Linear calibration curves

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. 

Calibration curve, linear response, fortified controls... 

The detection of HIV-related proteins is one of the most challenging tasks. This is especially true because AIDS should be diagnosed as early as possible to enable an early and effective therapy of this infection. Pavski and Le (57) used the aptamer strategy to detect reverse transcriptase (RT) of the type 1 human immunodeficiency virus (HIV-1). A direct and specific ACE method was proposed using laser-induced fluorescence (ACE/LIF) as detection principle. Single-stranded DNA aptamers as probes fluorescently labeled were synthesized. The resulting aptamer is specific for HIV-1 RT, and it exhibited no cross-reactivity with RTs of the enhanced avian myeloblastosis virus (AMV), the Moloney murine leukemia virus (MMLV), or denatured HIV-1 RT. An affinity complex of RT 26-HIV-l RT was stable, with calibration curves linear up to 50 nM (6 /xg/mL) HIV-1 RT concentration. Both... 

A radioimmunoassay method has been reported for the monitoring of therapeutic concentration of chlorpromazine and its 7-hydroxy metabolite in plasma by [184]. The limit of detection for chlorpromazine was reported to be 0.1 ng, and its calibration curve linear up to 2 ng. The limits of detection for the 7-hydroxy metabolite was reported as 0.1 ng, and the calibration curve linear up to 1.2 ng. 

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. 

Validation. Calibration curves linear over the range 20-580 ng/pl RSDs ranged from 1.1 to 1.6% and recoveries from 98.8 to 99.6% for assay of the compounds in a syrup and tablet. 

When the calibration curves were compared, several compounds at the low end of the calibrated concentration range were affected by components already present in the diesel/oil extract. For example, low-levels of some PNAs and phthalates, present naturally in these refined petroleum products, were detected in the unspiked diesel/oil extract. Also, some of the phenols in this dirty matrix were reactive in the injection liner indeed, the matrix itself can passivate the liner for some target compounds. Passivation in this sense means that the liner surface becomes coated with non-volatile components, forming a barrier between the analyte and the bare, more reactive glass surface. While this issue is not related to ion trap mass spectrometry per se, it will be present in any analytical GC/MS system. As illustrated in the example below, calibration curve linearity (as represented by relative percent standard deviation, or RSDs, of the relative response factor at each calibration concentration level) and correlation coefficients for most compounds in the pure solvent were identical statistically to those prepared in the 3000 ppm diesel/oil matrix spikes, as are shown in Figures 15.36 and 15.37. 

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