Three-way principal component analysis applied to food analysis: an example

The purpose of the study is to show how the interpretation of a complex multivariate data array can significantly be improved by the application of N-way principal component analysis (PCA). Two food related three-way data sets were studied; a sensory and a chromatographic data array. The Parafac and the Tucker3 models were applied and results were compared. Both N-way models presented here allow visualization of the data structure and give detailed information about the data set, notably allowing to understand relationships between objects and variables.     

Three-way principal component analysis of chemical data from Lake Como watershed

A large data set obtained by a one-year monthly determination of ions (F⁻, Cl⁻, Br⁻, NO₃⁻, NO₂⁻, PO₄³⁻, SO₄²⁻, Na⁺, K⁺, Ca²⁺, Mg²⁺, NH₄⁺) and trace metals of environmental concern (Ni, Co, Mn, Fe) from the tributaries of Lake Como (Lombardy, Northern Italy) was treated by three-way Principal Component Analysis. The results showed that the chemical features of the investigated rivers are mainly related to the lithology of the watershed. Some cases of contamination were evidenced and rationalized on the basis of anthropic pollution or on the basis of the geochemical features of the territory. The method here proposed allows an easy and quick interpretation of the chemical data by means of graphical devices. The information extracted by the three-way models would be very useful to regional agencies in developing a strategy to manage water resources in the whole basin of Lake Como.     

Evolution of Brassica rapa var. rapa L. volatile composition by HS-SPME and GC/IT-MS

Brassica rapa var. rapa L. (turnip) is highly appreciated and consumed by human. In this work, the volatile profile of B. rapa var. rapa was studied during the maturation process. The volatiles of seeds, sprouts with 6 and 9 days, and adult plant were determined using headspace solid-phase microextraction (HS-SPME) combined with gas chromatography/ion trap-mass spectrometry (GC/IT-MS).Several constituents, including alcohols, aldehydes, esters, ketones, norisoprenoids, nitrogen and sulphur compounds were characterized, totalizing 64 compounds. Isothiocyanates are the main volatiles in all matrices, being 3-butenyl isothiocyanate the major compound. Qualitative and quantitative differences were found among the analysed materials. Nitrogen and sulphur compounds decreased during the maturation process, while terpenes, aldehydes, norisoprenoids and ester compounds were present in higher amounts during germination, especially in sprouts with 9 days of development.     

顶空固相微萃取-气相色谱质谱联用测定烷基铅的研究

建立了顶空固相微萃取(HS SPME)与气相色谱 质谱(GC/MS)联用测定水样中四甲基铅和四乙基铅的方法,探讨了SPME萃取烷基铅的实验条件,并对GC/MS条件进行了优化。结果表明:四甲基铅和四乙基铅分别在5～1000ng/mL和1～500ng/mL范围内有良好的线性关系,检出限分别为四甲基铅5.19ng/mL,四乙基铅1.05ng/mL。方法用于合成水样分析,四甲基铅和四乙基铅的回收率在87.5%～110.6%之间,相对标准偏差在1.7%～6.5%之间。     

Determination of different recreational drugs in hair by HS-SPME and GC/MS

A simple procedure combining headspace solid-phase microextraction (HS-SPME) and gas chromatography–mass spectrometry (GC/MS) to detect and quantify amphetamines, ketamine, methadone, cocaine, cocaethylene and ∆⁹-tetrahydrocannabinol (THC) in hair is described. This procedure allows, in a single sample, even scant, analysis of drugs requiring different analytical conditions. A hair sample (10 mg) is washed and subjected to acidic hydrolysis. Then the HS-SPME is carried out (10 min at 90 °C) for amphetamines, ketamine, methadone, cocaine and cocaethylene. For derivatization of analytes, the fibre is introduced into the headspace of another closed vial containing acetic anhydride. After a chromatographic run, an alkaline hydrolysis for THC analysis is carried out in the same vial containing the hair sample previously used. For adsorption, the solid-phase microextraction needle is inserted into the headspace of the vial and the fibre is exposed for 30 min at 150 °C. For derivatization of analytes, the fibre is introduced into the headspace of another closed vial containing N-methyl-N-(trimethylsilyl)trifluoroacetamide. The GC/MS parameters were the same for both chromatographic runs. The linearity was proved to be between 0.01 and 10.00 ng/mg. The repeatability (intra- and interday precision) was below 10% as the coefficient of variation for all compounds. The accuracy, as the relative recovery, was 96.2–103.5% (spiked samples) and 88.6–101.7% (quality control sample). The limit of detection ranged from 0.01 to 0.12 ng/mg, and the limit of quantification ranged from 0.02 to 0.37 ng/mg. Application of the procedure to real hair samples is described. To the best of our knowledge, the proposed procedure combining HS-SPME and GC/MS is the first one be to successfully applied to the simultaneous determination of most of the common recreational drugs, including THC, in a single hair sample.     

