Detection limits for elements

The detection of impurities or surface layers (e.g., oxides) on thick specimens is a special situation. Although the X-ray production and absorption assumptions used for thin specimens apply, the X-ray spectra are complicated by the background and characteristic X rays generated in the thick specimen. Consequently, the absolute detection limits are not as good as those given above for thin specimens. However, the detection limits compare very favorably with other surface analysis techniques, and the results can be quantified easily. To date there has not been any systematic study of the detection limits for elements on surfaces however, representative studies have shown that detectable surface concentrations for carbon and... 

The detection limits for elements analyzed by ICP-mass spectrometry (ICP-MS) are significantly lower in most cases than the detection limits for other atomic techniques. See Table 10.1. See Workplace Scene 10.3. 

In AAS the hollow cathode lamp (HCL) is the most important excitation source for most of the elements determined. However, sufficient light must reach the detector for the measurement to be made with good precision and detection limits. For elements in this table with intensities of less than 100, HCLs are probably inadequate, and other sources such as electrodeless discharge lamps should be investigated. 

Helium MIPs are excellent for element-specific detection in gas chromatography, as has been commercially realized [451]. In this way, not only are the halogens and other elements relevant in pesticide residue analysis but also organolead and or-ganotin compounds determined down to low concentrations. This makes MIP-AES very useful for speciation work [321, 452]. It has been shown that the delocalized helium MIP gave low detection limits for elements with high excitation potentials... 

A special dc GD for combination with a sector-field instrument has been designed for the analysis of high-purity Si [593], The Si+ ion yield was found to increase with gas pressure, probably as a consequence of the enhancement in the Ar metastable population. The signals for the SiJ decrease perhaps as a result of an increase in dissociative collisions. Detection limits for elements such as Al, As, B, Cl, Fe, P and U are at a level of 6 x 1010-6 x 1013 atoms/cm3. 

Table 7.8 Detection Limits for Elements in High Purity Copper Using DC Arc Emission Spectrometry...

This list is not inclusive or comprehensive, but is meant to give the student a feeling for the types of instruments commercially available at the present time. Typical detection limits for elements determined by ICP emission spectrometry can be found in Appendix... 

All elements in the periodic table except hydrogen, helium and lithium can be detected. Detection limits for elements in the mid range of the periodic table 500 -1000 ppm. Detection limits are somewhat poorer for elements at either end of the periodic table. 

Detector windows, optional chamber windows, and the air gap formed between chamber and detector windows are X-ray absorbers, which modify the shape of the detected X-ray spectrum in an energy-dependent way. Optionally, additional absorbers can be made use of to optimize the analytical parameters. They are partly to keep away elastically scattered protons from the detector, and partly to improve the detection limits for elements with Z > 20 by cutting the background X-ray continuum, which is enhanced at low atomic numbers as shown in panel (4) of O Fig. 33.1. 

Absolute mass detection limits for elements with atomic number above 14 measured at the European Synchrotron Radiation Facility (ESRF) ID22NI nanoprobe corresponding to a beamsize of approximately 100 nm, beam Intensity of 6 x 10 photons/s and measuring times of 300 ms and 300 s... 

Power of Detection. For optimum power of detection, the analyte density in the plasma, the ionization, and the ion transmission must be maximized. The necessary power is 0.6-2 kW with the sample ca. 10-15 mm above the tip of the injector. The detection limits, obtained at single element optimum conditions, differ considerably from those at compromise conditions, but are still considerably lower than in ICP-AES (Table 6). For most elements they are in the same range, but for some they are limited by spectral interference. This applies to As ( As" with Ar CF), Se ( Se with Ar Ar ), and Fe ( Fe with Ar O ). The acids present in the measurement solution and the material of which the sampler is made (Ni, Cu, etc.) may have considerable influence on these sources of interference and the detection limits for a number of elements. The detection limits for elements with high ionization potential may be even lower when they are detected as negative ions (for CF Cl = 5 ng/mL and for Cr Cl = I ng/mL). 

With the formation of volatile hydrides, the detection limits for elements such as As. Se, Sb, and Pb can be improved [310]. The improvement is due to enhanced analyte sampling efficiency and to the decrease of cluster ion formation. 

LMMS is essentially a surface sensitive method structural atoms from organic samples issue from the upper 5-50 nm when a 1 /u.m thick sample is analysed. Detection limits for elemental ions are in the ppm range. Real depth-profiling experiments are hindered by the discrete nature of the laser interactions. 

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