PREPARATION OF ADSORBENT FILTERS PRE-LABELLED WITH STANDARDS FOR THE EVALUATION OF SAMPLING OF POLLUTANTS IN LIQUID AND AERIFORM MATRICES

Abstract

A filtering and adsorbent sampling and enrichment system comprising a stationary phase consisting of a felt of activated carbon fibres with a micro-meso porous conformation and specific surface area of about 1500 m2/g and sampling and/or enrichment standards, confined within a closed casing, is described, as well as the method for obtaining it and the relative process for the analysis of organic and inorganic analytes that uses said system.

Claims

1. A filtering and adsorbent sampling and enrichment system comprising: (a) a stationary phase comprising a felt-type fabric comprising activated carbon fibers having a micro-meso porous conformation and a specific surface area of about 1500 m.sup.2/g, and (b) sampling and/or enrichment standards, and (c) a closed casing, wherein the stationary phase and the sampling and enrichment standards are confined within the closed casing.

2. The filtering and adsorbent sampling and enrichment system according to claim 1, wherein the activated carbon fibers comprise functionalized carbon fibers or coated carbon fibers.

3. The filtering and adsorbent sampling and enrichment system according to claim 1, wherein the felt comprises a woven felt or a non-woven felt.

4. The filtering and adsorbent sampling and enrichment system according to claim 1, wherein the casing is made of a material selected from the group consisting of: natural or synthetic polymers, cellulose or silica based sheets, wire meshes or combinations thereof.

5. The filtering and adsorbent sampling and enrichment system according to claim 4, wherein the casing is made of a material selected from the group consisting of: a quartz fiber, polypropylene, nylon fibers, aldehydic fibers, phenolic fibers, amine fibers, filters of vinyl fibers, cellulose fibers, cellulose derivatives, metal screens and combinations thereof.

6. A method for the sampling, active or passive, of fluid, aeriform, gaseous and liquid matrices comprising filtering and enriching a fluid, an aeriform or a gaseous or a liquid matrix through a filtering and adsorbent sampling and enrichment system of claim 1.

7. A process for the preparation of a filtering and adsorbent sampling and enrichment system comprising: (i) a stationary phase consisting of felt type fabric of activated carbon fibres with a micro-meso porous conformation, (ii) a specific surface area of about 1500 m2/g, and (c) sampling and/or enrichment standards, wherein the stationary phase and the sampling and enrichment standards are confined within a closed casing comprising the following steps: (a) Purification of the stationary phase from organic or inorganic impurities; (b) Drying of the stationary phase obtained at the end of step a); (c) Addition of the sampling standards, and (d) Encapsulation and closure of the casing without the use of glues and/or adhesives.

8. The process according to claim 7 wherein in step a) the purification is carried out by a process comprising solvent extraction or by treatment with acids and oxidants and subsequent washes with water.

9. The process according to claim 7 wherein in step b) the drying of the stationary phase is carried out under vacuum if in step a) the purification took place with a solvent or by thermal dehydration if in step a) the purification took place with an acid and oxidant treatment.

10. The process according to claim 7 wherein in step c) the addition of the sampling standard takes place with a quantitative precision equal to 10 μl±0.20 μl.

11. The process according to claim 7 wherein in step c) the positioning of the sampling standards on the stationary phase takes place at n predefined positions.

12. The process according to claim 7 wherein in step c) the positioning of the sampling standards on the stationary phase comprises use of an automatic multi-tip dispenser.

13. The process according to claim 12 wherein in step c) in the automatic dispenser the stationary phase is positioned on a rotating disc or alternatively on an oscillatory plate with adjustable and constant speed.

14. The process according to claim 12 wherein in step c) the sampling standard is distributed simultaneously with the movement of the membrane positioned on a rotating disc or on an oscillatory plate.

15. The process according to claim 14 wherein in step c) the sampling standard is distributed concentrically in the case of a rotating plate.

16. The process according to claim 14 wherein in step c) the sampling standard is distributed on n lines in the case of oscillatory plates.

17. The process according to claim 7 wherein in step d) the casing is closed by means of a technique selected from the group consisting of: sewing, thermal welding, chemical welding, electrical welding, pneumatic welding, ultrasonic welding, bonding, melting, bending, punching, riveting and closure with external closures or closure with cohesive solvents without the addition of any type of adhesive or glue.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0045] FIG. 1 shows in graph the comparison of the average percentage recovery of a MIX of .sup.13C PCB congeners added on QFF (Quartz Fibre Filters) and ACF (Activated Carbon Fibre) filters after exposure at a temperature of 35° C. for 24 h, Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCB Congeners (L, Labelled).

