Model inversion and three-way decompositions in the analytical quality by design strategy for the determination of phthalates BY HS-SPME-GC-MS.

In this work, strategies within Analytical Quality by Design (AQbD) with tools of the Process Analytical Technology (PAT) were used in the development of a head space-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) procedure for the multiresidue analysis of four phthalic acid esters, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, dibutyl phthalate and diethyl phthalate (regulated by Commission Regulation (EU) No 10/2011). The approach is based on the fact that the intended quality of the resulting chromatograms is defined in terms of the loadings on the sample mode of a Parallel Factor Analysis (PARAFAC2) decomposition. These loadings are the ones used for the inversion of a Partial Least Squares (PLS2) prediction model that has been previously fitted.

Handling Variables, Inversion of Partial Least Squares Models for Class-Modelling, to Bring Defective Items to Non-Defective Ones.

In the context of binary class-modelling techniques, the paper presents the computation in the input space of linear boundaries of a class-model constructed with given values of sensitivity and specificity. This is done by inversion of a decision threshold, set with these values of sensitivity and specificity, in the probabilistic class-models computed by means of PLS-CM (Partial Least Squares for Class-Modelling). The characterization of the boundary hyperplanes, in the latent space (space spanned by the selected latent variables of the fitted PLS model) or in the input space, makes it possible to calculate directions that can be followed to move objects toward the class-model of interest.

Detection of cold chain breaks using partial least squares-class modelling based on biogenic amine profiles in tuna.

The maintenance of the cold chain is essential to ensure foodstuff conformity and safety. However, gaps in the cold chain may be expected so designing analytical methods capable to detect cold chain breaks is a worthwhile issue. In this paper, the possibility of using the amount of nine biogenic amines (BAs) determined in Thunnus albacares by HPLC-FLD for detecting cold chain breaks is approached.

Combining excitation-emission matrix fluorescence spectroscopy, parallel factor analysis, cyclodextrin-modified micellar electrokinetic chromatography and partial least squares class-modelling for green tea characterization.

In this study, an alternative analytical approach for analyzing and characterizing green tea (GT) samples is proposed, based on the combination of excitation-emission matrix (EEM) fluorescence spectroscopy and multivariate chemometric techniques. The three-dimensional spectra of 63 GT samples were recorded using a Perkin-Elmer LS55 luminescence spectrometer; emission spectra were recorded between 295 and 800 nm at excitation wavelength ranging from 200 to 290 nm, with excitation and emission slits both set at 10 nm. The excitation and emission profiles of two factors were obtained using Parallel Factor Analysis (PARAFAC) as a 3-way decomposition method.

Class-modeling analysis reveals T-cell homeostasis disturbances involved in loss of immune control in elite controllers.

Background: Despite long-lasting HIV replication control, a significant proportion of elite controller (EC) patients may experience CD4 T-cell loss. Discovering perturbations in immunological parameters could help our understanding of the mechanisms that may be operating in those patients experiencing loss of immunological control.

Methods: A case-control study was performed to evaluate if alterations in different T-cell homeostatic parameters can predict CD4 T-cell loss in ECs by comparing data from EC patients showing significant CD4 decline (cases) and EC patients showing stable CD4 counts (controls).

Ad-hoc blocked design for the robustness study in the determination of dichlobenil and 2,6-dichlorobenzamide in onions by programmed temperature vaporization-gas chromatography-mass spectrometry.

An 'ad-hoc' experimental design to handle the robustness study for the simultaneous determination of dichlobenil and its main metabolite (2,6-dichlorobenzamide) in onions by programmed temperature vaporization-gas chromatography-mass spectrometry (PTV-GC-MS) is performed. Eighteen experimental factors were considered; 7 related with the extraction and clean up step, 8 with the PTV injection step and 3 factors related with the derivatization step. Therefore, a high number of experiments must be carried out that cannot be conducted in one experimental session and, as a consequence, the experiments of the robustness study must be performed in several sessions or blocks.

Experimental design for the optimization of the derivatization reaction in determining chlorophenols and chloroanisoles by headspace-solid-phase microextraction-gas chromatography/mass spectrometry.

