Effect of the cleaning procedure of Tenax on its reuse in the determination of plasticizers after migration by gas chromatography/mass spectrometry

This paper presents the simultaneous determination of a UV stabilizer (benzophenone (BP)) together with four plasticizers (butylated hydroxytoluene (BHT), diisobutyl phthalate (DiBP), bis(2-ethylhexyl) adipate (DEHA) and diisononyl phthalate (DiNP)) in Tenax by gas chromatography/mass spectrometry and PARAFAC, using DiBP-d4 as internal standard. Regulation (EU) No. 10/2011 establishes Tenax as food simulant E for testing specific migration from plastics into dry foodstuffs. This simulant must be cleaned before its use to eliminate impurities. Tenax is expensive, so its reuse would save costs. A two-way ANOVA was used to study some parameters affecting the cleaning and the extraction of Tenax. The most adequate conditions were chosen taking the values of the coefficient of variation and the average recovery rates of spiked Tenax samples into account. A study to determine if some analytes remain in Tenax when it is reused and the effect that the cleaning procedure may have in the adsorption capability of Tenax was proposed. This study led to the conclusion that Tenax could not be reused in this multiresidue determination. All the analytes were unequivocally identified in all the stages of this work and trueness was verified at a 95% confidence level in all cases. A calibration based on PARAFAC provided the following values of capability of detection (CCβ): 2.28 μg L−1 for BHT, 10.57 μg L−1 for BP, 7.87 μg L−1 for DiBP, 3.04 μg L−1 for DEHA and 124.8 μg L−1 for DiNP, with the probabilities of false positive and false negative fixed at 0.05. The migration of the analytes from a printed paper sample into Tenax was also studied. The presence of BHT in the food simulant was confirmed and the amount released of this analyte from the paper was 2.56 μg L−1.Ministerio de Economía y Competitividad (CTQ2014-53157-R) and Junta de Castilla y León (BU012P1

Logical analysis of sample pooling for qualitative analytical testing

When the prevalence of positive samples in a whole population is low, the pooling of samples to detect them has been widely used for epidemic control. However, its usefulness for applying analytical screening procedures in food safety (microbiological or allergen control), fraud detection or environmental monitoring is also evident. The expected number of tests per individual sample that is necessary to identify all ‘positives’ is a measure of the efficiency of a sample pooling strategy. Reducing this figure is key to an effective use of available resources in environmental control and food safety. This reduction becomes critical when the availability of analytical tests is limited, as the SARS-CoV-2 pandemic showed. The outcome of the qualitative analytical test is binary. Therefore, the operation governing the outcome of the pooled samples is not an algebraic sum of the individual results but the logical operator (‘or’ in natural language). Consequently, the problem of using pooled samples to identify positive samples naturally leads to proposing a system of logical equations. Therefore, this work suggests a new strategy of sample pooling based on: i) A half-fraction of a Placket-Burman design to make the pooled samples and ii) The logical resolution, not numerical, to identify the positive samples from the outcomes of the analysis of the pooled samples. For a prevalence of ‘positive’ equal to 0.05 and 10 original samples to be pooled, the algorithm presented here results in an expected value per individual equal to 0.37, meaning a 63% reduction in the expected number of tests per individual sample. With sensitivities and specificities of the analytical test ranging from 0.90 to 0.99, the expected number of tests per individual ranges from 0.332 to 0.416, always higher than other pooled testing algorithms. In addition, the accuracy of the algorithm proposed is better or similar to that of other published algorithms, with an expected number of hits ranging from 99.16 to 99.90%. The procedure is applied to the detection of food samples contaminated with a pathogen (Listeria monocytogenes) and others contaminated with an allergen (Pistachio) by means of Polymerase Chain Reaction, PCR, test.This work was supported by Consejería de Educación de la Junta de Castilla y León through project BU052P20 co-financed with European Regional Development Funds. The authors thank Dr. Laura Rubio for applying the double-blind protocol to dope the samples and AGROLAB S.L.U, Burgos (Spain) for the careful preparation of the pooled samples

On the construction of experimental designs for a given task by jointly optimizing several quality criteria: Pareto-optimal experimental designs

