Polydimethylsiloxane stationary phase

Although these peak areas were sufficient to quantify quinaldic acid on Carbowax columns, residual water present in the extracts of the ion-exchange resins interfered in previous experiments using water-sensitive polydimethylsiloxane stationary phases. The change to a polyethylene glycol stationary phase eliminated the water interferences, and good linear calibration curves for methyl quinaldate were then obtained. 

Hexamethyldisilazane (HMDS) was obtained from Fluka, SE-30 polydimethylsiloxane stationary phase was purchased from Applied Science, aM decane solute was from Chem Service. All were used without further purification. 

KLO Kloskowski, A., Chrzanowski, W., Pilarczyk, M., and Namiesnik, J., Partition coefficients of selected environmentally important volatile organic compounds determined by gas-liquid chromatography with polydimethylsiloxane stationary phase, J. Chem. Thermodyn., 37,21,2005. 

Nitrobenzene, 2,4-dinitrotoluene and 2,6-dinitrotoluene were determined in water by GC-EC or GC-CLD thermal energy analyzer (TEA) and by EI-MS, CI-MS and NICI-MS455, after solid-phase microextraction (SPME) with polydimethylsiloxane coated fiber. SPME is a technique to concentrate organic compounds dissolved in an aqueous matrix by adsorption on a solid stationary phase immobilized on a fused silica fiber. The analytes were thermally desorbed directly into the GC injector LOD was 9 pg/L for nitrobenzene and 15 pg/L for the dinitrotoluenes456. 

Among the above-mentioned methods, SPME is relatively new. It combines sample preparation and injection of the sample into one step. Analytes are adsorbed on a polymeric fiber coated with a stationary phase such as polydimethylsiloxane, which is thermally desorbed in the injection port at 250 °C. The successful use of the technique for the GC/MS analysis of the nerve agents in water has been described (42). Levels of less than... 

At present, polydimethylsiloxane, polyacrylate, and carbowaxT -divinylbenzene or polydimethylsiloxane-divinylbenzene are most often used as stationary phases. Nonpolar analytes are isolated with the aid of polydimethylsiloxane for separation of polar compounds, polyacrylate is applicable. 

Retention of Rohrschneider-McReynolds standards of selected chiral alcohols and ketones was measured to determine the thermodynamic selectivity parameters of stationary phases containing (- -)-61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in poly(dimethylsiloxane) . Separation of selected racemic alcohols and ketones was achieved and the determined values of thermodynamic enantioselectivity were correlated with the molecular structure of the solutes studied. The decrease of the ionic radius of lanthanides induces greater increase of complexation efficiency for the alcohols than for the ketone coordination complexes. The selectivity of the studied stationary phases follows a common trend which is rationalized in terms of opposing electronic and steric effects of the Lewis acid-base interactions between the selected alcohols, ketones and lanthanide chelates. The retention of over fifty solutes on five stationary phases containing 61 (M = Pr, Eu, Dy, Er, Yb, n = 3, R = Mef) dissolved in polydimethylsiloxane were later measured ". The initial motivation for this work was to explore the utility of a solvation parameter model proposed and developed by Abraham and coworkers for complexing stationary phases containing metal coordination centers. Linear solvation... 

Solid phase micro extraction (SPME) is a widely used extraction technique that was developed by Pawlistyn and co-workers in 1990 (74). SPME uses a fused silica fiber that is coated on the outside with an appropriate stationary phase (a S to 100 pm thick coating of different polymers, e.g. polydimethylsiloxane, PDMS). The small size of the SPME flber and its cylindrical shape enables it to fit inside the needle of a syringe-like device. Target molecules from a gaseous or a liquid sample are extracted and concentrated to the polymeric fiber coating. SPME has been used coupled to GC and GC-MS (75), as well as to HPLC and LC-MS 7ll>). Figure 7 shows a conunercially available SPME device. 

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. 

Solid phase microextraction (SPME) involves extraction onto a thin fiber and the technique has become more prevalent recently and additionally provides a preconcentration of analytes prior to analysis. The fibers used in the technique can be coated with a range of stationary phases and a nonpolar phase such as polydimethylsiloxane (PDMS) is typically used for the extraction of derivatized organotin species. An equilibrium is established between the sample extract solution (or the headspace above the solution) and the stationary phase coating the fiber. The analytes are then typically desorbed from the fiber for analysis, for example, using thermal desorption during GC analysis. The technique allows rapid and solvent-free extraction of the analytes. Very good extraction has been achieved for water samples however, the technique has been shown to be more variable with more complex matrices. 

SPME uses a fused sihca fiber that is coated on the outside (occasionally internally if a capillary is used) with an appropriate stationary phase, typically an immobilized polymer, a solid adsorbent, or a combination of the two. A wide range of coatings is available, but probably the most widely used is polydimethylsiloxane (PDMS), weU known as a GC stationary phase that is thermally stable (can be used in a temperature range 20—320 ° C). The anal54es in the sample (liquid or gas) are directly extracted to the fibre coating, and are then thermally desorbed directly into the injection port of a GC or are extracted from the fiber using a suitable solvent for HPLC analysis this process provides high sensitivity because the complete extract can be analyzed. 

Figure 4.19 Structures of common WCOT column stationary phases, (a) Polysiloxanes for Rj = CH3 = R2, polydimethylsiloxane for Rj = CH3 = R2 for some monomers and Rj = CH3, R2 = phenyl for others (different ratios that should be specified), methylphenylpolysiloxanes for Rj = CH3 = R2 for some monomers and Rj = CH3, R2 = phenyl for some others and Rj = CH3, R2 = C3H5CN or C3H7CN for yet others (different ratios that should be specified), methylphenylcyanopolysiloxanes. (b) Poly ethyleneglycol, (c) Silylarene polymer.

Polydimethylsiloxanes are frequently utilized as stationary phases in analytical GLO to determine retention data for a large number of... 

High-resolution gas chromatography (HRGC) has been widely applied for the determination of PCB contents in water samples [112]. PCBs can be separated on a 30-50 m fused silica capillary column with various chemically bonded stationary phases. Table 20.6 shows combinations of column lengths, stationary phases, oven temperature programs, and detectors. Polysiloxane (95% dimethyl-5% phenyl) is the most widely used stationary phase, although 5% diphenyl polydimethylsiloxane, 7% methyl-7% cyanopropyl-phenyl polysiloxane, 95% dimethyl 5% phenyl polysiloxane, 50% phenyl-methyl-polysiloxane are also used. 

Existing separations of amino acid enantiomers, using commercially available stationary phases such as L-valine / r/-butylamide bound to polydimethylsiloxane (Chirasil-Val Figure 1) (7d), L-valine-5-l-(a-phenylethyl) amide bound to... 

The most commonly used stationary phases are silicon based, such as the apolar 100% polydimethylsiloxane phase. Addition of 5% diphenyldimethyl-polysiloxane makes the phase slightly more polar, favoring analysis for moderately polar compounds. Probably this is the most commonly used stationary phase in GC. To separate compounds of high polarity, polar phases (such as polyethylene glycol which has the trade name Carbowax) give the best results. Several other phases are used in practice, such as hydrocarbon, phtalate, glycol ester, or nitrile-based phases. Note that while these stationary phases are liquid. 

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