[0046] FIG. 2 shows graph the comparison of the average percentage recovery of a MIX of .sup.13C PCDD/Fs congeners added on QFF (Quartz Fibre Filters) and ACF (Activated Carbon Fibre) filters after exposure at a temperature of 35° C. for 24 h, Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCDD/Fs Congeners.

[0047] FIG. 3 shows in graph the comparison of the average percentage recovery of the Sampling Standard of .sup.13C PCB congeners added on QFF (Quartz Fibre Filters) and on ACF (Activated Carbon Fibre) filters wrapped with aluminium and sealed after exposure to an average temperature of 23.5° C. and relative humidity % of 55.9 for 15 days, Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCBs Congeners (L, Labelled).

[0048] FIG. 4 shows in graph the comparison of the average percentage recovery of the Sampling Standard of .sup.13C PCDD/Fs congeners added on QFF (Quartz Fibre Filters) and on ACF (Activated Carbon Fibre) filters wrapped with aluminium and sealed after exposure to an average temperature of 23.5° C. and relative humidity % of 55.9 for 15 days, Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCDD/Fs Congeners.

[0049] FIG. 5 shows in graph the comparison of the average percent recovery of the Sampling Standard of .sup.13C PCDD/Fs congeners added on ACF (Activated Carbon Fibres) type ACN 15 encapsulated, wrapped with aluminium and sealed, after 7 days, 30 days (1 month) and 90 days (3 months) at ambient temperature of about 20° C. and refrigerator temperature of about 4° C., Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCDD/Fs Congeners used as Sampling Standard.

[0050] FIG. 6 shows in graph the comparison of the average percent recovery of the Sampling Standard of .sup.13C PCBs congeners added on ACF (Activated Carbon Fibres) type ACN 15 encapsulated, wrapped with aluminium and sealed, after 7 days, 30 days (1 month) and 90 days (3 months) at ambient temperature of about 20° C. and refrigerator temperature of about 4° C., Y axis R % (Percentage Recovery), X axis .sup.13C-labelled PCBs congeners (L, Labelled) used as Sampling Standard.

[0051] FIG. 7 schematically shows the preparation of ACF filters type ACN 15 encapsulated with aluminium edge.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0052] Within the meaning of the present invention, carbon fibres (CF) refer to a material consisting of fibres about 5-10 microns in diameter and composed mainly of carbon atoms.

[0053] Within the meaning of the present invention, the activated carbon fibres (FCA) are fibrous carbonaceous adsorbents obtained by carbonization and activation of polymeric fibres, preferably of the phenol-aldehyde or poly (acrylonitrile) (PAN) type, such as those described for example in the Italian patent application no. 102015000041855, incorporated by reference.

[0054] Within the meaning of the present invention, the sampled organic and inorganic compounds are all classes of compounds of interest to analytical chemistry. Purely by way of example, they can be polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polychlorinated dibenzo-para-dioxins and polychlorinated dibenzofurans, chlorobenzenes, alkylbenzenes, alkanes, phthalic acid esters, polybrominated diphenyl ethers, perfluoroalkylated drugs, active ingredients, Perfluoroalkylated Substances (PFAS-PFOA), metabolites, Mercury in elemental and bound form, semi-volatile metal halides.

[0055] Within the meaning of the present invention, sampling standard refers to any compound that is analogous or similar to the analytes to be sampled, or the isotopically labelled analytes themselves, which are added to the sampling system to reduce aberrations and measurement errors and to assess the veracity of the measurement.

[0056] An object of the present invention is a filtering and adsorbent sampling and enrichment system comprising a stationary phase consisting of felt type fabric of activated carbon fibres with a micro-meso porous conformation and specific surface area of about 1500 m.sup.2/g [0057] and sampling and/or enrichment standards, [0058] confined within a closed casing.

[0059] If necessary, the activated carbon fibres can be functionalised or coated.

[0060] Preferably the activated carbon fibres are coated with a coating selected from the group consisting of: Squalene, Methylsilicone OV-1, Methylsilicone SE-30, methyl-phenyl-silicone (20% phenyl) OV-7, methyl-phenyl-silicone (50% phenyl) OV-17, cyanopropyl-methyl-phenyl-silicone OV-225, Carbowax 20M (Polyethylene glycol), nitroterephthalic ester of PEG (FFAP), diethylene glycol succinate (DEGS).

