Construction of a calibration curve

1 Empirical approach. In SEC, a calibration curve of log molecular mass (log M) V. retention volume (Fr) must first be constructed in order to calculate molecular mass averages of the polymers in question. It is usual to report the results as polystyrene equivalent molecular masses, using a calibration curve constructed with polystyrenes of known molecular masses having narrow MMD. For accurate estimation of copolymer molecular weight, one must use a calibration curve for the copolymer in question. Therefore, it is necessary and important to estimate molecular mass of the copolymer species eluted at retention volume i. 

For a copolymer consisting of components A and B, a calibration curve of log M V. Fr for the copolymer can be constructed from those for two 

When calibration curves for two homopolymers A and B are linear, another attempt at constructing a caUbration curve for a block copolymer has been reported [5]. When two calibration curves for homopolymers are parallel to each other, the following relation can be assumed  

When the linear calibration curves of two homopolymers are not parallel with each other. 

This treatment applies to diblock polymers, but there is no distinction among AB, ABA, and ABAB types. Equations (5.2) and (5.3) can be extended 

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Figure 4.4 shows an example for the use of several CRMs from NIST and BCR with certified or indicative values for chromium for the construction of a calibration curve. Increasing intakes of the CRMs were used covering the range 3-23 ng Cr. 

Measure absorbency of the diluted solutions with a spectrophotometer. This may or may not require the separate construction of a calibration curve. 

We should appreciate that a superior (although much more time-consuming) approach would be to start by constructing a calibration curve of /um (as y ) against Canaiyte (as x ) with known standards. The construction of a calibration curve is always a superior approach the methodology in the worked example... 

Table 1.4 Data used for the construction of a calibration curve for the spectrophotometric determination of procaine...

The interpretation and implementation of published methods invariably differ at different laboratories due to diversity of utilized instruments, their incidental elements and supplies, and the differences in method interpretation. Each analytical method must be validated at the laboratory before it is used for sample analysis in order to demonstrate the laboratory s ability to consistently produce data of known accuracy and precision. Method validation includes the construction of a calibration curve that meets the acceptance criteria the determination of the method s accuracy and precision and the MDL study. A method SOPs must be prepared and approved for use. Method validation documentation is kept on file and should be always available to the client upon request. 

In practice, the first step is the construction of a calibration curve A = f (c) from solutions of known concentration of the compound to be measured, submitted to the same treatment as the sample. This curve, which is most often a straight line for dilute solutions, allows determination of the concentration of the unknown sample. 

The method of standard addition is useful when analysis of only a limited number of samples is required. In such instances the construction of a calibration curve would be too time consuming. The apparatus is simplified by the fact that temperature control is unnecessary. On the other hand, because two curves (with and without addition of the standard) have to be recorded for each sample, the time spent on a single analysis is somewhat longer. 

The definition of calibration function does not specify that the measurement be made in the presence of potential interferants. This serves as an introduction to a discussion of the appropriate approach to calibration in an analytical method for veterinary drug residues, such as antibiotics. Construction of a calibration curve requires a sufficient number of standard solutions to define the response in relation to concentration, where the number of standard solutions used is a function of the concentration range. In most cases, a minimum of five concentrations (plus a blank, or zero ) is considered appropriate for characterization of the calibration curve during method validation. It is also typically recommended that the curve be statistically tested and expressed, usually through linear regression analysis. However, for LC/ESI-MS analysis of residues, the function tends to be quadratic. The analytical range for the analysis is usually defined by the minimum and maximum concentrations used in establishing the calibration curve. 

The application of a low-angle laser light-scattering (LALLS) detector for the measurement of absolute molecular mass of molecules eluted from SEC columns is very attractive, because the construction of a calibration curve in advance is not required. However, this method is not generally applicable to copolymers, because the intensity of light scattering is a function not only of the molecular mass of the copolymer but also of the specific refractive index in the solvent used as the mobile phase. The value of the specific refractive index for the copolymer is a function of composition. In general, the correct treatment of LS measurement for copolymers requires measurements in at least three solvents of different specific refractive index increments. 

Broadening and overlapping frequently are also observed in spectroscopy, which induce difficulty to select a resolved absorption band. An accurate result is obtained when a sharp and well-resolved peak is chosen. Quantitative analysis by spectroscopy methods is comparison of responses with standards or references. This requires either the determination of an absorption band ratio or construction of a calibration curve by plotting absorption ratio versus the DA. 

Under such conditions transfer of the analyte from the bulk solution to the electrode surface is principally by diffusion. A typical DC polarogram is presented in Figure 1. The half wave potential (Eyx) is characteristic of the analyte and hence yields qualitative analytical data. The analyte reduction current, produced at the electrode surface, is the limiting diffusion current (U) which is proportional to the concentration of the analyte in the solution, hence providing the quantitative information. Calibration is performed by internal standard additions or the construction of a calibration curve. 

The application of a light-scattering detector in SEC does not require the construction of a calibration curve using narrow molecular-weight distribution polymers. However, this method is not generally applicable to... 

Construction of a calibration curve using electronic dilution. (For color version of this figure, the reader is referred to the online version of this book.)... 

Factor analysis had previously been used by Culler et al. [100] for quality control monitoring of a polymeric composite system of y-aminopropyl-triethoxysilane (j/-APS) coupling agent on an E-glass mat substrate. In this system, factor analysis successfully indicated the number of pure components, extracted the spectra of the pure components, indicated the relative concentrations of spectra, and improved the S/N ratio in the extracted spectra. The construction of a calibration curve allowed factor analysis to be used as a QC monitor of the amount of coupling agent on the E-glass mats. 

Note In practice, four or five runs at increasing concentration of the standard, preferably from well above the detection limit to close to saturation, should be mn in a sequence to obtain the data for the construction of a calibration curve. Extrapolation to concentrations outside the range covered has to be strictly avoided. One should also bear in mind that the limit of quantitation (LOQ) of a compound is found at higher concentration than its limit of detection (LOD). 

Columns available for SE-HPLC and their properties Construction of a calibration curve for any SE-HPLC column and calculation of its specific resolution importance of particle size, pore size and column length Elution Systems Analysis of Eluate Fractions... 

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