Limit of detection, LOD

Limit of detection (LOD) The smallest amount of contaminant that can be reliably detected by a particular analytical method. 

Limit of Detection (LOD) The minimum concentration of a substance being measured that, in a given matrix and with a specific method, has a 99% probability of being identified, qualitatively or quantitatively measured, and reported to be greater than zero. 

The limit of detection (LOD) (see Figure 2.6) is defined as the smallest quantity of an analyte that can be reliably detected. This is a subjective definition and to introduce some objectivity it is considered to be that amount of analyte which produces a signal that exceeds the noise by a certain factor. The factor used, usually between 2 and 10 [11], depends upon the analysis being carried out. Higher values are used for quantitative measurements in which the analyst is concerned with the ability to determine the analyte accurately and precisely. 

Table V. Comparison of Limits of Detection (LOD) for Dansyl and NDA Derivatives Employing Fluorescence and Chemiluminescence Detection for RP-HPLC...

Different concepts of limit of detection (LOD) have been advanced over... 

Figure 2.14. The definition of the limits of detection, LOD, respectively quantitation, LOQ (schematic).

Figure 2.15. The limit of detection LOD the minimum signal/noise-ratio necessary according to two models (ordinate) is plotted against log 0(n) under the assumption of evenly spaced calibration points. The three sets of curves are for p = 0.1 (A), 0.05 (B), and 0.02 (C). The correct statistical theory is given by the fine points, while the model presented here is depicted with coarser dots. The widely used S/N = 3. .. 6 models would be represented by horizontals at y = 3. .. 6.

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 required limit of quantitation (LOQ) and limit of detection (LOD) have been extended to the parts per billion range as the European Community (EC) baby food -related guideline and the US consumer basket requirements became effective. 

Today, when a pesticide with no detectable residues is registered for use, a Tolerance or maximum residue limit (MRL) is established at the lowest concentration level at which the method was validated. However, for risk assessment purposes it would be wrong to use this number in calculating the risk posed to humans by exposure to the pesticide from the consumption of the food product. This would be assuming that the amount of the pesticide present in all food products treated with the pesticide and for which no detectable residues were found is just less than the lowest level of method validation (LLMV). The assumption is wrong, but there is no better way of performing a risk assessment calculation unless the limit of detection (LOD) and limit of quantification (LOQ) of the method were clearly defined in a uniformly acceptable manner. 

Several terms have been used to define LOD and LOQ. Before we proceed to develop a uniform definition, it would be useful to define each of these terms. The most commonly used terms are limit of detection (LOD) and limit of quantification (LOQ). The 1975 International Union of Pure and Applied Chemistry (lUPAC) definition for LQD can be stated as, A number expressed in units of concentration (or amount) that describes the lowest concentration level (or amount) of the element that an analyst can determine to be statistically different from an analytical blank 1 This term, although appearing to be straightforward, is overly simplified. If leaves several questions unanswered, such as, what does the term statistically different mean, and what factors has the analyst considered in defining the blank Leaving these to the analyst s discretion may result in values varying between analysts to such an extent that the numbers would be meaningless for comparison purposes. 

Adequate sensitivity should be demonstrated and estimates of the limit of detection (LOD) and the limit of quantitation (LOQ) should be provided. The slope of the calibration line may indicate the ability of the method to distinguish the tme analyte concentration. The LOD of a method is the lowest analyte concentration that produces a reproducible response detectable above the noise level of the system. The LOQ is the lowest level of analyte that can be accurately and precisely measured. For a regulatory method, quantitation is limited by the lowest calibration standard. The techniques for these estimations should be described. 

In addition, each workbook contained a summary table of all results and limit of detection (LOD) determinations. The table was organized with sample identifications in the left-hand column. Eor each analyte, the analytical result and the LOD appeared in adjacent columns, and analyte recoveries appeared above the results columns. The summary table was generated automatically from the analytical results in the individual worksheets, without operator intervention or re-entry of any information. 

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) is an important criterion of the efficiency of an analytical method. It is characterized by the smallest value of the concentration of a compound in the analytical sample. The detectable amount of anilide compounds is in the range 0.01-0.5 ng by GC and 0.1 ng by HPLC. The limit of quantitation (LOQ) ranges from 0.005 to 0.01 mg kg for vegetables, fruits and crops. The recoveries from untreated plant matrices with fortification levels between 10 and 50 times the LOD and the LOQ are 70-120%. The relative standard deviation (RSD) at 10-50 times the level of the LOD and LOQ are <10 % and <20%, respectively. 

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... 

