Carbowax/templated resin

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... 

For optimization, initial in vitro experiments were performed on a commercial Carbowax templated resin SPME assembly with samples in different volumes of PBS solution in 96-well microplates. No differences were found between 3.0- and 1.5-mL samples. Concentrations of 10 to 500 ng/mL in PBS, 50 to 5000 ng/mL in dog plasma, and 1 to 1000 ng/mL in whole blood were used for calibration extractions. The LC interface design for probe desorption from the fiber is shown in Figure 1.47. 

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. 

The commercially available fibers include polydi-methylsiloxane (PDMS 100, 30, and 7 pm), PDMS-divinylbenzene (PDMS-DVB 65 pm), polyacrylate (PA 85 pm), carboxen-PDMS (CAR-PDMS 75 and 85 pm), Carbowax-DVB (CW-DVB 65 and 75 pm), Carbowax-templated resin (CW-TPR 50 pm), and DVB-CAR-PDMS (50/30 pm). The type of fiber used affects the selectivity of extraction. In general, polar fibers are used for polar analytes, and nonpolar types are used for nonpolar analytes. Selectivity toward target analytes and interferences can be enhanced by surfaces common to affinity chromatography. Fibers can be reused up to 100 analyses or more depending on the sample matrix, on the care of the analyst, and on the applications for which used. 

Some carbamates (carbosulfan, benfuracarb, carbofuran, pirimicarb, diethofencarb, and diuron) and phenylurea pesticides (monuron and monolinuron) were sampled from different fruit juices by using 50-pm carbowax-templated resin (CW-TPR) and a 60-pm PDMS/DVB SPME fiber (Sagratini et al., 2007). The fiber desorption into the SPME-LC/MS interface chamber previously filled with 70% methanol and 30% water, was performed in static mode. 

Three fiber 50 /am Carbowax-templated resin (CW-TPR), 60 /am polydimethylsiloxane—DVB (PDMS-DVB) and 85 /am polyacrylate (PA) the most suitable CW-TPR... 

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. 

A solventless technique of solid-phase microextraction (SPME) has been also employed for HPLC determination of MC in a natural Microcystins sp. bloom in a freshwater, where three dominant MC variants MC-LR, -YR, and -RR were quantified. For this purpose a measuring system with commercial SPME-HPLC interface was employed. Microcystins were sorbed from acidified solutions using SPME fibers with carbowax/templated resin and polydi-methylsiloxane/divinylbenzene coating and desorbed at dynamic mode with HPLC eluent, which was used in isocratic elution mode and consisted of water and methanol with 0.05% TFA. For each toxin partition equilibrium was achieved within 60 min and example response obtained in SPME-HPLC system is shown in Fig. 6. The detection limits for all examined MC for 5 ml samples were reported at about 7 ppb. 

The crucial part of the SPME is the fiber coating, which provides the enrichment of the solute of interest selectively from the matrix components. Typical SPME fibers are [162,163] poly(dimethylsiloxane) (PDMS), polyacrylate (PA), PDMS-divinylbenzene (PDMS/DVB), Carboxen-PDMS, Carbowax-divinylbenzene (CW/DVB), and Carbowax-templated resin (CW/TPR). According to the principle of alike dissolves like, the more polar fibers (PA, PDMS-DVB, CW-DVB, and CW-TPR) have been found suitable for the extraction of phenols, whereas the PDMS fiber was not satisfactory because of its relative nonpolar nature. According to many publications, the most favorable extraction of phenols is performed using a PA fiber. 

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. 

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