Separation of Chlordane Residues From Aroclor 1248, 1254 and 1260 and Soil Degradation Products

Abstract

Polychlorinated biphenyls often occur simultaneously in environmental samples complicating the identification and quantification of chlordane. A method is presented for the separation of chlordane and two of its metabolites from several polychlorinated biphenyl mixtures. Soil samples were subjected to controlled environments so that degradation of PCB residues could be followed over a period of 10 months in order to examine interference to the method by PCB degradation products.     

Detection of PCB77 by Antibody-Coated Competitive Fluorescent Quantitative Immuno-PCR Using Molecular Beacon

Abstract

A rapid and quantitative technique is urgently needed in detecting toxicological and carcinogenic polychlorinated biphenyls (PCBs) in the environment. In this study, a high sensitive real time fluorescent quantitative immuno-PCR (FQ-IPCR) approach using molecular beacon (MB) was developed to detect PCB77, which was classified as a human carcinogen. MB-based FQ-IPCR was then performed on serial dilutions of known PCB77 concentrations equivalent to 10-fold dilutions of 10–10⁵ fg/mL. A correlation coefficient of 0.997 was identified, and a linear relationship between 10 fg/mL and 100 pg/mL, with y = 0.543x + 21.779, was obtained. Three soil samples were determined by MB-based FQ-IPCR to proof the validity of the method, and the results of which were further confirmed by conventional enzyme-linked immuno sorbent assay (ELISA). Based on sensitivity and reproduction, the MB-based real time FQ-IPCR technique will become a promising monitoring tool for environmental endocrine disruptors.     

Applications of maximum likelihood principal component analysis: incomplete data sets and calibration transfer

The application of a new method to the multivariate analysis of incomplete data sets is described. The new method, called maximum likelihood principal component analysis (MLPCA), is analogous to conventional principal component analysis (PCA), but incorporates measurement error variance information in the decomposition of multivariate data. Missing measurements can be handled in a reliable and simple manner by assigning large measurement uncertainties to them. The problem of missing data is pervasive in chemistry, and MLPCA is applied to three sets of experimental data to illustrate its utility. For exploratory data analysis, a data set from the analysis of archeological artifacts is used to show that the principal components extracted by MLPCA retain much of the original information even when a significant number of measurements are missing. Maximum likelihood projections of censored data can often preserve original clusters among the samples and can, through the propagation of error, indicate which samples are likely to be projected erroneously. To demonstrate its utility in modeling applications, MLPCA is also applied in the development of a model for chromatographic retention based on a data set which is only 80% complete. MLPCA can predict missing values and assign error estimates to these points. Finally, the problem of calibration transfer between instruments can be regarded as a missing data problem in which entire spectra are missing on the ‘slave’ instrument. Using NIR spectra obtained from two instruments, it is shown that spectra on the slave instrument can be predicted from a small subset of calibration transfer samples even if a different wavelength range is employed. Concentration prediction errors obtained by this approach were comparable to cross-validation errors obtained for the slave instrument when all spectra were available.     

Nondestructive Quantitative Analysis of Analgini Powder Pharmaceutical by Near-Infrared Spectroscopy and Artifical Neural Network Technique

ABSTRACT

This paper demonstrates the usefulness of near-infrared (NIR) spectra and artificial neural network (ANN) in nondestructive quantitative analysis of pharmaceuticals. Real data sets from near-infrared reflectance spectra of analgini powder pharmaceutical were used to build up an artificial neural network to predict unknown samples. The parameters affecting the network were discussed. A new network evaluation criterion, the degree of approximation, was employed. The overfitting was discussed. Owing to the good nonlinear multivariate calibration nature of ANN, the predicted result was reliable and precise. The relative error of unknown samples was less than 2.5%     

Evaluation of Multivariate Calibration Using a Tikhonov Regularization Approach and the Generalized Pair‐Correlation Method with Nonlinear Data

Abstract

In order to reduce data nonlinearity and overfitting with the multivariate calibration model y=Xb, a modified Tikhonov regularization (TR) algorithm is evaluated for selecting key variables from an X augmented with extra columns that contain the original measured variables (x _ij ) as squared terms (x _ij ²) and other orders. The TR approach simultaneously develops the multivariate calibration model. The new generalized pair‐correlation method (GPCM) is also studied for variable selection followed by partial least squares (PLS) for multivariate calibration. Results from synthetic spectral data are compared when using the modified TR approach, GPCM, and PLS without variable selection. The GPCM usually performs slightly better than the TR approach for tabulated bias and variance measures and in some cases, at a sacrifice to parsimony. The method of PLS without variable selection performs the worst. By using synthetic spectral data sets, how the methods work could be studied. Thus, results from this study will aid investigators of real spectral data sets exhibiting nonlinear behavior.     

