Preliminary results on direct quantitative determination of cocaine in impregnated materials by infrared spectroscopy

Microchemical Journal 143 (2018) 110–117

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Preliminary results on direct quantitative determination of cocaine in impregnated materials by infrared spectroscopy

T

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Clara Pérez-Alfonsob, Nieves Galipiensob, Salvador Garriguesa, , Miguel de la Guardiaa Department of Analytical Chemistry, University of Valencia, Research Building “Jeroni Muñoz”, Dr. Moliner st., 46100-Burjassot, Valencia, Spain Laboratorio de Control de Drogas de la Delegación de Gobierno en la Comunidad Valenciana, Área de Sanidad, Inspección de Farmacia, Muelle de la Aduana S/N, 46024 Valencia, Spain a

b

A R T I C LE I N FO

A B S T R A C T

Keywords: Cocaine determination Impregnated seized materials Attenuated total reflectance Middle infrared Diffuse reflectance Near infrared

Partial least squares models were built for the direct determination of cocaine in seized impregnated smuggled materials. Measurements are based on the attenuated total reflectance middle infrared spectra (ATR-MIR) and diffuse reflectance spectra in the near range (DR-NIR) obtained directly from the surface of the impregnated materials. The aforementioned procedures offer fast, cheap and environmentally friendly green alternatives to the reference method based on the extraction of the drug and its quantification by gas chromatography. Additionally it has been verified that results found are statistically comparable with those obtained by the reference method with root mean square errors of prediction (RMSEP) of 0.60% w/w and 0.88% w/w for MIR and NIR methods, and ratio of performance to deviation (RPD) values of 13.20 and 7.54, respectively. Examples of application for the quantification of cocaine in impregnated clothes, pulp paper and foam have been also provided.

1. Introduction The diversity of methods used in drug trafficking includes, additionally than packed pure compounds, the use of bottled liquids [1,2], impregnated paper [3], polymeric materials [4] and impregnated clothes [5,6]. So, nowadays official laboratories involved in abuse drug analysis have a tremendous problem to quantify cocaine in impregnated supports because the recommended method by the United Nations Office of Drug and Crime (UNODC) requires a preliminary full extraction of adsorbed cocaine followed by its determination by gas chromatography with flame ionization detection [5,6] and it consumes more than 24 h for analyte extraction and the handling of a big amount of samples. So, for screening purposes it becomes necessary to develop fast direct analytical procedures, suitable to provide quantitative data on the amount of cocaine present in impregnated materials without the need of a previous leaching of the drug and its preconcentration or dilution. Vibrational spectrometry techniques have been used for the discrimination and quantification of cocaine and adulterants in seized drug samples employing infrared spectroscopy and PLSR [7]; fast profiling of cocaine seizures by FTIR spectroscopy and GC–MS [8]; by ATR–FTIR [9] or quantitative determination by ATR-FTIR coupled with

chemometrics [10]. To do the in-situ detection of cocaine in clotting impregnated with the drug, Raman spectroscopy has been also extensively used by the UK group of Ali et al. being evidenced the applicability of the use of benchtop and portable instruments [11,12] to obtain high quality spectra suitable to be employed for the detection of cocaine hydrochloride in different types of textile fibers [13]. Additionally the use of confocal Raman microscopy provided clear evidences on the presence of cocaine and N‑methyl‑3,4‑methylenhidroxy‑amphetamine in natural and synthetic textile fibers [14]. However, the aforementioned methods have been used only for identification purposes not for cocaine quantification. On the other hand, ion mobility spectrometry has been employed for the detection of heroin and cocaine on incriminated materials using a vacuum cleaner for sampling and the direct desorption of analytes from a Teflon filter/membrane located inside the cleaner [15]. Additionally cocaine has been detected by using a mid-infrared (MIR) waveguide integrated with a microfluidic chip [16]. However in these later cases, as for classical attenuated total reflectance Fourier transform infrared spectroscopy in the middle range (ATR-MIR) [17], the MIR techniques require the use of reference methods based on gas chromatography and flame ionization (GC-FID) or mass spectrometry (GC–MS) detection and a preliminary extraction of cocaine into an

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Corresponding author. E-mail addresses: [email protected] (C. Pérez-Alfonso), [email protected] (N. Galipienso), [email protected] (S. Garrigues), [email protected] (M. de la Guardia). https://doi.org/10.1016/j.microc.2018.07.026 Received 21 May 2018; Received in revised form 20 July 2018; Accepted 20 July 2018 Available online 21 July 2018 0026-265X/ © 2018 Elsevier B.V. All rights reserved.