[0061] Preferably the felt is woven or non-woven.

[0062] Preferably the felt is of the ACN 15 type.

[0063] The term ACN 15 denotes the Kynol type non-woven Felt with SSA determined by iodine adsorption 1500 m.sup.2/g, mfibres 3.3 dtex, 80% non-crimped and 20% crimped for larger volumes.

[0064] The membranes of the present invention can be used in the sampling of analytes on site, through active or passive methods and also for the enrichment of samples from previously collected aeriform or liquid matrices.

[0065] In the latter, it is possible to also enrich the analytes present in the laboratory if a method requires it or if it is desired to lower the limits of quantification on an already collected sample or if it was not possible to use ACF at the sampling step.

[0066] A further object of the present invention consists in a process for the preparation of a filtering and adsorbent sampling and enrichment system comprising a stationary phase consisting of non-woven felt fabric of activated carbon fibres with a micro-meso porous conformation with a specific surface area of about 1500 m.sup.2/g and sampling and/or enrichment standards, confined within a closed casing comprising the following steps: [0067] a) purification of the stationary phase from organic or inorganic impurities; [0068] b) drying of the stationary phase obtained at the end of step a); [0069] c) addition of the sampling standards, [0070] d) encapsulation and closure of the casing without the use of glues and/or adhesives.

[0071] Preferably in step a) the purification is carried out by solvent extraction or by treatment with acids and oxidants and subsequent washes with water, most preferably MilliQ™ water.

[0072] Preferably in step b) the drying of the stationary phase is carried out under vacuum if in step a) the purification took place with a solvent or by thermal dehydration if in step a) the purification took place with acid and oxidant treatment.

[0073] In step c) the addition of the Sampling standard on the membranes is carried out in a uniform, reproducible and accurate manner.

[0074] Preferably in step c) the positioning of the sampling standards on the stationary phase takes place in n predefined positions. Preferably in step c) the positioning of the sampling standards on the stationary phase takes place by means of an automatic multi-tip dispenser which is able to dispense the sampling standard onto the membranes at different speeds in a fully repeatable and automatic manner.

[0075] In the automatic dispenser, the stationary phase is positioned on a rotating disk or oscillatory plate with adjustable and constant speed. The sampling standard is distributed simultaneously with the movement of the membrane, thus ensuring equal distribution over the entire surface.

[0076] The distribution of the sampling standard over the stationary phase can be concentric (n circles) in the case of a rotating plate or on n lines (continuous or interrupted, crossed or not) in the case of oscillating plates or in non-rotating movement.

[0077] Preferably the distribution of the sampling standard takes place with a quantitative precision equal to 10 μl±0.20 μl and 0.1% standard deviation.

[0078] Optionally in step c) stabilisers are added to the sampling standards.

[0079] The process avoids sampling standards being lost before measurement takes place, hence during the storage and/or the transport thereof.

[0080] For example, in the case of PCDD/Fs and PCBs, 4% tetradecane is added to the nonane solution in which the sampling standards are contained.

[0081] The sampling system is confined within a closed casing, wherein confinement is understood as a method for the closure on all sides thereof using a continuous material with a mesh size such that there is no release of the fibres to the outside.

[0082] Preferably the material of the casing is selected from the group consisting of: natural or synthetic polymers, cellulose or silica based sheets, wire meshes or combinations thereof.

[0083] More preferably, the material of the casing is selected from the group consisting of quartz fibre, polypropylene, nylon fibres, aldehydic fibres, phenolic fibres, amino fibres, vinyl fibre filters, cellulose fibres, cellulose derivatives and metal screens and combinations thereof.

[0084] The casing is closed by means of a technique selected from the group consisting of: sewing, thermal welding, chemical welding, electrical welding, pneumatic welding, ultrasonic welding, bonding, melting, bending, punching, riveting, closure with external closures or closure with cohesive solvents and the casing is never closed with a technique that involves the addition of any type of adhesive or glue.

[0085] The thus obtained filter is different from an encapsulated filter sandwiched between two filters.

[0086] The pre-labelled adsorbent filters with attenuated sampling standards can be stored at temperatures between 4 and 30° C.

