PDMS fiber

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],... 

SPME fiber PDMS 100-pm coating thickness, 1 cm length... 

Five commercially available fibers, PDMS, 100 fim PA, 85 /um CAR-PDMS, 75 /urn PDMS-DVB, 65 /cm and PDMS, 7 /nm were purchased from Supelco... 

Five different SPME fibers PDMS 100 fim, PA 80 fxm, PDMS-DVB 65 m, CWX-DVB 65 fim, and CAR-PDMS 75 fim PDMS-DVB was selected Cig SPE cartridges... 

Phthalates have also been analysed by SPME-GC using an ECD detector. Prokupkova et al. studied different SPME parameters including two fibers PDMS and PA. PA extraction at room temperature for 20 min was the experimental condition selected. Samples were stirred during extraction. Desorption was performed at 250°C for 50 min to minimize carryover. Quantification was based on calibration curves for distilled water after subtraction of blanks. 

Before applying solid-phase microextraction to the water extracts obtained from hot water extraction of rosemary, optimization of experiments were conducted to determine the optimum working conditions for SPME, including water volume, SPME time, and carry over effect. Polydimethylsiloxane fiber (PDMS, 100 tun, Supelco, Bellefonte, PA) was used for performing solid-phase microextraction. 

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. 

The SPME technique has been developed by Arthur and Pawliszyn [8] and now is well known as a simple, rapid, and sensitive sampling method for liquid or gaseous volatile samples. However, the analytes adsorbed on the SPME fiber generally depend on their polarities and the SPME fiber affinity. Because coffee aroma consists of compounds having many kinds of functional groups, proper selection of the type of fiber to use is important to obtaining accurate and reproducible results [15]. In 2000, in a comparison of three fibers (PDMS, PDMS/DVB, and Carboxen/PDMS) for brewed coffee headspace volatile compounds, it was reported that PDMS/DVB gave the overall best sensitivity, especially for phenols such as 2-methoxyphenol, 4-ethyl-2-methoxyphenol, 4-ethenyl-2-methoxy-phenol, and polar compounds such as 4-hydroxy-2,5-dimethyl-3(2//)-... 

Figure 2 T5 pical total ion chromatograms of the static headspace volatiles of ground roasted Ethiopia coffee beans (roast degree L23) obtained by three different solid-phase microextraction fibers. PDMS, polydimethyl siloxane DVB, divinylben-zene CAR, carboxen.

According to these results, the DH-SPME sampling parameters were determined as follows SPME fiber, PDMS/DVB roasted coffee beans used, 150g nitrogen gas flow rate, 600 mL/min SPME sampling time 8 min. The GCMS analyses conducted under these conditions showed that the coefficients of variation of peak area of the 47 volatile compounds, which corresponded to about 68% of total peak area detected on GCMS analysis, were less than 5% [18]. 

Solid-phase microextraction (SPME) was used for headspace sampling. The FFA were extracted from the headspace with PA, Car/PDMS, and CW/DVB fibers. It was examined whether addition of salt (NaCl) and decreasing the pH by addition of sulphuric acid (H SO ) increased the sensitivity. FFA were analyzed using gas chromatography coupled to mass spectrometry in selected ion monitoring. 

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... 

Soil leachates were analyzed for ametryn, prometryn, and terbuthylazine using 85-pm polyacrylate and 100-pm PDMS SPME fibers.The results obtained... 

A newer addition is in-tube SPME that makes use of an open capillary device and can be coupled online with GC, HPLC, or LC/MS. All these techniques and their utilization in pharmaceutical and biomedical analysis were recently reviewed by Kataoka.45 Available liquid stationary fiber coatings for SPME include polydimethylsiloxane (PDMS) and polyacrylate (PA) for extracting nonpolar and polar compounds, respectively. Also in use for semipolar compounds are the co-polymeric PDMS-DVB, Carboxen (CB)-PDMS, Carbowax (CW)-DVB, and Carbowax-templated resin (CW-TPR). A few examples of in-tube SPME extractions from biological matrices are shown in Table 1.19 and drawn from Li and coworkers.166... 

Diazepam Direct immersion PA (85) PDMS (7, 100) GC-FID (LOQ 0.25 nmol/mL) 1-Octanol-modified PA fiber, pretreated plasma (TCA) Krogh et al., 1997 (10)... 

In regard to the potential effects of silicone membrane or film thickness (e.g., polydimethylsiloxane [PDMS]) on partition coefficients, Paschke and Popp (2003) have shown that that at equilibrium an SPME fiber with a 7 xm thick film of PDMS had about a 6-fold higher ATpw than a similar fiber with a 100 xm thick film. However, this could be the result of interactions with the silica core. Recent research (Smedes, 2004) has shown that silicone sheeting with PRCs can be employed for water sampling with good results. 

Triacetone triperoxide (TATP) is a powerful explosive manufactured in clandestine laboratories and used by terrorists. As TATP subHmes easily, analysis was performed by SPME trapping of its vapor, using polydimethylsiloxane/divinyl benzene (PDMS/DVB) fiber, followed by desorption into a GC/MS injector [10]. Figure 6 shows the TIC, mass chromatogram and the El mass spectmm of headspace from a debris sample containing TATP [11]. The El mass spectmm contains a molecular ion at m/z 222 and several fragment ions. In the chemical ionization mass spectmm of TATP [12], the m or ions were at m/z 223 (100%), 222 (20%), 133 (20%), 117 (40%), 115 (20%), 103 (75%) and 100 (50%). 

SPME Fiber. A 65 pm poly(dimethylsiloxane)/divinyl benzene (PDMS/DVB) fiber coating (Supelco, Bellefonte, PA) was used in this method. This fiber coating was selected for its ability to retain the derivatizing agent and for its affinity for the PFBOA-aldehyde oxime (7). 

On the other hand, the type of fiber was only important for the lighter PCBs, mainly for PCB-28 and PCB-52. For these compounds, the PDMS-DVB fiber is more efficient than the PDMS fiber. The effect of the fiber factor appeared negative (Figure 2) because PDMS-DVB was selected as its low level (Table 1). For the highly chlorinated PCBs, the two fibers tested seem to have similar performance, and this factor lacks statistical significance. 

The SPMB fiber was coaled with 65 pm poly(dir tathyi-siloxane)/divinyl benzene (PDMS/DVB SPME). 

PDMS-fibers were analyzed by GC-electron capture detection using an HP 5890... 

PDMS-DVB fibers were analyzed by GC/MS-MS using a Varian 3800 GC with ion... 

HSSPME Extraction Procedure. Manual SPME holders were used with a 100- am poly(dimethylsiloxane) (PDMS) and 65- am poly(dimethylsiloxane)-divinylbenzene (PDMS-DVB) fiber assembly (Supelco, Bellefonte, PA). The fibers were conditioned as recommended by the manufacturer. 

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