Hmit of quantitation

The limit of detection, hmit of quantitation, precision and accuracy can then be determined. 

The properties of the periodic surfaces studied in the previous sections do not depend on the discretization procedure in the hmit of small distance between the lattice points. Also, the symmetry of the lattice does not seem to influence the minimization, at least in the limit of large N and small h. In the computer simulations the quantities which vary on the scale larger than the lattice size should have a well-defined value for large N. However, in reality we work with a lattice of a finite size, usually small, and the lattice spacing is rather large. Therefore we find that typical simulations of the same model may give diffferent quantitative results although quahtatively one obtains the same results. Here we compare in detail two different discretization... 

B.4.2.2 Nonbenzodlazeptnes GG-NPD was used by Kivisto et al. (1999) to quantitate the nonbenzodiazepine anxiolytic buspirone and its major metabolite, l-(2-pyrimidinyl)-piperazine, using separate extraction methods and separate assays. The hmit of quantification in plasma for both compounds was 0.2 ng/mL, which makes this assay useful for pharmacokinetic studies of this compound (Kivisto et al., 1999). A rapid, simple method for analysis of buspirone in rat brain requiring a single extraction step followed by GC-NPD has also been described (Lai. et al., 1997). 

Recently, a novel immunoassay has been developed for the quantitative determination of polybrominated biphenyls using indirect competitive format. The new method was optimized concenung the coating conjugate and antibody concentration, incubation time and temperature, the tolerance to organic solvents and so on. Under optimized conditions, PBB15 can be determined in the concentration range of 0.01-100 pg/L with a detection hmit of 0.02 pg/L. The cross-reactivities of the assays were below 8%. While water samples could be analyzed directly [94]. 

Two main types of analysis are required (a) qualitative determination of the presence of elements and (b) quantitative determination of the amount of elements or species of interest contained in pharmaceutical products. Most analyses for pharmaceutical applications involve separation steps combined with ICP-MS, such as HPLC-ICP-MS or gel electrophoresis and the analysis of gel blots by LA-ICP-MS. Phosphorylated proteins (e.g., (J-casein) have been measured by LA-ICP-MS with a detection hmit of 16 pmol. HPLC-ICP-MS has been employed for the identification and quantification of metabohtes of bradykinin in human and rat plasma. ... 

The main disappointment that appears in Table V is that the experimental limits of detection for the analytes in the 1% NaCl matrix and in the urine samples were approximately one order of magnitude greater than had been observed previously for 1% HNO3 solutions and for solutions containing both 1% NaCl and 1% HNO3 (2). We are at a loss to explain the apparent conflict of these observations. The unexpectedly high hmits of detection substantially reduced our expected capabihty for the quantitative determination of the normal levels of these analytes in urine. 

There are no official guidehnes on the sequence of validation experiments and the optimal sequence can depend on the method itself. A potentially useful sequence for a liquid chromatographic method is 1) Selectivity of standards (optimizing separation and detection of standard mixtures) 2) precision of retention times and peak areas 3) linearity, limit of quantitation, hmit of detection, range 4) selectivity with real samples 5) trueness or accuracy, at different concentrations 6) ruggedness. 

The ciurrent-time relationship can be evaluated for area within the hmits of the initial time and the time to reach quantitative completion by an integrator. It is apparent that the result will be obtained from ... 

ESI, triazines) [537]. Recoveries observed were > 80% except for carbendazim, bu-tocarboxim, aldicarb and molinate, all better than 67% [500]. An aoTOF-MS interfaced by ESI was used to screen and identify unknown compounds and pesticides in water samples by MS and MS/MS. Structures for compounds observed besides pesticides were proposed [538]. Traces of the phenylurea pesticides Hnuron and monolinuron in water were determined quantitatively. Calibration graphs obtained after Supelclean ENVI-18 SEE were Hnear with detection limits < 25 pg [511]. Large numbers of phenylurea herbicide analyses led to the elaboration of on-line preconcentration techniques coupled to ESI-LC-MS. The procedure was demonstrated and validated with several pesticides using 10 ml of sample, resulting in detection Hmits of about 10 ng [539]. ESI-LC-MS and MS/MS were applied to quantify and to confirm 16 different herbicides of sulfonylurea [527] type in surface water samples. Surface water samples were extracted by SPE (Spe-ed RP-102). As confirmation criteria RT, molecular ion and two fragment ions besides ion abundance ratios were defined. Quantitation at 0.1 and 1.0 ppb level was demonstrated [540]. 

For any analytical procedure, it is important to establish the smallest amount of an analyte that can be detected and/or measured quantitatively. In statistical terms, and for instrumental data, this is defined as the smallest amount of an analyte giving a detector response significantly different from a blank or background response (i.e. the response from standards containing the same reagents and having the same overall composition (matrix) as the samples, where this is known, but containing no analyte). Detection limits are usually based on estimates of the standard deviation of replicate measurements of prepared blanks. A detection hmit of two or three times the estimated standard deviation of the blanks above their mean, Xg, is often quoted, where as many blanks as possible (at least 5 to 10) have been prepared and measured. 

Limit of quantitation, unhke the hmit of detection, the limit of quantitation is confirmed by the... 

Test methods used in the laboratory are generally derived from pharmacopoeias such as the US Pharmacopoeia, British Pharmacopoeia, or European Pharmacopoeia. For test methods that are not from recognized pharmacopoeias, validation of the analytical methods is required. The validation includes testing for accuracy, specificity, ruggedness, robustness, precision, detection limit, quantitation hmit, and range. A discussion of analytical methods vahda-tion is presented in Section 9.6.5. 

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