Projection to latent correlative structures, a dimension reduction strategy for spectral-based classification.

Latent variables are used in chemometrics to reduce the dimension of the data. It is a crucial step with spectroscopic data where the number of explanatory variables can be very high. Principal component analysis (PCA) and partial least squares (PLS) are the most common.

Metabolomics profile responses to changing environments in a common bean (Phaseolus vulgaris L.) germplasm collection.

Metabolomics is one of the most powerful -omics to assist plant breeding. Despite the recognized genetic diversity in Portuguese common bean germplasm, details on its metabolomics profiles are still missing. Aiming to promote their use and to understand the environment's effect in bean metabolomics profiles, 107 Portuguese common bean accessions, cropped under contrasting environments, were analyzed using spectrophotometric, untargeted and targeted mass spectrometry approaches.

Mining for Peaks in LC-HRMS Datasets Using Finnee - A Case Study with Exhaled Breath Condensates from Healthy, Asthmatic, and COPD Patients.

Separation techniques hyphenated to high-resolution mass spectrometry are essential in untargeted metabolomic analyses. Due to the complexity and size of the resulting data, analysts rely on computer-assisted tools to mine for features that may represent a chromatographic signal. However, this step remains problematic, and a high number of false positives are often obtained.

Background correction in separation techniques hyphenated to high-resolution mass spectrometry - Thorough correction with mass spectrometry scans recorded as profile spectra.

Separation techniques hyphenated with high-resolution mass spectrometry have been a true revolution in analytical separation techniques. Such instruments not only provide unmatched resolution, but they also allow measuring the peaks accurate masses that permit identifying monoisotopic formulae. However, data files can be large, with a major contribution from background noise and background ions.

Variability of some diterpene esters in coffee beverages as influenced by brewing procedures.

Several coffee brews, including classical and commercial beverages, were analyzed for their diterpene esters content (cafestol and kahweol linoleate, oleate, palmitate and stearate) by high performance liquid chromatography with diode array detector (HPLC-DAD) combined with spectral deconvolution. Due to the coelution of cafestol and kahweol esters at 225 nm, HPLC-DAD did not give accurate quantification of cafestol esters. Accordingly, spectral deconvolution was used to deconvolve the co-migrating profiles.

Algorithm for comprehensive analysis of datasets from hyphenated high resolution mass spectrometric techniques using single ion profiles and cluster analysis.

Various algorithms have been developed to improve the quantity and quality of information that can be extracted from complex datasets obtained using hyphenated mass spectrometric techniques. While different approaches are possible, the key step often consists in arranging the data into a large series of profiles known as extracted ion profiles. Those profiles, similar to mono-dimensional separation profiles, are then processed to detect potential chromatographic peaks.

Liquid chromatography with diode array detection combined with spectral deconvolution for the analysis of some diterpene esters in Arabica coffee brew.

In this manuscript, the separation of kahweol and cafestol esters from Arabica coffee brews was investigated using liquid chromatography with a diode array detector. When detected in conjunction, cafestol, and kahweol esters were eluted together, but, after optimization, the kahweol esters could be selectively detected by setting the wavelength at 290 nm to allow their quantification. Such an approach was not possible for the cafestol esters, and spectral deconvolution was used to obtain deconvoluted chromatograms.

Introducing the concept of centergram. A new tool to squeeze data from separation techniques-mass spectrometry couplings.

In separation techniques hyphenated to mass spectrometry (MS) the bulk from the separation step is continuously flowing into the mass spectrometer where the compounds, arriving at each separation time, are ionized and further separated based on their m/z ratio. An MS detector is recognized as being a universal detector, although it can also be a very selective instrument. In spite of these advantages, classical two dimensional representations from these hyphenated systems, such as those based on the base peak of electropherogram/chromatogram or on the total ion of electropherogram/chromatogram, usually hide a large number of features that if correctly assessed will show the presence of co-migrating species and/or the low abundant ones.

