ES2393625A1 - Samplants of atmospheric contaminants. (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Samples of atmospheric pollutants. The present invention relates to a process for the synthesis of a compound consisting of the formula (sio2) (cyclodextrin)x, (where x represents the molar fraction and it takes actual values defined within the range 0 to 0.002), to the compound itself characterized by said formula, to the use of it as a solid phase or to fill samplers destined to the capture of atmospheric organic pollutants (vocs), and to the samplers themselves that comprise solid phase or filling said compound characterized by the formula (sio2) (cyclodextrin)x. (Machine-translation by Google Translate, not legally binding)

Description

SAMPLERS OF ATMOSPHERIC POLLUTANTS

FIELD OF THE INVENTION

The present invention refers to a method for the synthesis of a compound consisting of the phonula (Si02) (Cyclodextrin) x, (where x represents the molar fraction and takes defined real values within the range O to 0.002), to the compound itself characterized by said formula, to the use thereof as solid phase or filling of samplers intended for the capture of atmospheric organic pollutants (VOCs), and to the samplers themselves comprising as solid phase or filling said compound characterized by the formula (Si02) (Cyclodextrin) ) x.

Therefore, the present invention can be encompassed in the field of chemistry in general, particularly in the sectors of chemistry intended for environmental care and industrial hygiene.

STATE OF THE TECHNIQUE

Cyclodextrins (CDs) are cyclic polysaccharides consisting of glucopiranose units. They are crystalline compounds, not hygroscopic and with an O-ring structure. The three most characteristic CDs are a-cyclodextrin (a-CD), ~ -cyclodextrin (~ CD) and y-cycle dextrin (y-CD) containing 6, 7 and 8 glucopyranose units, respectively. The presence of hydroxyl groups in their structure means that they have a hydrophilic external surface and are soluble in water. In addition, CDs can be derivatized from selective sources thus obtaining synthetic CDs with physical and chemical properties different from those of natural CDs. On the other hand, the cavity of the toric structure of the CDs is of a nonpolar nature, which makes it possible to penetrate apolar molecules of adequate size and their union to the CDs by means of dipole-dipole interactions, hydrogen bonds or dispersion forces of London

CDs are widely used in the cosmetic and food industry, in the environmental field, the area of analytical chemistry and the pharmaceutical industry [5].

Thus, aqueous solutions of CDs and their derivatives have been used for the cleaning of soils contaminated by aromatic compounds [6,7] and the immobilization of CDs in nanosponges and nanocomposites has been described for the cleaning of contaminated water [8,9]. Particularly within the area of analytical chemistry, the main application of CDs is in their use, either as stationary phases or as components of the mobile phase, in chromatographic and electrophoretic separations [10-15]. In addition, the preparation of fibers and membranes with bound CDs for the extraction and determination of some organic compounds has been described. In this sense, they have been applied in the determination of anti-inflammatories, methamphetamine and ephedrine in urine samples [16,17], in the determination of phenols, amines and aromatic compounds in water samples using solid micro extraction [18-21], and in the extraction of polychrome diphenyl ethers from soil samples [22]. On the other hand, membranes with ligated CDs have been used for the determination of polycyclic aromatic compounds (PAHs) and phenols in waters [23]; The use of CDs solutions for the liquid micro extraction of PAHs in water has been described [24], and finally, CDs have been immobilized on solid supports in order to construct sensors capable of selectively detecting a specific type of substrate either because of its size, disposition of the functional groups of its molecule or the possibility of causing changes in some of the physical properties of the receptor system [25].

The immobilization of CDs can be carried out by different procedures. Thus, immobilization on polyurethane [20] or the use of reagents such as epichlorohydrin [19, 23] or hexamethylene diisocyanate [26] has been proposed. However, in most cases, immobilization is performed on silica. The procedures proposed in this regard require the interaction of cyclodextrin with 3glycidoxypropyltrimethoxysilane (GTMOS) and subsequent three-dimensional polycondensation with tetraethoxysilane (TEOS) after hydrolysis [18, 23, 27]. Finally, the polymer formed is bound to the hydroxy solidimethylsiloxane by polycondensation resulting in the formation of the phase. Generally, trifluoroacetic acid (TFA) is added as a catalyst which decreases the water content of the solvent, decreasing the rate of hydrolysis and favoring the CD-GTMOS binding.

Therefore, when the CDs are immobilized on silica in the prior art, said CDs are attached to the silica particles through an intermediate compound. That is, the silica particle is bound to a chemical species that acts as an intermediate compound and to this same intermediate the CDs would be attached. For this, intermediate compounds of different nature and different ways of carrying out the reaction have been proposed in the state of the art. The use of said intermediate in the solid phase or filling of contaminant samplers presents associated disadvantages, since the interactions of the contaminants with the solid phase may also be due to the presence of said intermediate, because the retention mechanism could be seen. altered since the VOCs can be retained in the solid phase through other interaction mechanisms and therefore, losses can occur during the conservation of the samples or non-quantitative recoveries caused by irreversible processes.

Commercial materials present in the state of the art comprising silica and CDs, are non-porous microparticles in which the CDs, as discussed above, are connected to the silica through an intermediate compound, 10 which is a disadvantage by reducing its adsorption capacity since the adsorption phenomenon depends on the effective area, which, in turn, depends directly on the porosity of the system.

On other occasions, simple or connected CDs forming pseudopolyotaxanes have been used as a template to prepare high surface porous silicas, after the extraction or thermal elimination of the organic component [28,29]. Thus, in this case, the use of the CDs as a template agent ends with its destruction and elimination by calcination in order to generate a pore system associated with the hole that the CDs initially occupied, giving rise to a final compound that is not hybrid , not understanding CDs, but purely inorganic based on silica.