[0087] In one embodiment of the present invention, the adsorbent filter is an ACF filter having a diameter of 102 millimetres, a thickness of 2 millimetres, and a surface area of about 1500 m.sup.2/g.

[0088] Other embodiments can provide for example for a rectangular shape (filters for high volume) or other shapes according to the needs of use, or other diameters, for example 47 mm.

[0089] The process for the analysis of organic and inorganic analytes by using the filtering and adsorbent sampling and enrichment system comprising a stationary phase consisting of activated carbon fibres and sampling and/or enrichment standards provides for a step of capture of the analytes on the filtering and adsorbent sampling and enrichment system, followed by a step of analyte extraction and quantification.

[0090] The analytes can be extracted from the filter using common extraction techniques.

[0091] The filtering and adsorbent sampling and enrichment system comprising a stationary phase consisting of activated carbon fibres and sampling and/or enrichment standards can be used for active or passive sampling of fluid, aeriform, gaseous and liquid matrices.

EXAMPLES

Example 1

[0092] The comparison reported in Table 1 between ISO 16000 13 and 14 with EPA TO 4A and 9A, known in the state of the art, shows that the Sampling Standard is added on the quartz fibre filter (QFF). In this study, the ability to keep the Sampling Standard and the PCDD/Fs and PCBs congeners unaltered over time on a quartz fibre filter with respect to an encapsulated ACF filter type ACN-15 was compared.

[0093] 5 102 mm felt type ACF filters, 2 mm thick, with SSA of about 1500 m.sup.2/g previously washed in Toluene were made. Out of them, three QFFs and three ACF filters were pre-labelled with a known quantity of Sampling Standard, containing .sup.13C.sub.12 PCDD/Fs and PCBs and subsequently encapsulated.

[0094] Since the Sampling Standards include only some congeners it was decided to also use a more complete Standard MIX .sup.13C.sub.12 to assess the effect on the remaining compounds. Hypothetically, it could be associated with the process that the compounds undergo once sampled during transport to the laboratory. For this reason out of the remaining pre-washed filters, 2 QFFs and 2 ACF filters were labelled with a known amount of Standard mix. The ACF filters were then encapsulated. It was decided to assess the most influential variable with regard to the volatilisation of the compounds, that is to say temperature.

[0095] For the ACF filter type ACN-15, the porosity and its distribution were assessed by BET analysis and Langmuir's equation, identifying the one with predominantly microporous distribution and the presence of slight mesoporosity as the preferred type of ACF.

[0096] The type of ACF used is derived from the carbonisation (activation) of phenolic fibres (novoloids) in an inert atmosphere which are conventionally referred to by a term that correlates with the BET number. Specifically, ACF-15 is the activation level that has been selected. The increase in the surface area leads to higher percentages of analyte adsorbed on the material, which can be explained by an increase in the absolute capacity of the material and the larger pore size. The presence of a higher porosity leads to a different energy distribution of the analytes adsorbed on the material. The internal structure of ACF is disordered, and the distance between the various pores greatly influences the force with which the adsorbate interacts with the substrate. The ACFs with a smaller surface area having a narrower porous structure guarantee a more homogeneous substrate on which the analytes can be distributed with a greater binding force (high energy pores) than the situation that would occur with ACF-20 and ACF-25. In the latter, in fact, layers of analytes are created in contact with the substrate with a consequent drastic decrease in the force of interaction among the analytes that are the furthest from the surface and the adsorbent itself.

[0097] The adsorbent suitable for sampling must be able to work even in potentially adverse environmental conditions. It is therefore also important to assess the adsorption isotherms of the analytes at different temperatures. ACF-15 exhibits a little variable behaviour going from 25° C. to 150° C. thus guaranteeing reproducible performance even in extreme conditions and at low concentrations.

[0098] ACF-15 therefore appears to be the best candidate and at the same time has a good surface area that allows quantitative sampling of the analytes present in the matrices at all concentrations. Moreover, from a macroscopic point of view, as the degree of activation increases, so does the degree of defibration, a negative characteristic of this type of adsorbent.

[0099] Filters with Mix of Standard .sup.13C.sub.12 PCDD/Fs and PCBs

[0100] The two filters in ACF and QFF were exposed to a constant temperature of 35° C. for 24 h.

[0101] The data obtained are shown in FIGS. 1 and 2.