Immobilized humic substances and immobilized aggregates of humic substances as sorbent for solid phase extraction.

In this work, humic substances (HS) immobilized, as a thin layer or as aggregates, on silica gel were tested as material for solid phase extraction. Some triazines (simazine, atrazine, therbutylazine, atrazine-desethyl-desisopropyl-2-hydroxy, ametryn and terbutryn), have been selected as test analytes due to their environmental importance and to span a large range of solubility and octanol/water partition coefficient (logP). The sorbent was obtained immobilizing a thin layer of HS via physisorption on a pre-coated silica gel with a cationic polymer (polybrene).

Dynamically formed admicelle layer to control the amplitude of cathodic electroosmotic flow.

In this manuscript, a method to precisely adjust the amplitude of a cathodic electroosmotic flow is described. The method uses a capillary pre-coated with a cationic polymer (polybrene), in presence of an anionic surfactant such as sodium dodecyl sulfate. At low concentration of surfactant, molecules will self-assemble to form an immobilized hemimicelle layer with the anionic "head" in contact with the cationic coating and the hydrophobic tail reaching into the background electrolyte.

Noise normalisation in capillary electrophoresis using a diode array detector.

When using capillary electrophoresis with a diode array detector, the wavelength at maximum absorbance is often chosen to quantify a given analyte. However, the background noise for every wavelength should be taken into account as it is by maximising the signal to noise ratio that the lowest limit of detection will be obtained. Here, we proposed an algorithm allowing to correct an electropherogram from its background absorption and to estimate the background noise.

Studying the interaction between triazines and humic substances--a new approach using open tubular capillary electrochromatography.

The strength of the interaction between a pesticide and the soil organic matter is a key parameter to assess the risk of it reaching to groundwater with potentially harmful effects to human health. In this work, a new approach that allows measuring such interactions in a few minutes using a purified fraction of the soil organic matter (humic substances) is detailed. The strength of sorption is assessed via the normalised difference of elution (retention factor, k') between the chemical of interest and a neutral marker transported via electroosmotic flow through an open tubular column supporting the immobilised humic substances (open tubular capillary electrochromatography).

Direct photodegradation of carbamazepine followed by micellar electrokinetic chromatography and mass spectrometry.

Carbamazepine, a widely consumed psychotropic pharmaceutical, is one of the most commonly detected drugs in the environment. To better assess the environmental persistence of carbamazepine in aqueous matrices, the effect of pH and dissolved oxygen on the direct photodegradation rate of this pharmaceutical was evaluated in this study, using simulated solar irradiation. In order to follow the degradation and the emergence of photoproducts, a micellar electrokinetic chromatography based method was developed, consisting on the use of a dynamically coated capillary column.

Comparison between MEKC and UV spectral deconvolution to follow sorption experiment in soil.

In this study a simple and rapid procedure for monitoring sorption of atrazine onto soil samples was developed. This method is based on a multiwavelength UV spectral deconvolution (UVSD) where the UV spectrum of a sample is considered as a linear combination of absorption spectra, named reference spectra. The combination of the reference spectra allows the restitution of the shape of the UV spectrum of any unknown sample.

Application of MEKC to the monitoring of atrazine sorption behaviour on soils.

Measuring interactions between soils and xenobiotics is critical to assess the threat to water resources posed by potentially harmful chemicals. Such studies are done via batch experiments where the chemical of interest is incubated with the soil for a long period of time. However, the analysis of the remaining concentration in the aqueous phase is often troublesome, due to dissolved organic matter that can interfere with the analysis.

Robustness of the co-ion transfer ratio in capillary electrophoresis.

In CE, indirect detection mode often exhibits a lower precision than its direct counterpart. Although various explanations have already been advanced, in this work, we aimed to investigate if this is due, in part, to problems of robustness of the co-ion transfer ratio (TR), thus being inherent to this particular detection scheme. This was investigated using simulation software that allows an accurate control of various parameters and validated using acetic acid as a test compound.