The paper shows some tools (its interpretation and usefulness) to optimize a derivatization reaction and to more easily interpret and visualize the effect that some experimental factors exert on several analytical responses of interest when these responses are in conflict. The entire proposed procedure has been applied in the optimization of equilibrium/extraction temperature and extraction time in the acetylation reaction of 2,4,6-trichlorophenol; 2,3,4,6-tetrachlorophenol, pentachlorophenol and 2,4,6-tribromophenol as internal standard (IS) in presence of 2,4,6-trichloroanisole, 2,3,5,6-tetrachloroanisole, pentachloroanisole and 2,4,6-trichloroanisole-d5 as IS. The procedure relies on the second order advantage of PARAFAC (parallel factor analysis) that allows the unequivocal identification and quantification, mandatory according international regulations (in this paper the EU document SANCO/12495/2011), of the acetyl-chlorophenols and chloroanisoles that are determined by means of a HS-SPME-GC/MS automated device.

Optimization of headspace experimental factors to determine chlorophenols in water by means of headspace solid-phase microextraction and gas chromatography coupled with mass spectrometry and parallel factor analysis.

In this work an analytical procedure based on headspace solid-phase microextraction and gas chromatography coupled with mass spectrometry (HS-SPME-GC/MS) is proposed to determine chlorophenols with prior derivatization step to improve analyte volatility and therefore the decision limit (CCα). After optimization, the analytical procedure was applied to analyze river water samples. The following analytes are studied: 2,4-dichlorophenol (2,4-DCP), 2,4,6-trichlorophenol (2,4,6-TrCP), 2,3,4,6-tetrachlorophenol (2,4,6-TeCP) and pentachlorophenol (PCP).

Usefulness of a PARAFAC decomposition in the fiber selection procedure to determine chlorophenols by means SPME-GC-MS.

In this work, a procedure based on solid-phase microextraction and gas chromatography coupled with mass spectrometry is proposed to determine chlorophenols in water without derivatization. The following chlorophenols are studied: 2,4-dichlorophenol; 2,4,6-trichlorophenol; 2,3,4,6-tetrachlorophenol and pentachlorophenol. Three kinds of SPME fibers, polyacrylate, polydimethylsiloxane, and polydimethylsiloxane/divinylbenzene are compared to identify the most suitable one for the extraction process on the basis of two criteria: (a) to select the equilibrium time studying the kinetics of the extraction, and (b) to obtain the best values of the figures of merit.

D-optimal designs and N-way techniques to determine sulfathiazole in milk by molecular fluorescence spectroscopy.

The present work proposes an analytical procedure to determine sulfathiazole in milk by using molecular fluorescence spectroscopy. For this sulfonamide the European Union in Regulation 37/2010 has established a maximum residue limit in milk of 100 μg kg(-1). The study includes the effect of six factors on the recovery of sulfathiazole.

Optimization of the derivatization reaction and the solid-phase microextraction conditions using a D-optimal design and three-way calibration in the determination of non-steroidal anti-inflammatory drugs in bovine milk by gas chromatography-mass spectrometry.

An experimental design optimization is reported of an analytical procedure used in the simultaneous determination of seven non-steroidal anti-inflammatory drugs (NSAIDs) in bovine milk by gas chromatography with mass spectrometry detection (GC-MS). This analytical procedure involves a solid-phase microextraction (SPME) step and an aqueous derivatization procedure of the NSAIDs to ethyl esters in bovine milk. The following NSAIDs are studied: ibuprofen (IBP), naproxen (NPX), ketoprofen (KPF), diclofenac (DCF), flufenamic acid (FLF), tolfenamic acid (TLF) and meclofenamic acid (MCL).

Optimization of a solid-phase extraction procedure in the fluorimetric determination of sulfonamides in milk using the second-order advantage of PARAFAC and D-optimal design.

The objective of this work is to optimize a solid-phase extraction procedure for the simultaneous determination of sulfadiazine, sulfamerazine, and sulfamethazine in milk by fluorimetric detection. For this task, an alternative strategy is employed, which allows one to reduce noticeably the number of experiments without losing the quality of the estimations. It consists of the use of a D-optimal design together with PARAFAC decomposition for the calculation of the response in the experimental design.

Study of robustness based on n-way models in the spectrofluorimetric determination of tetracyclines in milk when quenching exists.

An important step in the validation of an analytical procedure is the study of its robustness. In the case of spectrofluorimetric determinations, quenching introduces specific problems which are approached in this paper for the particular case of tetracyclines determination in milk. Quenching can be detected with excitation emission matrices (EEM) signals and a three-way Parallel Factor (PARAFAC) decomposition and modelled by means of a four-way PARAFAC decomposition which reproduces the physical model of this effect.