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cocaine and tetracosane peaks at retention times of 2.55 and 3.58 min, respectively, and using calibration lines stablished from cocaine standards with the IS directly prepared in ethanol.

organic solvent before deposition or injection in the measurement system. So, in our knowledge, there is a lack of a direct determination procedures suitable to quantify cocaine in impregnated materials and thus, the main objective of the present study was to evaluate the capability of vibrational spectroscopy methods, based on attenuated total reflectance in MIR or diffuse reflectance measurements in the NIR range, to provide fast, accurate and precise enough determination of cocaine in sized smuggled impregnated materials.

2.4. ATR-MIR procedure Impregnated materials were cut in pieces of 4 × 3 cm2 surface and ATR-MIR spectra obtained in different parts, from 4000 to 400 cm−1, by using a 1 reflection diamond ATR accessory. Samples were pressed to a constant value of 85 units (at the scale provided by the software Spectrum 10 to control the pressure applied to the UATR accessory) and spectra were recorded between 4000 and 400 cm−1, at 4 cm−1 resolution, being cumulated 10 spectra per sample using a background of the empty ATR cell, measured in the same instrumental conditions than samples. A PLS-model was built using as a calibration set 28 spectra selected from samples of different portions of textiles and 23 spectra of additional portions of samples were used as external validation set to evaluate the predictive capability of the method. Reference cocaine values of impregnated textile samples were obtained by the GC-FID method. Sample distribution for calibration and validation data set was made arbitrarily after a classification by principal component analysis (PCA).

2. Experimental part 2.1. Apparatus and reagents Attenuated total reflectance measurements were made with a Spectrum Two FT-IR spectrometer from Perkin Elmer (Waltham, USA) equipped with an extended range KBr beam splitter and a temperaturestabilized room temperature DTGS detector and using an UATR (single reflection diamond) accessory with a controlled pressure press. Instrument control and spectra handling was made using Spectrum 10 IR spectroscopy software also from Perkin Elmer. Diffuse reflectance measurements were obtained with a Fourier transform NIR instrument model Multipurpose Analyzer (MPA) from Bruker (Bremen, Germany). The system was equipped with a fiber optic probe and a TE-InGaAs detector for measuring samples directly in diffuse reflectance and transflectance modes. For instrument control and data acquisition, also for spectra treatment, data manipulation and chemometric data treatment, the OPUS program Version 6.5, from Bruker Gmbh, was employed. A gas chromatography system Agilent model 7890A (Palo Alto, CA, USA) equipped with a flame ionization detector and an Agilent HP-5 capillary column (30 m × 0.32 mm × 0.25 μm) was used to obtain reference data of samples employed through this study. A certified cocaine chlorhydrate (99.89%) from Lipomed (Arlesheim, Switzerland), tetracosane analytical grade from Fluka (Sigma-Aldrich Co, St. Louis, MO, USA) and absolute ethanol (99.5%) from Panreac (Barcelona, Spain) were used for GC analysis.

2.5. NIR procedure Samples impregnated and containing cocaine hydrochloride were sampled by using an optical glass fiber accessory. Diffuse reflectance NIR spectra, between 14,000 to 3900 cm−1, were obtained in different positions at a resolution of 4 cm−1, cumulating 10 spectra per sample, and using a background of Spectralon© diffuse reflectance standard. A PLS model was built from 24 spectra of portions of textile samples characterized by the reference GC-FID method and the selected PLS model was used to predict cocaine concentration in a separate set of spectra corresponding to 20 portions of textile samples. 3. Results and discussion

2.2. Samples

3.1. ATR-MIR spectra of the materials employed as support for impregnation

All samples used in this study were provided by the Laboratorio de estupefacientes de la Delegación de Gobierno en la Comunidad Valenciana (Spain) and were obtained from seizures carried out by the Spanish police. These samples are of 4 different types, including white textile tissue samples (20 × 40 cm2), a black textile tissue (20 × 40 cm2), a paper pulp sample (6 × 4 cm2) and a foam sample (4 × 3 cm2); all of them containing impregnated cocaine, with a concentration between 38.1% w/w and 54.1% w/w for textile tissues, 50.7% w/w for paper sample, and 68.1% w/w for the foam sample. Textile tissue samples were cut in different portions of approximately 4 × 3 cm2 to made individually infrared measurements.

