Relative detection limits

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

Figure 14.17—Relative detection limits of the main present methods in trace element analysis.

RELATIVE DETECTION LIMITS OF HALOETHYL ESTERS OF 4-CHLORO-2-METHYL-PHENOXYACETIC ACID (MCPA) AND 2,4-DICHLOROPHENOXYACETIC ACID (2,4-D) WITH THE USE OF ECD [500]... 

D7. Dawson, J. B., and Tucker, B. D., Relative detection limits in emission, absorption and fluorescence flame photometry. Int. Colloq. Spectrosc., 16th, Heidelberg 2, 347-351 (1971). 

Serum copper analysis was performed using a Perkin-Elmer atomic absorption spectrophotometer. Model 308. The previously described method by Prasad (136) was used after slight modification. For protein precipitation we used 7.5% trichloroacetic acid instead of 2N HCl used by Prasad. Analytical sensitivity for copper with this method was 0.2 jxg/ mL for 1% absorption and a relative detection limit of 0.005 fig/mL, Recovery studies done by adding known amounts of copper to the serum ranged between 96-104%. Analysis for ceruloplasmin was made by using commercially available immunodiffusion plates (Hyland, Inc. normal range, 20-35 mg/100 mL). Precision of the method has been tested by running 20 determinations for both copper and ceruloplasmin on one aliquot. CoeflBcient of variation did not vary by more than 3-5%. All samples were run in duplicates. 

Tab. 17.1 The most frequently used methods for quantification of mercury and their relative detection limits, adopted from Horvat (1996)...

Tab. 2.5 Typical relative detection limits (DL XgL or J,gl

Table 3 summarizes relative detection limits for the analytical methods mainly used at present, based on the arsenic concentration in a liquid analyte, in an analyte solution after... 

RELATIVE DETECTION LIMITS FOR ARSENIC USING VARIOUS ANALYTICAL METHODS... 

Mercury was included in a thorough review of XRF techniques in clinical studies (Leyden and Noddy, 1977). For normal XRF analysis of 1 g of dried soft tissue, the lower limit of detection was found to be a few mg/kg. For PIXE, the relative detection limits in biological material are in the order of a few tenths of mg/g. For soft tissue analysis, this is normally orders of magnitude too high, compared with "normal" levels of mercury. Thus, the X-ray techniques must be combined with a preconcentration stage. Preconcentration techniques prior to mercury determination means serious risks of losses due to the volatility. To minimize such losses, lenient concentration procedures, e.g. low temperature ashing (Pallon and Malmqvist, 1981), are required. 

In Table Ib [16] absolute rather than relative detection limits are compared for several techniques. Unless one looks at the footnotes however, it is not obvious that the detection limit for one method is based on a 1 pL sample size, another on a 5 pL sample size and another on a 1 mL sample size, thus biasing the careless observer of this table by 2 to 3 orders of magnitude. 

Relative detection limits are useful figures-of-merit for bulk XRF equipment, where it is usually relevant to know the lowest concentration level at which the spectrometer can be used for qualitative or quantitative determinations. In instalments where very small sample masses are being irradiated (e. g., in the pg range for microscopic XRF (p-XRF) and total-reflection XRF (TXRF)), the absolute detection limit is another useful figure-ofmerit since that provides information on the minimal sample mass than can be analysed in a given set-up. 

Table 11.3 WDXRF obtained relative detection limits (in ig g ) in various matrixes and using different instruments.

In Fig. 11.20, the spectra that result from direct excitation, secondary excitation and polarized direct excitation of a standard oil sample are compared, containing 21 elements at the 30 gg level. The relative detection limits obtained from the three spectra are summarized in Tab. 11.6 they indicate that the DL values by means of polarized excitation are on average 5 times better than those determined with direct excitation. The secondary target results are better by a factor of 2.5 than the polarized excitation values for elements efiSdently excited by the Mo-Ka line (e. g. Pb) however, elements such as Sn and Cd cannot be determined with the Mo secondary target while they are well excited by the polarized brems-strahlung radiation. 

In FES, the relative detection limit is defined as the concentration for which the intensity corresponds to twice the noise level. The absolute detection limit thus refers to the masses of this concentration. The... 

Flow-injection online preconcentration and separation with ion exchange or sorbent extraction in packed microcolumns and/or precipitation and collection in knotted reactors has proved to extend the capabilities of ET-AAS by allowing relative detection limits to be lowered by two to three orders of magnitude and troublesome matrices to be removed. 

In typical setups available relative detection limits (DL) are < 0.1 pg per g for elements of Z > 25 but DLs down to a few ppb are possible for quite a number of elements. Absolute DLs are < 1 fg for elements on the basis of a flux in the focused beam of 10 -10 pho-tonss . For the measurement of elemental distribution maps, spectra are taken as the sample is moved over the beam path. Two-dimensional mapping of the... 

Relative detection limits with ID18F (see Fig. 34.1) using a 100 component compound reflective lens set at 21 keV in a biological material (NIST SRM 1577a, bovine liver) and in NIST 613 glass SRM... 

The analytical characteristics (degree of polarization, absolute and relative limits of detection) of ID18F were determined bymeasuringa number of existing certified reference materials (CRMs). The degree of polarization is >99.5%. The available relative detection limits (DL) are <0.1 ppm for elements of Z > 25. Relative DLs down to a few ppb are possible for a number of elements on the basis of 1,000 s live time measurements and ppm DLs can be reached for measurements of a few seconds. The absolute DLs are less than 1 fg for elements of Z > 25. 

In PIXE analysis, using proton beam of 1-3 MeV for most favored elements in low-Z matrices and think targets, the best sensitivities down to 0.1 ppm have been obtained. These levels are achieved for elements near Z = 40 using K lines and Z = 80 using L lines. For elements with Z valves different from 40 and 80 the LLDs increase rapidly to 100 ppm and are >100 ppm for Z < 20. For thick targets and Z < 20 most matrices yield LLDs that are generally lower than 100 ppm and can be as low as 1 ppm under favorable conditions (absolute detection limits down to 10 g and relative detection limit down to 0.1 p.gg ). Compared to XRF, the detection limit offered by PIXE is better by one order of magnitude. 

Also shown in Fignre 1.4 are the relative detection limit ranges for SIMS when operated in both its Static and Dynamic modes, as well as the detection limits... 

Relative detection limits achieved by the described atomization techniques are presented in Table 2. 

Table 2 Selected relative detection limits (pg L- ) for different atomization techniques ...

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