Polydimethylsiloxane/divinylbenzene PDMS/DVB

In the early 90s, a new technique called solid-phase-micro extraction (SPME), was developed (Arthur and Pawliszyn, 1990). The key-part component of the SPME device is a fused silica fiber coated with an adsorbent material such as polydimethylsiloxane (PDMS), polyacrylate (PA) and carbowax (CW), or mixed phases such as polydimethylsiloxane-divinylbenzene (PDMS-DVB), carboxen-polydimethylsiloxane (CAR-PDMS) and carboxen-polydimethyl-siloxane-divinylbenzene (CAR-PDMS-DVB). The sampling can be made either in the headspace (Vas et al., 1998) or in the liquid phase (De la Calle et al., 1996) of the samples. The headspace sampling in wine analyses is mainly useful for quantifying trace compounds with a particular affinity to the fiber phase, not easily measurable with other techniques. Exhaustive overviews on materials used for the extraction-concentration of aroma compounds were published by Ferreira et al. (1996), Eberler (2001), Cabredo-Pinillos et al. (2004) and Nongonierma et al. (2006). Analysis of the volatile compounds is usually performed by gas chromatography (GC) coupled with either a flame ionization (FID) or mass spectrometry (MS) detector. 

Organochlorine fungicides nuarimol, triadimenol, triadimefon, fol-pet, voinclozolin, and penconazole in wine can be extracted by using a polydimethylsiloxane-divinylbenzene (PDMS/DVB) 60-pm fiber with immersion of the fiber into a 3mL sample at room temperature for 30min. Coupled with LC/DAD analysis, LODs ranging between 4 and 27 pg/L and were reported (Millan et al., 2003). 

We are interested in trace volatile sampling and measurement with emphasis on odour measurement. Commercially about 11 SPME fibre types are available such as those from Supelco , but in the case of odour (trace volatile) detection in air, we have found that three fibre types are most applicable. These comprise 100 pm polydimethylsiloxane (PDMS), 65 pm polydimethylsiloxane/divinylbenzene (PDMS/DVB) and 75 pm carboxen/polydimethylsiloxane (CAR/PDMS) types. Our previous work has investigated the use of both 100 pm PDMS and 65 pm PDMS/DVB fibre types, and we have adopted the latter after initial screening studies. 

One of the first applications of SPME to phthalate analysis was the development of a method for the extraction of DEP from water. The final analysis was done by LC-UV. Different parameters were optimized including four types of fibers. Carbowax-template resin (CW-TRP) and polydimethylsiloxane-divinylbenzene (PDMS-DVB) were found suitable to perform phthalate extraction. The other two fibers, polyacrylate (PA) and polydimethylsiloxane (PDMS), were discarded due to low response and broad peaks, respectively. Samples were extracted at room temperature by direct exposition of the fiber to the sample, previously enriched with 25% of NaCl. The linearity achieved was good from 5 to 50 /rg/1. Higher concentrations show a lost of linearity that could suggest the saturation of the fiber coating. Detection limit was 1 ng/ml. 

Lu et al. described the trace determination of sulfonamide residues in meat with a combination of SPME and LC-MS. Fiber coated with a 65 p,m thickness of polydimethylsiloxane/divinylbenzene (PDMS/DVB) was used to extract sulfonamides at optimum conditions. Analytes were desorbed with static desorption in an SPME-HPLC desorption chamber for 15 min and then determined by LC-MS. The linear range was 50-2000 p-g/kg, with RSD values below 15% (intra-day) and 19% (inter-day) and detection limits 16-39 pg/kg. Some meat samples collected from the local market contained residues of sulfonamides ranging from 66 to 157 pg/kg. The results demonstrated that the SPME-LC-MS system could effectively analyze residues of sulfonamides in meat products. 

Polydimethylsiloxane-divinylbenzene (PDMS-DVB) Nonpolar to moderate polar... 

Polydimethylsiloxane/ divinylbenzene (PDMS/DVB) 65 p.m Suitable for polar volatiles... 

A further example for application of SIDA in fragrance analysis is the quantification of skatole in soap. For this analysis, the SPME technique using 65 iim polydimethylsiloxane/divinylbenzene (PDMS/DVB) coated fiber was applied. Headspace sample was prepared as follows 1 g of soap was dispersed in 10 ml of distilled water, spiked with 1 ppm ds-skatole, and placed in a sealed 100-ml vial containing a Teflon magnetic stirring bar. The sample was equilibrated at 60°C for a period of 30 min. The fiber was carefully introduced in the headspace, and perfume oil constituents were extracted for 30 min under magnetic stirring. 

Fig.1 Relative peak areas and standard deviations after triplicate headspace extractions of 100-ng 2-cyclopentyl-cyclopentanone standard. Extraction time and temperature was 30 min at 80 °C. Fiber material PA = polyacrylate PDMS = polydimethylsUox-ane CW/DVB = carbowax/divinylbenzene PDMS/DVB = polydimethylsUoxane/divinyl-benzene, CAR/PDMS = carboxen/polydimethylsiloxane. Reprinted from [66] with permission of Elsevier. Elsevier (2004)...

