Upper limit of quantitation

Quality Control (QC) QC samples are used to check the performance of the bioanalytical method as well as to assess the precision and accuracy of the results of postdose samples. QC samples are prepared by spiking the analyte of interest and the IS into a blank/control matrix and processing similar to the postdose samples. QC samples cover the low (3 x LLOQ LLOQ = lower limit of quantitation), medium, and high (70-85% of ULOQ ULOQ = upper limit of quantitation) concentration ranges of the standard curve and are spaced across the standard curve and the postdose sample batch. 

VS/QCs should be prepared independently from the standard calibrators. Five or more levels of VS, including the low limit of quantitation (LLOQ), low, mid, high, and upper limits of quantitation (ULOQ) concentrations are often prepared. 

For all practical purposes, the upper limit of quantitation is the point where the calibration curve becomes nonlinear. This point is called the limit of linearity (LOL). These can be seen from the calibration curve presented in Figure 1.3. Analytical methods are expected to have a linear dynamic range (LDR) of at least two orders of magnitude, although shorter ranges are also acceptable. 

It is generally believed that as long as the same amount of an internal standard is added to all the samples in a batch (run), i.e., calibration standards, quality controls, and unknown samples, the concentration of an internal standard is not important. This is probably why not much information exists as how to determine an appropriate concentration for an internal standard. Some researchers proposed that the concentration of an internal standard should be approximately half of the upper limit of quantitation (ULOQ) of the analyte [13,14] or even higher than the ULOQ [2], while others suggested a relatively lower concentration corresponding to about the first third of the calibration range, in order to minimize potential interferences with the analyte due to potential impurities from SIL internal standards [15]. Unfortunately, none of these were followed by more detailed theoretical considerations or supporting experimental data. 

The quantitative abilities of the LC-TOF, although limited in the linear dynamic range, often allow measurement of metabolic profiles and PK profiles from the same samples. Zhang and co-workers [37] provide such an example. Quantitative results for a co-administration of five compounds to rats, with assay limits of quantitation (LOQ) between 1 and 5 ng/mL, and an upper limit of quantitation (ULQ) at 100 ng/mL were described. In this study, precision and accuracy were better than 20% for all five analytes, and comparable to triple-quadrupole quantitative data. More importantly, in addition to following the levels of dosed compound, the authors were able to identify several metabolites from the same full-scan data using the accurate mass capabilities ofthe LC/TOF-MS. 

Upper limit of quantitation (ULOQ) The highest concentration of an analyte in a test sample that can be determined quantitatively with suitable... 

At least three sets of QCs representing the entire range of the calibration (standard) curve are included low, medium, and high QC. The low QC sample often serves also as the LLOQ, and the high QC as the upper limit of quantitation (ULOQ) both of which can be measured with acceptable accuracy and precision. 

The lead electrode is sensitive to surface oxidation and requires periodical repoHshing. The linear response for the primary cation usually extends from 10 to 10 moll the detection limit is 10 moll . These statements hold only in the optimal pH range of 4—7. At higher pH values the formation of the hydroxides of the divalent metals reduces the upper limit of quantitation. At lower pH the solubility of the sulfides increases and this raises the lower detection limit. The selectivities over alkaH and alkaline earth metal ions are very good. 

Lower and Upper Limits of Quantitation (LLOQ and ULOQ) The lowest and highest analyte amounts (or concentrations) that can be quantified to witbin prespecified criteria (Section 8.4.2) for accuracy and precision correspond to lowest and highest points on the calibration curve, the LLOQ is sometimes referred to as the LOQ. 

A related problem concerns a scientifically defensible definition of the lower limit of quantitation (LLOQ). This is sometimes referred to simply as the LOQ but in fact the upper limit of quantitation (ULOQ) can also be an important parameter for validated analytical methods (see Chapter 9). A very important definition of LLOQ is that of the US FDA with regard to bioan-alytical data used in human clinical pharmacology and in bioavailabihty and bioequivalence studies requiring pharmacokinetic evaluation (FDA 2001) this guidance also applies to bioanalytical methods used for non-human pharmacology-toxicology studies and preclinical studies. According to this protocol, the LLOQ is accepted as the lowest standard on the cahbration curve provided that (a) the analyte response for this concentration (amount)... 

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. 

The translation model was refined and developed further in a later article (Lehmann and Kuhn, 1984). It is assumed that in the early stages of evolution, guanosine and cytidine were the most important building blocks for RNA syntheses, as they allow strong base pairing (via three hydrogen bonds). Quantitative considerations lead to an upper limit of about 50 nucleotides for a reasonable chain length. 

The upper limit depends quantitatively on the viscosity that can be processed through the casting fixtures in reasonable time. Too high a viscosity may also lead to problems under certain flow conditions as, for example, when propellant folds over on itself to form a void space which may remain as a defect in the cured grain. If the propellant grain is to be formed and cured by screw extrusion, however, somewhat higher viscosities can be handled. A viscosity of 1600 poise has been reported (9) for a PVC plastisol propellant processed this way. 

Though there is good evidence, as summarised above, of LCB in poly(vinyl chloride), there is as yet little quantitative information. Lyngaae-Jorgensen (201) has found that the ratio Aiw/Mn does not much exceed 2.0, and has used this quantity to set an upper limit of 2 x 10" 4 long branches per repeat unit for material polymerized at 55° C (conversion not stated). He has used light-scattering and GPC techniques to obtain an upper limit of 6 x 10-4 branches per repeat unit in commercial samples of this polymer (202). 

Intra-laboratory CVs range from 9.9% for ethylmalonate (at 102 pmol/1) to 40.7% for suberylglycine (at 48.6 pmol/1) and inter-laboratory CVs from 42.5% for ethylmalonate (at 102 pmol/1) to 757.4% for tiglyglycine at 83.5 pmol/1. This wide variation is also accompanied by marked variability in the reference ranges used by different laboratories an example is shown (Fig. 1.2.1) for a single return from 18 respondents who quantitated ethylmalonate in a single sample (sample 109) and reported both the result and the upper limit of normal used by their laboratory. Clearly the clinical significance of this apparently extreme variability depends upon the clinical context... 

Lower Limit of Quantification (LLOQ) The lowest concentration of the analyte of interest in a matrix that can be quantitatively determined using the standard curve with acceptable precision and accuracy. The LLOQ is usually defined as the lowest concentration at which the assay imprecision does not exceed 20%. Upper Limit of Quantification (ULOQ) The highest concentration of an analyte in a matrix that can be quantitatively determined using the standard curve with an acceptable precision and accuracy. If the analyte concentrations in the postdose samples are higher than the ULOQ, then a dilution QC is needed to cover the highest anticipated dilution. 

Nearly all heterotrophic denitrifiers are facultative anaerobes (Tiedje, 1988). Although various workers defined suboxia differently, the upper limit of oxygen concentration for the occurrence of denitrification is probably 5 pM, with quantitatively most denitrification in the marine environment taking place below about 2 pM (Cline and Richards, 1972 Codispoti et al., 2005 Devol, 1978 Murray et al., 1995). The ability to denitrify is not limited to the bacteria, archea and even some fungi are capable of denitrification (Knowles, 1996 Zumft and Korner, 1997). 

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