Interference of Transformer oil Matrices to the Internal Standards on PCB Quantification

Abstract

Polychlorinated biphenyls (PCBs) are toxic, perssstent, global environmental contaminants which were formulated as complex mixtures of congeners. Many methods have been developed in the past to analyze PCB in transformer oil samples for regulatory purposes. The most important consideration in the cleanup procedure is the ability to remove the oil from the sample matrix, since trace amount of oil will interfere with the subsequent GC-MS analysis. Electron capture detection (ECD) has been the most common method for gas chromatographic analysis of PCBs because of its high sensitivity toward halogenated compounds. ECD can also respond to some non-PCB compound resulting in biased concentrations of PCB. In this work, a two-stage cleanup method, using DMSO liquid/liquid extraction and HPLC column chromatography. has been applied to two types of transformer oil. Five internal standards have been selected to show their performance in the presence of different oil matrices. The comparison of the PCB quantification at different conditions for GC-MS and GC-ECD will be demonstrated.     

Multivariate Fluorimetric Determination of Mixture of Pyrene,Perylene and Triphenylene in Water Sample

ABSTRACT

Micellization is described as a successful media for simultaneous fluorimetric determination of perylene, pyrene and triphenylene in water samples by reducing interference between them. A multivariate method based on synchronous fluorescence scan to estimate perylene, pyrene and triphenylene in their mixture solution has been proposed. The method does not require solving of large amounts of data obtained from the whole spectrum of the samples, thus making the analysis simple and fast. The method gives the best result for perylene and satisfactory results for pyrene and triphenylene. Analysis of water samples of two different origins spiked with known amount of perylene, pyrene and triphenylene also gives satisfactory result. Presence of fluoranthene up to 1 μM does not interfere in the analysis.     

Analysis of Toxaphene (PCC) and Chlordane in Biological Samples by NCI Mass Spectrometry

Abstract

Several recent reports indicate that both toxaphene (polychlorocamphene, PCC) and chlordane are widespread pollutants in our environment. These insecticides, both complex mixtures of chlorinated hydrocarbons, are difficult to separate from each other. Thus the analyses of them in environmental samples are difficult and furthermore complicated by interferences from other chlorinated hydrocarbons such as PCB and DDT compounds. Mass fragmentography using the negative ions formed by chemical ionization proved to be useful to selectively detect the toxaphenes and the chlordanes without interferences from DDT. High concentrations of PCB still influence on the results and have to be removed in the clean-up procedure.     

Determination of Maneb Residues,in Tomatoes,by Spectrophotometric Method of Acid Hydrolysis,Through Multivariate Calibration

ABSTRACT

In this work, a chemometric method was applied through multivariate calibration, PLS (Partial Least Squares), to establish the analysis of ethylenebisdithiocarbamates residues in tomatoes samples by the hydrolysis method. The algorithm used to implement the PLS in the MatLab environment on IBM-compatible personal computer, was obtained from chemometrics package PLS_ToolBox. In samples with elevated levels of Maneb the univariate calibration showed similar results to the multivariate calibration. However, in samples with lower levels of residues increases occurred in the order of 15 to 47% in the levels detected by the multivariate calibration. In addition, there was a significant decrease in the standard deviations, in relation to those obtained, when the method of univariate calibration was used. The levels of contamination by Maneb found in tomatoes samples were below the maximum established by the Brazilian legislation.     

Determination of polychlorinated biphenyls by fast chromatography mass-spectrometry in environmental and biological samples

A method for the determination of polychlorinated biphenyls (PCB) by fast gas chromatography coupled with mass-spectrometric detection in selective ion monitoring mode has been developed. Chromatographic separation was carried out with HT-8 column (30 m × 0.25 mm) under sharp temperature increase from 80 to 320°C at a rate of 40°C/min. Duration of chromatography is 10 min. Fast chromatography conditions suggested by authors makes it possible to increase S/N ratios 10 times and so to reduce significantly the representative weight of the sample and develop an effective sample preparation technique. The method was used for PCB determination in Baikal area samples such as soil, snow, sediments from Lake Baikal and its tributaries, tissues of Baikal omul (Coregonus migratorius, Georgi, 1775) and blubber of Baikal seal (Phoca sibirica Gm.). The sample preparation stage includes PCB extraction from environmental samples and hydrolyzate of biological material with the following cleanup of the extract on the compact silica gel and florisil cartridges (0.5 g of the sorbent). The method enables the measurements of total PCBs and isomer groups of the same chlorination level with interlaboratory precision of no greater than 10% and the determination of indicator congeners (PCBs 28, 52, 101, 118, 138, 153, and 180) with a precision not exceeding 15%.     

