Atomic fluorescence sample preparation

The objective of this symposium and this book is to acquaint the readers with the latest advances in the field of elemental analysis and to focus on what avenues of future research to explore in this area. The subjects included are various elemental analysis techniques such as atomic absorption spectrometry, inductively coupled plasma emission and mass spectrometry, isotope dilution mass spectrometry. X-ray fluorescence, ion chromatography, gas chromatography-atomic emission detection, other hyphenated techniques, hetero-atom microanalysis, sample preparation, reference materials, and other subjects related to matrices such as petroleum products, lubricating oils and additives, crude oils, used oils, catalysts, etc. 

The very low Hg concentration levels in ice core of remote glaciers require an ultra-sensitive analytical technique as well as a contamination-free sample preparation methodology. The potential of two analytical techniques for Hg determination - cold vapour inductively coupled plasma mass spectrometry (CV ICP-SFMS) and atomic fluorescence spectrometry (AFS) with gold amalgamation was studied. 

The complex of the following destmctive and nondestmctive analytical methods was used for studying the composition of sponges inductively coupled plasma mass-spectrometry (ICP-MS), X-ray fluorescence (XRF), electron probe microanalysis (EPMA), and atomic absorption spectrometry (AAS). Techniques of sample preparation were developed for each method and their metrological characteristics were defined. Relative standard deviations for all the elements did not exceed 0.25 within detection limit. The accuracy of techniques elaborated was checked with the method of additions and control methods of analysis. 

The performance of microwave-assisted decomposition of most difficult samples of organic and inorganic natures in combination with the microwave-assisted solution preconcentration is illustrated by sample preparation of carbon-containing matrices followed by atomic spectroscopy determination of noble metals. Microwave-assisted extraction of most dangerous contaminants, in particular, pesticides and polycyclic aromatic hydrocarbons, from soils have been developed and successfully used in combination with polarization fluoroimmunoassay (FPIA) and fluorescence detection. 

Techniques for analysis of different mercury species in biological samples and abiotic materials include atomic absorption, cold vapor atomic fluorescence spectrometry, gas-liquid chromatography with electron capture detection, and inductively coupled plasma mass spectrometry (Lansens etal. 1991 Schintu etal. 1992 Porcella etal. 1995). Methylmercury concentrations in marine biological tissues are detected at concentrations as low as 10 pg Hg/kg tissue using graphite furnace sample preparation techniques and atomic absorption spectrometry (Schintu et al. 1992). 

Atomic absorption provides very high sensitivity but requires careful subsampling, extensive sample preparation, and detailed sample-matrix corrections. X-ray fluorescence requires little in terms of sample preparation but suffers from low sensitivity and the application of major matrix corrections. Inductively coupled argon plasma spectrometry provides high sensitivity and few matrix corrections but requires a considerable amount of sample preparation, depending on the process stream to be analyzed. 

The combination of preconcentration by electrodeposition with stripping by voltammetry is probably the most sensitive electroanalytical method in common use today. Consequently, this popular technique is discussed in more detail in Chapter 24. Preconcentration of material by an electrode reaction has been used in sample preparation for atomic absorption, neutron activation, x-ray fluorescence, microprobe, and several other spectroscopic techniques. 

Until now, little attention has been given to the analysis of ancient copper alloys with LA-ICP-MS. This type of material is usually analyzed with fast or instrumental neutron activation analysis (FNAA or INAA), particle induced X-ray emission (PIXE), X-ray fluorescence (XRF), inductively coupled plasma-atomic emission spectrometry or inductively coupled plasma-atomic absorption spectrometry (ICP-AES or ICP-AAS). Some of these techniques are destructive and involve extensive sample preparation, some measure only surface compositions, and some require access to a cyclotron or a reactor. LA-ICP-MS is riot affected by any of these inconveniences. We propose here an analytical protocol for copper alloys using LA-ICP-MS and present its application to the study of Matisse bronze sculptures. 

These techniques fall into two categories those considered as routine (e.g. atomic absorption and emission spectroscopy, X-ray fluorescence) and a growing number of microanalytical surface techniques (e.g. laser microprobe mass analysis [LAMMA] and sensitive high-resolution ion microprobe [SHRIMP]). Each analytical technique requires specific sample preparation prior to analysis, as summarised in Table 13.1. 

