Detection limits, reporting

Fluorescence detection, alone or with the aid of derivatizing reagents to enhance detector responses and improve the chromatographic resolution, has also been used for the determination of biogenic amines. Lakshmana and Trichur (1997) used native fluorescence to analyze NE, DA, and 5HT in rat brain utilizing an isocratic separation on an ODS CIS column. The detection limits reported were 100-250 pg on column. 

Table 11.3 gives detection limits reported for DOAS measurements of OH and the halogen oxide radicals at a path length of 5 km and assuming a detectable absorbance of 10 4. This method provides ppt to sub-ppt sensitivities for these radicals. 

Pulse polarographic studies have been described using a microcell of 0.5 mL capacity, which analyzed two 1,4-benzodiazepines, with the lowest detection limit reported to date being 10-20 ng/mL of blood [199]. Detailed construction of the cell and electrode assembly was also described (shown in Fig. 26.16). Further miniaturization of this type of three-electrode cell is not practical hence further increases in sensitivity will have to rely on electrochemical detector flow cells of microliter capacity such as those used in conjunction with liquid chromatography (see Chap. 27). 

Detection limits for 13 resolved PTH-amino acids ranged from 1.6 to 4.8.10 M, which was by a factor of ten superior to the detection limits reported for micellar electrokinetic chromatography [77]. Most of this improvement in detection limit is due to the higher thermo-optical enhancement produced by the high acetonitrile content in the buffer compared to the aqueous mobile phase used in the micellar electrokinetic separation. 

The detection limits reported were generally in excess of 5 ppt (3,17) due to interferences from substances not removed in the sample preparation. An additional, highly efficient separation step was employed to allow the lower detection limits required for meaningful determinations of TCDD in human milk. 

Comparisons with other systems. Data presented in Table VI provide a comparison of results obtained with the image dissector with results reported by others with other systems. Results in the second column represent multielement detection limits observed in this work. Results in the third and fourth columns represent detection limits reported for single element determinations with conventional optics and a silicon vidicon (12J and a commercial atomic absorption instrument (33). 

The multielement detection limits with the echelle/image dissector are comparable to, or better than, single element detection limits reported for a silicon vidicon and conventional optics. Detection limits for Cr, Cu, and Mn with the echelle/ image dissector compare favorably with single element data reported for a conventional atomic absorption instrument with a photomultiplier detector, but detection limits obtained here for Ni and Co are higher by factors of 10 or more than for the conventional instrument. The echelle/image dissector system should be adaptable to a so-called flameless atomizer and be subject to the same improvements in sensitivities and detection limits as conventional detector systems. 

Ocean floor sediment samples taken in 1971 from two munitions dumping areas located in the Pacific Ocean (85 miles west of Cape Flattery, Washington) and the Atlantic Ocean (172 miles south- southeast of Charleston, South Carolina) were analyzed for tetryl (Navy 1972). No tetryl was found in any of the sediment samples analyzed (no detection limit reported). 

Other analyses of oceanographic interest have been adapted to FI A. The detection limits reported for these analyses are often too high to be of use in oceanographic investigations. However, great improvements in detection limits can be made with the techniques just discussed. 

A schematic diagram of a typical LEI spectrometer is shown in Fig. 11. The bulk of LEI spectrometry and all of the detection limits reported in Fig. 2 have been accomplished using a premixed burner. In a premixed burner, the aspirated sample is mixed with the fuel and oxidant prior to combustion. A 10-cm slot burner head for acetylene-air has been used predominantly for LEI spectrometry 29 35) but results for a 5-cm... 

Detection limits reported by researchers or instrument companies may not apply to real samples. The values reported are usually obtained on ideal standards with optimized instruments. These limits are useful, however, in comparing methods or instruments. 

Based upon the previous procedure, Bellec et described a method for the separation and detection of volatile and nonvolatile A-nitrosamines with colorimetric detection by a Griess reagent of the nitrite generated by the cleave of nitroso compounds with a postcolumn photohydrolysis-UV photoreactor. The yield of the photohydrolysis depends upon pH and time of exposure under UV light. The detection limits reported were 8 pmol for A-diaUcylnitrosamines and 20 pmol for A-nitrosamines bearing two phenyl groups. 

An attempt is made to present an overall view of method detectivities, in Table 2.6, which lists an estimated intercomparison of detection limit-based method performance. For this purpose, for each method, over all elements, four measures were recorded and calculated range of the best detection limits reported, median of the population of best detection limits, range of the median detection limits reported and median of the median detection limits. By way of example, for the technique of... 

The active site of organophosphorus hydrolase (OPH) contains two metal atoms (zinc in the wild-type enzyme) and catalyzes hydrolysis of numerous organophos-phate compounds including pesticides as well as chemical warfare agents such as sarin and soman. Rates of OPH catalyzed hydrolysis of organophosphates exceed those of chemical hydrolysis by NaOH at 4°C by factors of 40 to 2450 [41-43]. The enzyme has been described for use in sensor systems with exceptional detection limits reported for response times on the order of 10 seconds [44-48]. However, the presence of OP/CWA is detected by the inhibition of enzymatic rate determined by comparing rate measnrements in the presence and absence of the analyte. 

The range of test kit applications, detection capabilities, and cross-reactivity profiles reported by the Biacore are shown in Table 5.7. The detection limits reported show the combination of the Biacore Q instrument and the QFlex kits to be very sensitive and capable of detecting the target analytes at concentrations below the current EU RLs or recommended concentrations (RCs) proposed by the EU CRTs. 

Table la. Detection Limits Reported for Atomic Absorption... 

In addition to the instrumental parameters normally optimized for solution nebulization, the laser ablation technique requires the optimization of the operation of the laser, the volume of the ablation chamber, and the transport distance from the chamber to the plasma. Detection limits reported in the literature indicate that microgram-per-gram determinations are possible. Precision obtained by laser ablation is somewhat degraded when compared to solution nebulization. For a number of different metal samples precisions between 3 and 11% (RSD) are obtained. The linearity of the calibration graphs is typically two or three orders of magnitude. Due to the nature of the laser beam, laser ablation is best suited for area-localized microanalysis. 

Some detection limits reported in the literature for hydride generation techniques are presented in Table 32. With respect to the detection limits published in the literature, hydride-plasma-AES is comparable with hydride-AAS, except for lead. Relative to solution nebulization, detection... 

Table 32 Some detection limits reported in the literature for volatile hydride-forming elements by continuous hydride generation technique and solution nebulization...

Table 34 Instrumental detection limits reported in the literature for some elements by ICP-MS using solution nebulization. (Sources A. L. Gray and A. R. Date, Analyst (London), 1983, 108, 1033 R. S. Houk, V. A. Fassen, G. D. Flesch and H. J. Svec, Anal. Chem., 1980, 52 2283 J. R. Garbarino and H. E. Taylor, Anal. Chem., 1987, 59, 1568)...

Slow Discharge Chamber. This is used for the analysis of solid metal samples. Atomization is produced by sputtering and intensive excitation radiation is focused onto the atom vapour formed. The fluorescence radiation produced is then detected at right angles to the incident radiation. The precision obtained has been about 2% for many metals and the detection limits reported have varied between 1 and 100 mgl . ... 

---