Sulfonylureas are not directly amenable to gas chromatography (GC) because of their extremely low volatility and thermal instability. GC has been used in conjunction with diazomethane derivatization, pentafluorobenzyl bromide derivatization, and hydrolysis followed by analysis of the aryl sulfonamides. These approaches have not become widely accepted, owing to poor performance for the entire family of sulfonylureas. Capillary electrophoresis (CE) has been evaluated for water analysis and soil analysis. The low injection volumes required in CE may not yield the required sensitivity for certain applications. Enzyme immunoassay has been reported for chlorsulfuron and triasulfuron, with a limit of detection (LOD) ranging from 20 to 100 ng kg (ppt) in soil and water. 

The MDCs are estimated from an S/N of the diphenyl ether peaks of at least of 3 in the recovery test. With fortification levels between 0.2 and 0.5mgkg recoveries of bifenox from brown rice matrices ranged from 85 to 102% with the limit of detection (LOD) and limit of quantitation (LOQ) being 0.010 mg kg according to the analytical method of the Notification of the Ministry of the Environment, Japan. By the residue analysis method described in Section 2.2.2(3), recoveries of chlornitrofen and CNP-NH2 from brown rice and vegetables with fortification levels of 0.04-0.10 mg kg ranged from 82 to 98%. The LOD for each sample was 0.005 mg kg for chlornitrofen and CNP-NH2. ... 

This enforcement method has been validated on the (raw agricultural commodities) (RAC) and processed parts of various crops. The method limit of quantitation (LOQ) was validated at 0.05 mg kg and the method limit of detection (LOD) was set at 0.01 mgkg for all of the crop matrices. The method flow chart is presented in Figure 1. 

Because acceptable recoveries were obtained at O.Olmgkg", the method LOQ is 0.01 mg kg for flucarbazone-sodium and O.Olmgkg" for Af-desmethyl flucarbazone in all wheat samples. Linearity curves in both solvent and matrix blanks were mn from 0.005 to 0.100 mg kg . Because 0.005 mg kg of each analyte was reliably detected, the method limit of detection (LOD) was 0.005 mg kg in all wheat samples. 

For plant samples, the average recovery of flumioxazin from untreated confiol samples fortified within the range 0.1-0.01 mgkg ranged from 75 to 106%. The limit of quantitation (LOQ) is 0.01 mg kg and the limit of detection (LOD) is 0.005 mg kg. ... 

Method validation determined the limit of detection (LOD) to be 1 ngL (ppt) for isoxaflutole, 1 ngL for RPA 202248 and 3 ngL for RPA 203328. However, after experience with a number of surface waters with high levels of matrix components, the method LOD was increased to 3 ng L for all three analytes. RPA 202248 also proved to be particularly sticky and prone to carry over. Over time, this produced abackground level, which also prevented determinations below the 3ngL method LOD. 

Third, the bulk of the items in Table 1 address method performance. These requirements must be satisfied on a substrate-by-substrate basis to address substrate-specific interferences. As discussed above, interferences are best dealt with by application of conventional sample preparation techniques use of blank substrate to account for background interferences is not permitted. The analyst must establish a limit of detection (LOD), the lowest standard concentration that yields a signal that can be differentiated from background, and an LOQ (the reader is referred to Brady for a discussion of different techniques used to determine the LOD for immunoassays). For example, analysis of a variety of corn fractions requires the generation of LOD and LOQ data for each fraction. Procedural recoveries must accompany each analytical set and be based on fresh fortification of substrate prior to extraction. Recovery samples serve to confirm that the extraction and cleanup procedures were conducted correctly for all samples in each set of analyses. Carrying control substrate through the analytical procedure is good practice if practicable. 

For detection, MS is rapidly becoming the method of choice for multiclass, multiresidue analysis owing to its many advantages, recent improvements in technology, and availability of cost-effective commercial instrumentation. Detection systems in general are continually being improved, and in combination with the improvements in chromatographic instruments and techniques, an exceptionally low limit of detection (LOD) is possible for pesticide residues. 

The method has been validated in 22 different crop matrices at fortification levels from 0.01 to 0.5 mg kg Mean recoveries in each crop type ranged from 80 to 99% with the limit of detection (LOD) estimated to be 0.001-0.003 mg kg ... 

With fortification levels between 0.010 and 0.50mgkg, average recoveries from untreated plant matrices range from 78 to 106% with the limit of quantification (LOQ) and the corresponding limit of detection (LOD) of famoxadone being as follows ... 

Net recoveries of tebuconazole from matrices fortified at 0.01-7.0 mg kg ranged from 78 to 116%. The limit of detection (LOD) based on control interferences in matrices ranged from 0.001 to 0.01 mg kg. The limit of quantification (LOQ) based on recoveries was established at 0.01 mgkg ... 

With a fortification level of 0.1mgkg recoveries from untreated plant matrices ranged from 90 to 104%. The limit of detection (LOD) was 0.005 mg kg (fruits and vegetables). With regard to green tea (powder and leachate), the method recoveries were 95 and 98%, respectively, at the 0.5 mg kg fortification level. The LOD was 0.05mgkg ... 

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