In order to characterize the materials, they were washed for 72 h by immersion in ethanol, changing the washing liquid every 24 h. Subsequently, materials were allowed to dry and the obtained spectra were compared for tissues of different nature. The spectra of a white textile support after washing and removing cocaine was measured and compared to the spectra obtained for textile samples of wool, cotton, blends cotton/polyester felt and polyester felt, respectively (see Fig. S1 of Supplementary material). After comparing spectra it was concluded that the spectrum of the white support after washing and eliminating the cocaine coincides with that of polyester felt, but not with the rest of materials where differences are observed in the characteristic bands.

2.3. CG-FID reference procedure

3.2. ATR-MIR spectra of cocaine impregnated materials

For cocaine analysis in impregnated smuggled materials a method based on the United Nations GC procedure was employed. Samples were divided into quadrants and portions of approximately 1 g were sampled. These sample portions were treated with 50 mL of absolute ethanol during 24 h. After a 1:10 dilution, tetracosane was added as an internal standard (IS) to the final solution with a concentration of 0.02% m/v. 0.5 μL of the aforementioned solution were directly introduced in the gas chromatograph by means of an automatic injector, in the split mode, using a nitrogen carrier gas of 7.0 mL/min and analyzed in the isothermal mode with an injector and detector temperature of 280 °C and an oven temperature of 220 °C. Cocaine concentrations were obtained from the area values of the

Fig. 1 shows the ATR spectra, in the MIR range, of four different types of impregnated samples corresponding to a black textile tissue, white textile tissue, paper pulp and an impregnated foam sample, all of these obtained from smuggled seized samples. Additionally it is indicated the spectrum of a cocaine hydrochloride standard. As it can be seen the main bands of cocaine hydrochloride correspond to 1728 and 1712 cm−1 (stretching vibration of the two carbonyl groups), 1265 cm−1, 1230 and 1105 cm−1 (acetate CeO stretching), 1071 cm−1, 1025 and 729 cm−1 (mono substituted benzene stretching and the last one an out-of-plane bending). A distinctive band attributed to the NeH stretching due to the hydrochloride salt formation is also observed around 2535 cm−1 [18]. These IR peaks were obtained in all 111

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Impregnated white felt

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Impregnated black felt

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ATR

Impregnated paper pulp

3500

Impregnated foam

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Cocaine hydrochloride standard

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3500

3000

Wavenumber (cm-1) Fig. 1. ATR-MIR spectra of cocaine standard and different impregnated samples.

889 and 654 to 542 cm−1. Data were mean centered and pre-treated by using first derivative. To build the PLS-ATR-MIR model 6 latent variables were required and their corresponding loadings are indicated in Fig. S4A of Supplementary material. It evidenced that the first loading corresponds to the first derivative signal of cocaine. In these selected conditions PLS-ATR-MIR model provides a root mean square error of calibration (RMSEC) of 1.12% w/w with a root mean square error of cross-validation (RMSECV) of 1.54% w/w. For a separate set of 23 spectra of sample portions used as validation set and not employed to build the calibration model a root mean square error of prediction (RMSEP) of 0.60% w/w was obtained, with a ratio of performance to deviation (RPD) of 13.2 and a coefficient of determination between predicted and reference value of 0.978, with any evidence of bias.

the samples, thus evidencing the capability of ATR-MIR to detect this drug in impregnated materials. Spectra were measured in both sides of the impregnated materials, obtaining the spectra on the same opposite point. It was observed that both sides of the same sample, at the same sampling point, provide comparable ATR spectra which indicate that the tissue was impregnated, probably, by immersion in a concentrated cocaine solution (for details, see Fig. S2 of Supplementary material that also shows the system employed for recording the ATR-MIR spectra in impregnated textile tissues). 3.3. NIR reflectance spectra of cocaine impregnated materials Fig. 2 shows the spectra obtained with a NIR probe fiber of different seized samples, corresponding to a black textile tissue, white textile tissue and a standard of cocaine hydrochloride. As it can be seen, NIR spectra found for samples offer the same bands that cocaine powder (see reference [19] for band assignation), thus evidencing the strong detection capability of NIR to identify positive samples which, in this case, are in general free from cutting agents and it facilitates the identification of the drug which, in general, is present between 38.1% till 54.1% w/w cocaine. Additionally, it can be concluded that spectra measured from both sides of the same impregnated tissue are comparable (as it can be seen in Fig. S3 of Supplementary material).

