Calibration by standard addition

Calibration by Standard Addition Method (SAM). When matrix effects appear or are to be expected and matrix-matched calibration samples are not available, the standard addition method (SAM) can be the calibration method of choice. 

The most useful index of excessive exposure to lead is a blood-lead analysis, and the majority of methods discussed here are concerned with this measurement. Many of the earlier ETA—AAS methods used little or no sample pretreatment and in almost all cases the variety of matrix interferences encountered necessitated strict control of ETA conditions, and made calibration by standard additions mandatory. The problem of diffusion of liquid blood samples into the graphite atomisers was overcome as an... 

Normally, there is also an uncertainty in the concentrations of the calibration samples used both in the case of calibration with synthetic calibration samples as well as in calibration by standard additions. In both cases these errors can also be included in the calculation of the analytical error [34]. 

Also in the case of calibration by standard additions, the uncertainty in the amount added in the case of one standard addition can be taken into account. When... 

For arsenic, one laboratory using HICP performed a pre-reduction to As(III) with Kl/ascorbic acid of which the yield depends strongly on the composition of the digest solution calibration by standard additions of As(V) was therefore recommended. 

For cadmium, one participant remarked that without using standard additions, only 50% of the Cd content was recovered. A strong requirement is therefore to perform calibration by standard additions for estuarine water analysis. As mentioned earlier, the participants stressed that the extraction efficiency has to be verified, particularly for Cd, as it depends on the content of complexing agents present in estuarine water matrices. The risk of incomplete extraction should be checked by repeated extractions. The problem raised by the presence of organic matter may be overcome in many cases by the use of UV irradiation or addition of acids. This possible pretreatment should... 

Measurements were suspected to be affected by iron interferences and calibration by standard addition was strongly recommended for ETAAS. 

Consequently, the RM 424 was not certified and will be considered as a research material for laboratories willing to evaluate techniques such as GC-FPD, GC-MS or HPLC-ICP-MS. Figure 5.2 presents the results obtained by GC-FPD, GC-MS, GC-MIP-AES and HPLC-ICP-MS. The good agreement found between these methods gave a good confidence that no systematic error was left undetected. Owing to the potential risks of interferences, calibration by standard additions is a prerequisite. 

When calibrating by standard addition, the concentration of the unknown sample can be determined graphically. This is done by extrapolating to zero the curve of the signals from samples to which known amounts of analyte have been added plotted against the added amounts. Standard addition can be very useful in atomic absorption and... 

Hydride generation increases the power of detection of atomic spectrometric methods for the determination of certain elements, and allows their matrix-free determination. However, the technique is prone to a number of systematic errors. First, the hydride-forming elements must be present as inorganic compounds in a well-defined valence state. This may require sample decom x>sition prior to analysis. In water analysis, treatment with H2SO4/H2O2 may be effective [106]. Traces of heavy metals such as Cu" may have a catalytic influence on the formation and dissociation of the hydrides, as investigated by Welz et al. [107] in atomic absorption with quartz cuvettes. These in-terferents can be masked by complexation with tartaric acid or coprecipitated with La(OH>3. Calibration by standard addition is advisable. 

A dimethyl formamide solution of the sample containing 0.2 M tetrabutyl ammonium iodide base electrolyte is polarographed at start potentials of -2.0 V (styrene) and -1.7 V (acrylonitrile). The styrene and acrylonitrile waves are evaluated. The method is calibrated by standard additions of the two monomers. 

The procedure could be used for the determination of As in natural waters and in dissolved river sediments, provided that calibration by standard addition was applied. 

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