Measuring multi-component analysis

Most current automated measurement techniques focus on one or possibly two air pollutants. A survey of recent developments shows major advances in multi-component analysis. Examples include ... 

According to Beer s law, the measured absorbance of a solution of a single light-absorbing species is directly proportional to its concentration. For a solution containing a mixture of absorbing species, the measured absorbance is then simply the linear combination of the absorbances of all species in that solution, each measured at the same wavelength. When the different species in the mixture have different spectra, we can do a multi-component analysis and extract the concentrations of the individual species. 

Coggeshall has listed some criteria for a successful multi-component analysis. Stated briefly, they are (a) Pure compounds must be available, (b) each component must somewhere possess uniqueness or dominance, (c) precise measurements are necessary, (d) one must have knowledge of, or the ability to eliminate, interferences, and (e) there must be mathematical feasibility or leverage. 

The simplest IR sensor would consist of a source, a sample interface and a detector. Although quite sensitive, such an arrangement would have no selectivity as any IR absorbing substance would cause an attenuation of the detected radiation. To get the selectivity that is a main driving force behind the application of IR systems, the radiation has to be spectrally analysed. This can be accomplished either by measurement at discrete wavelengths or, for multi-component sensors or samples containing (potentially) interfering substances, by full spectral analysis of the collected radiation. 

Bioanalyzer can be considered another version of commercial biosensors for off-line analysis. It was developed to have capabilities of complete analysis, short response time, specificity, and sensitivity that allows a quick clinical test. Abbott Vision, Boehringer-Mannheim Reflectron, and Kodak Ektachem DT60 (IBI Biolyzer is the new name) are used for cholesterol measurement in doctors offices. Bioanalyzer consists of biological and transducing component that are not physically connected. The uniqueness of this separation provides the versatility of analysis, i.e., use of disposable and different biological component for multi-components measurements. In authors laboratory, Kodak Ektachem DT60 was used successfully to determine cholesterol in some food matrices as well as in off-line process control. The analysis time was only 10 minutes compared to 1-2 days for the GC and HPLC methods. Complicated... 

Although the systems investigated here exhibited predominantly macropore control (at least those with pellet diameters exceeding 1/8" or 0.32 cm), there is no reason to believe that surface diffusion effects would not be exhibited in systems in which micropore (intracrystalline) resistances are important as well. In fact, this apparent surface diffusion effect may be responsible for the differences in zeolitic diffusion coefficients obtained by different methods of analysis (13). However, due to the complex interaction of various factors in the anlaysis of mass transport in zeolitic media, including instabilities due to heat effects, the presence of multimodal pore size distribution in pelleted media, and the uncertainties involved in the measurement of diffusion coefficients in multi-component systems, further research is necessary to effect a resolution of these discrepancies. 

Multi-port valves belong to the key components in screening. Most equipment for analysis exists only in single-channel versions. Exceptions are, for example, radiation beam measurements of Atkins and Senkan [114] and tools for parallel analysis at Symyx. As long as equipment for parallel analysis does not exist for every type of desired measurement, multi-port valves will always be an essential part of every screening device. 

There are limits on this method which are imposed by the la e pacing of laser mode-noise peaks (130 MKz), setting an upper decay time limit of 7 ns, by detector noise background setting a lower Ifanit of 200 ps, of cost (of a spectrum analyser) and of difficulties in analysis of multi-component fluorescence. Since however any source could in principle be used to measure a noise spectmm, the method is worth further consideration. 

An extension to multi-component systems is straightforward, by injecting more than one component. A prerequisite is the measurement of the concentration profile of each solute during the elution. This can be achieved either by using solute-specific detectors or by collection of multiple fractions and subsequent chemical analysis... 

In the analysis of a multi-component mixture, the zone of one compound may be superimposed on the zone of another compound. It is necessary, therefore, to develop a method that would make it possible to record and measure only the nitrogen peak. The area of this peak is proportional to the content of nitrogen in a given component and in the mixture as a whole. This type of analysis is carried out with the use of carbon dioxide as the carrier gas [59]. In this instance TCD is unable to detect the carbon... 

The generalized Maxwell-Stefan equation provides a rational basis for the analysis of sorption rate measurements and membrane permeation in multi-component systems. For a binary Langmuir system ... 

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