3.5. PLS-DR-NIR model Based on the obtained 44 spectra of portions of impregnated textile tissue samples, in Kubelka-Munk units, a PLS model was built using the spectral range from 6136.5 to 5882.0, 5876.2 to 5523.3, and 5197.4 to 4142.5 cm−1 with a mean centering and a vector normalization pretreatment of data from 24 reference spectra. In these conditions it was selected a calibration model with 6 latent variables (loadings can be seen in Fig. S4B of Supplementary material) and providing values of 0.43% w/w and 1.94% w/w for RMSEC and RMSECV, respectively. This PLS-DR-NIR model provided a RMSEP of 0.88% w/w and a RPD of 7.54, with a coefficient of determination of 0.997 between predicted and reference values of cocaine, when it was applied to a separate validation set of 20 spectra of portions of textile tissue samples, without evidencing any bias in the obtained results.

3.4. PLS-ATR-MIR model Different models, based on different pretreatment of 28 spectra corresponding to portions of textile samples containing from 38.1% w/ w till 54.1% w/w cocaine were assayed being found the best prediction model using spectral ranges from 3108 to 2370, 1392 to 1267, 989 to 112

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12

Black tissue

8 4

Kubelka-Munk

0 12

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12000

10000

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10000

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4000

White tissue

8 4 0 12

Cocaine standard

8 4 0 12000

Wavenumber (cm-1) Fig. 2. DR-NIR spectra of black textile tissue sample, white textile tissue sample and cocaine standard.

impregnated tissue measured in three independent days. That provided an average value of 41.8 ± 2.0% w/w, with a relative standard deviation of 5%, being of the same order than that obtained by the reference method (see Table 2). So, it can be concluded that PLS-ATR-MIR and reference GC-FID provided the same results for the considered samples.

3.6. Validation of the PLS selected models In order to evaluate the suitability of the models to predict the concentration of cocaine in new samples, a previous PCA was employed. The two dimensions scores plot was represented for each of the two selected models including the spectra of impregnated tissues with cocaine. Fig. 3 shows the distribution of the new samples in the scores plot. It can be observed that in both cases the samples are grouped together with samples of white tissue impregnated with a cocaine content of 38.1% w/w. This could be an indication that the model is suitable for the determination of cocaine in new samples. In order to verify the accuracy of the selected PLS models validation was performed using new samples from impregnated white tissues. The predicted values from de ATR-MIR and DR-NIR spectra using the selected models were compared with the reference method GC-FID. The average value of 10 determinations of cocaine concentration in both sides of an impregnated tissue using the selected PLS-DR-NIR model (see Table 1) was 42.6 ± 0.4 with a variation coefficient of 1%. The comparison of this value with that obtained by the reference method, 41.4 ± 2.6% w/w, from the analysis of five replicate portions of the same sample, provided an experimental t value of 0.82 which is clearly lower than the tabulated one of 4.3 for a probability level of 95%. So, it can be concluded that the PLS-DR-NIR method developed for the direct determination of cocaine in impregnated samples is as accurate as the reference chromatography procedure. Using the PLS-ATR-MIR model the average value of 16 determinations of cocaine concentration in an impregnated tissue was 42.1 ± 1.7 with and a variation coefficient of 4%. The reference value found for the replicate analysis of the same sample by GC-FID was 41.4 ± 2.6% w/w, being obtained a Student t value of 0.64 for a probability level of 95% with is clearly lower than the tabulated 2.10. Table 1 summarizes data and results obtained for cocaine in the different sampling points of the two sides of a same sample being obtained these values by using the PLS selected models. From the aforementioned PLS-ATR-MIR model data of precision seems worse than that of the PLS-DR-NIR model. The intermediate precision of the method was also evaluated and expressed as a result the average of 16 independent determinations of the cocaine concentration in an