Many researchers have attempted to determine mercury levels in the blood, urine, tissues, and hair of humans and animals. Most methods have used atomic absorption spectrometry (AAS), atomic fluorescence spectrometry (AFS), or neutron activation analysis (NAA). In addition, methods based on mass spectrometry (MS), spectrophotometry, and anodic stripping voltametry (ASV) have also been tested. Of the available methods, cold vapor (CV) AAS is the most widely used. In most methods, mercury in the sample is reduced to the elemental state. Some methods require predigestion of the sample prior to reduction. At all phases of sample preparation and analysis, the possibility of contamination from mercury found naturally in the environment must be considered. Rigorous standards to prevent mercury contamination must be followed. Table 6-1 presents details of selected methods used to determine mercury in biological samples. Methods have been developed for the analysis of mercury in breath samples. These are based on AAS with either flameless (NIOSH 1994) or cold vapor release of the sample to the detection chamber (Rathje et al. 1974). Flameless AAS is the NIOSH-recommended method of determining levels of mercury in expired air (NIOSH 1994). No other current methods for analyzing breath were located. 

Nickel and vanadium along with iron and sodium (from the brine) are the major metallic constituents of crude oil. These metals can be determined by atomic absorption spectrophotometric methods (ASTM D-5863, IP 285, IP 288, IP 465), wavelength-dispersive X-ray fluorescence spectrometry (IP 433), and inductively coupled plasma emission spectrometry (ICPES). Several other analytical methods are available for the routine determination of trace elements in crude oU, some of which allow direct aspiration of the samples (diluted in a solvent) instead of time-consuming sample preparation procedures such as wet ashing (acid decomposition) or flame or dry ashing (removal of volatile/combustible constituents) (ASTM D-5863). Among the techniques used for trace element determinations are conductivity (IP 265), flameless and flame atomic absorption (AA) spectropho-... 

The method to be employed for measurement of the analytical signal largely determines the form of the sub-sample and, consequently, the extent and type of sample preparation required. Nuclear activation methods, x-ray fluorescence techniques, graphite furnace atomic absorption, classical emission spectroscopy and many mass spectrome-... 

Human biological materials to be investigated include (a) hard calcified tissues, e.g. bone, teeth, other calcified formations (b) semi-hard tissue, e.g. hair, nails (c) soft body tissues and (d) various biological fluids and secretions in the human body. The treatment of each of these materials varies from one material to another and, as stated earlier, is often determined by the instrumental method to be employed for measuring the analytical signal, the elements to be determined and the concentration levels at which these are present. For the purposes of this discussion, it shall be generally assumed that the analytical techniques employed include atomic absorption spectrometry both with (F-AAS) as well as with a furnace (GF-AAS), neutron activation analysis (NAA), flame emission spectrometry (FES) voltammetric methods and the three inductively coupled plasma spec-trometric methods viz. ICP-atomic emission spectrometry, ICP-mass spectrometry and ICP-atomic fluorescence spectrometry. The sample preparation of biological methods for all ICP techniques is usually similar (Guo, 1989). 

The great advance for AFS in mercury analysis is associated with the CV atomization technique. The sample preparation procedures are the same as for CV-AAS. Most of the methods described below utilize the CV technique for liberation of mercury from the sample solution. Unless othenwise stated, the aeration gas was argon and the mercury fluorescence was measured directly at the outlet of the gas stream carrying the Hg(0) from the reaction vessel into the atmosphere (a "windowless cell"). 

Qualitative analysis X-ray fluorescence is useful for elements with atomic numbers greater than 4, including metals and nonmetals. For qualitative analysis, no sample preparation is required and the method is generally nondestructive. 

Sodium silicate is somev at more difficult to analyze than many other materials because of the formation of the relatively long lived radionuclide Na whose emissions interfere with the detection of other elements. Nevertheless we were able to determine, in a sample of sodium silicate, that many heavy elements of toxicological concern were undetectable down to the ppm to ppb level in the undiluted silicate (13), An XRF spectrometer can be configured to perform sequential multi-elemental analyses. It is less sensitive to the elements of lower atomic number. Also, since the X-rays penetrate only to a depth of about 10 urn, the sample must be homogeneous. Solid samples must be presented to the X-ray beam with a flat surface. However, the relative ease of sample preparation and the ability to run glasses and solutions with only minor dilution make X-ray fluorescence a useful technique where analysis for a wide range of impurities is required,... 

For atomic absorption, plasma atomic emission, and atomic fluorescence spectrometric analysis the sample is normally introduced in the liquid form. The pretreatment of the sample depends on the sample type, element to be determined, and its concentration, as well as the analysis technique used. Any general sample preparation which would fit all kinds of samples cannot be employed. Sometimes the sample can be analysed without any pretreatment, sometimes complex sample treatment procedures are needed. 

Slejkovec et al. [125] used HPLC-atomic fluorescence to separate and quantify the anionic arsenic compounds found in urban aerosol samples. The initial sample preparation produced aqueous extracts. These were found to contain only arsenate, although the separation worked for mixtures of arsenite, arsenate, monomethylar-sonic acid, and dimethylarsonic acid. The detection limit for arsenate was 80 pg mL . ... 

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