Multivariate calibration techniques

A spectrophotometric method for determination of primary and secondary amines requires development for each particular compound, determining the kinetics of reaction of the amine with sodium l,2-naphthoquinone-4-sulfonate (143) and the UVV absorption spectrum of the product, under a set of fixed conditions. The procedure was applied to determination of ephedrine (30) and amphetamine (28) in pharmaceutical samples339. Reagent 143 in a FLA. system was used for the fast determination of lysine (144) in commercial feed samples by multivariate calibration techniques, without need of chromatographic separation340. 

Concentration, Characteristic, or Property Matrix (C) Different characteristics or properties of chemical systems can be predicted using multivariate calibration techniques. Throughout this book, the word concentration is often used as a generic term to represent concentration, characteristic, or property. 

M. L. Griffiths, D. Svozil, P. J. Worsfold, S. Denham and E. H. Evans, Comparison of traditional and multivariate calibration techniques applied to complex matrices using inductively coupled plasma atomic emission spectroscopy, J. Anal. At. Spectrom., 15, 2000, 967-972. 

Properly controlling the different steps of the production process requires knowledge of the API concentration throughout the process (from the raw materials to the end product). The characteristics of the NIR spectrum require the use of multivariate calibration techniques in order to establish a quantitative relationship between the spectrum and the chemical (composition) and/or physical parameters (particle size, viscosity and density). 

Glucose absorption at physiological concentrations is several orders of magnitude lower than that from water, which is the major background absorber in tissue. In addition, molecular overtone and combination bands are typically broad, leading to overlapping, yet distinctive, spectral features.44 As a result of this spectral overlap, multivariate calibration techniques are required to extract quantitative analyte-specific information.45... 

The concept of the PCSA method is general and this method should be applicable to many types of multivariate calibration techniques. As near-infrared and other spectroscopic methods are developed further for noninvasive in vivo clinical measurements, it is critical to understand the chemical basis of measurement selectivity. Unfortunately, calibration models generated from multivariate statistics are typically accepted without further investigation. Application of the PCSA method can help to establish the chemical or spectroscopic basis of predicted concentrations. 

Partial Least Squares Regression (PLS) is a multivariate calibration technique, based on the principles of Latent Variable Regression. Originated in a slightly different form in the field of econometrics, PLS has entered the spectroscopic scene.46,47,48 It is mostly employed for quantitative analysis of mixtures with overlapping bands (e.g. mixture of glucose, fructose and sucrose).49,50... 

In more recent development, chemometric or multivariate calibration techniques have been applied into spectrophotometric methods. As reported by Palabiyik and Onur [24], principal component regression and partial least square were used to determine ezetimibe in combination with simvastatin. This method offers advanfages such as no chemical prefreafmenf prior to analysis as well as no need to observe graphical spectra and calculations as with the derivative method. In addition, the instrumentation used is also simpler. 

Although less important than peak frequencies, peak intensities obviously play a role in quantitative analysis and, in many cases, qualitative identification. Multivariate calibration techniques and their transferability depend on reproducible relative peak heights. A possibly lengthy method development procedure may fail when a different spectrometer is used, if the observed intensities vary. Reproducibility of absolute signal is difficult to achieve between labs or even between instruments of the same design, but it is important for a particular instrument. Absolute intensities can at least be used to evaluate day-to-day instrument performance and to detect hardware or alignment problems. 

When the ratio of the two rate constants is small, determination of both species is still possible by more complex methods of data treatment. Many of these methods use chemometric, multivariate calibration techniques similar to those described in Feature 8-3. The details of multicomponent kinetic methods are beyond the scope of this text. ... 

NIR.spectral bands are normally broad and often overlapping. There arc rarely clean spectral bands that allow simple correlation with analyte concentration. Instead. multivariate calibration techniques are used." Most commonly, partial least squares, principal compti-nents regression, and arlificial neural networks are eni-... 

Cerrato Oliveros et al. (2002) selected array of 12 metal oxide sensors to detected adulteration in virgin olive oils samples and to quantify the percentage of adulteration by electronic nose. Multivariate chemometric techniques such as PCA were applied to choose a set of optimally discriminant variables. Excellent results were obtained in the differentiation of adulterated and non-adulterated olive oils, by application of LDA, QDA. The models provide very satisfactory results, with prediction percentages >95%, and in some cases almost 100%. The results with ANN are slightly worse, although the classification criterion used here was very strict. To determine the percentage of adulteration in olive oil samples multivariate calibration techniques based on partial least squares and ANN were employed. Not so good results were carried out, even if there are exceptions. Finally, classification techniques can be used to determine the amount of adulterant oil added with excellent results. 

On the other hand, atomic emission spectra are inherently well suited for multivariate analysis due to the fact that the intensity data can be easily recorded at multiple wavelengths. The only prerequisite is that the cahbration set encompasses all likely constituents encountered in the real sample matrix. Calibration data are therefore acquired by a suitable experimental design. Not surprisingly, many of the present analytical schemes are based on multivariate calibration techniques such as multiple linear regression (MLR), principal components regression (PCR), and partial least squares regression (PLS), which have emerged as attractive alternatives. 

Near infrared (NIR) spectroscopy has been a useful analytical technique employed for many years in the pharmaceutical, cosmetic and textile industries. Its utility has been enhanced by the addition of multivariate calibration techniques. In addition, the ease of sample preparation and speed of analysis make NIR ideal for use as a quality control method. 

An e-tongue with multivariate calibration techniques (PCA-ANN) was found able to quantify catechins and caffeine in green tea in contrast to reverse phase HPLC... 

Statistical Techniques Experimental Design Optimization Strategies Multivariate Classification Techniques Multivariate Calibration Techniques Expert Systems Multicriterla Decision Making Signal Processing... 

See alsa Blood and Plasma. Chemometrics and Statistics Multivariate Calibration Techniques. Chromatography Overview. Electrophoresis Clinical Applications. Enzymes Enzymes in Physiological Samples Enzyme-Based Assays. Quality Assurance Quality Control Primary Standards Laboratory Information Management Systems. Sample Handling Automated Sample Preparation. 

See also Chemometrics and Statistics Statistical Techniques Multivariate Classification Techniques Multivariate Calibration Techniques. Food and Nutritional Analysis Overview. Fourier Transform Techniques. Fuels Oil-Based. Infrared Spectroscopy Overview. Pharmaceutical Analysis Drug Purity Determination. Process Analysis Ovenriew. Proteins Foods. Quality Assurance Ouality Control. Textiles Natural Synthetic. 

See also-. Bioassays Overview. Chemometrics and Statistics Multivariate Calibration Techniques. Infrared Spectroscopy Near-Infrared. Liquid Chromatography Size-Exclusion Liquid Chromatography-Mass Spectrometry Liquid Chromatography-Nuclear Magnetic Resonance Spectrometry. Pharmaceutical Analysis Drug... 

See also Chemometrics and Statistics Multivariate Calibration Techniques. Gas Chromatography Column... 

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