Determination of Low Level Sulfides in Environmental Waters by Automated Gas Dialysis/Methylene Blue Colorimetry

Abstract

A sensitive and rapid automated method has been developed for the selective analysis of acid extractable sulfide in environmental samples by combining gas dialysis separation techniques with methylene blue detection procedures. Acid extractable sulfide is separated from the sample matrix by the gas dialysis membrane and subsequently trapped in a dilute sodium hydroxide receiving stream. This stream is reacted with N, N-dimethyl-p-phenylenediamine and ferric chloride to produce methylene blue which is then quantitated colorimetrically at 660 nm. For standards and nonturbid environmental samples, there is good agreement between the results obtained by this procedure and the standard methylene blue method. The effect of interferences on the accurate determination of sulfide by both methods was also examined and it was found that cupric ions significantly interfered with sulfide estimation. To obtain adequate sulfide recoveries in tap water and environmental samples ascorbic acid must be added as an antioxidant. A detection limit of 2 μg/L of sulfide has been obtained using this procedure.     

The University of Surrey database of elemental composition of human hair

The elemental composition of human hair obtained from different studies at Surrey University over a period of 25 years has been recorded and forms part of a database, for biological and environmental samples, which is being developed. Instrumental neutron activation analysis (INAA), using reactor neutrons, was the principal method employed and from which reported data are presented.Elemental concentrations of Br, Ca, Ce, Cl, Co, Cr, Cs, F, Fe, Hf, K, Mg, Mn, Na, Rb, Sb, Sc, Se, V and Zn were obtained and recorded in the database. Chronological variations in two sets of subjects separated by a period of time of 16 years are also given. Variations in the concentration values of some elements related to the state of health and disease were reported for hair samples collected from subjects suffering from manic depression, senile dementia and breast cancer. Concentration values of some elements with relation to the nationality of subjects from Bulgaria, England, Kenya, Nigeria and Wales are presented and compared. This study is part of on-going research in the analysis of biomedical and bioenvironmental materials. The database is still in its infancy. This revised version was published online in August 2006 with corrections to the Cover Date.     

New strategy to identify radicals in a time evolving EPR data set by multivariate curve resolution-alternating least squares

Electron paramagnetic resonance (EPR) spectroscopy is a powerful technique that is able to characterize radicals formed in kinetic reactions. However, spectral characterization of individual chemical species is often limited or even unmanageable due to the severe kinetic and spectral overlap among species in kinetic processes. Therefore, we applied, for the first time, multivariate curve resolution-alternating least squares (MCR-ALS) method to EPR time evolving data sets to model and characterize the different constituents in a kinetic reaction. Here we demonstrate the advantage of multivariate analysis in the investigation of radicals formed along the kinetic process of hydroxycoumarin in alkaline medium. Multiset analysis of several EPR-monitored kinetic experiments performed in different conditions revealed the individual paramagnetic centres as well as their kinetic profiles. The results obtained by MCR-ALS method demonstrate its prominent potential in analysis of EPR time evolved spectra.     

Assessment of Organic Source Contributions in Coastal Waters by Principal Component and Factor Analysis of the Dissolved and Particulate Hydrocarbon and Fatty Acid Contents

Abstract

Principal component (PCA) and factor analysis (FA) are evaluated for the interpretation of the information contained in large datasets resulting from the study of environmental samples by gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS). A case involving the identification and quantitation of 64 variables (hydrocarbons and fatty acids) in 87 water samples (dissolved and particulate fractions) of a coastal system (Ebre Delta) has been selected for examination.

PCA has evidenced important differences between the dissolved and particulate materials, as well as between the particulates collected in the bays and those obtained in the river and channels. PCA has also allowed the identification of outlier samples in the dissolved fraction. Independent application of FA to each of these groups has provided a useful method for the characterization of diverse algal, terrestrial, microbial and anthropogenic inputs. Direct correspondences between these source inputs and factor loadings have provided a selection of representative components of each contribution in the coastal system.     

Systematic Analytical Errors: Influence on the Grouping and Classification of Samples

Abstract

Two different sets of data have been subjected to distortion by induced systematic errors of types that are common in analytical chemistry. By means of eigenvector projections and a disjoint principal components analysis it is demonstrated that even gross systematic errors do not significantly influence the classification of the samples.     