The procedures for carrying out the sampling of COY s in the atmosphere that exist in the state of the art, can be classified, in general, in active sampling and passive sampling and use adsorbent beds that have, for example, activated carbon, silica gel, sieves molecular, porous polymers or reagent impregnated tubes. Unfortunately, these compounds used as solid phases in the state of the art provide low retention of the analytes and low yields thereof due to their loss by volatilization, or their chemical decomposition, increasing the difficulty of their recovery.

Thus, for example, in the case of hygroscopic adsorbents such as silica gel, high humidity conditions can displace retained contaminants, less volatile compounds can be displaced from the adsorbent by COz and, finally, in the presence of gases Reagents such as nitrogen or sulfur oxides may alter the analytes [1-4]. Furthermore, said solid phases used in the state of the art require toxic compounds and contaminants for the realization of desorption, such as CSz.

DESCRIPTION OF THE INVENTION

The present invention refers to a process for the synthesis of a hybrid compound (based on silica and CDs) and microporous that can be effectively used as a solid phase or filler in samplers for the uptake of VOCs. In addition, the present invention refers to the compound itself, and even to samplers that comprise and allow the efficient collection of samples from contaminated atmospheres and the recovery of analytes for further analysis.

In the present invention, "micropore" or "microporous" is understood as a pore with an average diameter of less than 2 nm.

Furthermore, in the present invention "solid phase" or "filler" is understood as that part of the sampler formed by a compound capable of adsorbing atmospheric pollutants, particularly the lubricated compound (based on silica and CDs) and microporous of the invention.

The process for the synthesis of the compound of the invention is simple and reproducible ("one pot" type, that is, it comprises a single step with the joint addition of all reagents). The porosity of the final compound is generated at the synthesis stage itself without requiring further steps (which involve the removal of the CDs) for this purpose. Therefore, the process of the invention does not require the steps used in the procedures known in the state of the art in which post-synthesis steps are carried out in order to generate the pores by eliminating the organic phase. (CDs) through, for example, the pyrolysis of said material finally giving rise to a porous compound that is not hybrid but an inorganic compound based on silica. It is important to emphasize that the generation of the pore system of the compound of the invention does not require chemical extraction processes or pyrolysis of the CDs, which on the other hand would lead to the undesirable elimination of the CDs. The conservation of CD molecules is necessary because they act as centers of interaction with VOCs. Thus, the removal of the CD molecules, either by pyrolysis or chemical extraction, would lead to possible porous materials but lacking the ability to interact with VOC.

Therefore, it can be said that the process of the invention is capable of generating a lubricated compound (based on silica and CDs) and microporous, which can be effectively used as a solid phase or filler in samplers for the collection of VOCs, so simple, in a short period of time and more economically compared to known procedures.

More specifically, the process of the invention is based on obtaining the final compound by reacting an aqueous solution of CDs (both natural and substituted CDs can be used) and tetraethylorthosilicate, preferably at pH in the range 1.7-2.0. The resulting tetraethylorthosilicate and cyclodextrin mixtures are subjected to a hydrolysis and condensation reaction in an acid medium that produces gelation of the inorganic component, trapping the organic molecules. The resulting material has microporosity accessible to different VOCs without the need, as mentioned above, to eliminate CD molecules. The mixture obtained is stirred until the reaction is complete and the alcohol formed is evaporated at 70 ° C, using a rotary evaporator. The hybrid material thus obtained is dried at 50 ° C in the oven for 24 hours, crushed and sieved to adapt its particle size to the required analytical application and, finally, it is introduced into the samplers. The material obtained, which turns out to be microporous without requiring pyrolysis or extraction of the organic component, is used as a solid phase or sampler filling.

Thus, the compound obtained is characterized by its hybrid nature, consisting of the formula (SiOz) (Cyclodextrin) x, where x represents the molar fraction that defines the empirical composition of the porous material and takes definite real values within the range O to 0.002, and cyclodextrin (CD) may preferably be selected from: a-CD, p-CD, 2-hydroxypropyl-P-cyclodextrin (P-HPCD), methyl-p-cyclodextrin (PMCD) and y-CD, or mixtures thereof. same. This compound is also microporous and accessible to volatile organic pollutants without any post-treatment.

The compound of the present invention does not have intermediate compounds between silica and CDs, but the CDs are directly linked to the silica and the CDs are not covalently connected to the silica, but are trapped in the microporous amorphous structure of the same. This is an advantage over the simplicity of the synthesis method since it is not necessary to use additional reagents, and it is carried out in its synthesis in a single stage. In addition, the microporosity of the compound is a clear advantage because the adsorption phenomenon depends on the effective area which, in turn, depends on the porosity. In addition, the resulting microporosity is adequate in size for the inclusion and diffusion of VOC molecules.

In addition to its chemical composition, other distinguishing features of the compound of the invention are the following:

•

It presents X-ray diffraction diagrams in which there are no diffraction peaks at low or high angles. This indicates their amorphous nature, which allows a more efficient incorporation of CD molecules.

•

It has a morphology, according to the images of SEM (scanning electron microscope) and TEM (transmission electron microscope),

constituted by particles of micrometric size. High resolution images show the presence of a single system of pores of small size and absence of long-range order. This micropore system is a requirement to allow the diffusion of VOCs to CD molecules.

•

It has a unimodal pore distribution (it presents a single pore system) according to the experiences of nitrogen adsorption and desorption. The material is characterized by pores with an average diameter of less than 2 nm, typically close to 1.5-1.8 nm. These diameter values are more than enough to allow access and dissemination of VOCs.