[0102] Filters with the Sampling Standard

[0103] The 6 filters (3 in QFF and 3 in ACF) were labelled with 1000 pg of the Sampling Standard .sup.13C.sub.12 of PCDD/Fs and PCBs. They were then packaged in the same way: wrapped with aluminium previously cleaned with DCM and sealed in airtight packaging. The filters were placed at an average temperature of 23.5° C. (MAX 37.4° C.; MIN 9.8° C.) and an average relative humidity of 55.9% (MAX 89.3%; MIN 30.7%) for 15 days. Assuming the transport of pre-labelled filters during the summer months, the temperature considered was in any case underestimated. Following exposure, the 6 filters were extracted separately to assess the R % of the standards. FIGS. 3 and 4 show the average % recoveries for PCDD/Fs and PCBs.

[0104] The data reported in FIGS. 1-4 show that the adsorbent medium commonly used (QFF) for air sampling of PCDD/Fs and PCBs does not have the same ability to maintain the Sampling standard, let alone the Standard MIX unaltered over time. Temperature, a parameter judged to be among the most influential in this process, appears to alter the original concentration of Standard affixed on the adsorbent medium.

[0105] The ACF filter subjected to thermal stress maintains satisfactory average R % such that, regardless of temperature, they can be used as if the Sampling Standard had been recently added (FIGS. 3 and 4). Similarly, it was demonstrated that the filters simulating a sampling do not undergo any alteration due to temperature (FIGS. 1 and 2). The same does not apply for quartz fibre filters, which have been treated in exactly the same way as ACF filters and show satisfactory recoveries only for the higher molecular weight classes.

[0106] This demonstrates how quartz fibre filters are susceptible to errors and underestimation if they are pre-labelled and can be subject to large losses of sampled analytes.

Example 2

[0107] In the case of use for the ISO 16000 13A method, a felt type ACF fibre filter ACN 15 is cut with a diameter of 102 mm, thickness of 2 mm, with SSA of about 1500 m.sup.2/g. This method is aimed at the sampling PCDD/Fs and PCBs for this reason tetradecane is added to the nonane solution in which the sampling standards are contained.

[0108] Optimal conditions were identified in order to position the PCDD/Fs and PCBs sampling standards on the ACN 15 type ACF membranes and subsequently encapsulated. After that, the capture systems were stored in aluminium sheets pre-washed with Dichloro Methane (DCM) and sealed in airtight bags.

[0109] The packaged membranes were allowed to rest by assessing two out of the factors that affect the system's ability to maintain the standard unaltered: temperature and time.

[0110] It was decided to assess an exposure of 7 days, 1 month and 6 months; each test was carried out at two temperatures, both ambient temperature of 22° C. and refrigerator temperature of 4° C. All tests were performed in triplicate to ensure reproducibility of the result.

[0111] The results are shown in FIGS. 5 and 6.

[0112] The data reported so far show that ACF has the ability to maintain the concentrations of the standards added to it unaltered over time for up to 6 months. This makes it possible to assume that several filters can be prepared and can be used over a long distance.

Example 3

[0113] According to the studies carried out on the activated carbon fibres as an enrichment or sampling medium in water (Cerasa et al. 2020, Validation studies on activated carbon fibre passive sampler for PCDD/Fs and PCBs in water, Chemosphere, January; 239:124666. doi: 10.1016/j.chemosphere.2019.124666. Epub 2019 Aug. 25) it can be stated that this filter can also be used for aqueous matrices. In fact, in “Validation studies on activated carbon fibre passive sampler for PCDD/Fs and PCBs in water” the material is assessed as suitable according to the requirements of the ISO 1613B and 1668B methods (for PCDD/Fs and PCBs, respectively).

[0114] The object of the present invention does not exclude its use in aqueous matrices, which in the present example relates to the micropollutants PCDD/Fs and PCBs, but which in general does not exclude the possibility of extension to other micropollutants. Assuming a passive system such as the one of POCIS (Polar Organic Chemical Integrative Sampler) could be, the ACF filter (encapsulated) is perfectly suited for passive sampling in watercourses. In addition, a use as an active enrichment system can be assessed if inserted into SPE cartridges inside which the water sample is flushed through pumps as in the case “Innovative fast SPE for the extraction of PCDD/Fs and dl-PCBs in aqueous samples D preliminary assessment”.

