Packings material

The closure of the twist-off jars is rather labor-intensive. In addition there is also a risk of leakage, even when using the twist-off lid system. Particularly with fatty materials, the jars can become fatty and slippery on their outer surface. The consequence can be that the closing machine cannot fix the jar in one position and the jar start to rotate during closure, resulting in a poorly closed lid, which can start to leak 

The more solid materials are transferred to tins or jars by hand, using an ice-spoon. The more liquid materials are transferred to the jars or tins by opening the tap of the round-bottomed flask. This flask can be heated if necessary when filling the jars. 

Shortly after closing the twist-off lids or sealing the tins, at least on the same day of filling, the jars or tins are sterilized by autoclaving for 30 min at I20°C, whilst maintaining a pressure of 2 bar. The cooling time is 30 min. A disadvantage of the 

The between-homogeneity was determined by analyzing the CBs 52, loi, 118, 153 and CB 180 in 15 lots of the candidate CRM. The within-homogeneity was determined by five analyses of the same CBs in one lot of mussels. In addition the Rsd values of a ten-fold analysis of a standard solution and of a five-fold analysis of a fat 

For what is now commonly referred to as conventional liquid chromatography separations were performed at low pressures using totally porous inorganic oxide or porous 

Porous silica (or silica gel) is by far the most important adsorbent for liquid-solid chromatography and is also the substrate used to prepare most chemically bonded phases, giving it a preeminent position in modem column technology [3-15]. Silica particles are mechanically strong and easily prepared in a wide range of particle size ranges and pore diameters suitable for chromatography. As a substrate for the 

COLLOIDAL SILICA PARTICLES (5-100 nm) DISPERSED IN AN AQUEOUS MEDIUM 

IRREGULAR POROUS SILICA PARTICLES OF CONTROLLED PORE AND PARTICLE SIZE RANGES 

Physical properties of Nucleosil porous silicas for liquid chromatography 

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Nylon A class of synthetic fibres and plastics, polyamides. Manufactured by condensation polymerization of ct, oj-aminomonocarboxylic acids or of aliphatic diamines with aliphatic dicarboxylic acids. Also rormed specifically, e.g. from caprolactam. The different Nylons are identified by reference to the carbon numbers of the diacid and diamine (e.g. Nylon 66 is from hexamethylene diamine and adipic acid). Thermoplastic materials with high m.p., insolubility, toughness, impact resistance, low friction. Used in monofilaments, textiles, cables, insulation and in packing materials. U.S. production 1983 11 megatonnes. 

A narrow bored column that usually does not contain a particulate packing material. 

One of the most important advances in column construction has been the development of open tubular, or capillary columns that contain no packing material (dp = 0). Instead, the interior wall of a capillary column is coated with a thin film of the stationary phase. The absence of packing material means that the mobile phase... 

A chromatographic technique in which the mobile phase is a gas and the stationary phase is a liquid coated either on a solid packing material or on the column s walls. 

To minimize the multiple path and mass transfer contributions to plate height (equations 12.23 and 12.26), the packing material should be of as small a diameter as is practical and loaded with a thin film of stationary phase (equation 12.25). Compared with capillary columns, which are discussed in the next section, packed columns can handle larger amounts of sample. Samples of 0.1-10 )J,L are routinely analyzed with a packed column. Column efficiencies are typically several hundred to 2000 plates/m, providing columns with 3000-10,000 theoretical plates. Assuming Wiax/Wiin is approximately 50, a packed column with 10,000 theoretical plates has a peak capacity (equation 12.18) of... 

Samples and calibration standards are prepared for analysis using a 10-mL syringe. Add 10.00 mL of each sample and standard to separate 14-mL screw-cap vials containing 2.00 mL of pentane. Shake vigorously for 1 min to effect the separation. Wait 60 s for the phases to separate. Inject 3.0-pL aliquots of the pentane layer into a GC equipped with a 2-mm internal diameter, 2-m long glass column packed with a stationary phase of 10% squalane on a packing material of 80/100 mesh Chromosorb WAW. Operate the column at 67 °C and a flow rate of 25 mL/min. 

Open tubular microcolumns also have been developed, with internal diameters of 1-50 pm and lengths of approximately 1 m. These columns, which contain no packing material, may be capable of obtaining column efficiencies of up to 1 million theoretical plates.The development of open tubular columns, however, has been limited by the difficulty of preparing columns with internal diameters less than 10 pm. 

In liquid-liquid chromatography the stationary phase is a liquid film coated on a packing material consisting of 3-10 pm porous silica particles. The stationary phase may be partially soluble in the mobile phase, causing it to bleed from the column... 

A liquid stationary phase that is chemically bonded to a particulate packing material. 

Equation 12.33 defines the packing material s exclusion limit. 

Packer fluid Packing material Packing parameters Packings... 

Diamide Chiral Separations. The first chiral stationary phase for gas chromatography was reported by GH-Av and co-workers in 1966 (113) and was based on A/-trifluoroacetyl (A/-TFA) L-isoleucine lauryl ester coated on an inert packing material. It was used to resolve the tritiuoroacetylated derivatives of amino acids. Related chiral selectors used by other workers included -dodecanoyl-L-valine-/-butylamide and... 

Fig. 2. Packing materials for packed columns, (a)—(f) Typical packing elements generally used for random packing (g) example of stmctured packing.

Polystyrene. There are two types of expandable polystyrene processes expandable polystyrene for molded articles and expandable polystyrene for loose-fill packing materials. 

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