•

It has a high specific surface area (BET), superior in all cases to 150 m2g-I, and usually in the range 350-600 m2g-I. The presence of a system of pores allows maximizing the surface against the case of massive silicas (silica of variable particle size but in no case presenting any porosity). In this way it is possible to maximize the number of CDs accessible to VOCs as well as minimize the dissemination paths.

•

It has a higher pore volume usually greater than 0.15 cm3g-I, typical of microporous systems with the advantages discussed previously.

•

All the porous materials of the invention have various NMR (nuclear magnetic resonance) (MAS) signals of 29 if characteristic of oxygenated silicon environments in the range of chemical displacement between -80 and -115 ppm. The relative proportion of environments of type Q2 are minor, dominating the Si centers of type Q3 and Q4 (this nomenclature refers to and reports the degree of condensation of silica, thus environments type Q4, Q3 and Q2 refer to atoms of Si connected by siloxane bridges to 4, 3 and 2 silicon centers, respectively; the rest of the positions around each silicon are completed with OK groups: O, 1 and 2 for environments Q4, Q3 and Q2, respectively). The combination of dominant environments type Q4 and Q3 in the compounds of the invention makes it possible to combine a high stability of the siliceous support (due to Q4 centers) and a high degree of hydrophilicity due to the Q3 centers that favors interaction with the external part of the cyclodextrin molecules

•

In all the compounds of the invention it is possible to adapt the grain size

by grinding and using suitable sieves. This possibility, postsynthesis, penr.ite adapt the compound to the requirements of each sampler.

• The mentioned characteristics are independent of the grain size and coincide with those of the solids formed in monoliths (pieces with controlled form and variable size from a few millimeters to centimeters). It should be noted that a process such as that described that can be included in sol-gel techniques, allows from the initial stage to favor the obtaining of pieces in the form of monoliths. The milling process therefore does not alter any of the physicochemical characteristics of the compounds of the invention.

Thus, the compound of the invention can be used effectively as a solid phase or filler in air pollutant samplers. The samplers of the present invention comprising as solid phase or filler the compound of the invention defined above, constitute an improved alternative to the commercial samplers described in the state of the art that use silica gel or active carbon as solid phases, since The samplers of the present invention have a high analyte retention capacity due to the particular form of interaction between the CDs and the analytes, forming inclusion complexes, more independently to external parameters such as temperature and / or humidity. Thus, the retention of pollutants is not so affected by environmental conditions and the recoveries obtained make them suitable for the evaluation of exposure to these pollutants in work environments.

Furthermore, desorption of the analytes retained in the sampler of the present invention can be carried out easily and without requiring such toxic solvents and contaminants. Said desorption can be carried out, for example, with a few milliliters of acetonitrile, which reduces the generation of toxic waste as well as the risk of contamination of the operators, resulting in a cleaner and safer procedure than the one used when sampling tubes are used. activated carbon and carbon disulfide to carry out desorption [31]. The desorption of the contaminants retained in the samplers carried out in the present invention can also be technical, which has the advantage of shortening the analysis time and reducing the generation of waste. The solid phase of the invention can be used for the construction of passive diffusers simply by adapting the amount of solid phase and its particle size.

In the present invention, as demonstrated in the examples, samplers have been prepared from solid phases of a-CD, p-CD, 2-hydroxypropyl-Pcyclodextrin (P-HPCD), methyl-p-cyclodextrin (P -MCD) and immobilized y-CD, selecting the most suitable solid phase depending on the type of pollutant to be analyzed. In addition, the retention and desorption conditions with solvent have been optimized for the determination of major volatile organic compounds in the atmosphere such as BTEX (benzene, toluene, ethylbenzene, o-xylene, m-xylene and pxylene) for subsequent determination by chromatography of gases, although the samplers of the invention can also be used for other COY s. On the other hand, in the present invention comparative tests of the results obtained for the determination of BTEX have been carried out using the sampler of the invention, with those provided using active carbon beds for sampling. In addition, BTEX contamination in different samples has been determined using the solid cyclodextrin phases of the invention.

The samplers are preferably prepared using glass tubes with an internal diameter of 4 mm and a length of 80 mm, and contain two solid phase sections separated by a porous medium. The particle size of the filler is between 600 and 1000 Jlm, and the front part contains twice the solid phase as the back. The amount of solid phase determines the load capacity of the sampler, so they can be adapted to the sampling needs.

The reproducibility of intra-synthesis results (obtained from replicas of the same synthesis) and inter-synthesis (obtained from values from different syntheses) indicates that the process for obtaining the solid phase is safe and reproducible. . The recoveries obtained for BTEX indicate, according to UNE 1076: 1997 [30], that the designed sampling tubes are suitable for use in active sampling in the field of industrial hygiene. Also, by adapting the amount of phase, the flow rate and the sampling time, the designed samplers are suitable for sampling pollutants in the atmosphere.

Therefore, the present invention relates in a first aspect to a process for the synthesis of a microporous compound consisting of the formula (Si02) (Cyclodextrin) x where x has a value between O and 0.002, which comprises the reaction between the dextrin cycle and a silica precursor compound (Si02), characterized in that the micropores of the compound are generated in the same reaction step between the cyclodextrins and a silica precursor compound (Si02) without the need to remove the cyclodextrin molecules. In a preferred embodiment of the invention the precursor compound of silica (Si02) is tetraethylorthosilicate. This procedure also includes the following stages:

to.

Stir the reaction mixture until complete.

b.

Evaporate the alcohol formed, preferably at a temperature of 70 ° C.

C.

Dry the material obtained, preferably at 50 ° C for 24 hours.

d.

