Calibration range, linear

If the IS contributes to the signal of the analyte, but the reverse is not true, a linear calibration curve with a positive intercept is obtained. Provided that the variance on the isotope ratios measured is uniform throughout the whole calibration range, linear regression analysis may be applied. Otherwise, weighting factors should be introduced, e.g., the reciprocals of the variances at different concentration levels (Claeys et al., 1977 Schoeller, 1976). 

Table 5.11 Calibration ranges, linear regression parameters and evaluation limits for the quantification of CFSV in wine-similar matrixes (Fedrizzi et al., 2007a).

Calibrated range—linearity, quantitative concentration range... 

Table 4.14 Retention time, SRM conditions, calibration range, linearity and reproducibility of pesticide components investigated.

The linear dynamic range of this method is 0.1 p.gl to 100 J.gl i The method detection limit (MDE) depends on selected operating conditions and a calibration range. It is important to use high purity reagents in all determinations. 

Instrument makers nonetheless provide this less-than-useful information, but hardly anybody recognizes as the outflow of the wide calibration range, the linear concentration-to-signal transfer function, and the excellent repeatability. 

Calibration range Not specified usually > 4 Not specified but at least one calibration in each sequence Linearity not required any vahd calibration is accepted Calibration with standards in matrix strongly recommended... 

The calibration curve is generated by plotting the peak area of each analyte in a calibration standard against its concentration. Least-squares estimates of the data points are used to define the calibration curve. Linear, exponential, or quadratic calibration curves may be used, but the analyte levels for all the samples from the same protocol must be analyzed with the same curve fit. In the event that analyte responses exceed the upper range of the standard calibration curve by more than 20%, the samples must be reanalyzed with extended standards or diluted into the existing calibration range. 

Nano-structuring also results in a decreased detection limit. Since the latter has different explanations in analytical literature, we define it as the lower limit of the linear calibration range. For nano-structured Prussian blue the detection limit was found to be of 1 X 10 9 mol L 1 (Fig. 13.6). 

The resulting Prussian blue-based nano-electrode arrays in FIA demonstrate a sub-ppb detection limit (1 X 10 9 mol I. ) and a linear calibration range starting from the detection limit and extending over seven orders of magnitude of H202 concentrations (1 X 10 9 1 X 10 2 mol L ), which is the most advantageous analytical performance in electroanalysis. As a conclusion from the evidence in this chapter, Prussian... 

Sample preconcentration was performed by means of an automated on-line SPE sample processor Prospekt-2 (Spark Holland, Emmen, The Netherlands). Oasis HLB cartridges (Waters, Barcelona, Spain) were used to preconcentrate cannabi-noids present in the water samples whereas isolation of the rest of the compounds was done in PLRPs cartridges (Spark Holland). Before extraction, influent samples were diluted with HPLC water (1 9, v/v) to reduce matrix interferences and to fit some analyte concentrations, e.g., cocaine (CO) and benzoylecgonine (BE), within the linear calibration range. A sample volume of 5 mL was spiked with the internal standard mixture (at 20 ng/L) in order to correct for potential losses during the analytical procedure, as well as for matrix effects. Elution of the analytes to the LC system was done with the chromatographic mobile phase. 

The curve can be any non-linear shape to demonstrate the effect. The curve helps to explain the importance and limitations of calibration. Points A and B represent a calibration range of input values between which linearity is likely. The curve demonstrates how linearity cannot be assured outside this range. The DINAMAP monitor behaves in a similar way. It tends to overestimate at low blood pressure (BP) and underestimate at high BP while retaining accuracy between the calibration limits. 

The methods used were those of Mitchell ( 1 ), Kurtz, Rosenberger, and Tamayo ( 2 ), and Wegscheider T ) Mitchell accounted for heteroscedastic error variance by using weighted least squares regression. Mitchell fitted a curve either to all or part of the calibration range, using either a linear or a quadratic model. Kurtz, et al., achieved constant variance by a... 

Optimization of Linear Calibration Methodology. The accuracy of linear calibration methods for utilization of polydisperse calibration standards depends upon (1) how well the column set approximates true linearity over the molecular weight calibration range and (2) the extent to which instrumental band broadening affects the elution volume profile of the polydisperse standard. 

Preparation of standard samples always should be as accurate as possible Therefore gravimetric procedures should be preferred compared to volumetric ones and several dilutions should be avoided since each dilution step adds to the uncertainty. For a basic calibration we need 6 to 10 standard samples. They should be distributed equidistant over the whole working range. Linear regression requires equidistant distribution. Otherwise... 

Linear equations of the type v = ct — C, where c and C are constants, relate kinematic viscosity to efflux time over limited time ranges. This is based on the fact that, for many viscometers, portions of the viscosity—time curves can be taken as straight lines over moderate time ranges. Linear equations, which are simpler to use in determining and applying correction factors after calibration, must be applied carefully as they do not represent the true viscosity—time relation. Linear equation constants have been given (158) and are used in ASTM D4212. 

Typical parameters that are generally considered most important for validation of analytical methods are specificity, selectivity, precision, accuracy, extraction recovery, calibration curve, linearity, working range, detection limit, quantification limit, sensitivity, and robustness. 

It is not reliable to extrapolate any calibration curve, linear or nonlinear, beyond the measured range of standards. Measure standards in the entire concentration range of interest. 

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