LOQ

Apparatus 100-ml round-bottomed flask with a stopper, and shaking machine (vibrator), or a lOQ-ml round-bottomed flask with a mechanical stirrer. 

The smallest concentration or absolute amount of analyte that can be reliably determined (LOQ). 

As shown in Figure 4.12c, the limit of identification is selected such that there is an equal probability of type 1 and type 2 errors. The American Chemical Society s Committee on Environmental Analytical Chemistry recommends the limit of quantitation, (Sa)loq> which is defined as ... 

Limit of quantification (LOQ) The smallest amount of contaminant that can be... 

Figure 5.67 Reconstructed ion chromatograms for Idoxifene and internal standard (ds-Idoxifene using LC-ToF-MS for (a) double-blank human plasma extract, (b) extract of blank human plasma containing internal standard (IS), and (c) control-blank human plasma spiked with Idoxifene at 5 gml , the LOQ of the method. Reprinted from 7. Chromatogr., B, 757, Comparison between liquid chromatography-time-of-flight mass spectrometry and selected-reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of Idoxifene in human plasma , Zhang, H. and Henion, J., 151-159, Copyright (2001), with permission from Elsevier Science.

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

Signal is replaced by the calculated analyte concentration Xlod at LOD resp. LOQ... 

Figure 4.7. Consequences for the case that the proposed regulation is enforced The target level for an impurity is shown for several assumptions in percent of the level found in the official reference sample that was accepted by the authorities. The curves marked A (pessimistic), B, and C (optimistic) indicate how much the detected signal needs to be below the approved limits for assumptions concerning the signal-to-noise relationship, while the curves marked 1-3 give the LOQ in percent of this limit for LOQs of 0.02, 0.01, resp. 0.005. The circle where curves B and 1 intersect points to the lowest concentration of impurity that could just be handled, namely 0.031 %. The square is for an impurity limit of 0.1%, for which the maximal signal (<= 0.087%) would be just a factor of = 4.4 above the highest of these LOQs.

Table 4.12. Accepted and Target Impurity Concentrations (Target Concentrations for Impurities, Under Assumption of the Regression Line in Fig. 4.7 (B a = 0.92, b = -0.743, m = 1) If the LOQ of the Method were 0.03%, the Target Concentration in the Last Line (0.011) Would he Inaccessible to Measurement ...

Consequences While this may still appear reasonable, lower accepted impurity limits AIL quickly demand either very high m or then target levels TL below the LOQ, as is demonstrated in Fig. 4.7. If several impurities are involved, each with its own TL and AIL, the risk of at least one exceeding its AIL rapidly increases (joint probabilities, see Section 4.24). For k impurities, the risk is [1 - (1 - 0.05) ], that is for k = 13, every other batch would fail ... 

Situation and Criteria A method was to be developed to determine trace amounts of cyanide (CN ) in waste water. The nature of the task means precision is not so much of an issue as are the limits of detection and quantitation (LOD, LOQ), and flexibility and ease of use. The responsible chemist expected cyanide levels below 2 ppm. 

Legend No number of measurement. Cone concentration in fig, CN"/100 ml Absorb absorbance [AU] slope slope of regression line t CV intercept see slope res. std. dev. residual standard deviation Srts -n number of points in regression LOD limit of detection LOQ limit of quantitation measurements using a 2-fold higher sample amount and 5-cm cuvettes—i.e., measured absorption 0. .. 0.501 was divided by 10. 

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