Optionally crush and sift the material obtained in step c) to adapt its particle size to that required by the analytical application to be carried out.

A second aspect of the present invention refers to a microporous compound consisting of the formula (Si02) (Cyclodextrin) x where x has a value between O and 0.002. In preferred embodiments of the invention x has a value of 0.0013. The cyclodextrin is preferably selected from: u-cyclodextrin, ~ cyclodextrin, 2-hydroxypropyl- ~ -cyclodextrin, methyl- ~ -cyclodextrin and y-cyclodextrin,

or mixtures thereof. The pores have an average diameter of less than 2 nm, preferably between 1.5 and 1.8 nm and a volume greater than 0.15 cm3g-l.

Another aspect of the invention refers to the use of the compound of the invention, mentioned above, as a solid phase or filling of a sampler intended for

arrest of volatile organic pollutants, and to the solid phase or filler

proper.

A further aspect of the invention refers to a sampler for use in the determination of volatile organic pollutants comprising as solid phase or filler the compound of the invention described above.

The last aspect of the present invention refers to a process for sampling volatile organic pollutants comprising the retention of contaminants in the solid phase of a sampler comprising the compound of the invention described above and the desorption of contaminants by means of the use of solvents or by technical desorption.

Description of the figures

Figure 1 Transmission electron microscopy image of the hybrid compound of the invention prepared according to the method described in Example 1.

Figure 2 Nitrogen adsorption-desorption isotenna of the hybrid compound of the invention prepared according to the method described in Example 1. The relative pressure is represented on the abscissa axis and the amount of adsorbed nitrogen on the ordinate axis. The adsorption curve is typical of microporous materials with type 1 isotennes, in which significant nitrogen adsorption occurs at low partial pressures.

Figure 3 Nuclear Magnetic Resonance Spectrum of 29Si in solid state of the hybrid compound of the invention prepared according to the method described in Example 1. The abscissa axis represents the chemical displacement in parts per million (ppm) and in the axis of ordered signal strength in arbitrary units. A

predominance of silica centers of type Q3 and Q4: typical signals at -106 and -115 ppm.

Figure 4

12C Nuclear Magnetic Resonance Spectrum in solid state of the hybrid compound of the invention (a) prepared according to the method described in Example 1. The corresponding pure sugar (unmodified CD) is also shown (b) for comparative purposes. The abscissa axis represents the chemical shift in parts per million (ppm) and the signal intensity in the ordinate axis. Concordance in both chemical shift and relative intensities between the spectra corresponding to the hybrid compound of Example 1 and pure cyclodextrin, clearly indicates that the structure of the CD is completely preserved after its inclusion in the microporous silica matrix.

Figure 5 Sampler scheme described in Example 2. The solid phase is distributed between the previous section and the subsequent section, the solid phase mass of the previous section being twice that of the solid phase mass in the subsequent section.

Figure 6 Recovery obtained for benzene, toluene, ethylbenzene, o-xylene, m-xylene and pxylene using different amounts of ~ -HPCD and carrying out the desorption with 2 mL of internal standard solution in acetonitrile at 75 ° C for 15 minutes . See Example 3. The solid phase mass is represented on the abscissa axis and the recovery percentage on the ordinate axis. From the figure it is concluded that the samplers should preferably contain at least 400 mg of solid phase, 500 mg being the preferred mass.

Figure 7 Recovery obtained for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene using different volumes of internal standard solution in acetonitrile at 75 ° C for 15 minutes and 0.5 g of solid phase of ~ -HPCD for retention See Example 3. On the abscissa axis different types of contaminants are represented at different dissolution volumes of the internal standard in acetonitrile and on the ordinate axis the recovery percentage. Therefore it is concluded that the recovery is optimal working with 2 and 3 mL of internal standard solution, so it is recommended to perform desorption with 2 mL since in this way the recovery is adequate while avoiding dilution of The sample and the procedure are more sensitive.

Figure 8 Recovery obtained at different desorption temperatures for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene using 2 mL of internal standard solution in acetonitrile and 15 minutes for desorption, and 0.5 g of solid phase of pHPCD for retention. See Example 3. On the abscissa axis different types of pollutants are represented at different desorption temperatures and on the ordinate axis the recovery percentage. Therefore it follows that desorption is more efficient when performed hot, although an excessive increase in this can cause volatilization losses. It is therefore recommended to work between 65 ° C and 75 ° C.

Figure 9 Recovery obtained for benzene, toluene, ethylbenzene, o-xylene, m-xylene and pxylene using 2 mL of internal standard solution in acetonitrile and 75 ° C for desorption, 0.5 g of solid phase of p-HPCD for retention and at different heating times. See Example 3. On the abscissa axis different types of pollutants are represented at different heating times and on the axis of ordinates the recovery percentage. The results obtained indicate that recovery is quantitative after 10 minutes. The use of 15 minutes of heating at 75 ° C is recommended since in this way the procedure is safe and the analysis time is not extended excessively.

Figure 10

Recovery obtained based on the total amount of contaminants injected for benzene, toluene, ethylbenzene, o-xylene, m-xylene and p-xylene from multi-component mixtures. See Example 4. On the abscissa axis, the total moles injected are represented and on the ordinate axis the recovery percentage. Therefore, adequate recoveries are obtained as long as the carrying capacity of the solid phase is not exceeded, that is, provided that the total moles of contaminant are equal to or less than the moles of dextrin cycle contained in the solid phase.