GCB = graphitized carbon black SPME = solid-phase microextraction PDMS = polydimethylsiloxane PS = polystyrene DVB = divinylbenzene SDB = styrene-divinylbenzene. 

Solid-phase microextraction (SPME) consists of dipping a fiber into an aqueous sample to adsorb the analytes followed by thermal desorption into the carrier stream for GC, or, if the analytes are thermally labile, they can be desorbed into the mobile phase for LC. Examples of commercially available fibers include 100-qm PDMS, 65-qm Carbowax-divinylbenzene (CW-DVB), 75-qm Carboxen-polydimethylsiloxane (CX-PDMS), and 85-qm polyacrylate, the last being more suitable for the determination of triazines. The LCDs can be as low as 0.1 qgL Since the quantity of analyte adsorbed on the fiber is based on equilibrium rather than extraction, procedural recovery cannot be assessed on the basis of percentage extraction. The robustness and sensitivity of the technique were demonstrated in an inter-laboratory validation study for several parent triazines and DEA and DIA. A 65-qm CW-DVB fiber was employed for analyte adsorption followed by desorption into the injection port (split/splitless) of a gas chromatograph. The sample was adjusted to neutral pH, and sodium chloride was added to obtain a concentration of 0.3 g During continuous... 

Boyd-Boland and Pawliszyn [77] pioneered the SPME analysis of APEOs by SPME-HPLC using normal-phase gradient elution with detection by UV absorbance at 220 nm. The Carbowax-template resin (CW-TR) and Carbowax-divinylbenzene (CW-DVB) fibres allowed the analysis of APEO with a linear range of 0.1-100 mg L 1. The former coating produced the best agreement between the distribution of ethoxymers before and after extraction. This CW-TR fibre provided a limit of detection for individual AP ethoxamers at the low ppb level. The determination of NP in water by SPME-GC (FID) was accomplished by Chee et al. [78] using a polydimethylsiloxane (PDMS) fibre. The linear range was between 1 and 15 mg L 1 with an estimated detection limit of 0.1 mg L-1. 

Concentrator materials of choice are often polymers. Polydimethylsiloxane (PDMS), or a polydimethylsiloxane/divinylbenzene copolymer (PDMS/DVB) are favored choices for explosive molecules. PDMS are often used in the form of solid-phase microextraction (SPME) fibers. PDMS/DVB is often used in the form of microspheres with diameters in the 50- to 75-pm range. Detailed considerations for use of SPME fibers is given on a website maintained by the University of Western England [19], It references a more complete treatise [20], Other geometries, such as stacked spheres, have also been used successfully [21],... 

The fiber carboxen-polydimethylsiloxane-divinylbenzene (CAR-PDMS-DVB 50/30 xm x 2cm) proved to be optimal in the GC-MS analysis in terms of the maximum signal recorded for each compound and the simpler sampling procedure and operating conditions (ionic strength, sample temperature, adsorption time) (Fedrizzi et al., 2007a). 

Accurate studies of grape juice and wine matrix effects in the headspace (HS)-SPME analysis of 3-alkyl-2-methoxypyrazines using a triphase fiber divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/ PDMS) was reported by Kotseridis et al. (2008). Also, PDMS/DVB and CAR/PDMS were selected as suitable fibers for analysis of wines (Sala et al., 2002 Galvan et al., 2008 Ryan et al., 2005). The optimized analytical conditions found are described in Table 4.2. 

A, air H, water W, waste Al, aliphatic amine AA, aromatic amine PAA, polyaromatic amine ABDAC, alkylbenzyldimethylammonium chloride AME, alkylamine ethoxylates T, tertiary amine PE, polyethylene PS/DVB, polystyrene/divinylbenzene PDMS, polydimethylsiloxane PA, polyacrylate PAB, polyacrilonitrilbutadiene. 

The copolymer vinyl-divinylbenzene (DVB)-polydimethylsiloxane (PDMS) PDMS-DVB, a 65 fim thick coating... 

Solid-phase micro-extraction (SPME) first became available to analytical researchers in 1989. The technique consists of two steps first, a fused-silica fiber coated with a polymeric stationary phase is exposed to the sample matrix where the analyte partitions between the matrix, and the polymeric phase. In the second step, there is thermal desorption of analytes from the fiber into the carrier gas stream of a heated GC injector, then separation and detection. Headspace (HS) and direct insertion (DI) SPME are the two fiber extraction modes, whereas the GC capillary column mode is referred to as in-tube SPME. The thermal desorption in the GC injector facilitates the use of the SPME technology for thermally stable compounds. Otherwise, the thermally labile analytes can be determined by SPME/LC or SPME/GC (e.g., if an in situ derivatization step in the aqueous medium is performed prior to extraction). Different types of commercially-avarlable fibers are now being used for the more selective determination of different classes of compounds 100 /rm polydimethylsiloxane (PDMS), 30 /rm PDMS, 7 /rm PDMS, 65 /rm carbowax-divinylbenzene (CW-DVB), 85 /rm polyacylate (PA), 65 /rm PDMS-DVB, and 75 /rm carboxen-polydimethyl-siloxane (CX-PDMS). PDMS, which is relatively nonpolar, is used most frequently. Since SPME is an equilibrium extraction rather than an exhaustive extraction technique, it is not possible to obtain 100% recoveries of analytes in samples, nor can it be assessed against total extraction. Method validation may thus include a comparison of the results with those obtained using a reference extraction technique on the same analytes in a similar matrix. 