Classification of byzantine glass samples by principal component analysis

Summary Nine samples of byzantine glass classified previously by cluster analysis are classified by principal component analysis (PCA). A visual inspection of plots in coordinates of the first two principal components gives essentially the same results as cluster analysis. In addition, PCA indicates relationships among the classification variables.

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Klassifizierung byzantinischer Glasproben durch Analyse der Hauptbestandteile

     

GC-MS及主成分分析法用于咖啡香精的指纹图谱分析和微差样品的识别

采用正己烷溶剂萃取法提取咖啡香精中的挥发性和半挥发性成分,并通过气相色谱-质谱法建立了咖啡香精的色谱指纹图谱,共定性了22个组分,占总量的87％,采用共有峰率、组分含量的相对标准偏差及相似度等几个指标对6个不同批次的样品进行了评价,结果表明它们之间具有很大的一致性,通过相似度比较和主成分分析的投影显示法区分微差样品。该色谱指纹图谱可用作咖啡香精的质量控制。     

Differentiation of resin-modified paints by pyrolysis-gas chromatography/mass spectrometry and principal component analysis

The combination of pyrolysis (Py) with gas chromatography/mass spectrometry (GC/MS) is already well established for polymer analysis. A first approach is reported using this method for detailed quality monitoring of a complex technical polymer system. Six similar solvent-based paints (one standard and five modifications) have been used for evaluation. The major pyrolysis products were identified and qualitative and quantitative modifications were detected and specified. Principal component analysis (PCA) was applied for visualization of differences and similarities.     

Differentiation of resin-modified paints by pyrolysis-gas chromatography/mass spectrometry and principal component analysis

The combination of pyrolysis (Py) with gas chromatography/mass spectrometry (GC/MS) is already well established for polymer analysis. A first approach is reported using this method for detailed quality monitoring of a complex technical polymer system. Six similar solvent-based paints (one standard and five modifications) have been used for evaluation. The major pyrolysis products were identified and qualitative and quantitative modifications were detected and specified. Principal component analysis (PCA) was applied for visualization of differences and similarities.     

SVD-based principal component analysis of geochemical data

Principal Component Analysis (PCA) was used for the mapping of geochemical data. A testing data matrix was prepared from the chemical and physical analyses of the coals altered by thermal and oxidation effects. PCA based on Singular Value Decomposition (SVD) of the standardized (centered and scaled by the standard deviation) data matrix revealed three principal components explaining 85.2% of the variance. Combining the scatter and components weights plots with knowledge of the composition of tested samples, the coal samples were divided into seven groups depending on the degree of their oxidation and thermal alteration. The PCA findings were verified by other multivariate methods. The relationships among geochemical variables were successfully confirmed by Factor Analysis (FA). The data structure was also described by the Average Group dendrogram using Euclidean distance. The found sample clusters were not defined so clearly as in the case of PCA. It can be explained by the PCA filtration of the data noise.     

Application of microcalorimetry and principal component analysis

Thermogravimetric analysis was used in order to study the reduction in air of submicronic powders of Co_3−x Mn _x O₄ spinels, with 0 ≤ x ≤ 1. For x = 0 (i.e. Co₃O₄), cation reduction occurred in a single step. It involved the Co^III ions at the octahedral sites, which were reduced to Co²⁺ on producing CoO. For 0 < x ≤ 1, the reduction occurred in two stages at increasing temperature with increasing amounts of manganese. The first step corresponded to the reduction of octahedral Co^III ions and the second was attributed to the reduction of octahedral Mn⁴⁺ ions to Mn³⁺. From the individual weight losses and the electrical neutrality of the lattice, the Co^III and Mn⁴⁺ ion concentrations were calculated. The distribution of cobalt and manganese ions present on each crystallographic site of the spinel was determined. In contrast to most previous studies that took into account either Co^III and Mn³⁺ or Co²⁺, Co^III and Mn⁴⁺ only, our thermal analysis study showed that Co²⁺/Co^III and Mn³⁺/Mn⁴⁺ pairs occupy the octahedral sites. These results were used to explain the resistivity measurements carried out on dense ceramics prepared from our powders sintered at low temperature (700–750 °C) in a Spark Plasma Sintering apparatus.     