[0115] The sampling standards pre-spiked on the ACF therefore allow to streamline the processes on site by proceeding with the simple operation of inserting the filter in housings prepared for the adsorbent medium. The presence of Standards allows correcting errors due to losses and any breakthrough related to the sampled water volumes. The results show that the pre-packaged ACF filter in one of the possible methods with the addition of the Sampling Standards, which in the example shown are PCDD/Fs and PCBs, is able to retain these compounds unaltered over time for up to 6 months. The estimated percentage recoveries from the replicates allow filters with the pre-spiked Standard to be considered as usable.

Example 4

[0116] In order to assess the importance of the stripping phenomenon, the quantitative results of 3 encapsulated ACF filters were compared with 3 ACF filters used as such.

[0117] The encapsulation involved placing the ACF between 2 quartz filters ringed with 2 aluminium rings all of them with a diameter of 102 mm and SSA greater than 1500 v.1 m2/g.

[0118] The Sampling Standard of PCDD/Fs and PCBs in nonane stabilised in tetradecane is added on all membranes in ACF (those encapsulated before closure).

[0119] The membranes thus packaged were treated by simulating a sampling of ambient air. In this regard, all the membranes were stored for a short time (less than 1 hour) in aluminium sheets, transported to a monitoring station for ambient air, mounted on a Large Volume sampler (Echo Hi-Vol Tecora), starting the sampler for only 5 minutes at a flow of 200 l/min. The membranes were then placed in aluminium sheets and transported to the laboratory. This experiment was used to assess the possible losses due to the stripping of the ACF fibres. During the experiment, as to the unsealed membranes, residual fibres both on the aluminium sheets used for transport and storage and the fibres on the filter holder grid of the high volume sampler were visually observed. All membranes were extracted in Soxhlet through the use of a quartz filter thimble. Upon insertion of the unsealed ACF membranes into the thimble, additional fibre losses were noted in the air and outside the thimble. The samples were spiked with .sup.13C.sub.12-labelled extraction standards of PCDD/Fs and PCBs. After the 36-hour hot extraction in toluene, the extract was concentrated and the samples relative to the unsealed membranes with quartz filters and aluminium ferrule, showed some residual fibres in the test tube. It was therefore necessary to filter the samples and in order not to alter the experimentation, the solutions from the sealed ACF samples were also filtered, although they did not require filtration. Filtration was performed with 47 mm quartz filters, with subsequent elution of the residue with further 5 ml of toluene.

[0120] The reported data show that the sampling standards found on the unsealed adsorbent are on average about 10% lower for both PCBs and PCDD/Fs.

TABLE-US-00003 TABLE 3 R % ACF Sealed ACF vs ACF Sealed ACF ACF free fibres 1,2,3,7,8-PentaCDF* (SS) 97.2 89.4 1,2,3,7,8,9-HexaCDF* (SS) 98.7 91.1 1,2,3,4,7,8,9-HeptaCDF* 105.1 93.5 (SS) Average recoveries % 100.3 91.3

TABLE-US-00004 TABLE 4 R % ACF Sealed ACF vs ACF Sealed ACF ACF free fibres 2,3,4,4′-TetraCB* (SS)  60 L 93.2 84.2 3,3′,4,5,5′-PentaCB* (SS) 127 L 94.5 84.1 2,3,3′,4,5,5′-HexaCB* (SS) 159 L 100.1 91.0 Average recoveries % 95.9 86.4

[0121] A more pronounced difference is observed on the R % of the extraction standards. This difference (about 20% for PCDD/Fs and even about 30% for PCBs) can be attributed precisely to the adsorption action of the fibres that were transported by the toluene during the extraction step in Soxhlet. These free fibres present on the extract adsorbed the standards and the filtration following elution/washing with 5 ml of toluene were not sufficient to recover the analytes of interest.

TABLE-US-00005 TABLE 5 Sealed ACF Unsealed ACF PCBs R % R % 3.4.4′.5-TetraCB*  81 L 90.7 61.4 3.3′.4.4′-TetraCB*  77 L 94.8 61.9 123 L 95.6 63.9 118 L 97.6 63.0 114 L 98.3 70.2 105 L 100.1 71.0 126 L 95.1 67.0 167 L 98.8 69.8 156 L 95.4 73.7 157 L 101.5 19.7 169 L 95.6 82.6 189 L 107.6 84.2 Average recoveries % 97.6 65.7

