Quantitative surface analysis by Auger and x-ray photoelectron spectroscopy

Recent developments in quantitative surface analysis by Auger (AES) and x-ray photoelectron (XPS) spectroscopies are reviewed and problems relating to a more accurate quantitative interpretation of AES/XPS experimental data are discussed. Special attention is paid to consideration of elementary physical processes involved and influence of multiple scattering effects on signal line intensities. In particular, the major features of core-shell ionization by electron impact, Auger transitions and photoionization are considered qualitatively and rigorous approaches used to calculate the respective transition probabilities are analysed. It is shown that, in amorphous and polycrystalline targets, incoherent scattering of primary and signal Auger and photoelectrons can be described by solving analytically a kinetic equation with appropriate boundary conditions. The analytical results for the angular and energy distribution, the mean escape depth, and the escape probability as a function of depth of origin of signal electrons as well as that for the backscattering factor in AES are in good agreement with the corresponding Mote Carlo simulation data. Methods for inelastic background subtraction, surface composition determination and depth-profile reconstructions by angle-resolved AES/XPS are discussed. Examples of novel techniques based on x-ray induced photoemission are considered.     

气相色谱—微波等离子体发射光谱法研究农药1605与人唾液的相互作用

用ＧＣ－ＡＥＤ联用技术研究了农药１６０５，得到１６０５所含六种元素的元素色谱图，并用该方法研究了人唾液与１６０５的相互作用。     

Improving the accuracy of carbon-to-hydrogen ratio determination for P,N, S,O, Cl,and Br-containing organic compounds using atomic emission detection

The objective of this work was to investigate the dependence of atomic emission detector C and H response on microwave-induced plasma conditions and to improve the accuracy of carbon-to-hydrogen ratio determination for trialkylphosphates, herbicides, chlorophenols, and sulfur-containing organic compounds. Compounds which differed structurally from the analytes were used as reference compounds. It was found that when the oxygen concentration in the helium was the maximum for the instrument (9%) relative errors in carbon-to-hydrogen ratio determination were 3–8%, irrespective of analyte and reference compound structure, whereas when working in the mode of operation recommended by the manufacturer of the instrument (1.5% oxygen in helium) the respective errors were 10–20% or higher. This improvement in the accuracy of carbon-to-hydrogen ratio determination was accompanied by a factor of ten decrease in sensitivity.     

Speciation of organotin compounds in waters and marine sediments using purge-and-trap capillary gas chromatography with atomic emission detection

A procedure for the simultaneous determination of six organotin compounds, including methyl-, butyl- and phenyltins, in waters and marine sediments is developed. The analytes were leached from the solid samples into an acetic acid:methanol mixture by using an ultrasonic probe. The organotins were derivatized with sodium tetraethylborate (NaBEt₄) in the aqueous phase, stripped by a flow of helium, pre-concentrated in a trap and thermally desorbed. This was followed by capillary gas chromatography with microwave-induced plasma atomic emission spectrometry as the detection system (GC-AED). Each chromatographic run took 22 min, including the purge time. Calibration curves were obtained by plotting peak area versus concentration and the correlation coefficients for linear calibration were at least 0.9991. Detection limits ranged from 11 to 50 ng Sn l⁻¹ for tributyltin and tetramethyltin, respectively. The seawater samples analyzed contained variable concentrations of mono-, di- and tributyl- and monophenyltin, ranging from 0.05 to 0.48 μg Sn l⁻¹, depending on the compound. Some of the sediments analyzed contained concentrations of dibutyl- and tributyltin of between 6.0 and 13.0 ng Sn g⁻¹. Analysis of the certified reference material PACS-2, as well as of spiked water and sediment samples showed the accuracy of the method. The proposed method is selective and reproducible, and is considered suitable for monitoring organotin compounds in water and sediment samples.     

The Importance of Solvent Venting to Reduce Memory Effects with On-Line LC-GC-AED

Conventional operation of the GC Atomic Emission Detector (AED) system involves backflushing of the microwave induced plasma (MIP) during the elution of small volumes of solvent from the GC column. When performing multi-dimensional, on-line LC-GC-AED, significantly larger solvent volumes are introduced into the system and must subsequently be removed. Thus solvent venting procedures are required and the backflushing of the plasma must be extended to facilitate solvent but not solute removal. This study demonstrates the significance of memory effects imparted upon the MIP of the AED if solvent venting is incomplete. Comparison of conventional GC-AED and multi-dimensional LC-GC-AED is made with respect to a fossil fuel sample.     