Structure-Activity Relationships in the Control of Chemical Risks

Abstract

Cluster significance analysis is a tool that allows the identification of ‘embedded clusters’ in QSAR datasets. It is successfully applied to an eye irritation data set to show that these data are indeed asymmetric. The method identifies five parameters that form an embedded cluster of eye irritants amongst non irritants, although full separation is not achieved. This method has considerable potential to identify potential non-linearity in toxicology data sets and for parameter reduction. It is shown also that this can be obtained relatively quickly with an analysis performed on 100,000 subsets containing the same information as an analysis on 1,000,000 subsets.     

Three-block bi-focal PLS (3BIF-PLS) and its application in QSAR

When X and Y are multivariate, the two-block partial least squares (PLS) method is often used. In this paper, we outline an extension addressing a special case of the three-block (X/Y/Z) problem, where Z sits "under" Y. We have called this approach three-block bi-focal PLS (3BIF-PLS). It views the X/Y relationship as the dominant problem, and seeks to use the additional information in Z in order to improve the interpretation of the Y-part of the X/Y association. Two data sets are used to illustrate 3BIF-PLS. Example I relates to single point mutants of haloalkane dehalogenase from Sphingomonas paucimobilis UT26 and their ability to transform halogenated hydrocarbons, some of which are found as organic pollutants in soil. Example II deals with soil remediation capability of bacteria. Whole bacterial communities are monitored over time using "DNA-fingerprinting" technology to see how pollution affects population composition. Since the data sets are large, hierarchical multivariate modelling is invoked to compress data prior to 3BIF-PLS analysis. It is concluded that the 3BIF-PLS approach works well. The paper contains a discussion of pros and cons of the method, and hints at further developmental opportunities.     

MALDI-ToF mass spectrometry coupled with multivariate pattern recognition analysis for the rapid biomarker profiling of Escherichia coli in different growth phases

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-ToF MS) has been exploited extensively in the field of microbiology for the characterisation of bacterial species, the detection of biomarkers for early disease diagnosis and bacterial identification. Here, the multivariate data analysis technique of partial least squares-discriminant analysis (PLS-DA) was applied to ‘intact cell’ MALDI-ToF MS data obtained from Escherichia coli cell samples to determine if such an approach could be used to distinguish between, and characterise, different growth phases. PLS-DA is a technique that has the potential to extract systematic variation from large and noisy data sets by identifying a lower-dimensional subspace that contains latent information. The application of PLS-DA to the MALDI-ToF data obtained from cells at different stages of growth resulted in the successful classification of the samples according to the growth phase of the bacteria cultures. A further outcome of the analysis was that it was possible to identify the mass-to-charge (m/z) ratio peaks or ion signals that contributed to the classification of the samples. The Swiss-Prot/TrEMBL database and primary literature were then used to provisionally assign a small number of these m/z ion signals to proteins, and these tentative assignments revealed that the major contributors from the exponential phase were ribosomal proteins. Additional assignments were possible for the stationary phase and the decline phase cultures where the proteins identified were consistent with previously observed biological interpretation. In summary, the results show that MALDI-ToF MS, PLS-DA and a protein database search can be used in combination to discriminate between ‘intact cell’ E. coli cell samples in different growth phases and thus could potentially be used as a tool in process development in the bioprocessing industry to enhance cell growth and cell engineering strategies.     

The Determination of Ampicillin in Epicillin by the Curvature Inversion Method

Abstract

A method based on the curvature inversion technique has been developed for the determination of ampicillin in epicillin. The results for four epicillin samples are compared with the results obtained by thin-layer chromatography.     

Comparison of chemometric methods for the screening of comprehensive two-dimensional liquid chromatographic analysis of wine

Two chemometric methods are compared for the rapid screening of comprehensive two-dimensional liquid chromatographic (LC × LC) analysis of wine. The similarity index and Fisher ratio methods were both found to be able to distinguish geographical variability and to determine potentially significant peaks for further quantitative and qualitative study. An experimental data set consisting of five different wine samples and multiple simulated data sets were analyzed in the investigation of the screening methods. Several statistical analyses are employed in the understanding and verification of the results from the similarity index and Fisher ratio methods. The sum rank difference (SRD) method was used to compare the rankings of the two different methods as applied to the different data sets and to determine the amount of variability associated with the ranking of the peak differences. The major advantage the similarity index method offers is that it is an unsupervised method; no a priori knowledge of the samples (i.e., class identification) is required, while the Fisher ratio method is supervised. Both methods are rapid and require little user intervention other than the determination of a threshold for inclusion/exclusion of compounds from further analysis.