Limit of quantitative determination

From eqs. (15.2) and (15.3) it is evident that the limits of quantitative determination depend on the cross section a of the nuclear reaction, the flux density 0 of the projectiles and the ratio f/fi/2 (time of irradiation to half-life). 

The elements Be, B, C, which are not activated by irradiation with thermal neutrons, can also be determined by charged particle activation. Limits of quantitative determination down to the order of about 1g/g can be achieved. The same holds for F which gives a nuclide of short half-life ( °F, fj/2 = 11 s). 

Table II. Comparison of Trace Element Concentrations for Human Urine with ICP—AES Limits of Quantitative Determination...

Element Range of Reported C oncentrations" (ng/mL) Model Urine Concentration (ng/mL) Limit of Quantitative Determination (ng/mL)... 

The limit of quantitative determination is defined as the least concentration of the analyte which can be determined with an expected precision of 10%. The values reported here are equal to five times the experimental limit of detection, CL(3Sbi), for the elements in 1% nitric-acid solution (P). 

The state of the art with respect to the potential of ICP-AES for the determination of trace elements in urine can be assessed by comparing the model concentration and range of concentrations for each of the elements (computed from the data in Table I) to the corresponding experimental limit of quantitative determination (LQD) for that element in aqueous solutions with 1% (vol) nitric acid, as is done in Table II. If the trace element concentrations in urine are as shovm in the table, and if the LQDs which can be achieved for urine samples are not substantially different from those observed for 1% nitric acid solutions, then ICP-AES should be applicable for the quantitative determination of many of the trace elements occurring in urine. 

Many impurities can be detected at the 1-10 ng/g level in simple systems. However, the limit of quantitative determination in practical... 

The method limit of quantitation and limit of detection must be determined as well as the limit of linearity. The limit of quantitation is defined as the level at which the measurement is quantitatively meaningful the limit of detection is the level at which the measurement is larger than the uncertainty and the limit of linearity is the upper level of the measurement rehabihty (39). These limits are determined by plotting concentration vs response. 

Limit of quantitation The smallest quantity of an analyte that can be determined with accuracy and precision. 

Determine the limit of detection LOD and limit of quantitation LOQ according to the interpolation at level y = a + CL of the regression line and its lower CL this is sensitive to the calibration-point pattern ... 

The limit of determination [or limit of quantitation (LOQ)] is defined in Directive 96/46/EC as the lowest concentration tested at which an acceptable mean recovery (normally 70-110%) and acceptable relative standard deviation (normally <20%) are obtained. The specific requirements for LOQ in crops, food, feed, soil, drinking and surface water, air, body fluids, and tissues are described in Section 4. Because the abbreviation LOD usually means limit of detection rather than limit of determination, the authors prefer not to use this abbreviation here in order to avoid confusion, and LOQ is used throughout. According to Directive 96/46/EC no data with regard to the limit of detection must be given. 

Each commodity required a specifically customized workbook, containing a worksheet for each analyte determined in the commodity. Each laboratory received electronic copies of either three or four workbooks, which served as templates for the three or four commodities assigned to the laboratory. Each set of up to 10 commodity samples scheduled for colleetion and analysis required the creation of a copy of the appropriate template. Each workbook template contained one primary worksheet for each analyte, in which analytical data were recorded and residue levels were calculated, as described below. Eor example, the template for green beans contained 17 primary worksheets, one for each of the 17 analytes determined in each green bean sample. Additional worksheets were inserted into copies of the template as needed, to describe results of further analyses, such as confirmation of analytes present above the limit of quantitation (LOQ) or dilutions to bring the concentration of the analyte into the calibration range. 

Sensitivity is a measure of the smallest concentration that can be either measured [limit of detection (LOD)] or accurately quantitated [limit of quantitation (LOQ)]. In the USA, the method for measuring LOD or LOQ is left up to the method developer. European requirements for determining LOD and LOQ are very specific the LOD is based on the mean plus three standard deviations for 20 control blank samples, and the LOQ is defined as the lowest concentration giving an acceptable CV. 

The limit of detection (LOD) and limit of quantitation (LOQ) were statistically determined in alfalfa and clover raw agricultural commodities (rotational crops). The method LOD and LOQ for the EMA-producing metabolite were 0.004 and 0.012 mg kg respectively, and the LOD and LOQ for the HEMA-producing metabolite were 0.004 and 0.014mgkg respectively, for the alfalfa and clover... 

Determination and evaluation, recoveries, limit of detection, limit of quantitation and calculation of residues... 

Wheat samples are extracted with dilute ammonia on the ASE200. The extracts are amended with isotopically labeled internal standards. The extracts are purified by sequential octadecyl reversed-phase solid-phase extraction (Cig SPE) and ethylenediamine-iV-propyl anion exchange (PSA) SPE. The samples are analyzed by LC/MS/MS. This method determines crop residues of flucarbazone-sodium and A-desmethyl flucarbazone with a limit of quantitation (LOQ) of 0.01 mgkg for each analyte. 

In some cases, a limit of quantitation (quantification) may need to be considered where it is necessary not only to detect the presence of an analyte but also to determine the amount present with a reasonable statistical certainty. The limit of quantitation of an individual analytical procedure is the smallest amount of an analyte in a sample, which can be quantitatively determined with acceptable uncertainty. More detail can be found in Section 4.6.4. 

Method validation is defined in the international standard, ISO/IEC 17025 as, the confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use are fulfilled. This means that a validated method, if used correctly, will produce results that will be suitable for the person making decisions based on them. This requires a detailed understanding of why the results are required and the quality of the result needed, i.e. its uncertainty. This is what determines the values that have to be achieved for the performance parameters. Method validation is a planned set of experiments to determine these values. The method performance parameters that are typically studied during method validation are selectivity, precision, bias, linearity working range, limit of detection, limit of quantitation, calibration and ruggedness. The validation process is illustrated in Figure 4.2. 

The limit of quantitation (LoQ) is the lowest concentration of analyte that can be determined with an acceptable level of uncertainty. This should be established by using an appropriate reference material or sample. It should not be determined by extrapolation. Various conventions take the approximate limit to be 5, 6 or 10 times the standard deviation of a number of measurements made on a blank or a low-level spiked solution. 

Accuracy, precision, and linearity of standards — The linear dynamic range was established as 10.22 pg/mL to 2.037 ng/mL with coefficient of determination (r2) below 0.996190 when using 1/x2 weighing for three consecutive accuracy and precision runs. The lower limit of quantitation (LLOQ) was accurate (inter-run mean bias = 1.1%) and precise (inter-run mean CV = 14.1%). Three levels of QCs were prepared. The inter-run mean bias varied from -4.3 to 1.0% and the inter-run mean CV varied from 4.6 to 6.6% for all QC levels. 

Another example of a well-designed method for the quantitative XRPD determination of polymorphs was developed for the phase analysis of prazosin hydrochloride [49]. As an example of an XRPD method for the determination of solvatomorphs, during the quantitation of cefepine dihydrochloride dihydrate in bulk samples of cefepine dihydrochloride monohydrate, a limit of detection of 0.75% w/w and a limit of quantitation of 2.5% w/w were associated with a working range of 2.5-15% w/w [50],... 

---