Experimental 1

Experimental 1 - Introduction The evolution of analytical...

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Introduction The evolution of analytical chemists has come around due to the technological advancements and the need to explore and understand issues of increased complexity. This technological advancement includes the increased resolving power of analytical instruments and the relative ease of accessing to computing facilities, allowing more emphasis to be placed on data analysis. This advancement in data analysis has even impacted calibration model construction whereby the analytical chemists are able to move away from univariate regression and are presented with an ever increasing rang of multivariate regression methods. The term used as regression methods involves collecting predictor and response values for common samples, and then fitting a predefined mathematical relationship to the collected data. For example, in analytical chemistry, spectrophotometric measurements are made on solutions with known concentrations of a given compound (known standards). Regression is then used to relate concentration to spectrum. Once you have built a regression model, you can predict the unknown concentration for new samples, using the spectroscopic measurements as predictors. The advantages are obvious if the concentration is difficult or expensive to measure directly. For systems whose components influence each other and whose spectra overlap such as the one used in the experiment, it is of an advantage to use multivariate calibration standards. In that way the interaction between the components of a sample can be allowed for in calibration, and the influence of the chemical matrix effects can be minimised. Having performed the calibration, unknown solutions can be analysed to determine the respective analyte concentrations, using the concentration matrix (KHKFHAHFLKHFLNH) derived from the absorptivity matrix (lalkjldajjlfdjl). In such multicomponent analysis experiments, it appears that generally the more over determined the system is (i.e. the greater the excess of wavelengths than components, and similarly for the number of standards than components), the greater the accuracy of the determinations. However, computer error in the calculation of matrix inverses can become significant for large matrices and actually decrease the degree of accuracy. Another example of the resolved power of analytical instruments is Fourier transform infrared spectrometer (FTIR). It is a technique which is used to obtain an infrared spectrum of absorption , emission of a solid, liquid or gas. An FTIR spectrometer simultaneously collects spectral data in a wide spectral range. This confers a significant advantage over a dispersive spectrometer which measures intensity over a narrow range of wavelengths at a time, giving rise to a greater signal to noise ratio by a factor of 30 over a desired range. Other advantage in FTIR is the inherent computer used in this form of spectrometer. The computer allows for easier data manipulation, duplication, transfer and cataloguing of results. These advantages are essential in analytical chemistry because
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This note was uploaded on 04/27/2011 for the course SCIENCE 02 taught by Professor Apfd during the Spring '10 term at Alabama.

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Experimental 1 - Introduction The evolution of analytical...

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