TABLE-US-00006 TABLE 6 Sealed ACF Unsealed ACF PCDD/Fs R % R % 2,3,7,8-TetraCDD 85.9 69.9 1,2,3,7,8-PentaCDD 86.2 71.6 1,2,3,4,7,8-HexaCDD 96.7 73.7 1,2,3,6,7,8-HexaCDD 98.3 77.9 1,2,3,7,8,9-HexaCDD 97.5 75.4 1,2,3,4,6,7,8- 101.5 72.3 HeptaCDD OctaCDD 104.3 71.8 2,3,7,8-Tetra CDF 84.8 68.7 1,2,3,7,8-PentaCDF 78.8 67.8 2,3,4,7,8-Penta CDF 77.7 70.3 1,2,3,4,7,8-HexaCDF 89.7 74.0 1,2,3,6,7,8-HexaCDF 88.3 75.2 2,3,4,6,7,8-HexaCDF 94.5 72.8 1,2,3,7,8,9-HexaCDF 85.9 73.4 1,2,3,4,6,7,8- 86.6 76.9 HeptaCDF 1,2,3,4,7,8,9- 91.7 71.0 HeptaCDF OctaCDF 102.7 71.8 Average recoveries % 91.2 72.6

Example 5

[0122] While the experimental tests were carried out on a handmade laboratory prototype, an embodiment was prepared using an industrialised system and the product gave the same results as in example 4.

[0123] In particular, the process consists in the preparation of the material of the casing which in its original form is typically in sheets. Each sheet is cut to the required dimensions, slightly exceeding those of the stationary phase, and placed on two matrices prepared for thermoforming (male matrix for forming the lid and female matrix for forming the bottom), which is then carried out by punching. The stationary phase is placed in the thermoformed bottom and is then spiked with the sampling/enrichment standards by means of a micro-droplet diffusion system with high quantitative precision (quantitative precision: 10 μl±0.20 μl)

[0124] After placing the covering casing to the inside of the lid, a pre-welding step takes place, under controlled atmosphere conditions by means of nitrogen insufflation in order to eliminate any excess solvent, until a continuous ring welding is obtained around the membrane. This is followed by final welding in the circular edge around the central membrane in order to obtain a good structural stiffness for the final product to allow easy handling.

Example 6

[0125] At the same time, the chemical-physical characterisation of the ACF identified as the one with the most suitable activation degree ACN-15 was carried out. In particular, the analysis of the Specific Surface Area according to the Brunauer Emmett and Teller (BET) method and the application of the Langmuir equation based on nitrogen absorption is reported below. Prior to the measurements, the sample was degassed at 150° C. with nitrogen flow.

[0126] Nitrogen adsorption increases rapidly and the resulting Langmuir isotherm is equivalent to the one of type I: perfectly microporous material. There is a slight hysteresis point in the isotherm which demonstrates the presence of mesoporosity.

[0127] This dual aspect is confirmed by the results of the porous distribution (PSD), which identifies 1.2 nm (microporosity) and 22 nm (mesoporosity) as the average diameter.

[0128] The characterisation of the active groups that are mainly attributable to the porosity cavities through Boehm titration was also carried out (K. K. Beltrame, A. L. Cazetta, P. S. C. de Souza, L. Spessato, T. L. Silva, V. C. Almeida, Adsorption of caffeine on mesoporous activated carbon fibers prepared from pineapple plant leaves, Ecotoxicol. Environ. Saf. 147 (2018) 64-71. https://doi.org/10.1016/j.ecoenv.2017.08.034.).

[0129] Based on the literature data previously reported in Example 3, it is believed that the ACF in the table type ACN-15 with which the tests were carried out, may have better performance. Not only for the ease of adsorption even at low ACN concentrations with SSA at 1500 compared to that at 2000 m.sup.2/g, but also for the lower presence of acidic groups that tend to coordinate water molecules and remove active sites for the adsorption of the pollutants.

[0130] In which we see a clear prevalence of basic groups compared to total acidic groups consisting for the most part of phenolic groups.

TABLE-US-00007 TABLE 7 ACN 15 Kynol SSA >1500 m.sup.2/g Pore diameter 1.2 nm; 22 nm Microporous solid with presence of slight mesoporosity Chemical Characterization (in 10.sup.−6 meq/m.sup.2) by Boehm Titration. Carboxylic groups 3 Lactonic groups 16 Phenolic groups 53 Pyronic groups 130 Acidic groups 72