柚皮蒸馏产物的GC/MS分析

用水蒸气蒸馏法对柚皮外果皮进行了挥发性成分提取。用GC/MS分析法进行了分离鉴定,初步分离出50余个峰,鉴定了44种物质,用面积归一法测定其质量分数。在被测物质中,烃类化合物有13种和含氧有机化合物有31种,主要物质为柠檬烯(75.09%),α 蒎烯(0.84%),β 月桂烯(6.71%),芳樟醇(1 08%),芳樟酯(1.43%),萘酮(4.89%)。     

Characterization of some new polysiloxane stationary phases by principal component analysis

Summary In this study, several new stationary phases were characterized by principal component analysis. Fourteen new stationary phases, including substituted phenyl and oligoethyleneoxide functionalities on polysiloxane polymers, were tested and compared to three well known stationary phases. The main features of these phases were studied using a series of test solutes of varying chemical characteristics representing the data set for principal component analysis. Two principal compounds were found to account for 99.20% of the variance (the first accounted for 94.96% and the second for 4.24%). The data were represented as a two-dimensional map for visual representation of the characteristics of these stationary phases. The first principal component represented a selectivity based on polarity (r²=0.998), while the second showed Lewis acid-base characteristics of the phases. Polarizable and amphoteric characteristics of these phases also became evident using this evaluation method.     

Choice of paraffin inhibitors for crude oils by principal component analysis

Accumulation of paraffin wax in the equipment for petroleum production causes large financial losses. The most effective and most economic means of avoiding deposition is often to add chemical additives to the crude oil, but it is not easy to find the most suitable additive for a particular situation because the phenomena involved are too complex for traditional approaches. Principal component analysis is used for data reduction of parameters to represent chemical additives and crude oils. On the basis of physicochemical properties (including spectral parameters) and the activity of additives on the crystallisation temperature of the paraffin wax, crude oils are classified into two families and chemical inhibitors into three families. A model for predicting the activity of additives is discussed.     

Headspace sampling and GC analysis of volatile urinary metabolites

A method requiring only 1 to 3 ml of sample is developed for the analysis of volatile metabolites in urine. Trace volatiles are stripped with helium and concentrated on Porapak Q and activated charcoal traps in series. Volatiles are thermally desorbed into a fused silica capillary column for analysis by gas chromatography. Variables affecting the process are studied. Profiles of untreated and acid hydrolyzed urine are presented.     

Rapid determination of volatile compounds in grapes by HS-SPME coupled with GC-MS

Volatile compounds of grapes are responsible of varietal aroma. At the moment, methods used for analysis of these compounds are solvent-based, time-consuming and generally require large amounts of sample. In order to obtain an appropriate technique to study grape volatile compounds, HS-SPME method has been developed. The optimal sampling conditions were: 70 °C for 20 min with a 65-μm PDMS/DVB fibre. Sixteen volatile compounds have been quantified in pulp and skins of Muscat grapes. Terpenes, mainly linalool, geraniol and nerol, have been the volatiles present in the highest concentration, since these compounds contribute, to a larger extent, to the aroma of Muscat grapes and wines. So the proposed technique can be used for the characterisation of grape varieties or cultivars and for the determination of the aromatic maturity of grapes.     

Application of principal component analysis to the extraction of pure mass spectra in chemical analysis by gas chromatography/mass spectrometry

In this work, we investigated the possibility of the purification of mass spectra of coeluted substances containing at least one characteristic value of m/z using principal component analysis. Simulated and real gas chromatographic/mass spectrometric data were analyzed. For the simulated data, the resolution of the chromatographic peaks varied from 0.075 to 0.75, and the ratio of component concentrations ranged from 0.01 to 100. Noise-free simulated data and simulated data with randomly distributed noise were considered. It was shown that the method gave satisfactory results even when the chromatographic resolution (R _s ) was less than 0.05.     

Investigation of sport supplements quality by Raman spectroscopy and principal component analysis

In this work, sport supplements were investigated by Raman spectroscopy. Samples were obtained from health foods shops, gyms and sports centers covering a wide range of available supplement powders. A systematic comparison of Raman spectra of the analyzed supplements allowed identifying the supplement type through the characteristic vibrational modes of carbohydrates and proteins. The protein supplements were identified by Raman bands at 1650, 1250 and 1004 cm⁻¹, while the spectral range between 1200 and 800 cm⁻¹ was useful to identify the carbohydrate supplements. Due to the diversity in composition of sport supplements, a chemometric tool such as principal component analysis (PCA) was employed to assist in the interpretation of Raman spectra, allowing also the identification of compounds present in sport supplements. Especially, the Raman scattering of aromatic and aliphatic amino acids residues contributes to the existence of bands characteristic for the different types of proteins. This kind of information is very important for the quality control of these products, for detecting the presence of fraud or a sample composition in disagreement with the label, thus ensuring the provenance of the supplements.