Comparison of glass fragments by neutron activation analysis

A method of comparing glass fragments of potential application to forensic sicence has been developed and evaluated. A representative sample of window glass from England and Wales has been collected and analysed for about 25 elements. An automated radiochemical separation followed by gamma-spectroscopy was used in order to determine the concentration of the maximum number of elements. Frequency distributions of the elemental concentration are shown and used to assess the discrimination of the technique and compare it with the measurement of refractive index. A few simulated cases have been included to demonstrate the possible application to forensic science problems.     

Determination of scandium in sea-water by atomic-absorption spectroscopy

A method for the determination of scandium in sea-water at the sub-microgram level has been developed. Scandium is coprecipitated with iron(III) hydroxide at pH 8-9, and then separated from the iron by ion-exchange. The final concentration is achieved by extracting the scandium into a solution of oxine in butanol. A nitrous oxide-acetylene flame is used for the determination by atomic-absorption spectroscopy. Recoveries of 99-100% are obtained. The storage of the solutions before analysis has been investigated by radiometric techniques with (46)Sc. The scandium concentration in surface waters of the South China Sea was found to be 0.01 +/- 0.005 microg/l .     

Determination of lead in stainless steel by atomic-absorption spectroscopy

A method has been developed for the determination of lead in stainless steels by atomic-absorption spectrometry after removal of iron by solvent extraction and volatilization of chromium as chromyl chloride. The method proposed is suitable for the determination of lead in the range from 5 to 100 ppm.     

Forensic comparative glass analysis by laser-induced breakdown spectroscopy

Glass samples of four types commonly encountered in forensic examinations have been analyzed by laser-induced breakdown spectroscopy (LIBS) for the purpose of discriminating between samples originating from different sources. Some of the glass sets were also examined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Refractive index (RI) measurements were also made on all glass samples and the refractive index data was combined with the LIBS and with the LA-ICP-MS data to enhance discrimination. The glass types examined included float glass taken from front and side automobile windows (examined on the non-float side), automobile headlamp glass, automobile side-mirror glass and brown beverage container glass. The largest overall discrimination was obtained by employing RI data in combination with LA-ICP-MS (98.8% discrimination of 666 pairwise comparisons at 95% confidence), while LIBS in combination with RI provided a somewhat lower discrimination (87.2% discrimination of 1122 pairwise comparisons at 95% confidence). Samples of side-mirror glass were less discriminated by LIBS due to a larger variance in emission intensities, while discrimination of side-mirror glass by LA-ICP-MS remained high.     

Rapid determination of selenium and tellurium by atomic-absorption spectrophotometry

A rapid method has been developed for the determination of selenium and tellurium in geological and biological samples. It involves acid digestion of the sample with mineral acids, addition of arsenic as a carrier, reduction of arsenic to co-precipitate selenium and tellurium, dissolution of the precipitate in dilute nitric acid and subsequent determination of selenium and tellurium by conventional atomic-absorption spectrophotometry. Selenium and tellurium have been measured on a routine basis, down to 0.1 ppm.     

Rapid determination of antimony in steel by flameless atomic-absorption

A method for the determination of 1-30 ppm or more of Sb in steel by using flameless atomic absorption has been developed. The sample was dissolved in aqua regia and 10 mul were pipetted into the Massmann-type furnace. It was shown that interferences from HCl, HNO(3), Ni and Fe could be eliminated if oxygen was excluded and the heating rate was sufficiently high. Chromium was added to the samples and standards to compensate for its influence. Cu, Co, Mn, Ti and Sn did not interfere. An intercomparison with other laboratories showed that this method gives the same result as extraction with TOPO in MIBK. The time for a complete analysis including dissolution was 15 min.     

Determination of nanogram amounts of nickel by flameless atomic-absorption spectroscopy

A simple flameless atomizer, made from a heated graphite resistor, was investigated for the determination of nickel in various salts. The parameters characterizing its behaviour were optimized, to yield an absolute detection limit of 0.1 ng of nickel.     

