Methylsilicone, stationary phase

TMS derivatives of amino acids were also combined with other procedures and some difficulties were thus avoided. N-TMS-methyl and -ethyl esters of most protein amino acids were prepared by the action of TMSDEA on alkyl esters of amino acids and were chromatographed on methylsilicone stationary phases [246], Their retention times were found to be 15—20% lower than those of the corresponding TMS derivatives. Despite having an additional step in comparison with direct silylation, the procedure was applied by Hardy and Kerrin [259] to the GC analysis of twenty protein amino acids, including Hypro and CysH. Amino acids were esterified with a 3 N HC1 solution in n-butanol at 150°C for 15 min with subsequent silylation with BSTFA for 90 min at the same temperature. Acetonitrile and methylene chloride were used as solvents for the silylation. In the former solvent double derivatives of Gly and Lys (bis- and tris-) were produced, whereas in the latter the less silylated form only was produced. As Arg, in contrast to direct silylation, also leads to one peak in this instance, methylene chloride is recommended as the silylation solvent. The separation of all twenty amino acids was achieved on a simple column with 2% of OV-7 on GLC-110 textured glass beads (100—120 mesh). 

WCOT column containing a methylsilicone stationary phase which elutes the aromatic hydrocarbons according to their boiling points. A column containing a relatively thick film of stationary phase, such as 4 to S pm, is recommended to prevent column sample overload. 

The stationary phases coated on the inert supports are similar in the two classes of columns. Liquids of different polarities are chosen for the separation of non-polar or polar compounds a relatively small number of solvents, chemically inert and heat resistant, are sufficient for most residue analyses. The most commonly used for organophosphorus compounds vary from low-polarity hydrocarbons, methylsilicones, phenylsilicones, phenylmethylsilicones or carboranesiloxanes 165 168 175 178 180 182 184 192,195,197,198,... 

The N-alkylation of 2-methyl-6-ethylaniline (MEA) with methoxy-2-propanol (MOIP) was investigated in the same flow microreactor under atmospheric pressure. Feed MEA MOIP = 0.5 (3 ml/h) and hydrogen (4,7 ml/min). The reaction product was condensed in a cooling trap. Each catalyst was tested for 24 h and 7 samples were collected and analyzed separately by GLC on a fused silica capillary column with methylsilicon fluid (Hewlett Packard) as stationary phase. 

The stationary phase consists of a thin layer (ca. 0.2 pm) of a non-volatile liquid, such as methylsilicone or methylphenylsilicone, tightly adsorbed to the inert surfaces of the column. The liquid stationary phases are classified according to their polarity, non-polar phases are used most often because they are easier to handle and are stable over a wide temperature range. The mobile phase is an inert carrier gas such as nitrogen, helium or hydrogen which flows at a constant, but adjustable rate through the column. Current capillary columns, with internal diameters between 0.1-0.6 mm, are constructed of fused silica, specially prepared from pure silicon tetrachloride, and formed into spirals up to 100 m long. Injectors, columns and detectors are located in separately thermostatable compartments. 

The DB-5 is a low-polarity column in which the stationary phase, consisting of 5% phenyl- and 95% methylsilicones, is chemically bonded onto silica. In a similar manner, a DB-1 column consists of 100% methyl-silicone. 

Third method a mixture of HCl/water was added to 500 mg of sample. The extraction was by addition of a mixture of acetone/toluene (clean-up) and back-extraction into toluene extraction recovery was (90 4)%. The separation was by capillary gas chromatography (column of 25 m length, internal diameter of 0.53 mm stationary phase BP-1 (methylsilicone), 1.0 pm film thickness automatic injection of 1 pL temperature of the injector of 200 °C, temperature of the ECD detector of 250 °C, column temperature of 90 °C N2 as carrier gas at 12.2 mLmin" and as make-up gas type at 47 mLmin ). Calibration was by calibration graph with CH3HgCI in toluene. 

First method ca. 1 g sediment was extracted ultrasonically with 20 mL diethyl ether/HO in tropolone (the recovery ranged from 97 to 108% for the three butyltin compoimds as assessed by spiking the CRM with the respective compounds). Derivatization was performed by addition of 2 mol L PeMgBr in diethyl ether. The final extract was cleaned up with silica gel. Separation was by CGC (colunm of 25 m length, 0.32 mm internal diameter, methylsilicone as stationary phase, 0.8 pm film thickness He as carrier gas at 1 mL min injector temperature at 280 °C column temperature ranging from 80 to 280 °C ... 

Traditional gaseous fuel analysis is based on packed columns. Multidimensional chromatography, i.e. the use of columns with different retention characteristics coupled in series in one GC system, improves resolution of complex samples. But packed-column systems are not normally able to separate all compounds. To obtain more precise information about the composition of a gas sample, capillary columns were introduced in fuel analysis. The first were wall-coated open tubular (WCOT) columns with a nonpolar methylsilicone as stationary phase for hydrocarbon separation. However, the permanent gases were still separated in packed columns containing cross-linked polystyrene carbosieve, and molecular sieve as separation phases. 

For a fixed column radius (t. = constant), the retention factor of a solute at a given temperature (/f = constant), doubles when the film thickness is increased by a factor of 2. Guidelines for the. selection of film thickness for the stationary phase methylsilicone are listed below (values depend on column length and stationary phase) ... 

The importance of the stationary phase in GC can, once again, be deduced from the resolution equation (Eq. 3,4). In Figure 8, the influence of the plate number N. the separation or selectivity factor a. and the retention factor k on peak resolution is represented graphically. The peak resolution of two solutes (k = 5) with a = 1.05 on a column with a plate number of 20000 (e.g., lOmxO.Smm coated with 0.2 pm methylsilicone) is 1.4. This value, the crossing point of the curves, is taken as reference. The curves are obtained by changing... 

The discrimination power of PGC in a paint comparison is markedly linked to the gas chromatographic stationary phase employed (241). However, in an effort to increase the reproducibility most laboratories have adopted a single (15-30-m) fused-silica capillary column with a nonpolar (methylsilicone) or medium-polar (phenylmethylsilicone) stationary phase. Over the years many different types of phases of various polarities have been evaluated for their discriminating power of paint samples by PGC, including, but not limited to, Carbowax 20 M and Porapak Q. 

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