Capillary column guard columns

Glycerin is used in Nasonex primarily as a humectant. For its quantification, both capillary gas chromatography method and HPLC methods may be selected. The GC is equipped with a flame-ionization defector, a 0.53 mm x 30 m fused silica analytical column coated with 3.0-p,mG43 stationary phase, and a 0.53 mm x 5 m silica guard column deactivated with phenylmethyl siloxane. The carrier gas was helium with a linear velocity of about 35 cm/s. The injection port and detector temperature was maintained at 240 and 260°C, respectively. The injection mode is splitless. The column temperature is programmed to be maintained at about 40°C for 20 min, then to increase to 250°C at a rate of 10°C/min and to hold at 250°C for 15 min. 

In gas chromatography, a guard column and a retention gap are each typically a 3- to 10-meter length of empty capillary in front of the capillary chromatography column. The capillary is silanized so that solutes are not retained by the bare silica wall. Physically, the guard column and the retention gap are identical, but they are employed for different purposes. 

Once suitable ionization conditions have been established, LC separation can be optimized. As with any LC system, attention needs to be paid to column choice, correct tubing diameters, zero dead volume connections, use of guard columns, and mobile phase filtration and de-gassing. Modem LC pumps can deliver reliable gradients at low flow rates but for capillary LC, precolumn flow splitting or specialized pumps may be necessary. Mobile phase composition and pH should be chosen to... 

Lanolin Diazinon, Diclofenthion, Bromophos ethyl. Lindane, Dieldrin System I 30 M x 053 mm l.D. fused Sillica bonded with G1 (1.5 pm) and a 6 M x 0.53 mm l.D. uncoated guard column System II 30 M x 0.53 mm l.D. Fused Silica Capillary Bonded with G3 (1 pm) and a6M x 0.53mm l.D. uncoated guard column Helium 200 ECD Flameiphoto-metroc Detector Chlorpyrifos USP (24, p. 953)... 

An example of the separation of coumarins with comprehensive normal-phase x reversed-phase LC systems has been published by Dugo etal for coumarins and psoralens in cold-pressed lemon oil. For the separation in the first dimension, the authors used a capillary normal-phase 1.0 mm X 300 mm 5 pm silica column with isocratic elution (eluent -hexane ACN (75 25)) at 20 pi min-1. In the second dimension, a monolithic 4.6 mm X 25 mm C18 silica column (including a 4.6 mm X 5 mm guard column) was employed with linear gradient elution (eluent A water and eluent B ACN) at 4 ml min-1. The interface between the first and the second dimension was a 10-port, 2-position valve equipped with two storage loops. The incompatibility of the solvents that were used in the two dimensions (NPC and RPC) and its effects in the separation were overcome by using a combination of a capillary column in the first dimension and an analytical monolithic column in the second dimension. With this NPC X RPC system, 11 heterocyclic compounds were analyzed and depicted in 2D contour plots. 

A retention gap serves two purposes to provide space for the injected solution to vaporize and expand, thus permitting injection of solvent volumes (>1 pL) that could not otherwise be injected into capillary tubing and to provide surface area for the deposition of co-extractives, thereby protecting the analytical column from buildup of nonvolatiles that can cause loss of efficiency and analyte decomposition or adsorption. In this role, the retention gap often is called a "guard column." Properly installed, a retention gap will not noticeably reduce column efficiency. 

A retention gap, which is a short capillary with stationary phase giving less relative retention than the separation column, is often used, and functions as a guard column to protect the separation column from contamination. 

The reaction coil is 20 cm of coiled stainless steel capillary tubing. The guard column (1.5 cm length, inside diameter) which protects the more expensive Cjg reversed-phase separating column (length = 30 cm, inside diameter = 3.9 mm) is packed with silica-based Cig material. Typical electrochemical detector cells which can be used are (i) Model TL-5 thin layer detector cell obtained from Bioanalytical Systems, (ii) Model EA 1096 wall jet detector cell obtained from Metrohm. 

Fig. 5. An analysis of a coarse atmospheric aerosol extract by CE and IC [49]. CE conditions a 57 cmX75 xm I.D. capillary, distance to detector, 50 cm. Electrolyte 2.25 mM PMA (pyromel-litic acid), 0.75 mM HMOH (hexamethonium hydroxide), 6.50 mM NaOH and 1.60 mM TEA (triethanolamine), pH 7.7 or 2.0 mM NDC (2,6-naphthalenedicarboxylic acid), 0.5 mM TTAB (tetradecyltrimethylammonium bromide) and 5.0 mM NaOH, pH 10.9 30 kV (PMA) or 20 kV (NDC) pressure injection for 10 s indirect UV detection at 254 nm (PMA) or 280 nm (NDC). IC conditions an IonPac-ASlO column with an IonPac-AGlO guard precolumn conductivity detection using an anion self-regenerating suppressor (ASRS-I) in the recycle mode. Analytes 2, chloride 3, sulfate 5, nitrate 6, oxalate 7, formate 10, hydrocarbonate or carbonate 11, acetate 12, propionate 14, benzoate.

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