3.7. Validation of the PLS-ATR-MIR model considering other materials Selected models are useful for the determination of cocaine in impregnated felt tissues, the most common supports usually found in this type of seizures. Considering other types of materials, the analysis of an impregnated paper pulp support is presented below. In this case, it was decided to use the PLS-ATR-MIR model which allows to obtain a great number of measures in the supports of small size and that is the one that was available at that moment. A sheet of 6 × 4 cm2 paper pulp, impregnated with cocaine, was measured on both sides. 12 measurements were obtained at different opposite points on the surface of each of the sides of the support, thus obtaining a total of 24 ATR-MIR spectra. Fig. 4 shows the ATR-MIR spectra on the same point at both sides of the impregnated paper pulp and as can be seen, spectra are very similar; which would indicate that impregnation on both sides is similar. As in the case of impregnated felts, the main bands in the spectra correspond to those of the cocaine hydrochloride, which suggests that no interferences should occur for the quantification of cocaine related to the sample matrix. A PCA study was carried out, taking into account paper pulp samples and those used to build the PLS-ATR-FTIR model for impregnated felts. In the score plot PC2 vs PC1 (see Fig. S5A of Supplementary material) it can be verified that the impregnated pulp spectra are grouped together and next to the set of the impregnated white felt supports (specifically with the sample containing 38.1% (w/w) of cocaine base), also presenting a low dispersion. This could indicate that the PLS-ATR-MIR method developed for impregnated felt could be suitable for the analysis of pulp samples. In addition, the proximity of the points in the scores plot would indicate that the impregnation is quite homogeneous and similar for both sides. The spectra of the 113

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A

Fig. 3. Scores plot of the PLS models including new felt impregnated samples: PLS-ATR-MIR (A) and PLS-DR-NIR (B). Note: Calibration set ( ), validation set ( ), new felt impregnated samples ( ). Numbers 1, 2 and 3 refer to the type of sample to which the spectra correspond.

2 1

3

B 2 3 1

It has been also considered the analysis of cocaine impregnated polyurethane foam of dimensions 4 × 3 cm2. As it can be seen due to the morphological differences of both sides of the material, the impregnation is not homogenous. Fig. 5 shows the differences of the ATRMIR spectra of both sides of the impregnated foam which suggests that the cocaine content will also be different for each of the sides of the sample. A PCA study was carried out for the foam sample. Differences and a clear dispersion of the measurements for each of the sides in the scores plot, PC2 vs PC1 (see Fig. S5B of Supplementary material for details), can been observed. While the spectra corresponding to the A side are grouped together with those of the impregnated tissues, the rest of spectra form a new group that presents a great dispersion. This means that the impregnation of both sides of the foam can be clearly different, being side B less absorbent that side A. Table 4 shows the prediction of the cocaine values with the PLSATR-MIR method for the analysis of the foam sample. In the A side, the values showed a dispersion below 2%, similar to that obtained for the

impregnated paper pulp were processed with the PLS-ATR-MIR felt model. Results obtained for each of the measurement points are indicated in Table 3. The average values obtained for both sides were comparable to each other and to the reference value obtained in the analysis by GC-FID. Therefore, it can be confirmed that, as indicated by the PCA study, the PLS-ATR-MIR model build from impregnated felt is adequate for the quantification of cocaine in impregnated paper pulp samples. As had been assumed from the scores plot, the accuracy of the results obtained in the measurement of each one of the sides of the material confirms that the impregnation can be considered homogeneous. In conclusion, quantification models using ATR-MIR measures are adequate when samples present a homogenous impregnation even though the matrix could be different. In general, it is not usual to find samples of non-homogeneous impregnation, since most of the materials used for this purpose are felt-type materials such as those used for the developed PLS models, and cocaine was normally deposited by immersion in a concentrated solution and subsequent drying of the solvent [20]. 114

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Table 1 Direct determination of cocaine in impregnated tissue using the selected models.

PLS-DR-NIR model Sampling point

Table 2 Reproducibility of PLS-ATR-MIR determination of cocaine in impregnated materials.