Several SP materials have been used for the extraction of FRs from aqueous samples, plasma and milk (Table 31.7). Similar materials have been used for all FRs. Typical SP materials include Ci8 and Cg bonded to porous silica, highly cross-linked poly(styrene divinylbenzene) (PS-DVB), and graphitized carbon black (GCB). It is also possible to use XAD-2 resin for extraction of various FRs, pesticides, and plastic additives from large volumes of water (100 1). The analytes can then be either eluted from the resin by acetone hexane mixture, or Soxhlet extracted with acetone and hexane. For a specific determination of diphenyl phosphate in water and urine, molecularly imprinted polymers have been used in the solid phase extraction. The imprinted polymer was prepared using 2-vinylpyridine as the functional monomer, ethylene glycol dimethacrylate as the cross linker, and a structural analog of the analyte as the template molecule. Elution was done with methanol triethylamine as solvent. Also solid phase microextraction (SPME) has been applied in the analysis of PBDEs in water samples. The extraction has been done from a headspace of a heated water sample (100°C) using polydimethylsiloxane (PDMS) or polyacryl (PA) as the fiber material. ... 

PDMS/DVB, polydimethylsiloxane/divinylbenzene coated fiber SPME, solid-phase microextraction. 

Armitt et al. investigated the influence of acid vapors (98% H2SO4,35% H2SO4, and 37% HCl) on the decomposition of a solid sample of TATP placed into a crimped vial, where the TATP was separated from the deposited 100 pL liquid acid sample by a plug of cotton wool [62]. The headspace in the sealed vials was sampled with polydimethylsiloxane/Carboxen/divinylbenzene (PDMS/Carboxen/DVB) SPME fibers of film thickness 30 and 50 pm, at 1, 3, 5, and 8 h, and at 1,3, 7, and 10 days. Analysis of the headspace from the TATP samples exposed to vapor from the two sulfuric acids produced similar results, with the sample exposed to the 98% sulfuric acid vapor decomposing at a more rapid rate. The principle decomposition products were DADP and acetone, with some minor production of acetic acid. After 7 days, acetone was the major species observed in the headspace. The analysis of the headspace of the TATP samples exposed to HCl vapors showed rapid decomposition of TATP, with no detection of TATP or DADP after 1 day. Additionally, various chlorinated acetones were also observed, indicating a different decomposition pathway than that observed for the TATP exposed to sulfuric acid vapors. 

SPME fibers (100 mm polydimethylsiloxane (PDMS), 70 mm carbowax-divinylbenzene (CW-DVB), and 75 mm Carboxen-PDMS) were obtained from Supelco (Bellefonte, PA, USA). 

LLE, liquid-liquid extraction MAE, microwave-assisted extraction SEE, solid-phase extraction SPME, solid-phase microextraction LPME, liquid-phase microextraction SOME, single-drop microextraction D-LLLME, dynamic liquid-liquid-liquid microextraction SEE, supercritical fluid extraction MIP, molecularly imprinted polymers sorbent SPMD, device for semipermeable membrane extraction PDMS, polydimethylsiloxane coated fiber PA, polyacrylate coated fiber CW-DMS, Carbowax-divinylbenzene fiber PDMS-DVB, polydimethylsiloxane divinylbenzene fiber CAR-PDMS, Carboxen-polydimethylsiloxane coated fiber DVB-CAR-PDMS, divinylbenzene Carboxen-polydimethylsiloxane coated fiber CW-TPR, Carbowax-template resin HS-SPME, headspace solid-phase microextraction MA-HS-SPME, microwave-assisted headspace-solid-phase microextraction HEM, porous hollow fiber membrane PEl-PPP, polydydroxylated polyparaphenylene. 

PDMS = polydimethylsiloxane. PA = polyacrylate. CW = Carbowax. DVB = divinylbenzene. FID = flame ionization detection. NPD = nitrogen-phosphorus detection. TSD = thermionic-specific detection. LOQ = limit of quantitation. LOD = limit of detection. TCA = trichloroacetic acid. PICI-MS = positive ion chemical mass spectrometry. SIM = selected ion monitoring. 

Note PDMS = polydimethylsiloxane DVB = divinylbenzene (3- to 5-pm particles) Carboxen = Carboxen 1006 (contains micro-, meso-, and macro-tapered pores 3- to 5-pm particles). RMM range is ideal range for optimum extraction. Ranges can be extended by varying extraction times, but results will not be optimized. 

Also, a HS-SPME-GC/MS method for analysis of 4-ethylcatechol in wine was performed using a triphase divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/PDMS) fiber after derivatization of the sample with acetic anhydride (Carrillo and Tena, 2007). 

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