Experimental designs for a given task should be selected on the base of the problem being solved and of some criteria that measure their quality. There are several such criteria because there are several aspects to be taken into account when making a choice. The most used criteria are probably the so-called alphabetical optimality criteria (for example, the A-, E-, and D-criteria related to the joint estimation of the coefficients, or the I- and G-criteria related to the prediction variance). Selecting a proper design to solve a problem implies finding a balance among these several criteria that measure the performance of the design in different aspects. Technically this is a problem of multi-criteria optimization, which can be tackled from different views. The approach presented here addresses the problem in its real vector nature, so that ad hoc experimental designs are generated with an algorithm based on evolutionary algorithms to find the Pareto-optimal front. There is not theoretical limit to the number of criteria that can be studied and, contrary to other approaches, no just one experimental design is computed but a set of experimental designs all of them with the property of being Pareto-optimal in the criteria needed by the user. Besides, the use of an evolutionary algorithm makes it possible to search in both continuous and discrete domains and avoid the need of having a set of candidate points, usual in exchange algorithms.Projects CTQ2011-26022(SpanishMinisteriodeEconomíayCompetitividad)andBU108A11-2(JuntadeCastillayLeón)

Optimization of a headspace solid-phase microextraction and gas chromatography/mass spectrometry procedure for the determination of aromatic amines in water and in polyamide spoons

In this work, a headspace solid-phase microextraction and gas chromatography coupledwith mass spectrometry (HS-SPME-GC/MS) method for trace determination of primary aromatic amines was developed. The following analytes were investigated: aniline (A), 4,4′-diaminodiphenylmethane (4,4′-MDA) and 2,4-diaminotoluene (2,4-TDA) using 3-chloro-4-fluoroaniline (3C4FA) and 2-aminobiphenyl (2ABP) as internal standards. Prior to extraction the analytes were derivatized in the aqueous solution by diazotation and subsequent iodination. The derivativeswere extracted byHS-SPME using a PDMS/DVB fiber and analyzed by GC/MS. A D-optimal design was used to study the parameters affecting the HS-SPME procedure and the derivatization step. Two experimental factors at two levels and one factor at three levels were considered: (i) reaction time, (ii) extraction temperature, and (iii) extraction time in the headspace. The interaction between the extraction temperature and extraction time was considered in the proposed model. The loadings in the sample mode estimated by a PARAFAC (parallel factor analysis) decomposition for each analyte were the response used in the design because they are proportional to the amount of analyte extracted. The optimum conditions for the best extraction of the analytes were achieved when the reaction time was 20 min, the extraction temperature was 50 °C and the extraction time was 25 min. The interaction was significant. A calibration based on a PARAFAC decomposition provided the following values of decision limit (CCα): 1.07 μgL−1 for A, 1.23 μg L−1 for 2,4-TDA and 0.83 μg L−1 for 4,4′-MDA for a probability of false positive fixed at 5%. Also, the accuracy (trueness and precision) of the procedurewas assessed. Furthermore, all the analyteswere unequivocally identified. Finally, the method was applied to spiked water samples and polyamide cooking utensils (spoons). 3% (w/v) acetic acid in aqueous solution was used as food simulant for testing migration from polyamide kitchenware. Detectable levels of 4,4′-diaminodiphenylmethane and aniline were found in food simulant from some of the investigated cooking utensils.Ministerio de Economía y Competitividad (CTQ2011-26022) and Junta de Castilla y León (BU108A11-2

Improvement in the identification and quantification of UV filters and additives in sunscreen cosmetic creams by gas chromatography/mass spectrometry through three-way calibration techniques

The simultaneous determination of 2,6-di-tert-butyl-4-methyl-phenol (BHT), benzophenone (BP), benzophenone-3 (BP3) and diisobutyl phthalate (DiBP) in seven sunscreen creams was carried out by gas chromatography/mass spectrometry (GC/MS) using DiBP-d4 as internal standard. The content of BP3, which is a UV filter, must not exceed 6% (w/w) in cosmetic products according to Regulation (EU) 2017/238 and the use of DiBP in cosmetic products shall be prohibited according to Regulation (EC) No 1223/2009. The conclusions obtained with the univariate standard methodology in the identification of the analytes contained in the creams were wrong. However, a calibration based on PARAFAC or PARAFAC2 decompositions, where the samples of the prediction set were projected on the model obtained previously with the calibration set, enabled the unequivocal identification and quantification of the analytes even in the presence of interferents not considered in the calibration model. The PARAFAC2 decomposition was used to overcome the shifts in the retention time of BP and BP3. These three-way calibration techniques are needed to avoid false negative results. The method had not proportional or constant bias. The presence of BHT was detected in the seven sunscreen creams analysed at an amount of 6.48 10−2%, 8.53 10−2%, 1.70 10−4%, 1.11 10−4%, 2.51 10−3%, 3.20 10−5% and 6.35 10−3%. The concentrations of DiBP found in four creams were 3.49 10−2%, 3.19 10−2%, 3.26 10−2% and 2.51 10−2%. On the other hand, BP was only detected in two of the cosmetic creams analysed at an amount of 7.84 10−3% and 1.04 10−2%. In addition, BP3 was detected in six of the creams at an amount of 4.73%, 3.49%, 4.94 10−3%, 1.98 10−3%, 6.62 10−1% and 1.73%. Therefore, none of the cosmetic creams contained BP3 in an amount higher than 6%.Spanish MINECO (AEI/FEDER, UE) through project CTQ2017‐88894‐R and by Junta de Castilla y León through project BU012P17 (both co‐financed with European FEDER funds). L. Valverde-Som thanks JCyL for her postdoctoral contract through BU012P17 project