PLS-ATR-MIR model

Cocaine base,

Sampling point

% (w/w)

Cocaine base, % (w/w)

Cocaine base, % (w/w)

Side A 1 2 3 4 5

42.56 43.02 43.04 42.87 41.93

1 2 3 4 5 6 7 8

42.20 42.32 39.55 41.32 41.43 43.16 41.10 41.16

Average value

42.7 ± 0.5

Average value

41.5 ± 1.1

6 7 8 9 10

43.02 42.23 42.39 42.43 42.51

Side B

Average value

42.5 ± 0.3

9 10 11 12 13 14 15 16

42.81 42.87 41.57 45.16 40.12 43.97 40.03 45.22

Average value

42.7 ± 2.0

42.6 ± 0.4

Average value

Comparison of the values obtained by both models

Day 3

Side A 1 2 3 4 5 6 7 8 Average value

42.20 42.32 39.55 41.32 41.43 43.16 41.10 41.16 41.5 ± 1.1

42.08 40.54 41.98 42.84 39.70 38.99 42.14 38.67 40.9 ± 1.6

43.09 40.19 44.17 44.07 42.07 43.08 37.04 42.52 42.0 ± 2.4

Side B 9 10 11 12 13 14 15 16 Average value

42.81 42.87 41.57 45.16 40.12 43.97 40.03 45.22 42.7 ± 2.0

39.98 42.43 40.13 43.09 46.56 42.66 38.05 38.30 41.4 ± 2.8

42.67 44.23 41.88 40.34 41.11 41.17 43.75 43.60 42.3 ± 1.4

Mean sides A + B Average value

42.1 ± 1.7

41.1 ± 2.2

42.2 ± 1.9

41.8 ± 2.0 4.7%

results can be quickly obtained with the advantage that previous extraction of the cocaine from the impregnated material is not required. So, measurements can be directly obtained and it is a non-destructive technique.

1.13 2.10

4. Comparison of the analytical methods employed

41.4 ± 2.6 (n = 5) 0.82 4.30

Day 2

42.1 ± 1.7

Comparison of results obtained with the PLS models with the reference value (GC-FID method) Reference value

Day 1

Average value (3 days) RSD (%)

Sides A+B Average value

Sampling point

0.64 2.10

The direct determination of cocaine in samples impregnated with cocaine hydrochloride by using both, ATR-MIR and DR-NIR measurements, has been compared with the reference gas chromatography method being obtained comparable results as indicated in previous sections. Table 5 evaluate the main parameters of three methods employed, GC-FID, PLS-ATR-MIR and PLS-DR-NIR. As it can be seen the single advantage offered by the reference GC-FID method is based on the easy calibration from alcoholic standards of cocaine hydrochloride containing tetracosane as internal standard. On the contrary, both methods, ATR-MIR and DR-NIR, require a calibration with previous analyzed samples. Additionally the automation of sample measurement by GC-FID after extraction and dilution permits to do determination during the whole day without operator control in front of the fact that automation of measurement on DR-NIR and ATR-MIR is not an easy process. However the complete procedure includes sample extraction, which requires more than 24 h, and an extra cost in energy, reagents and wastes, thus making the reference procedure more expensive and less environmentally friendly than the proposed direct measurement by ATR-MIR and diffuse reflectance NIR, especially when this later one is made using an optical glass fiber that avoids the direct contact between operator and sample. So, it can be concluded that vibrational spectroscopy offers green and sustainable alternatives to the determination of cocaine in illegal seized impregnated materials, which permits, additionally, the preservation of the original samples for new determinations without destroying or altering crime evidences. PCA study has proved useful to establish the suitability of the developed model for the determination of cocaine in new samples, considering that both PLS-ATR-MIR and PLS-DR-NIR models are adequate

