Search results for "square"
showing 10 items of 1317 documents
Determination of critical eluent composition for polyethylenglycols using on-line liquid chromatography-Fourier transform infrared spectrometry.
2008
In this work, it has been extended to methanol:water mobile phases, the use of a background correction method for on-line LC-FTIR measurements named Univariate background correction based on the use of a reference spectra matrix (UBC-RSM) and absorbance ratios. It permits to overcome the problem related to spectral changes occurring during the gradient elution, which in the past limited the on-line coupling of LC and FTIR to isocratic elutions. The combined use of the aforementioned background correction technique in on-line isocratic and gradient LC-FTIR, and partial least squares (PLS) has been applied for the search of the critical conditions for polymers. Polyethylenglycol (PEG) has bee…
Direct determination of Mancozeb by photoacoustic spectrometry
2006
Abstract A solvent free, fast and environmentally friendly photoacoustic-infrared-based methodology (PAS-FTIR) was developed for the determination of Mancozeb in agrochemicals. This methodology was based on the direct measurement of the transmittance spectra of solid samples and a multivariate calibration model to determine the active ingredient concentration. The proposed partial least squares (PLS) model was made using nine standards prepared by mixing different amounts of kaolin and Mancozeb, with concentrations between 5.43 and 88.10% (w/w). A hierarchical cluster analysis was made in order to classify the samples in terms of similarity in the PAS-FTIR spectra. From their spectra differ…
Prediction of wheat dough W and P/L inflation test parameters by capillary zone electrophoresis of a protein extract followed by multivariate regress…
2004
A procedure for the evaluation of the wheat flour hardness, based on capillary electrophoresis of a protein extract in an isoelectric acidic buffer, was developed. The 13 flour samples were extracted twice, and two injections of each extract were made. Separations were performed in a background electrolyte (BGE) containing 40 mM aspartic acid, 6 M urea, and 0.5% hydroxyethylcellulose at 60 degrees C. Using the normalized and corrected areas of 79 peaks and peak groups, a partial least squares regression (PLS1) model was able to predict the flour strength or dough deformation work (W) and the dough tenacity/extensibility ratio (P/L) (Alveograph parameters) with an average relative standard d…
Determination of cow's milk and ripening time in nonbovine cheese by capillary electrophoresis of the ethanol-water protein fraction
2000
A novel method is reported for analyzing adulteration of goat and ewe cheeses with cow's milk: capillary zone electrophoresis (CZE) in isoelectric, acidic buffers (50 mM imino diacetic acid, IDA, pH = pI 2.3). The cheese samples were extracted with a 20:80 v/v ethanol-water mixture in presence of 3 M urea and 1% beta-mercaptoethanol for 1 h. After centrifugation and lipid extraction, the samples were dissolved in 50 mM IDA, 6 M urea and 0.5% hydroxyethyl cellulose and analyzed by CZE at 700 V/cm. A total of 18 characteristic peaks were resolved among the three types of cheeses and 18 variables were defined as their respective areas. There was excellent similarity among the electrophoretic p…
Comparison of two vibrational procedures for the direct determination of mancozeb in agrochemicals.
2007
The direct determination of mancozeb in agrochemicals has been made by diamond attenuated total reflectance (ATR) Fourier transform infrared spectroscopy in the middle range (DATR-MIR) and diffuse reflectance infrared Fourier transform spectroscopy in the near range (DR-NIR) methods using in both cases a previous identification of the samples using a dendrographic classification and an appropriate partial least squares (PLS) calibration established from a set of nine external standards and optimized for each type of sample. It was analyzed a heterogeneous population of 11 samples obtained from the Spanish market, containing different co-formulated products, such as fosetyl-Al, copper oxychl…
Origin based classification of crude oils by infrared spectrometry and chemometrics
2019
Abstract Crude oil samples from different Iranian petrol resources in both, raw and mixture forms have been characterized by attenuated total reflectance mid infrared spectroscopy. Obtained spectra were classified by chemometric techniques to propose a method for geological based classification of crude oil samples. Totally 251 samples from 7 petrol fields and 3 mixtures were analyzed. Mean centering and principal component analysis (PCA) supported – leverage value based outlier detection were used as preprocessing approaches. PCA, cluster analysis and soft independent modeling of class analogy (SIMCA) were utilized to classify the spectra. Obtained results confirmed that SIMCA is a robust …
Sweeteners determination in table top formulations using FT-Raman spectrometry and chemometric analysis
2004
Abstract A partial least squares (PLS) Fourier transform Raman spectrometry procedure based on the measurement of solid samples contained inside standard glass vials, has been developed for direct and reagent-free determination of sodium saccharin and sodium cyclamate in table top sweeteners. A classical 22 design for standards was used for calibration, but this system provides accuracy errors higher than 13% w/w for the analysis of samples containing glucose monohydrate. So, an extended model incorporating glucose monohydrate (23 standards) was assayed for the determination of sodium saccharin and sodium cyclamate in all the samples. Mean centering spectra data pre-treatment has been emplo…
Investigating semi-hard cheese aroma: Relationship between sensory profiles and gas chromatography-olfactometry data
2012
Abstract The purpose of this study was to investigate semi-hard cheese aroma by explaining sensory characteristics of cheese by gas chromatography–olfactometry (GC–O) data obtained via intensity ratings. Sensory (13 odour attributes) and GC–O profiles obtained by trained panels were carried out on seven non-processed semi-hard cheeses. Intensity scores for significant sensory attributes and significant odour-active compounds were analysed by partial least squares to determine correlations between these datasets. A total of nine sensory attributes and 15 odour-active molecules significantly discriminated between the cheeses. There were strong correlations (89% of the sensory data was explain…
Identification of compounds responsible for the odorant properties of aromatic caramel
2012
Aromatic caramel results from the heat treatment of sugars under specific temperature conditions. Because of its richness in aroma compounds and its pleasant organoleptic properties, caramel is widely used in the food industry. However, the composition of the volatile odorant fraction has not been completely elucidated. The aim of this work was thus to identify the volatile odorant compounds responsible for caramel sensory properties using a multivariate statistical technique. Four aromatic caramels differing in terms of their carbohydrate composition and cooking process were chosen. Odorant compounds were screened by gas chromatography–olfactometry (GC-O) and identified by GC–mass spectrom…
Determination of lecithin and soybean oil in dietary supplements using partial least squares-Fourier transform infrared spectroscopy.
2008
Lecithin and soybean oil in dietary supplements were determined by Fourier transform infrared spectrometry transmission measurements in dichloromethane in combination with a partial least squares (PLS) regression. Two different PLS models were developed, using 16 synthetic mixtures of analytes in dichloromethane, making measurements in the spectral range from 931.8 to 1252.3 cm(-1) for lecithin and from 911.4 to 1246.9 cm(-1) and 1695.3 to 1774.5 cm(-1) for soybean oil. Seven products from the Spanish market with lecithin concentrations between 21.1% and 99.1% and soybean oil concentrations between 0% and 37.2% were analyzed by the proposed method and the data was compared to a chromatograp…