Time of flight versus ion trap MS coupled to CE to analyse intact proteins.

In this work, two different CE-MS instruments, namely, CE-ESI-IT-MS and CE-ESI-TOF-MS, applied to analyse intact proteins from complex samples are investigated. The aim of this work was to compare both instruments in terms of LOD, number of proteins detected, and precision and repeatability in the determination of the protein relative molecular mass. Results show that although CE-ESI-IT-MS provides cleaner MS spectra of intact proteins, CE-ESI-TOF-MS allows the identification of a higher number of proteins from complex matrices in an easier way.

CE-MS of zein proteins from conventional and transgenic maize.

In this work, an original CE-MS method has been developed to analyze the complex zein protein fractions from maize. A thorough optimization of: (i) zein protein extraction, (ii) CE separation, and (iii) electrospray-MS (ESI-MS) detection is carried out in order to obtain highly informative CE-MS profiles of this fraction. The developed CE-MS method provides good separation of multiple zein proteins based on their electrophoretic mobilities as well as adequate characterization of these proteins based on their M(r).

Reproducible and efficient separation of aggregatable zein proteins by CZE using a volatile background electrolyte.

Zein proteins are a complex mixture of polypetides that belong to the alcohol-soluble storage proteins group (prolamines) in corn. These proteins constitute about 50-60% of the total endosperm protein and are classified in different groups on the basis of differences in their solubility and sequence. Among them, zein proteins are considered the majority group showing a high tendency to aggregate what makes their analysis by any analytical method very difficult.

Simplified 2-D CE-MS mapping: analysis of proteolytic digests.

It has been demonstrated that CE-MS is a very useful hyphenated technique for proteomic studies. However, the huge amount of data stored in a single CE-MS run makes it necessary to account with procedures able to extract all the relevant information made available by CE-MS. In this work, we present a new and easy approach capable of generating a simplified 2-D map from CE-MS raw data.

Measuring the length of hydrodynamically injected plugs in capillary electrophoresis using the electrical current monitoring.

Although CE is nowadays a worldwide separation technique, it is generally recognized that one of its main limitations is its poor robustness for quantitative analysis. Although this limitation can partially be surpassed using internal standards (ISs), it is well known that to find adequate standards is a very difficult task when too complex mixtures have to be analyzed. In this work, an alternative method to improve quantitation by CE is presented using the electrical current profile monitored during any CE run.

Field amplified separation in capillary electrophoresis: a capillary electrophoresis mode.

In field-amplified injection in capillary electrophoresis (CE), the capillary is filled with two buffering zones of different ionic strength; this induces an amplified electrical field in the low ionic strength zone and a lower field in the high ionic strength zone, making sample stacking feasible. The electroosmotic flow (eof) usually observed in CE, however, displaces the low field zone and induces an extra band broadening preventing any CE separation in the field-amplified zone. These limitations have originated the restricted use of field amplification in CE only for stacking purposes.

Capillary electrophoresis using copolymers of different composition as physical coatings: a comparative study.

In this work, a comparative study on the use of different polymers as physically adsorbed coatings for CE is presented. It is demonstrated that the use of ad hoc synthesized polymers as coatings allows tailoring the EOF in CE increasing the flexibility of this analytical technique. Namely, different polymers were synthesized at our laboratory using different percentages of ethylpyrrolidine methacrylate (EpyM) and N,N-dimethylacrylamide (DMA).

Electromigration dispersion in capillary zone electrophoresis. Experimental validation of use of the Haarhoff-Van der Linde function.

This paper provides experimental validation of the use of the Haarhoff-Van der Linde (HVL) peak fitting function to fit experimental capillary zone electrophoresis (CZE) electropherograms. The test mixtures were composed of paraquat over a five order of magnitude concentration range (1.2 microM to 120 mM) and 4-aminopyridine at constant concentration (0.