Figure 11 Recovery obtained based on the total amount of contaminant for mxylene. See Example 4. In the abscissa axis the moles of contaminant injected are represented and in the axis of ordinates the recovery percentage. Therefore, adequate recoveries are obtained as long as the carrying capacity of the solid phase is not exceeded, that is, provided that the moles of m-xylene are equal to or less than the moles of cyclodextrin contained in the solid phase. The conclusions obtained coincide with those of Figure 10, so it can be concluded that the load capacity of the sampler depends on the total amount of contaminants and not on their nature. It follows that the retention mechanism is mainly due to the formation of inclusion complexes.

EXAMPLES

Example 1. Preparation of the hybrid micro porous compound of the invention of formula (Si02) (CD) x (x = 0.0013; 3.0%, weight percentage).

60 mL of an aqueous solution of p-HPCD (0.015 M) and 48 mL of tetraethylorthosilicate are mixed under vigorous stirring by adjusting the pH in the range 1.7-2.0 by the addition of hydrochloric acid. The initial mixture, with an inhomogeneous appearance, is kept under stirring until complete reaction (at least 30 minutes), that is, until a single phase is observed in the reaction flask. The alcohol formed is then evaporated at 70 ° C using a rotary evaporator. The resulting solid is dried at 50 ° C in the oven for 24 hours. Finally, said dry solid is screened to adapt its particle size to the desired analytical application.

The hybrid material of the invention thus obtained turns out to be microporous without the need to eliminate the cyclodextrin which is in a molar ratio with respect to Si equal to 1: 0.0013 according to the elementary analysis carried out. Micropores are generated during gelation of the inorganic component that traps cyclodextrin molecules. This microporous hybrid material has no peak in its X-ray diffraction diagram at low angles, 10 which indicates the absence of an orderly mesostructure and denotes its amorphous character. On the other hand, the low synthesis temperatures used do not favor the crystallization of the silica, so that high-angle X-ray diffraction signals are not observed either. These characteristics are typical of microporous silica xerogels. The TEM image (see Figure 1) clearly shows the morphology of the particles and the absence of order in the pore system. Micrometric size particles are observed. At the particle edges white spots corresponding to disorganized micropores are detected (according to the X-ray diffraction data). The surface area is SBET = 535.7m2 / g (see Figure 2), the average pore diameter is less than 1.8 nm. The material

It has a total pore volume of 0.25 cm3g- • This porosity, as expected and will be verified in the following examples, is sufficient to allow the inclusion of COY molecules within the porous hybrid material.

The solid state 29Si NMR spectrum shows three signals corresponding to centers Q2, Q3 and Q4 at chemical shift values of -91, -106 and -115 ppm, respectively (see Figure 3). Type Q2 centers are minority. Centers Q3 and Q4 dominate. The signal intensity associated with Q3 sites is characteristic of a highly hydroxylated silica surface, and therefore very hydrophilic. This hydrophilic layer will interact with the outer (hydrophilic) part of the dextrin cycle molecules.

The presence of CD in the hybrid compounds of the invention has been studied by elemental analysis and spectroscopic techniques. The results obtained by elementary analysis indicate that the material contains 3% ~ -HPCD. On the other hand, the similarity, both in number of signals and in their relative intensity between the solid state 12C NMR spectra of the hybrid material with ~ -HPCD (see Figure 4a) and the pure CD (see Figure 4b) indicates that The CD does not degrade when it is included in the silica gel and it maintains the conformation of the pure ~ -HPCD.

From the IR spectra the apparent content curves of both the synthesized solid phase and the pure cyclodextrin and synthetic mixtures of silica and cyclodextrin were calculated. Finally, parameter Q was calculated from the three curves of

ll l

apparent content working at 971 cm-, 975.8 cm- and 985.44 cm- resulting in 0.28.0.29 and 0.28, respectively, for the solid phase with ~ -HPCD. The Q parameter is indicative of the presence of cyclodextrin in the solid phase [32].

In summary, a lubricated compound preferably containing ~ -HPCD with micropores of size large enough to trap a large variety of VOCs in the gas phase has been obtained in the invention. The hybrid compound of the invention is insensitive to various experimental / environmental factors that interfere or

15 make it difficult to obtain reproducible / reliable analytical measures.

The tests performed with other CDs have led to hybrid compounds of the invention with similar characteristics. Table 1 shows some data related to their physicochemical characterization.

20 Table 1

cn

% (wt) x BET area m2 / g Micropore area m 2 / g Pore volume cm 3 / g Pore size nm

a.-cn

3.1% 0.0020 927.5 284.2 0.46 1.95

p-cn

1.3% 0.0007 352.2 307.5 0.16 1.87

p-HPCn

3.0% 0.0013 535.7 360.2 0.25 1.85

p-MCn

3.8% 0.0017 476.4 353.7 0.22 1.90

y-cn

3.4% 0.0016 137.5 128.5 0.06 1.78

Examples of solid phases Si02 (cyclodextrin) x that can be prepared by the general procedure described in Example 1.

Example 2. Construction of the samplers.

For the construction of the samplers, glass tubes with an internal diameter, preferably 4 mm and a length of 80 mm, were used. The glass tubes contain two solid phase sections separated by a porous medium such as glass wool. The anterior part contains twice the solid phase than the posterior. Specifically, 500 and 250 mg of lubricated material have been used in the front and back, respectively.

The filler material has a particle size between 600 and 1000¡tm since smaller sizes could cause a significant loss of load during sampling, preventing working with the usual flow rates (between 100 and 250 mLlmin). The samplers once prepared are sealed until they are used (see Figure 5).

Example 3. Retention and desorption of BTEX using solid phases of eD.

In this test, the retention and desorption conditions of the majority volatile organic pollutants (BTEX) were optimized using solid phases of immobilized uCD, p-CD, p-HPCD, p-MCD Y and CD, of the invention.