impregnated tissues or the impregnated paper pulp, which confirms that the impregnation could be considered to be quite homogeneous and comparable with at the previous supports, as expected from the PCA graphic. For the B side, the obtained values showed a great dispersion, obtaining in some cases negative results. It indicates that only the measurements of one of the sides could be used for the quantification of cocaine with adequate precision. Regards the accuracy of measurements, the comparison between result obtained for the A side with those obtained by the reference method, are not coincident, being the value obtained by PLS-ATR-MIR significantly lower than the reference value. Therefore, ATR-MIR measures would only be useful as a screening technique to establish quickly the possible presence of cocaine in non-homogeneously impregnated materials. However, the level of concentration and the degree of homogeneity/heterogeneity in the distribution of cocaine in this type of samples can be easily stablished. The information provided by ATR-MIR measures would be useful to establish the most appropriate sampling strategy based on the characteristics of samples, in order to correctly apply a reference method. The scores plot in the PCA study helps us to evaluate the utility of the technique to predict cocaine values in impregnated materials. So this strategy would only be adequate, from the quantitative point of view, when the samples have an homogeneous impregnation on both sides and the texture/consistency of the material is similar to that used to build the PLS models. The technique is useful to confirm the presence of cocaine as an alternative to another way as mass spectrometry and 115

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0.07

A

0.05 0.03

ATR

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0.06 0.04 0.02 0.00 4000

Wavenumber (cm-1) Fig. 4. ATR-MIR spectra corresponding to both sides of an impregnated paper pulp (A) and system employed for spectra acquisition (B). Table 3 Results obtained for PLS-ATR-FTIR determination of cocaine in impregnated paper pulp. Sampling point (side A)

Cocaine base, % (w/w)

Sampling point (side B)

Cocaine base, % (w/w)

1 2 3 4 5 6 7 8 9 10 11 12 Mean side A

51.31 48.60 49.15 50.33 49.78 48.27 48.59 50.52 49.11 48.82 54.35 51.19 50.0 ± 1.5

13 14 15 16 17 18 19 20 21 22 23 24 Mean side B

53.49 51.25 51.22 50.88 51.27 51.86 51.60 50.19 52.28 52.62 51.78 51.80 51.7 ± 0.8

Average value Reference value tcal ttab

Table 4 Results obtained for the PLS-ATR-FTIR determination of cocaine in an impregnated foam sample. Sampling point

Cocaine base, % (w/w)

1 2 3 4 5 6 7 8 9 Average value RSD (%) Reference value

Side A

Side B

51.63 51.97 50.63 49.84 51.79 50.49 50.99 49.10 51.94 50.9 ± 0.9 1.9% 68.1 ± 2.2% (w/w) (n = 3)

10.66 <0 41.10 <0 62.41 11.68 13.63 16.80 60.41 31 ± 23 75%

50.8 ± 1.6% (w/w) 50.7 ± 2.5% (w/w) 0.211 2.05

0.30

A

B

0.20

ATR

0.10 0.00 4000

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0.30 0.20 0.10 0.00 4000

Wavenumber (cm-1) Fig. 5. ATR-MIR spectra corresponding to both sides of an impregnated foam (A) and system employed for spectra acquisition (B). 116

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Table 5 Comparison of methods employed for cocaine determination in impregnated materials. Characteristic

GC-FID

PLS-ATR MIR

Analysis time Calibration Sample handling Sample preservation Operator risk Environmental risk Cost Automation

More than 24 h Easy injection Extraction, dilution, addition of internal standard Destruction Exposed to solvent and drugs Solvent & wastes Instrumentation + gases + energy + reagent + solvent Use of autosampler after extraction and dilution

Minutes

for the determination of cocaine in impregnated tissues when precharacterized impregnated textile tissue samples are used to build the calibration models. The PLS-DR-NIR model, because of its measurement characteristics, could be more useful in the case of larger supports, since it allows to perform a mapping of a large surface of the impregnated supports, while the PLS-ATR-MIR would be preferable in the case of samples of small dimensions, since the size of the tip would allow to obtain a great number of measures.

PLS-NIR

Minutes Use of analyzed samples Direct measurement Complete preservation Contact with the sample Contact with the fiber No reagents nor solvents Instrumentation + energy Not easy automation