Applicability of solid-phase microextraction combined with gas chromatography atomic emission detection (GC-MIP AED) for the determination of butyltin compounds in sediment samples

The performance of solid-phase microextraction (SPME) applied to the determination of butyltin compounds in sediment samples is systematically evaluated. Matrix effects and influence of blank signals on the detection limits of the method are studied in detail. The interval of linear response is also evaluated in order to assess the applicability of the method to sediments polluted with butyltin compounds over a large range of concentrations. Advantages and drawbacks of including an SPME step, instead of the classic liquid–liquid extraction of the derivatized analytes, in the determination of butyltin compounds in sediment samples are considered in terms of achieved detection limits and experimental effort. Analytes were extracted from the samples by sonication using glacial acetic acid. An aliquot of the centrifuged extract was placed on a vial where compounds were ethylated and concentrated on a PDMS fiber using the headspace mode. Determinations were carried out using GC-MIP AED.     

Speciation of arsenic using capillary gas chromatography with atomic emission detection

A gas chromatography method with atomic emission detection (GC-AED) for the determination of dimethylarsinic acid (DMA), monomethylarsonic acid (MMA) and inorganic arsenic was optimized. The analytes were derivatized in the sample solutions with methyl thioglycolate (TGM) and the products were extracted into cyclohexane before an aliquot of this organic phase was directly injected into the chromatograph. The procedure was applied to the analysis of seawaters, wines, beers and infant foods, the last requiring an additional enzymatic reaction prior to analyte derivatization. Detection limits in seawaters and beverages were 0.05, 0.15 and 0.8 ng mL⁻¹ for DMA, MMA and inorganic arsenic, respectively. In infant foods the detection limits were 1, 10 and 25 ng g⁻¹ for DMA, MMA and inorganic arsenic, respectively. Inorganic arsenic was detected in some of the seawater samples and three of the wines analyzed at concentration levels in the range 1-40 ng mL⁻¹, and DMA in several of the infant foods in the range 20-80 ng g⁻¹. The method was validated by analyzing a certified reference material and by recovery studies. All the samples were also analyzed by hydride generation and atomic fluorescence spectrometry (HG-AFS), which provided data for the total arsenic content.     

Determination of HCN sampled from gasification product gases by headspace gas chromatography with atomic emission detector

Nitrogen-containing fuels produce hydrogen cyanide when the fuel is gasified. The gas is poisonous and produces nitrogen oxides when it is burned. HCN is usually sampled into alkaline solutions and analysed using an ion selective electrode. The method is tedious and the electrode response is temperature-dependent. Samples are not stable and must be analysed immediately, and they contain ions which are poisonous to the electrode. Therefore a new gas chromatographic method was developed. In this new method HCN is released from the alkaline solutions with sulphuric acid in a headspace sampler and analysed by a gas chromatograph connected to an atomic emission detector. Measurements on carbon emission line 193.1 nm gave the limit of detection 0.05 mg CN^–/l in the solution. The calibration curve was linear to 1000 mg CN^–/l and the correlation was 0.997. The relative standard deviation of the calibration was 1.7% at the concentration of 5 mg CN^–/l and 1.0% at 25 mg CN^–/l. The developed headspace method allows automated analysis and it needs less sample preparations than the ion selective electrode method. This paper also reports the effect of sample preparation and storage time on the stability of the samples.     

FCC汽油GS中硫化物的分布特点

FCC汽油样品GS按沸点切割成六个组分，然后使用配有原子发射光谱检测器的气相色谱仪（GC/AED）分别分析每个馏分样品中的含硫化合物。数据表明，样品中含硫化合物以噻吩和烷基取代噻吩类为主，而且含硫化合物在样品中的分布是不均匀的，随着切割段沸点的提高，含硫化合物含量明显增加，多碳数取代噻吩类化合物含量增加。数据还可以用来参考确定轻、重馏分油切割点，以对轻、重馏分油采取不同的脱硫方法，达到最佳经济效益。