Interference comparison with other techniques

The wide application of atomic absorption spectrometry (AAS) in the determination of various metallic elements in diverse media is based primarily on the following factors (a) in most cases AAS has sufficient sensitivity for precise determination of the metallic elements (b) AAS is relatively free from interference (c) the required investment for establishing AAS capabilities is small and (d) the cost per analysis is usually low in comparison with other techniques. The determination of the concentration of metals in the air of workplace environments is achieved by AAS analysis of particulates that have been collected by filtering the air of workplace environments with the exposed filter dissolved in acid. 

The selectivity of the method is usually investigated by studying its ability to measure the analyte of interest in test portions to which specific interferences have been deliberately introduced (those thought likely to be present in samples). Where it is unclear whether or not interferences are already present, the selectivity of the method can be investigated by studying its ability to measure the analyte by comparison with other independent methods or techniques. 

MALDI is relatively less sensitive to contamination by salts, buffers, detergents, and so on in comparison with other ionization techniques [41], The analyte must be incorporated into the matrix crystals. This process may generally serve to separate in solid phase the analyte from contaminants. However, high concentrations of buffers and other contaminants commonly found in analyte solutions can interfere with the desorption and ionization process of samples. Prior purification to remove the contaminants leads to improvements in the quality of mass spectra. For instance, the removal of alkali ions has proven to be very important for achieving high desorption efficiency and mass resolution. 

The mechanism depends on the energy transfer from excited energy state of Sm to the singlet excited state of the Ramipril. In comparison with other spectrofluo-rimetric techniques, this method is simple, relatively interference free from coexisting substances and can successfully be applied to the determination ofRamipril in pharmaceutical preparations and in serum samples with remarkably satisfactory results. The Ramipril was determined in each tablet (Corpril or Ramipril or Tritace) and serum samples data are summarized in Table 14.2. 

The AC impedance technique coupled to the complex plane method of analysis is a powerful tool to determine a variety of electrochemical parameters. To make the measurements, instrumentation is somewhat more complex than with other techniques. It requires a Wheatstone bridge arrangement with series capacitance and resistance in the comparison arm, a tuned amplifier/detector, and an oscillator with an isolation transformer. A Wagner ground is required to maintain bridge sensitivity, and a suitably large inductance should be incorporated in the electrode polarization circuit to prevent interference from the low impedance of this ancillary circuitry. Sophisticated measurement instruments or frequency response analyzers with frequency sweep and computer interface are currently available such as the Solartron frequency response analyzers. Data obtained can be analyzed or fitted into proper equivalent circuit using appropriate software. 

A reference method is an analytical method with thoroughly documented accuracy, precision and low susceptibility to interferences. The accuracy and precision shall be demonstrated by direct comparison with the definitive method and primary reference material or, where not available, with other well-characterized and documented analytical approaches) (Boutwell, 1977). As long as accuracy and imprecision are within the limits, each technique or method is acceptable as a reference method. However, for reference methods one always looks for a method easily applicable in the laboratory. Therefore, the expensive instrumentation and the relatively low sample capacity make IDMS suitable as a definitive method rather than as a reference method. For some applications, however, IDMS is the method of choice, allowing a more specific detection than the existing methods in the laboratory. 

The use of ion-exchange chromatography to purify sialic acids after mild acid hydrolysis and calibration of losses using a standard sialic acid sample has been suggested (Svennerholm 1958, 1963 b, Schauer 1978, Caimi et al 1979) and is routinely carried out in the authors laboratory. Comparison of this technique with others designed to eliminate interference has underlined its value (e.g. Sarris and Palade 1979, Roboz et al 1981). 

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