Determination and identification, according to European Union Decision 2002/657/EC, of malachite green and its metabolite in fish by liquid chromatography-tandem mass spectrometry using an optimized extraction procedure and three-way calibration.

This paper reports a multiresponse optimization of an extraction procedure in the simultaneous determination of malachite green (MG) and its metabolite (leucomalachite green, LMG) in fish by liquid chromatography with triple quadrupole mass spectrometry (LC-MS/MS). Prior to optimization, the active factors of the extraction procedure were determined by a screening experimental design. Then, in the optimal experimental conditions of the extraction, MG and LMG have been determined by using a three-way calibration model based on parallel factor analysis (PARAFAC).

Usefulness of parallel factor analysis to handle the matrix effect in the fluorescence determination of tetracycline in whey milk.

The determination of tetracycline by fluorescence spectrophotometry in complex matrices has some difficulties, because the presence of other compounds in the matrix affects the analytical signal. In this work, the effect of some inorganic species that are present in whey milk on the fluorescence signal of tetracycline is studied using a D-optimal experimental design. Next, an experimental strategy is proposed in conjunction with Parallel Factor Analysis, PARAFAC, modeling that leads to suitably modeling the severe matrix effect in the determination of tetracycline in whey milk.

Robust regression techniques A useful alternative for the detection of outlier data in chemical analysis.

The validation of an analytical procedure means the evaluation of some performance criteria such as accuracy, sensitivity, linear range, capability of detection, selectivity, calibration curve, etc. This implies the use of different statistical methodologies, some of them related with statistical regression techniques, which may be robust or not. The presence of outlier data has a significant effect on the determination of sensitivity, linear range or capability of detection amongst others, when these figures of merit are evaluated with non-robust methodologies.

Optimization of a FIA system with amperometric detection by means of a desirability function: determination of sulfadiazine, sulfamethazine and sulfamerazine in milk.

A sensitive and cheap FIA, with amperometric detection, analytical procedure is developed in this paper to determine sulfadiazine, sulfamethazine and sulfamerazine in milk. A multicriteria optimization based on the use of a desirability function is used for optimizing two analytical responses (peak height and its variability) since single-objective optimizations lead to conflicting experimental conditions. In the optimum conditions, the determination of the three sulfonamides in milk samples is carried out, the analytical procedure being validated according to Commission Decision 2002/657/EC.

Advantages of PARAFAC calibration in the determination of malachite green and its metabolite in fish by liquid chromatography-tandem mass spectrometry.

This paper reports the properties and advantages of the three-way calibration models based on parallel factor analysis (PARAFAC) in the simultaneous determination of malachite green (MG) and its metabolite (leucomalachite green, LMG) in trout. A recently method proposed by community reference laboratory AFSSA-LERMVD (Fougères, France) has been used. The method is based on liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS) in multiple reaction monitoring (MRM) mode.

Performance characteristics according to Commission Decision 2002/657/EC in the fluorimetric determination of tetracycline in the absence and in the presence of magnesium.

The fluorimetric determination of tetracycline is usually carried out in the presence of some metals that, through the formation of a complex with this antibiotic, enhance its fluorescence emission, giving more sensitive determination methods. It is well established that magnesium is one of these metals. However, it is possible that higher signals do not mean a real improvement in the quality of the analytical method.

Multiresponse optimization and parallel factor analysis, useful tools in the determination of estrogens by gas chromatography-mass spectrometry.

This paper reports an experimental design optimization of a recently proposed silylation procedure that avoids the introduction of false positives and false negatives in the simultaneous determination of steroid hormone estrone (E1) and 17-alpha-ethinylestradiol (EE2) by gas chromatography-mass spectrometry (GC/MS). The figures of merit for several calibration procedures were evaluated under optimum conditions in the silylation step. Internal standardization strategies were applied and global models were constructed by gathering signals recorded on three non-consecutive days.

Identification and quantification of enrofloxacine in poultry feeding water through excitation emission fluorescence and three-way PARAFAC calibration.

In this work an excitation emission molecular fluorescence technique with PARAFAC calibration is proposed for enrofloxacine determination in feeding water from poultry farms. In accordance with the working criteria of the 2002/657/EC European Decision, the proposed method has a capability of detection, CCbeta, of 6.8 microg l(-1), for both probabilities of false positive and false negative of 5%.