Determination of cochineal and erythrosine in cherries in syrup in the presence of quenching effect by means of excitation-emission fluorescence data and three-way PARAFAC decomposition

The simultaneous determination of two food colorants (cochineal (E-120) and erythrosine (E-127)) was achieved by means of excitation-emission fluorescence matrices and three-way PARAFAC decomposition together with the use of a calibration set that contained binary mixtures of both analytes. In the measured conditions, the amount of cochineal present in the sample affected the fluorescence signal of erythrosine since cochineal caused a quenching effect in the fluorescence of the other food additive. However, the signal of cochineal was not affected by the presence of erythrosine. A calibration line for erythrosine was built for each different concentration level of cochineal. The slopes of these regressions were different depending on the amount of quencher, whereas the intercepts were statistically equal to 0 at a 95% confidence level. The quantification of erythrosine was possible using the regression “amount of cochineal” versus “the slope of the calibration line for erythrosine”. Using this procedure, the mean of the absolute values of the relative errors in prediction for mixtures of both colorants were 5.86% (n = 10) for cochineal and 4.17% (n = 10) for erythrosine. Both analytes were unequivocally identified by the correlation between the pure spectra and the PARAFAC excitation and emission spectral loadings. Pitted cherries in syrup were analyzed. Cochineal and erythrosine were detected in those cherries at a concentration of 185.05 mg kg−1 and 10.76 mg kg−1, respectively. These concentration values were statistically equal to the ones obtained with a HPLC/DAD method.Spanish MINECO (AEI/FEDER, UE) through projects CTQ2014–53157-R and CTQ2017‐88894‐R and by Junta de Castilla y León through project BU012P1

The behaviour of Tenax as food simulant in the migration of polymer additives from food contact materials by means of gas chromatography/mass spectrometry and PARAFAC

The migration of benzophenone (BP), an antioxidant (2,6-di-tert-butyl-4-methyl-phenol (BHT)) and three plasticizers (diisobutyl phthalate (DiBP), bis(2-ethylhexyl) adipate (DEHA) and diisononyl phthalate (DiNP)) from different food contact materials into Tenax as food simulant was studied. The packaging materials analysed were: polyethylene (PE) and polyvinyl chloride (PVC) cling-films, paper bread bag, brown paper popcorn bag intended to be heated in a microwave oven and polypropylene (PP) coffee capsules. The analysis was carried out using PARAFAC and PARAFAC2 decompositions and gas chromatography/mass spectrometry (GC/MS), being DiBP-d4 the internal standard. Tenax has been used as food simulant for specific migration of dry foodstuffs according to Commission Regulation (EU) 10/2011. PARAFAC and PARAFAC2 decompositions enabled the unequivocal identification and quantification of all the analytes despite some of the m/z ratios of the coeluting interferents were shared with the analytes. Otherwise, the presence of the analytes could not have been ensured according to the EU legislation in force. BHT, DiBP and DEHA were contained in the Tenax blanks in some of the analyses. The amount of BP and DiBP migrated from the PVC film was 83.53 μg L−1 and 31.30 μg L−1, respectively; whereas 71.62 μg L−1 of BP and 27.45 μg L−1 of DiBP migrated from the PP coffee capsules. None of the analytes were detected above the capability of detection in the non-spiked migration samples of the rest of the food contact materials analysed. The efficiency of Tenax as an adequate food simulant has also been studied through the values of its adsorption capability which were different depending on the analytes and the materials. In the spiked migration samples, these values ranged from 25.33% to 99.37%.Spanish MINECO (AEI/FEDER, UE) through projects CTQ2014-53157-R and CTQ2017‐88894‐R and by Junta de Castilla y León through project BU012P17 (all co‐financed with European FEDER funds)