parts in Peru, Microgram. Bull. 36 (2003) 271. [7] T.S. Grobério, J.J. Zacca, E.D. Botelho, M. Talhavini, J.W. Braga, Discrimination and quantification of cocaine and adulterants in seized drug samples by infrared spectroscopy and PLSR, Forensic Sci. Int. 257 (2015) 297–306. [8] M. Monfreda, F. Varani, F. Cattaruzza, S. Ciambrone, A. Proposito, Fast profiling of cocaine seizures by FTIR spectroscopy and GC-MS analysis of minor alkaloids and residual solvents, Sci. Justice 55 (2015) 456–466. [9] M.C. Marcelo, K.C. Mariotti, M.F. Ferrão, R.S. Ortiz, Profiling cocaine by ATR–FTIR, Forensic Sci. Int. 246 (2015) 65–71. [10] S. Materazzi, A. Gregori, L. Ripani, A. Apriceno, R. Risoluti, Cocaine profiling: implementation of a predictive model by ATR-FTIR coupled with chemometrics in forensic chemistry, Talanta 166 (2017) 328–335. [11] E.M.A. Ali, H.G.M. Edwards, M.D. Hargreaves, I.J. Scowen, In situ detection of cocaine hydrochloride in clothing impregnated with the drug using benchtop and portable Raman spectroscopy, J. Raman Spectrosc. 41 (2010) 938–943. [12] E.M.A. Ali, H.G.M. Edwards, Screening of textiles for contraband drugs using portable Raman spectroscopy and chemometrics, J. Raman Spectrosc. 45 (2014) 253–258. [13] E.M.A. Ali, H.G.M. Edwards, I.J. Scowen, Rapid in situ detection of street samples of drugs of abuse on textile substrates using microRaman spectroscopy, Spectrochim. Acta A 80 (2011) 2–7. [14] E.M.A. Ali, H.G.M. Edwards, M.D. Hargreaves, I.J. Scowen, In-situ detection of drugs-of-abuse on clothing using confocal Raman microscopy, Anal. Chim. Acta 615 (2008) 63–72. [15] F.E. Dussy, C. Berchtold, T.A. Briellmann, C. Lang, R. Steiger, M. Bovens, Validation of an ion mobility spectrometry (IMS) method for the detection of heroin and cocaine on incriminated material, Forensic Sci. Int. 177 (2008) 105–111. [16] Y.C. Chang, P. Wägli, V. Paeder, A. Homsy, L. Hvozdara, P. van der Wal, J. Di Francesco, N.F. de Rooij, H.P. Herzig, Cocaine detection by a mid-infrared waveguide integrated with a microfluidic chip, Lab Chip 12 (2012) 3020–3023. [17] U S Drug Enforcement Administration, Cocaine in wicker baskets (from Peru) at the George Bush Intercontinental Airport, Houston, Texas, Microgram. Bull. 39 (2006) 72. [18] N.V.S. Rodrigues, E.M. Cardoso, M.V.O. Andrade, C.L. Donnici, M.M. Sena, Analysis of seized cocaine samples by using chemometric methods and FTIR spectroscopy, J. Braz. Chem. Soc. 24 (2013) 507–517. [19] C. Perez-Alfonso, N. Galipienso, S. Garrigues, M. de la Guardia, A green method for the determination of cocaine in illicit samples, Forensic Sci. Int. 237 (2014) 70–77. [20] M. Mc Nicholas, Maritime Security: An Introduction, Butterworth-Heinemann, Burlington. USA, 2016.

Acknowledgements Authors gratefully acknowledge the financial support of Ministerio de Economía y Competitividad (Project CTQ2014-52841-P). Appendix A. Supplementary material Supplementary data to this article can be found online at https:// doi.org/10.1016/j.microc.2018.07.026. References [1] S. Grabherr, S. Ross, P. Regenscheit, B. Werner, L. Oesterhelweg, S. Bolliger, M.J. Thali, Detection of smuggled cocaine in cargo using MDCT, Am. J. Roentgenol. 190 (2008) 1390–1395. [2] U S Drug Enforcement Administration, Cocaine in canned milk can in Huelva, Spain, Microgram. Bull. 38 (2005) 48. [3] U S Drug Enforcement Administration, Heroin in book bindings in Fort Lauderdale, Florida, Microgram. Bull. 36 (2003) 199. [4] U S Drug Enforcement Administration, Water soluble matrix (containing cocaine) seized in or nearby Villavicencio, Colombia, South America, Microgram. Bull. 38 (2005) 137. [5] S.D. McDermott, J.D. Power, Drug smuggling using clothing impregnated with cocaine, J. Forensic Sci. 50 (2005) 1423–1425. [6] U S Drug Enforcement Administration, Cocaine impregnated silicone in baseball cap

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