coupled Plasma Atomic Emission Spectrometry Using a Tungsten Coil and Slurry Sampling

Slurry sampling in combination with ETV-ICP-AES was employed for the direct determination of trace amounts of impurities in silicon dioxide and silicon nitride. The ETV device consisted of a double layer tungsten coil in a quartz apparatus. Spectral interferences and background emission caused by tungsten ablation of the coil were reduced by coating the coil with tungsten carbide. The background was measured either with a high-purity sample, the suspension medium or close to the analyte emission line, depending on matrix and analyte, or it was calculated using relative emission intensities of tungsten. The concentrations of Al, B, Be, Ca, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb and Zn were measured simultaneously, whereas K and Na were determined in the sequential mode. Calibration was performed using the standard additions method. The accuracy was checked by comparison with the results of independent methods. Limits of detection between 0.035 (Mg) and 130 µg g–1 (B) and between 0.01 (Be, Mg) and 34 µg g–1 (B) were achieved in silicon dioxide and silicon nitride, respectively.

Improved Slurry Sampling Electrothermal Vaporization System Using a Tungsten Coil for Inductively Coupled Plasma Atomic Emission Spectrometry

An improved ETV system for the determination of trace elements in diverse samples by slurry sampling ETV–ICP-AES is presented. It consists of a tungsten coil vaporizer, a simple computer controlled power supply with high reproducibility of the output voltage and a fast and efficient data acquisition and processing system for the short transient signals. Coupling the ETV system with the spectrometer and control of additional functions were performed by means of an interface connected to the ETV computer, allowing operation with a high degree of automation. The ablation of tungsten in the vaporization step could be significantly reduced by coating the coil with tungsten carbide and by a decrease in the concentration of traces of oxygen in the Ar–H2 carrier gas using a high-voltage discharge cell. The tungsten ablation was investigated for aqueous solutions and also for silicon carbide as an example of a refractory matrix. The transport losses of the analyte elements Au, As, Ca, Cr, Cu, Co, Fe, La, Mn, Na, Sb and Sc were determined for several matrices by means of the radiotracer technique. Transport losses were found to be in the range from 7% (La) to 54% (Cu).

Electrothermal vaporization inductively coupled plasma atomic emission spectrometric technique using a tungsten coil furnace and slurry sampling

A simple and inexpensive electrothermal vaporization device consisting of a double-layer tungsten coil, of the type normally manufactured for halogen lamps, was used for the simultaneous determination of Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni and Ti in aqueous suspensions of silicon carbide powder by inductively coupled plasma atomic emission spectrometry (ICP-AES). Possible interferences were investigated and background correction are discussed. Excluding Al, the limits of detection achievable were at the sub-µg g–1 and µg g–1 level. The accuracy was checked by comparison of the results with those obtained by instrumental neutron activation analysis (INAA), slurry sampling electrothermal atomic absorption spectrometry and ICP-AES involving decomposition of the sample. The precision expressed as relative standard deviation was between 3.3%(for 210 µg g–1 of Ti) and 13.5%(for 8.9 µg g–1 of Ni).

Determination of trace elements in high-purity copper by ETV-ICP OES using halocarbons as chemical modifiers

Inspired by the globule arc technique a new electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP OES) method was developed for the analysis of high-purity copper materials. The performance of the method was investigated for the analytes Ag, Al, As, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, S, Sb, Se, Si, Sn, Te, Ti, Zn and Zr. ETV parameters were optimized regarding the release of the analytes, the transport efficiency and the quality of analytical results in terms of precision, trueness and power of detection. The influence of CCl2F2, CHClF2, C2H2F4 and CHF3 as gaseous halogenation modifiers was investigated. A sufficient in situanalyte matrix separation was achieved by using CHF3 as halogenating reagent avoiding a high matrix input from the molten copper sample into the ETV system and the plasma. A complete release from the samples was obtained for all investigated analytes except Se and Te. Acceptable results for the determination of the trace elements Ag, Al, As, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, S, Sb, Si, Sn, Ti, Zn and Zr in high-purity copper were achieved. The method includes a preceding sample preparation step of oxidizing the surface of copper samples which results in a significantly enhanced sensitivity. In addition to the calibration with copper samples, the feasibility of the calibration with liquid multi-element solutions was investigated. Except for Ag, Mg and Ni all analytes could be analyzed using aqueous calibration solutions. The trueness of the method was tested by the determination of analyte contents of certified reference materials. Limits of quantification ranging from 0.6 ng g−1 to 29 ng g−1 were achieved. The developed direct solid sampling method is time and cost effective and well suited for the characterization of high-purity copper materials. The method can be automated to a large extent and is applicable for processes accompanying analyses. In contrast to all other investigated trace elements, Se and Te were not released from the matrix at measurable levels under the used conditions. The determination of these elements is still under investigation and will be reported in a succeeding publication.

Determination of 22 trace elements in high-purity copper including Se and Te by ETV-ICP OES using SF6, NF3, CF4 and H2 as chemical modifiers

In supplementary work to the one published earlier, experiments with SF6, NF3, CF4 and H2 as new modifier gases for the matrix studied were performed. Our investigations were continued to improve the described analytical method and to achieve additional insights into the mechanism of analyte release. Our new survey is split in two parts. At first fluorinating modifiers were used to investigate the behaviour of a variety of trace elements (Ag, Al, As, Au, Bi, Cd, Co, Cr, Fe, Mg, Mn, Ni, P, Pb, Sb, Se, Si, Sn, Te, Ti, Zn and Zr). Most of them (exceptions Au, Se, and Te) could be effectively released from the copper matrix by thermo-halogenation reactions and by partial sub-sample evaporation. Using SF6 and NF3 as modifier gases, low limits of quantification (LOQs) were achieved for the 19 well released trace elements (typical ≤0.1 mg kg−1). Most elements (exceptions Ag, Mg, and Ni) could be calibrated by using aqueous calibration solutions without any sample pretreatment. For the trace determination of Se, Te, and Au, a further analytical method of ETV-ICP OES is described in the second part based on thermo-hydrogenation reactions by using a hydrogen/argon mixture as a modifier gas. The determination of Se and Te with very high analytical performance (LOQ < 0.1 mg kg−1) can either be carried out in a second analytical step succeeding the halogenation procedure, or the sub-sample is directly treated with H2 without previous halogenation procedure whereby the sub-sample can either be partially or totally evaporated. In this case some other analytes (Ag, Au, As, Bi, Cd, Fe, Mg, Ni, Pb, Sb, Sn, and Zn) can additionally be quantified simultaneously with Se and Te.