Fluorescence determination of cochineal in strawberry jam in the presence of carmoisine as a quencher by means of four-way PARAFAC decomposition

The determination of cochineal (E-120) in strawberry jam was carried out in the presence of carmoisine (E-122) using the four-way PARAFAC decomposition and excitation-emission fluorescence matrices. In the measured conditions, there was no fluorescence signal for carmoisine due to a strong quenching effect and this colorant also led to a decrease of the fluorescence signal of cochineal. The European Union has fixed a maximum residue level, MRL, for cochineal in jam (100 mg kg−1). Therefore, the addition of other food colorant (carmoisine) in the jam could lead to false compliant decisions. The four-way PARAFAC decomposition avoided false compliant decisions caused by the quenching effect. Cochineal was unequivocally identified. Detection capability (CCβ) was 0.72 mg L−1 for probabilities of false positive and false negative fixed at 0.05. Cochineal was detected in the jam (104.63 mg kg−1) above the MRL. This amount was compared with the one obtained using a HPLC/DAD method.Spanish MINECO (AEI/FEDER, UE) through project CTQ2017‐88894-R and by Junta de Castilla y León through project BU012P17 (all co‐financed with European FEDER funds)

Procedure to build a signal transfer set, independent of the target analytes, between a portable fluorimeter based on light-emitting diodes and a master fluorimeter

The need of performing “in situ” analytical determinations together with the availability of high-power deep UV-LEDs have led to the use of fluorescence spectroscopy. However, it is necessary to register excitation-emission matrices (EEM) to obtain three-way data which can be decomposed using parallel factor analysis for enabling the unequivocal identification of the analytes. In this context, the feasibility of transferring EEM between a portable fluorimeter based on LEDs and a master fluorimeter based on a xenon source has been recently reported without losing analytical quality. To build the transfer function, the signals of the same N samples must be recorded in the portable and in the master fluorimeter. In literature, these samples always contained the target analytes so the EEM signal transfer methodology is very limited in practice. Therefore, the challenge is to search for a set of samples whose EEM enable to perform the signal transfer without previously knowing the target analytes. The aim of this work is the design of a procedure to build N mixtures of P fluorophores so the N EEM would be optimal for the signal transfer. Five criteria have been defined a priori to identify the quality of a transfer set made up of N EEM. Then, a procedure has been designed to obtain the n mixtures of the P fluorophores “in silico” using the Pareto front of the optimal solutions and a desirability function to choose the desired N EEM. The procedure has been used to find five mixtures of the three chosen fluorophores for the signal transfer (coumarin 120, DL-Tyrosine and DL-Tryptophan) which are chemically different from the analytes of interest (enrofloxacin and flumequine) and are contained in a different matrix. These two analytes are antibiotics which have maximum residue limits set in the EU legislation in force. The correlation coefficients between the experimental reference spectra and the PARAFAC spectral loadings of the data registered with the master fluorimeter were greater than or equal to 0.999 in all cases. On the other hand, the correlation coefficients obtained with the portable fluorimeter ranged from 0.900 to 0.950 once the procedure was applied to the two antibiotics. Therefore, the unequivocal identification of the analytes was ensured.Spanish MINECO (AEI/FEDER, UE) through project CTQ2017‐88894‐R and by Junta de Castilla y León through project BU012P17 (all co‐financed with European FEDER funds)

Signal transfer with excitation-emission matrices between a portable fluorimeter based on light-emitting diodes and a master fluorimeter

In this work, the transfer of the excitation-emission matrices between a portable fluorimeter based on LEDs and a master fluorimeter based on a xenon source was carried out. Enrofloxacin was the analyte of interest and it was measured alone or in binary mixtures with flumequine (partially overlapped signals) or with ciprofloxacin (fully overlapped signals). The maintenance and transfer of the unequivocal identification of the fluorophores between both instruments are shown. The precision in the determination performed with the portable fluorimeter approximated to that made with the master fluorimeter using this transfer and it did not introduce bias. The correlation coefficients of the calibrations based on PARAFAC using EEM signals were higher than 0.999, whereas the values of the capability of detection ranged from 14.8 to 26.9 μg L−1 for probabilities of false positive and false negative fixed at 0.05. These results contribute to the effort to perform the fluorimetric detection outside the laboratory and to promote the use of databases of fluorescence spectra for the unequivocal identification in remote of fluorophores of interest and/or regulated.Spanish MINECO (AEI/FEDER, UE) through projects CTQ2014-53157-R and CTQ2017‐88894‐R and by Junta de Castilla y León through project BU012P17 (all co‐financed with European FEDER funds