Trace analysis by flameless atomic-absorption spectrometry

The operating conditions of an atomic-absorption system based on flameless atomization have been investigated for trace analysis for Al, Cr, Cu, Fe, Mg and Mn. The sample solution on a tantalum strip was atomized by electrical heating in an inert atmosphere within an absorption chamber. This technique allows the use of small sample sizes and results in a higher sensitivity than that with the conventional flame technique. Some interference effects and applications were investigated.     

Determination of tellurium in geochemical materials by flameless atomic-absorption spectroscopy

A method is described for the determination of tellurium at nanogram levels in rocks and in other complex materials by the use of flameless atomic-absorption spectroscopy. A very selective organic extraction procedure is applied to avoid matrix interference effects during extraction of Te and the atomization stage in the graphite furnace. Prior separation of iron and other interfering elements is achieved by a combined cupferron-ethyl acetate extraction. Tellerium is extracted from 6M hydrochloric acid with MIBK and stripped into aqueous medium. Pipetting of the aqueous extract into the graphite furnace gives fairly good instrumental reproducibility (2-3% error). Detection limits of about 10 ppM Te for a 0.5-g sample have been achieved with the medium-performance apparatus used. Results for Te in some geochemical reference materials are reported. Indications are given for the determination of Sb and Mo in the same solutions.     

Equilibrium effects in the determination of tantalum by atomic-absorption spectroscopy

The effect of solution variables on the efficiency of tantalum atom formation in hot flames is considered in terms of competing equilibria.     

Role of solution equilibria in atomic-absorption spectroscopy

The interference effects observed in series of absorption studies using nitrous oxide/acetylene or air/acetylene flames are interpreted in terms of the nature of the chemical species present in solution. The elements studied include Nb, Ta, Ti, Y, V, W and Ni, and species shown to influence the atomic absorption include hydrofluoric, phosphoric and sulphuric acids, the ions of Ca, K, Al, Fe and Mn, and compounds such as EDTA and ammonium acetate.     

Analysis by means of atomic-absorption spectroscopy,using a tantalum boat

Summary A technique for flameless atomic absorption with a tantalum boat method is described. Detection limits for 13 elements were determined and a special analysis procedure for mercury was worked out. The study of this technique also included a detailed investigation of some important parameters, namely heating rate, argon flow and sample volume. Interferences were studied for Cu, Mn and Pb and the results showed less interferences from some common salts than the carbon rod technique does. A brief study of applications to trace element determination in milk samples is also reported. Three different atomic-absorption instruments were used in this work. One of them had microwave-excited electrodeless discharge lamps instead of hollow-cathode lamps. Detection limits are comparable with other flameless techniques. The analysis time is very short (about 1 min for 10-l samples) and the boat needs no water-cooling. The equipment used is of simple construction and is considerably less expensive than the commercially made flameless accessories.

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Zusammenfassung Die Messung der Atomarabsorption ohne Flamme mit Hilfe eines Tantal-Schiffchens wurde beschrieben. Die Nachweisgrenzen für 13 Elemente wurden bestimmt und eine besondere Arbeitsvorschrift für Quecksilberanalysen ausgearbeitet. Außerdem wurden einzelne wichtige Versuchsparameter untersucht: die Geschwindigkeit des Erhitzens, die Argonströmung und das Probenvolumen. Die Störungen bei Cu, Mn und Pb wurden geprüft, wobei sich ergab, daß der störende Einfluß einiger üblicher Salze geringer ist als bei dem Kohlestab-Verfahren. Die Anwendung auf die Bestimmung von Spurenelementen in Milchproben wurde ebenfalls erörtert. Drei verschiedene Atomarabsorptionsgeräte wurden verwendet. Eines davon war an Stelle der Hohlkathodenlampen mit elektrodenlosen Entladungslampen ausgerüstet, die mit Mikrowellen angeregt wurden. Die Nachweisgrenzen sind mit denen anderer flammenloser Arbeitsweisen vergleichbar. Die Analysendauer ist sehr kurz (etwa 1 min. für 10-l-Proben). Das Schiffchen bedarf keiner Wasserkühlung. Die verwendete Ausrüstung ist einfach und billiger als handelsübliche Geräte.

