Linear calibration

FIGURE 16.5 Broad standard calibration (linear mode) of a semipreparative Sephacryl S-IOOO system (95 x 1.6 cm) with an aqueous mixture of Blue Dextran, Dextran T-SOO, and glucose eluent 0.005 M NaOH V, i = 75 ml. = 162 ml. 

Linear calibration 2nd-order calibration Linear calibration 2nd-order calibration ... 

The linearity of the detector can be obtained by diluting the analyte stock solution and measuring the associated responses, while the linearity of the analytical method can be determined by making a series of concentrations of the analyte from independent sample preparations (weighing and spiking) [15]. It is also essential that the basic calibration linear curve be obtained by using independent samples, and not by using samples that have been prepared by dilution and injected into HPLC/GC, or spotted on one TLC plate. 

Single level calibration Linear through zero and response factor... 

Multi-level calibration Linear, point to point, cubic spline, inverse linear, log-log linear, quadratic, cubic, fourth-order, and fifth-order. 

The advantages of using plasma emission sources include the ability to perform multi-element analysis, a calibration linear dynamic range of more than three orders of magnitude and for some elements the limits of detection are comparable to those found by GFAAS. The ability to perform multi-element analysis is essential when the purpose of the experiments is to study element interaction effects. 

Reliable laboratory instrumentation is required to guarantee the safety of food products and enforce government regulations. Two main types of commercial instruments are available. One uses chilled mirror dew-point technology, while the other measures relative humidity with sensors that detect changes in electrical resistance or capacitance. Each has advantages and disadvantages. The methods vary in accuracy, repeatability, speed of measurement, stability in calibration, linearity, and convenience of use. 

The limit of detection, limit of quantitation, and linear dynamic range are to be determined by serial dilution of a sample. Three replicate measurements at each level are recommended, and the acceptance criterion for calibration linearity should be a prespecilied correlation coefficient (say, an r2 value of 0.995 or greater). 

CAL-41S Calibrator, Linear and Angular Displacement Transducers, Catalog 101, Lucas Schaevitz, Pennsauken, NJ, p. 30 (1990). 

With these factors in mind, it is good operating practice to use the manufacturer s recommendation as a starting point and then determine empirically the current which gives the optimum combination of signal-to-noise ratio and calibration linearity. The major consideration is not to exceed the maximum rated current. 

All four elements are best determined using the nitrous oxide-acetylene flame although Ca, Mg and Zn may be determined with adequate sensitivity in the air—acetylene flame. The nitrous oxide—acetylene flame gives greater freedom from interference effects and also gives rise to improved calibration linearity. 

Analytical Methods Committee Is my calibration linear AMC technical brief. No. 3, December 2000. 

In the latter case the laboratory must provide evidence that it can carry out this method competently (verification). What is required to validate a method is clear in the case of regulated pharmaceutical laboratories, and although some of the accepted validation statistics may be questioned (for example r> 0.999 for calibration linearity [4]), the process may be said to produce the desired result, i.e. methods employed to analyse pharmaceuticals are fit for purpose. 

Calibration linearity Six levels each with three replicates from 50% to 150% of target concentration. r> 0.999... 

Solutions of potassium dichromate (K2Cr207) are also used for overall checks on photometric accuracy. These also provide an indication of wavelength calibration, linearity, cuvet light path, and freedom from stray fight in the UV region. 

Electronic suppression is possible if the eluent is properly chosen for extra-low conductivity which is e.g. the case with phthalate buffers. The detector must be able to compensate for the background conductivity by its electronics. Such a set-up gives good calibration linearity over a wide range but its detection limit is rather poor. For historical reasons it is also termed single-column ion chromatography. 

Figure 3 shows the typical response peaks of the FIA system for formaldehyde. The precision of all measurements was very good. The relative standard deviation for sets of 15 injections were 1.5% and 0.4% at concentrations of 1 and 10 pg/ml, respectively. Aqueous formaldehyde standards were used for the calibration. Linearity was observed for the concentration range from 1 to 15 pg/ml. The equation describing the linear portion of the calibration plot is given by Y 0.098 X + 0.031 where Y is the peak height in absorbance unit and X is the concentration of pg/ml. The calibration plot is shown in figure 4. studies between the FIA and the chromotropic acid Fifteen samples with formaldehdye concentrations to 10.8 pg/ml were determined by both methods and a... 

In this step of the validation it is investigated whether the matrix influences the signal of the detector. The study concerns either an extract or a digest this new matrix may influence parameters defined in the previous step. All the conclusions obtained in the first step have to be verified (calibration, linearity, chromatographic conditions and performance, internal standard etc.). For the determination of trace organic contaminants this step is of great importance as it has to assure that no interfering compounds remain because quantification is often performed with non specific detectors (e.g. ECD, FID,... 

In the proposed assay, there was no interference in the measurement of the aequorin activity by biotinylated luciferase. The sensitivity of aequorin was 7.58xl0 0 mol/assay (blank + 3SD, Fig. 2, left), the calibration linearity of the assay ranged from 1.21 X lO mol/assay to 1.94 x lO mol/assay and the intra-assay coefficients of variation (CV) for 8 replicates with each standard point were from 1.0 to 3.2%. These results are similar to the results from the separate assay. 

Table 1.1 Comparison between thermometers, calibrated linearly from 0° to 100°C and the perfect gas scale...

It is highly desirable, especially for routine analysis, that the readout of the atomic absorption instrument be capable of being calibrated linearly and directly in concentration. Many commercially available spectrophotometers are capable of being converted to this type of operation, while some of the newer instruments have direct concentration read out built in. 

Calibration, linearity, and hysteresis Calibration drift time, temperature, pressure, etc. 

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