Absolute detection limit

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... 

Hyphenation in capillary electrophoresis is still in its infancy. Critical aspects of CE hyphenation include the minute volumes of sample injected (typically a few nL) and small flow-rates (in the order of nLmin-1). Interfaces are not commercially available. CZE-UV can be used for the analysis of higher polyamide oligomers in HF1P solution [859]. A solvent elimination design with nebuliser has been described for CE-FTIR and CEC-FTIR coupling absolute detection limits are hundreds of pg [860]. An advantage of CE-FTIR is that analytes may be detected and identified without derivatisation. CE(C)-NMR [861-863] is advancing rapidly. 

Plasma sources were developed for emission spectrometric analysis in the late-1960s. Commercial inductively coupled and d.c. plasma spectrometers were introduced in the mid-1970s. By comparison with AAS, atomic plasma emission spectroscopy (APES) can achieve simultaneous multi-element measurement, while maintaining a wide dynamic measurement range and high sensitivities and selectivities over background elements. As a result of the wide variety of radiation sources, optical atomic emission spectrometry is very suitable for multi-element trace determinations. With several techniques, absolute detection limits are below the ng level. 

Modem trace analysis is interested in detailed information about the distribution of elements in microareas and their chemical binding forms (specia-tion). The limited sample mass implies methods with absolute detection limits as high as possible. Use of the sputtering process as a sampling technique localises the analytical zone at the outer layers of a solid, and allows analysis to progress into the interior. 

With the exception of GC-MIP-AES there are no commercial instruments available for speciation analysis of organometallic species. Recently, a prototype automated speciation analyser (ASA) for practical applications was described [544,545], which consists of a P T system (or focused microwave-assisted extraction), multicapillary GC (MC-GC), MIP and plasma emission detection (PED). MCGC-MIP-PED provides short analysis times ([Pg.676]

Table 8.80 shows the present status of speciation methodology. For trace-metal speciation, atomic absorption detectors feature a relatively high absolute detection limit (10 pg level), as compared to the 0.1 to 1 pg sensitivity level for molecular ion MS techniques as well as for MIP-AES. The detection limit of LEI-ToFMS is in the attogram range. Speciation has been reviewed [550]. Various monographs deal with speciation analysis [542,551,552]. 

FIGURE 25.6 Amounts of lutein present (pmole/mm2) in yellow, black, and white epidermal samples from nine individual animals. Each value is the combined result of analysis of between 3 and 8 punches from a single animal providing samples ranging from 0.39 to 1.7 mm2. The absolute detection limit of the HPLC for carotenoids was O.lpmole. The black sample for animal 3 was lost during analysis. 

Sturgeon et al. [59] have described a hydride generation atomic absorption spectrometry method for the determination of antimony in seawater. The method uses formation of stibene using sodium borohydride. Stibine gas was trapped on the surface of a pyrolytic graphite coated tube at 250 °C and antimony determined by atomic absorption spectrometry. An absolute detection limit of 0.2 ng was obtained and a concentration detection limit of 0.04 pg/1 obtained for 5 ml sample volumes. 

Soo [96] determined picogram amounts of bismuth in seawater by flameless atomic absorption spectrometry with hydride generation. The bismuth is reduced in solution by sodium borohydride to bismuthine, stripped with helium gas, and collected in situ in a modified carbon rod atomiser. The collected bismuth is subsequently atomised by increasing the atomiser temperature and detected by an atomic absorption spectrophotometer. The absolute detection limit is 3pg of bismuth. The precision of the method is 2.2% for 150 pg and 6.7% for 25 pg of bismuth. Concentrations of bismuth found in the Pacific Ocean ranged from < 0.003-0.085 (dissolved) and 0.13-0.2 ng/1 (total). 

In this method, inorganic lead in seawater samples are converted to tetra-ethylead using sodium tetraethylboron (NaB(C2H5)4) which is then trapped in a graphite furnace at 400 °C. Quantitation is achieved by using a simple calibration graph prepared from aqueous standards. An absolute detection limit of (3relative standard deviation. 

Sample volume Precision Accuracy Absolute detection limit Relative detection limit Organic solvent consumption Equipment cost Cost of supplies Manual labor Automation Preparative... 

Lobinski et al. [72] optimized conditions for the comprehensive speciation of organotin compounds in soils and sediments. They used capillary gas chromatography coupled to helium microwave induced plasma emission spectrometry to determine mono-, di-, tri- and some tetraalkylated tin compounds. Ionic organotin compounds were extracted with pentane from the sample as the organotin-diethyldithiocarbamate complexes then converted to their pentabromo derivatives prior to gas chromatography. The absolute detection limit was 0.5pg as tin equivalent to 10-30pg kg-1. 

The ionic tin compounds were extracted as diethyldithio-carbamates into pentane then converted to pentyl magnesium bromide derivatives prior to gas chromatography. The absolute detection limit was 0.05pg tin, equivalent to 10-30ng kgy1. 

The thiohydantoin derivatives of amino acids obtained from 4-(4-dimethyaminophenyl-azo)phenyl isothiocyanate (141) and fluorescein isothiocyanate (133) can be separated by CZE. Lowering the absolute detection limits of thiohydantoin derivatives of the amino acids is a basic requirement for the development of highly sensitive protein sequencer based on Edman-like processes. Thus, the absolute LOD of thiohydantoin derivatives are at present of the order of 1CT16 mol for 141 and 10-21 mol for 133331. 

Joannon and Pin.50 A low detection limit was achieved in quadrupole ICP-MS when the pressure in the interface was reduced from approx. 2 to 0.85 mbar. Lariviere et al.51 developed a selective extraction procedure for the preconcentration of 226Ra from uranium ores and biological samples. The measurements were performed by ICP-QMS with a hexapole collision cell in order to reduce possible interferences. An absolute detection limit of 0.02 fg (0.75 mBq) was obtained using less than 4 mg of solid sample or 25 ml of liquid sample. 

Fig. 29.10.2 Chromatograms of ivermectin. A, Absolute detection limit (250 pg) B, standard solution (3.6 ng) C, blank meat sample D, spiked meat sample (22.5 ppb). (From Ref. 351.).

Table 6 Absolute Detection Limits (DLs) of Fat-Soluble Vitamins Using Standard-Bore (4.0-mm-ID) and Narrow-Bore (2.0-mm-ID) Columns and UV Detection...

A further study by Vela and Caruso [128] evaluated the effects of interface temperature, oven temperature, C02 pressure, mobile phase composition and column length in order to optimise the separation of several tetra and tri organotin compounds. The same interface, described by Shen [127], was used. It was found that the introduction of C02 did not require nebuliser flow-rate and RF power optimisation if the ion lenses were tuned sufficiently. The addition of a polar solvent to the non-polar mobile phase did not yield any improvement in resolution. Longer columns were found to yield broader chromatographic peaks. Absolute detection limits for TBT, tributyltin chloride, triphenyltin chloride and TPT were in the range 0.20-0.80 pg Sn. 

Iron-containing compounds in biological and clinical samples have been studied by separating them on chromatographic columns that were coupled to inductively coupled plasma mass spectrometers. Four iron-containing proteins, namely ferritin, haemoglobin, myoglobin and cytochrome-c were separated on a gel permeation column (Takatera and Watanabe, 1991). The absolute detection limits were 0.01-1 mg for the four proteins when 10 ml injections of samples were analysed. In other research, excess iron accumulations in human and animal... 

The absolute detection limit for manganese was 8-22pg for various organomanganese compounds including methyl cyclopentadienyl manganese tricarbonyl. 

Some absolute detection limits are shown in Table 9-3. 

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