The optimization of the conditions was carried out following the procedure of the tube added [30], and the extracts obtained have been analyzed by gas chromatography [13].

The variables considered in this study were the type and amount of solid phase, the nature and volume of the solvent used for desorption, and the temperature of desorption. To carry out the study, 10 ... tL of multicomponent solution in acetonitrile containing 65.9 ... tg of benzene, 65.0 ... tg of toluene, 65.9 ... tg of o-xylene were injected , 64.8¡tg of m-xylene, 64.6¡tg of p-xylene and 65.0¡tg of ethylbenzene, and desorption was performed with 2 mL solution of 52 mglL internal standard (propylbenzene) in each of the solvents tested (ethanol, cyclohexane, acetate

of ethyl, dichloromethane, carbon disulfide and mixtures of cyclohexane and aqueous phase a

acidic pH and acetonitrile), stirring in hennetic tubes for 15 minutes at 75 ° C.

The best results are obtained using substituted CDs (Table 2), 500 mg of solid phase (see Figure 6), 2 mL of acetonitrile as solvent (see Figure 7), performing desorption at 75 ° C (see Figure 8) and stirring for 15 minutes in hennetic tubes (see Figure 9).

Table 2

Compound

p-MCD a.-CD p-CD y-CD p-HPCD

benzene

79% 67% 74% 68% 84%

Toluene

88% 69% 81% 86% 91%

ethylbenzene

99% 98% 79% 79% 97%

m-xylene

98% 88% 85% 92% 95%

p-xylene

98% 88% 85% 92% 95%

o-xylene

99% 75% 83% 93% 97%

10 Recoveries obtained using solid phases with different immobilized CDs

Example 4. Influence of the amount of contaminant on the recovery of BTEX using solid phases p-HPCD.

15 To evaluate the loading capacity of the sampler, different amounts of m-xylene, as well as a mixture of BTEX, were injected into a sampler containing 500 mg of p-HPCD in the front.

From the elementary analysis carried out, it was concluded that in 500 mg of solid phase of the invention 1.1 10-5 moles of p-HPCD are bound, so the study was carried out by injecting amounts lower and higher than the contaminating stoichiometric ratio: p-HPCD. Specifically, following the procedure of the added tube [30], 10 ~ L were injected containing the moles of VOCs indicated in the

25 Table 3.

Table 3

benzene

Toluene o-xylene m-xylene p-xylene ethylbenzene totals

TO

20410-7, 20410-7,

B

1 02 10-o, 1 02 10-o,

and

338 10-15, 29710-1, 261 10-1, 257 10-1, 25610-1, 5 11 10-1, 1.62 lO-o

D

204 10-o, 204 10-o,

AND

67610-15, 59410-1, 522 10-1, 5 14 10-1, 5 12 10-1, 1 02 10-o, 323 lO-o,

F

845 10-1, 70710-1, 622 10-1, 6 11 10-1, 60910-1, 6.13 10-1 4.01 lO-o

G

1 35 10-1, 1 19 10-o, 1 04 lO-o, 1 03 lO-o, 1 02 10-o, 2,0410-6 646 10-o,

H

1 02 1O- ~, 1 02 1O- ~,

one

270 10-1, 237 lO-o, 209 lO-o, 205 lO-o, 205 lO-o, 40910-6, 1 29 1O- ~,

J

204 10-), 2 04 1O- ~,

K

676 10-1, 59410-6, 522 10-6, 5 14 lO-b, 5 12 10-b, 1 02 10-5, 3 23 1O- ~,

L

1 35 lO-o, 1 19 10 -:>, 1.0410 -:> 1 03 10 -:>, 1 02 10 -:>, 20410-5, 646 10 -:>,

Moles of injected VOCs

Desorption was performed with 2 mL of 52 mglL solution of internal standard 5 (propylbenzene) in acetonitrile in airtight tubes for 15 minutes at 75 ° C. Extracts were analyzed by gas chromatography [13].

The results obtained are shown in Figures 10 and 11. In all cases, recovery decreases when the 1: 1 mole ratio is contaminated: ~ 10 HPCD, regardless of whether it is a multi-component mixture when there are several analytes (see Figure 10) or a single analyte (see Figure 11) .

Example 5. Storage time of the samples, reuse and humidity of the solid phase.

To study the possibility of reusing the solid phase of the invention, it was collected after use and cleaned with acetonitrile while stirring for 15 minutes. Once cleaned, it was filtered to remove the solvent and allowed to dry at room temperature. Sampler tubes containing this solid phase of the invention were then prepared and recovery of BTEX was obtained. To do this, following the procedure of the added tube [30], 1 O ~ L of multicomponent solution in acetonitrile containing 65.9 ~ g of benzene, 65.0 ~ g of toluene, 65.9 ~ g of o-xylene were injected , 64.8 g of m-xylene, 64.6 g of p-xylene and 65.0 g of ethylbenzene.

5 Desorption was performed in airtight tubes with 2 mL of a 52 mg / L internal standard solution (propylbenzene) in acetonitrile at 75 ° C and stirring for 15 minutes. Likewise, three targets were processed. Extracts were analyzed by gas chromatography [13].

The recoveries obtained for the contaminants do not differ significantly from those obtained using the solid phase of the new invention, specifically the differences ranged between + 5% and -7%. In addition, whites indicated that the solid phase is clean after the treatment performed. Therefore, it is concluded that the solid phase of the invention can be reused.

15 The maximum storage time of the samples is established as the time that they can be stored from their collection until they are processed. To carry out the study, 1 O ~ L of the multicomponent solution in acetonitrile containing 65.9 ~ g of benzene, 65.0 ~ g of toluene, were injected into the sampling tubes.

