Optical systems atomic absorption spectrometry

The most frequently applied analytical methods used for characterizing bulk and layered systems (wafers and layers for microelectronics see the example in the schematic on the right-hand side) are summarized in Figure 9.4. Besides mass spectrometric techniques there are a multitude of alternative powerful analytical techniques for characterizing such multi-layered systems. The analytical methods used for determining trace and ultratrace elements in, for example, high purity materials for microelectronic applications include AAS (atomic absorption spectrometry), XRF (X-ray fluorescence analysis), ICP-OES (optical emission spectroscopy with inductively coupled plasma), NAA (neutron activation analysis) and others. For the characterization of layered systems or for the determination of surface contamination, XPS (X-ray photon electron spectroscopy), SEM-EDX (secondary electron microscopy combined with energy disperse X-ray analysis) and... 

Atomic absorption spectrometry was introduced approximately 18 years ago into laboratories concerned with the analysis of materials connected with ferrous metallurgy. Thus, literature references for this area of analysis only cover this period [89, 103, 134, 135, 151, 154]. Atomic absorption apparatus has been improved significantly during the past decade. Analysts have made demands upon manufacturers which have led to the development of sophisticated electronics and improvements in optical systems [33, 34,52, 53,59,148,149]. 

Laborious, yet very reliable, is the complete extraction of the dried, mortared and homogenized sediment sample using appropriate acids. Usually a microwave pressure extraction in a closed system composed of PTFE or a similarly inert and resistant material is applied for this purpose nowadays. With this method, all the sedimentary constituents are dissolved without exception by applying various mixtures of HF, HCl and HNO (HCLO can be avoided in most cases) at temperatures between 250 and 260 °C and a pressure ranging from 30 to 50 bars. In the ultimately received, slight nitric solution - hydrofluoric acid is left to evaporate in the course of the procedure -practically all elements (including the rare earth elements) can then be analyzed markedly above their limit of detection by atom absorption spectrometry (AAS), optical plasma emission spectrometry (ICP-OES) and/or plasma mass spectrometry (ICP-MS). 

Gas-diffusion separators have been integrated with detection cells to produce more compact systems both in optical sensing and atomic absorption spectrometry. These will be described in more detail in the sections on the coupling to individual detectors (cf. Sec. 5.4.2, 5.5.2)... 

Although originally FIA was conceived as a special technique for delivery of a sample segment into the instrument, the combination of flow injection as a sample pretreatment tool with atomic spectrometry has been shown to be of great potential for enhancing the selectivity and sensitivity of the measurements. Moreover, contamination problems are reduced due to the closed system used, making this interface suitable for ultratrace determination of metal species. Hyphenated techniques such as FIA/ SIA with flame atomic absorption spectrometry, inductively coupled plasma (ICP)-optical emission spectrometry, and ICP-mass spectrometry (MS) have been exploited extensively in recent years. The major attraction of FIA-ICP-MS is its exceptional multi-elemental sensitivity combined with high speed of analysis. In addition, the possibility of... 

Principle of atomic absorption spectrometry. 1, primary radiation source 2, atomizer 3, sample 4, combustion gases 5, optical dispersive system 6, detector 7, data acquisition and processing and 8, data editing. (From Ebdon, L. and Evans, E.H., An Introduction to Analytical Atomic Syectrometry, John Wiley Sons, West Sussex, 1998,206. With permission.)... 

Flame Atomic Absorption Spectrometry. It is usually considered that about 95% of the observed problems are related to the light system, the nebuliser/ burner and the instrument cleanliness the instrument s optics and electronics rarely fail. For example, most commonly problems accounting for absorbance lower than expected are related to ... 

Some of these less used systems have limited applications in specific areas and combine HPLC with, for instance, chemiluminescence techniques [48], viscometry [49], optical activity measurement [50], piezoelectric crystals for mass scanning [51], atomic absorption and emission spectrometry [52-54], photoacoustic monitors [55], nuclear magnetic resonance [56], electron spin resonance [57], Raman [58] and photoconductivity measurement [59]. Details on these and other innovative detection systems are presented in the review by Bruckner [60]. 

There are different spectrophotometric techniques for analysis of contaminants in biofuels. Simultaneous detection of the absorption spectrum and refractive index ratio with a spectrophotometer for monitoring contaminants in bioethanol has been carried out by Kontturi et al., 2011. Inductively Coupled Plasma Atomic Emission Spectrometry and optical emission spectral analysis with inductively coupled plasma (ICP-OES) have also been used to analyze biodiesel samples for trace metals (ASTM, 2007 ECS, 2006). An ICP-MS instrument fitted with an octopole reaction system (ORS) was used to directly measure the inorganic contents of several biofuel materials. Following sample prepwation by simple... 

This article provides some general remarks on detection requirements for FIA and related techniques and outlines the basic features of the most commonly used detection principles, including optical methods (namely, ultraviolet (UV)-visible spectrophotometry, spectrofluorimetry, chemiluminescence (CL), infrared (IR) spectroscopy, and atomic absorption/emission spectrometry) and electrochemical techniques such as potentiometry, amperometry, voltammetry, and stripping analysis methods. Very few flowing stream applications involve other detection techniques. In this respect, measurement of physical properties such as the refractive index, surface tension, and optical rotation, as well as the a-, //-, or y-emission of radionuclides, should be underlined. Piezoelectric quartz crystal detectors, thermal lens spectroscopy, photoacoustic spectroscopy, surface-enhanced Raman spectroscopy, and conductometric detection have also been coupled to flow systems, with notable advantages in terms of automation, precision, and sampling rate in comparison with the manual counterparts. 

However, I is the emission intensity emitted over the whole space angle. Here, the % of space angle with which the radiation is collected into the optical system is to be considered, together with the transmittance of the spectrometer [according to Eq. (156) and the characteristics of the radiation detector, Eqs. (186-189)]. Evidently, in all the equations cited many constants are not exactly known and all types of atomic spectrometry are relative methods nevertheless, the intensities measured can be traced back to the concentrations of the analyte in the sample in a stringent way. This also applies to the other atomic emission, atomic absorption, atomic fluorescence, and mass spectrometric methods discussed here. 

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