Carboxen

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... 

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... 

SPME was carried out in 20 ml headspace vials (Shimadzu) with a CTC Combi Pal system auto injector at 70 °C for 60 min using a StableFlex fibre with an 85 pm Carboxen / PDMS coating (Sigma). Prior to analyses 0.8 pg -camphor solved in 4 pi isopropanol were added as internal standard. 

Elemental composition H 5.92%, S 94.08. Hydrogen sulfide may be distinguished by its characteristic odor. The gas turns a paper soaked in lead acetate solution black. Many infrared sensors are commercially available for in-situ measurements of H2S. It may be monitored semiquantitatively by Draeger tubes. It also may be analyzed by GC following trapping over molecular sieves and thermal desorption. Either a flame photometric detector or a sulfur chemiluminescence detector may be used for GC analysis. It may be separated on a capillary column such as Carboxen 1006 PLOT or SPB-1 SULFUR (Supelco Catalog 1999 Supelco Inc., BeUefonte, PA). 

Helmig, D., and L. Vierling, Water Adsorption Capacity of the Solid Adsorbents Tenax TA, Tenax GR, Carbotrap, Carbotrap C, Car-bosieve Sill, and Carboxen 569 and Water Management Techniques for the Atmospheric Sampling of Volatile Organic Trace Gases, Anal. Chem., 67, 4380-4386 (1995). 

An SPME unit consists of a piece of fused-silica fibre coated with a layer of a stationary phase such as non-polar poly(dimethylsiloxane) or polar polyacrylate or divinylbenzene/Carboxen/poly(dimethylsiloxane). The latter, for example, was suitable to trap the odorants (including sotolon) of soy sauce [19]. In the analytical procedure the fibre is exposed to the headspace of a food sample for 10-15 min. Then, the fibre is inserted into the injection port of a GC-mass spectrometry (MS) system. After desorption, the odorants are analysed. To improve the yields of the odorants, the fibre is placed in the effluent of a food sample purged with nitrogen [20]. 

Carbon molecular sieves, e.g., Carbosieves, Carboxen, and Ambersorb Traps small volatiles well Other volatiles not well trapped In combination with other adsorbents... 

PDMS/Carboxen (PDMS/CAR) Trace level volatiles... 

Carbon molecular Sieves 400-1200 Carbosieve, Ambersorb, Spherocarb Carboxen Solvent/ Thermal Non-polar and slightly polar VOCs (>- 80 °C) Low >400°C Low-medium... 

Coeur, C., Jacob, V., Denis, I. and Foster, P. (1997) Decomposition of a-Pinen and sabinen on solid sorbents, Tenax TA and Carboxen. Journal of Chromatography A, 786, 185-7. 

GC column (Packed) Molecular Sieve 5A or Carboxen 1004 micropacked or equivalent in stainless steel column. 

GC column molecular sieve 5A, 13X Chromosorb 102 (80/100 mesh), Carboxen 1004, Haye Sep Q, Carbosieve, Carbosphere, silica gel, activated alumina, or any other equivalent material. Fused silica nonpolar capillary column may be used for low sample volume. 

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. 

Multiple-component phases were developed to exploit adsorbent processes for SPME. Adsorbent blended phases commercially available for SPME contain either divinylbenzene (DVB) and/or Carboxen particles suspended in either PDMS, a nonpolar phase, or Carbowax (CW), a moderately polar phase [55]. The solid particle is suspended in a liquid phase to coat it onto the fiber. 

DVB/Carboxen-PDMS is a multiple-component bipolar phase that contains a combination of DVB-PDMS (50 pm) layered over Carboxen-PDMS (30 pm) [55,137], This arrangement expands the analyte molecular weight range, because larger analytes are retained in the meso- and macropores of the outer DVB layer, while the micropores in the inner layer of Carboxen retain smaller analytes [55], The dual-layered phase is used for extraction of odor compounds and volatile and semivolatile flavor compounds with GC analysis. DVB sorbents have a high affinity for small amines consequently, the combination coating of DVB over Carboxen is the best sorbent choice for extracting isopropylamine [138],... 

Carboxen/PDMS 75, 85 GC/HPLC for gases and low-molecular-weight compounds... 

Nevertheless, the most studied ethanol effect is related to its capacity to modify solution polarity, thus altering the gas-liquid partition coefficient. An increase in ethanol content has been shown to decrease the activity coefficients of many volatile compounds in wine because of an increase in solubility (Voilley et al. 1991). Hartmann et al. (2002) showed a decrease in the recovery of 3-alkyl-methoxy-pyrazynes extracted with a divinylbenzene/carboxen SPME fibre from wine model systems when the ethanol content increased from 0% to 20%. Similarly, Whiton and Zoecklein (2000) reported that a small increase in ethanol content (from 11 % to 14%), in general, reduced the recovery of typical wine volatile compounds. Both of these studies suggest that increasing the alcohol content will reduce the release of volatile compounds from wines. 

Carbosieve S III Carboxenes Mainly gases 400 800 Strong or irreversible sorption of heavier molecules... 

Needle Trap Device Particularly interesting is development of the needle trap device (NTD) in an attempt at miniaturization of the sorption traps used in the analysis of gas samples. A sorbent bed positioned inside a needle (mounted in a gas-tight syringe) acts as a sorption trap. Different materials such as polydimethyl-siloxane (PDMS), carboxenes, carbopacks, Tenax, divinylbenzene (DVB), and other polymers have been employed as sorbents. 

This method utihzes a fused silica rod coated with a thin layer of stationary phase mounted in a holder. During extraction, the fiber is exposed to the sample, and analytes are adsorbed onto the stationary phase and concentrated. After a defined extraction time, the fiber is withdrawn in the holder and then analytes are thermally desorbed in the GC injector. Several types of coatings are commercially available, such as PDMS, polyamide, Carbowax-DVB, Carboxen-PDMS, and PDMS-DVB. Coatings prepared with three kinds of materials are also available (e.g., DVB-Carboxen-PDMS) [71]. Selection of the fiber is mainly based on the principle like dissolves like. For example, PDMS sorbent is suitable for the extraction of hydrocarbons, and the sorbent should be polar for the extraction of alcohols or ketones. The thickness of the coating film determines the sorption capacity of the fiber. Changing the temperature, pH, or ionic strength of the hquid... 

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