Sensitivity calibration

A sample was analyzed for the concentration of two analytes, A and B, under two sets of conditions. Under condition 1, the calibration sensitivities are... 

As can be seen from equation 8.14, we may improve a method s sensitivity in two ways. The most obvious way is to increase the ratio of the precipitate s molar mass to that of the analyte. In other words, it is desirable to form a precipitate with as large a formula weight as possible. A less obvious way to improve the calibration sensitivity is indicated by the term of 1/2 in equation 8.14, which accounts for the stoichiometry between the analyte and precipitate. Sensitivity also may be improved by forming precipitates containing fewer units of the analyte. 

Sensitivity For a coulometric method of analysis, the calibration sensitivity is equivalent to tiF in equation 11.25. In general, coulometric methods in which the analyte s oxidation or reduction involves a larger value of n show a greater sensitivity. 

The calibration sensitivity of the analytical method employed is simply determined as the slope of the calibration curve. For example, in the case of methyl paraben, the value of calibration sensitivity obtained was 1.6 mAl I/min///M (Figure 6.22). Analytical sensitivity is defined as the ratio between calibration sensitivity and the value of the standard deviation obtained at each concentration.10 The value of the standard deviation encountered for a concentration of 0.6 //M was 0.1, resulting in an analytical sensitivity for methyl paraben at 0.6 //M of 16 m. II/min///M. As indicated for LOD and LOQ, the values obtained for linearity and sensitivity depend on the analytes employed and the corresponding method and instrumental parameters. For example, Liu et al.9 evaluated the LOD and LOQ for Drug A (released from OROS) for a particular analytical method employing //Pl.C to be 0.5 //g/ml. and 2.0 //g/mL, respectively. 

Calibration Sensitivity, Analytical Sensitivity, and SEs for DNS, DNSsg, Nelson-Somogyi (Nelson lOmL), Modified Nelson-Somogyi (Nelson 5mL), PAHBAH, and BCA assays... 

Calibration sensitivity (xlO-3) Associated SE (xlO-3) Analytical sensitivity Associated SE (xlO-2) SD (xlO-3)6 Reference concentrationc... 

Calculated as the ratio of the calibration sensitivities (or slope m) of the different cellodextrin standard curves to the glucose standard curve. Thus, a ratio of 1 is expected, theoretically, for a true reducing sugar assay, which has the same molar color yield for a series of saccharides. 

The sensitivity of a method (or an instrument) is a measure of its ability to distinguish between small differences in analyte concentrations at a desired confidence level. The simplest measure of sensitivity is the slope of the calibration curve in the concentration range of interest. This is referred to as the calibration sensitivity. Usually, calibration curves for instruments are linear and are given by an equation of the form... 

Before a new analytical method or sample preparation technique is to be implemented, it must be validated. The various figures of merit need to be determined during the validation process. Random and systematic errors are measured in terms of precision and bias. The detection limit is established for each analyte. The accuracy and precision are determined at the concentration range where the method is to be used. The linear dynamic range is established and the calibration sensitivity is measured. In general, method validation provides a comprehensive picture of the merits of a new method and provides a basis for comparison with existing methods. 

For univariate calibration, the International Union of Pure and Applied Chemistry (IUPAC) defines sensitivity as the slope of the calibration curve when the instrument response is the dependent variable, i.e., y in Equation 5.4, and the independent variable is concentration. This is also known as the calibration sensitivity, contrasted with the analytical sensitivity, which is the calibration sensitivity divided by the standard deviation of an instrumental response at a specified concentration [18], Changing concentration to act as the dependent variable, as in Equation 5.4, shows that the slope of this calibration curve, f, is related to the inverse of the calibration sensitivity. In either case, confidence intervals for concentration estimates are linked to sensitivity [1, 19-22],... 

An intermediate concentration standard is reanalyzed after approximately every 20 injections, to calibrate sensitivity drift. 

The inhibition of triazophos was proportional to its concentration in two ranges, from 0.03 to 7.8 pM and 7.8 to 32 pM, with correlation coefficients of 0.09966 and 0.9960, respectively. The calibration sensitivity was 6.78, 0.87% pM1 and the detection limit was 0.01 pM, respectively. AFM results show the surface morphological differences between the various films and confirm the presence of AChE in the composite film (Fig. 5). 

The word sensitivity is often used in describing an analytical method. Unfortunately, it is occasionally used indiscriminately and incorrectly. The most often-used definition of sensitivity is the calibration sensitivity, or the change in the response signal per unit change in analyte concentration. The calibration sensitivity is thus the slope of the calibration curve, as shown in Figure 8-14. If the calibration curve is linear, the sensitivity is constant and independent of concentration. If nonlinear,. sensitivity changes with concentration and is not a single value. 

The calibration sensitivity does not indicate what concentration differences can be detected. Noise in the response signals must be taken into account to be quantitative about what differences can be detected. For this reason, the term analytical sensitivity is sometimes used. The analytical sensitivity is the ratio of the calibration curve slope to the standard deviation of the analytical signal at a given analyte concentration. The analytical sensitivity is usually a strong function of concentration. 

Figure 8-1 4 Calibration curve of response, R, vs. concentration, c. The slope of the calibration curve is called the calibration sensitivity, m. The detection limit, DL, designates the lowest concentration that can be measured at a specified confidence level.

For the quantitative analysis calibrated sensitivity factors, obtained from pure oxides, were used. These were 0 Is = 1, Ti... 

However, this method is not applicable to all situations. Figure 3.8 d shows that detecting the input/output characteristics at several points is not sufficient to calibrate sensitivity and offset errors if there are nonlinear effects involved. Here, a complete system identification might be necessary, depending on the order of the effects. Calibration of this kind of error is possible in theory, but not practicable, considering the expense in time and money. 

An odour standard of n-alkane vapours is used to calibrate sensitivity and specificity of the zNose . Specificity is what allows the instrument to recognize known chemicals and/or chemical groups (odour signatures) and to deliver the appropriate alarms. The zNose is an ultra-fast GC which separates and measures the concentration of the individual chemicals of an odour directly, typically in 10 seconds. Individual chemicals are recognized by their retention time relative to the retention times of the linear-chain alkanes. Tabulating the retention times and detector counts (cts) provides a complete and quantitative measure of any odour or fragrance. 

Note that the analytical sensitivity i.s quite concent ration dependent. lieeause of this, it is not reported as often its the calibration sensitivity. Applyinit F.quatioii 1-12,... 

Consider, for example, a sample containing an analyte A as well as potential interfering species li and C. If t A. i h. and C(- are the concentrations of the three species and m.,.. m. and rn - arc their calibration. sensitivities, then the ntlal instrument signal will be given by a tnodilied version of Equation I-10. That is. 

Schladow, S.G. and Hamilton, D.P. (1 997) Prediction of water quality in lakes and reservoirs. Part II. Model calibration, sensitivity analysis and application. EcologicalModelling96,111-123. 

Metrology Science of measurement dealing with the design, calibration, sensitivity, accuracy, and precision of measuring instruments. 

The quantitative definition of sensitivity that is accepted by the International Union of Pure and Applied Chemistry (lUPAC) is calibration sensitivity, which is the slope of the calibration curve at the concentration of interest. Most calibration curves that are used in analytical chemistry are linear and may be represented by the equation... 

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