     

Application of total reflection X-ray fluorescence spectrometry to small glass fragments.

Total reflection X-ray fluorescence spectrometry (TXRF) has been applied for trace elemental analysis of small glass fragments. A small glass sample (a fragment with weight less than 0.5 mg) was decomposed by 100 microg of HF/HNO3 acid; the material was condensed to 10 microl and was dried on a Si wafer. Since the size of the dried residue on the Si wafer was less than 1 cm in diameter, an incident X-ray beam with about 1 cm in width could effectively excite elemental components in such a small glass fragment. The precision of the present technique was checked by analyzing the glass fragments (<0.5 mg) from NIST SRM612; the relative standard deviations (RSD) of less than 8.1% were achieved for elemental ratios that were normalized by Sr. Fragments (<0.5 mg) obtained from 23 figured sheet glasses were used as samples for estimating the utility of this technique to forensic discrimination. Comparison of five elemental ratios of Ti/Sr, Mn/Sr, Zn/Sr, Rb/Sr, and Pb/Sr calculated from X-ray fluorescence spectra was effective in distinguishing glass fragments that could not be differentiated by their refractive indexes (RI).     

Determination of ruthenium and iridium in anode coatings by atomic-absorption spectroscopy

A method is described for the determination of ruthenium and iridium coated on an electrode surface. The coating is chemically removed from the electrode by fusion with alkali, and the resulting solution prepared for analysis. Interelement interferences are eliminated by using a titanium-potassium matrix solution as a releasing agent. Recovery and precision data are given for ruthenium and iridium. The AAS determination of ruthenium compares favourably with a standard colorimetric method.     

Rapid analysis of Radix puerariae by near-infrared spectroscopy

A new, rapid analytical method using near-infrared spectroscopy (NIRS) was developed to differentiate two species of Radix puerariae (GG), Pueraria lobata (YG) and Pueraria thomsonii (FG), and to determine the contents of puerarin, daidzin and total isoflavonoid in the samples. Five isoflavonoids, puerarin, daidzin, daidzein, genistin and genistein were analyzed simultaneously by high-performance liquid chromatography-diode array detection (HPLC-DAD). The total isoflavonoid content was exploited as critical parameter for successful discrimination of the two species. Scattering effect and baseline shift in the NIR spectra were corrected and the spectral features were enhanced by several pre-processing methods. By using linear discriminant analysis (LDA) and soft independent modeling class analogy (SIMCA), samples were separated successfully into two different clusters corresponding to the two GG species. Furthermore, sensitivity and specificity of the classification models were determined to evaluate the performance. Finally, partial least squares (PLS) regression was used to build the correlation models. The results showed that the correlation coefficients of the prediction models are R = 0.970 for the puerarin, R = 0.939 for daidzin and R = 0.969 for total isoflavonoid. The outcome showed that NIRS can serve as routine screening in the quality control of Chinese herbal medicine (CHM).     

Rapid in-situ analysis of liquid steel by laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma allow a quantitative chemical analysis of the target material. LIBS is a fast, non-contact method allowing large working distances between the sample under investigation and the detection system. These properties make LIBS applicable to process control in metallurgy. We describe an apparatus designed for rapid in-situ analysis of solid and molten metals at variable distances of up to 1.5 m. A variable lens system allows compensation for varying positions of the liquid steel surface. The LIBS signal is guided by a fiber optic bundle of 12-m length to the spectrometer. Analysis of an element's concentration takes 7 s. Laboratory experiments using an induction furnace showed that the addition of admixtures to liquid steel results in rapid response of the system. Results including the in-situ monitoring of Cr, Cu, Mn and Ni within certain concentration ranges are presented (Cr: 0.11–13.8 wt.%; Cu: 0.044–0.54 wt.%; Mn: 1.38–2.5 wt.%; Ni: 0.049–5.92 wt.%).