20 65.9 g of o-xylene, 64.8 g of m-xylene, 64.6 g of p-xylene and 65.0 g of ethylbenzene, the tubes were covered and stored in the refrigerator at + 4 ° C until analysis.

The desorption was performed at 24, 72 and 144 hours. Extracts were analyzed by gas chromatography [13]. The results obtained do not show differences

25 significant in recovery, so that the conservation time is at least six days (see Table 4).

Table 4

Time (hours)

Benzene Toluene Ethylbenze no m-xylene p-xylene o-xylene

24

89% 90% 91% 88% 88% 87%

72

90% 89% 91% 90% 90% 90%

144

82% 82% 87% 84% 84% 81%

Recovery after 24, 72 and 144 hours conservation

The influence of moisture on the recovery of BTEX was studied from the recoveries obtained using sampled tubes prepared with solid phase 5 dried at room temperature, at 50 ° C in an oven, and at 50 ° C at high vacuum (2 Ilm Hg) , and finally, using a solid phase moistened with a few drops of water.

To carry out the study, we proceeded as in the previous cases, that is, the multicomponent solution was injected, the desorption was carried out and the extracts were

10 analyzed by flame chromatography using a flame ionization detector (GC-FID). The recoveries were analogous using solid phase dried at room temperature and at 50 ° C in an oven. However, they diminish when the phase has dried under vacuum or has been moistened with water (see Table 5).

15 Table 5

Solid phase

Benzene Toluene Etilben Ceno m-xylene p-xylene o-xylene

Moistened phase

55% Four. Five% 41% 3. 4% 3. 4% 41%

Dried phase Ambient T

to 88% 91% 96% 94% 94% 96%

50 ° C dried phase

to 89% 88% 91% 89% 89% 87%

Empty dried phase

to 63% 64% 62% 65% 65% 63%

Recovery using solid phases with different humidity

Example 6. Intra and inter-synthesis reproducibility using solid phases of pHPCD for BTEX sampling.

The reproducibility study was carried out from the recoveries obtained for each of the pollutants tested using solid phases of ~ -HPCD from different syntheses. Specifically, three independent syntheses called synthesis A, synthesis B and synthesis C.

5 To carry out the study, 10 llL of the multi-component solution in acetonitrile containing 65.9 llg of benzene, 65.0 llg of toluene, 65.9 llg of o-xylene, 64.8 lg of m- were injected in triplicate. xylene, 64.6 llg of p-xylene and 65.0 llg of ethylbenzene. Desorption was performed in airtight tubes with 2 mL of a 52 mglL solution of

10 internal standard (propylbenzene) in acetonitrile at 75 ° C and stirring for 15 minutes. Extracts were analyzed by gas chromatography [13].

The results obtained (see Table 6) indicate good reproducibility with a coefficient of variation of less than 6% in all cases. In addition, there is no significant difference between the coefficients of intra-synthesis and inter-synthesis variation, that is, the reproducibility obtained for replicas of the same synthesis (intra-synthesis reproducibility) is similar to the reproducibility obtained for the values from the different syntheses (inter-synthesis reproducibility). Therefore, it follows that the solid phase of the invention obtained from synthesis

20 independents have similar characteristics and the process for obtaining them is safe and reproducible.

Table 6

benzene

Toluene ethylbenze no m-xylene p-xylene o-xylene

Recovery Synthesis A

88.3% 92.0% 90.8% 89.4% 89.4% 86.3%

Reproducibility Synthesis A

5.6% 4.0% 3.4% 3.2% 3.2% 3.4%

Recovery Synthesis B

85.8% 84.9% 89.7% 84.1% 84.1% 87.3%

Reproducibility Synthesis B

5.8% 5.1% 4.6% 6.5% 6.5% 5.0%

Recovery Synthesis C

92.6% 92.8% 92.9% 90.2% 90.2% 87.5%

Reproducibility Synthesis e

6.3% 1.4% 1.8% 1.9% 1.9% 1.8%

Intrasynthesis Reproducibility

5.9% 3.5% 3.3% 3.9% 3.9% 3.4%

Average recovery

88.9% 89.9% 91.1% 87.9% 87.9% 87.0%

Reproducibility Intersynthesis

3.9% 4.8% 1.8% 3.8% 3.8% 0.8%

Intra-synthesis and inter-synthesis reproducibility

On the other hand, the recoveries obtained for each of the analytes are greater than 75%, so the samplers are suitable for use in active sampling [30].

Example 7. Determination of toluene, o-xylene, m-xylene, p-xylene and ethylbenzene in polluted air using solid phases of p-HPCD.

The arrest of toluene, o-xylene, m-xylene, p-xylene and ethylbenzene has been carried out in polluted air samples using p-HPCD samplers, the results obtained are compared with those provided by the reference method based on the use of solid phases of activated carbon. The analysis of the extracts is performed using GC-FID [13].

15 The procedure is as follows: after the calibration of the low flow sampling pump with the sampling medium to be used, the sample is collected

using a previously selected sampling time. Once the samples are collected, the two ends of the tube are covered tightly and stored at 4 ° C until analysis. To proceed with desorption, the two solid phase sections of the samplers are removed and placed in threaded glass tubes containing the extractant solution (solvent containing 52 mglL internal standard). In the case of activated carbon, desorption is carried out using 1 mL of internal standard solution in CS2 at room temperature and stirring occasionally for a period of 30 minutes [30] and in the case of cyclodextrin phases with 2 mL of internal standard solution in acetonitrile at 75 ° C and stirring for 15 minutes. The extracts were analyzed by

10 gas chromatography [13]. The concentration of contaminants in the sample is calculated taking into account the flow rate and sampling time.

In the extracts obtained from the posterior section of the tubes, the presence of none of the analytes was detected, indicating that the sampling was performed correctly. The results obtained from the extracts of the front section are shown in Table 7.

Table 7

Sampler tube

Toluene p-xylene Ethylbenzene m-xylene o-xylene

Active carbon

23 ± 3 11 ± 4 4.2 ± 0.9 20 ± 7 10 ± 5

~ -HPCD

23 ± 4 12.6 ± 1.8 4.3 ± 0.8 20.6 ± 1.1 10.84 ± 0.15

, ..

Results obtained for the analysis of the samples expressed as a medw ± value of standard SERVICE 20 in mUm3 (n = 3)

It can therefore be concluded that the results obtained using the samplers proposed in the present invention and by the reference method are comparable so that the designed samplers are a clear alternative to the active carbon samplers recommended by the reference method.

25 Example 8. Determination of BTEX in work atmospheres using solid phases of p-HPCD.

The assessment of exposure to chemical agents in a work atmosphere is carried out based on the exposure rates calculated as a ratio between the daily exposure (ED) and the environmental limit value of daily exposure (VLA-ED). To calculate the daily exposure it is necessary to determine the environmental concentration of the contaminants. Different sampling strategies can be followed, in this case a type B sampling has been performed considering that the exposure is homogeneous throughout the working day.

BTEX exposure was evaluated in two work environments, a gas station (MI) and an underground car park (M2). For this, it was sampled using samplers of the invention of ~ -HPCD at a flow rate of 200 mLlmin for a period of 1 hour and 1 hour 20 minutes, respectively.

The procedure is as follows: after the calibration of the low flow sampling pump with the sampling medium to be used, the sample is collected using the previously selected sampling time. Once the samples are collected, the two ends of the tube are covered tightly and stored at 4 ° C. To proceed with desorption, the two solid phase sections of the samplers are removed and placed in threaded glass tubes containing 2 mL of the 52 mglL internal standard solution in acetonitrile. Desorption is carried out at 75 ° C and stirring for 15 minutes. Finally, the extracts are injected into the gas chromatograph [13] and the concentration of the contaminants in the sample is calculated taking into account the flow rate and the sampling time.

In the extracts obtained from the posterior section of the tubes, the presence of none of the analytes was detected, which indicates that the sampling has been carried out correctly. The results obtained from the analysis of the extracts of the frontal section are shown in Table 8. In both cases the concentration of the contaminants is below the detection limit (LOD), so the exposure is acceptable.

Table 8

Sample

benzene Toluene p-xylene Ethylbenzene m-xylene o-xylene

ME

<0.017 <0.018 <0.014 <0.014 <0.016 <0.019

1 <0.017 1 <0.018 1 <0.014 1 <0.014 1 <0.016 I <0.019

Results obtained for the analysis of the samples in mUm3

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Claims (17)

one.

Method for the synthesis of a microporous compound consisting of the formula (Si02) (Cyclodextrin) x where x has a value between O and 0.002, which comprises the reaction between cyclodextrin and a silica precursor compound (SiOz).

2.

Method according to claim 1, characterized in that the micropores of the compound are generated in the same reaction step between the cyclodextrin and a precursor compound of the silica (Si02), without the need to remove the cyclodextrin molecules.

3.

Process according to claim 1, wherein the silica precursor compound (Si02) is tetraethylorthosilicate.

Four.

Method according to claim 1, further comprising:

to.

Stir the reaction mixture until complete.

b.

Evaporate the alcohol formed, preferably at a temperature of 70 ° C.

C.

Dry the material obtained, preferably at 50 ° C for 24 hours.

d.

Optionally crush and sift the material obtained in step c) to adapt its particle size to that required by the analytical application to be carried out.

5.

Microporous compound consisting of the formula (Si02) (Cyclodextrin) x where x has a value between O and 0.002.

6.

Compound according to claim 5, wherein x has a value of 0.0013.

7.

Compound according to claim 5, characterized in that the cyclodextrin is selected from: u-cyclodextrin, ~ -cyclodextrin, 2-hydroxypropyl- ~ cyclodextrin, methyl- ~ -cyclodextrin and y-cyclodextrin, or mixtures thereof.

8.

Compound according to claim 5, characterized by having pores with an average diameter of less than 2 nrn, preferably between 1.5 and 1.8 nrn.

9.

Compound according to claim 5, characterized by having a pore volume greater than 0.15 crn 3g-1.

10.

Use of the compound of claims 5 to 9 as a solid phase or filler of a sampler intended for the determination of volatile organic pollutants.

eleven.

Solid phase or filling of a sampler intended for the determination of volatile organic pollutants comprising the compound of claims 5 to 9.

12.

Sampler for use in the determination of volatile organic pollutants comprising the solid or filler phase of claim 11.

13.

Sampler according to claim 12, characterized in that it comprises at least 400 mg of solid phase or filler, preferably 500 mg.

14.

Method for sampling volatile organic pollutants comprising the retention of contaminants in a sampler comprising the solid or filler phase of claim 11, and the desorption of said contaminants by the use of solvents or by thermal desorption.

fifteen.

Method according to claim 14, characterized in that it is carried out with at least 400 mg of solid phase or filler, preferably 500 mg.

16.

Process according to claim 14, characterized in that the desorption of volatile organic pollutants is carried out with at least 2 mL of acetonitrile as solvent.

Method according to claim 14, characterized in that the desorption of volatile organic pollutants is carried out at a temperature between 65 ° C and 75 ° C. 18. Method according to claim 14, characterized in that the time 10 used for desorption is at least 10 minutes, preferably 15 minutes.