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Restek Capillary Column Installation Guide - Section III: Operational Information

 
  1. Standby operation
  2. Column removal and storage
  3. Protection against dirty samples
  4. Connecting fused silica tubing
  5. Connecting stainless-steel tubing
  6. Column maintenance
  7. Injecting water and other solvents
 

A. Standby Operation

If the column is not going to be used for several days but the instrument must remain on standby, reduce the split vent flow rate to 10 cc/min (to conserve carrier gas) and maintain an oven temperature between 100 °C and 150 °C. Keeping the oven slightly hot minimizes septum bleed accumulation at the head of the column and reduces the need for excessive conditioning when the column is used. Make sure there is a sufficient carrier gas supply when leaving the column in standby operation. If the column will be unused for three or more days, it is best to shut down all heated zones and leave the column in the GC with a low flow of carrier gas. Never leave the column in the GC without carrier gas flowing.

 

B. Column Removal and Storage

Remove the column from the GC. Make sure that there are no ferrule fragments in the injector or detector fittings. If a graphite ferrule sticks in the fitting, remove it by using a tapered needle file (cat.# 20106). Insert the file and spin it slightly until it is latched inside the ferrule. Then move the file slightly from side to side while applying force until the ferrule slips out of the fitting. If the ferrule does not come out in one piece, disassemble the fitting and inspect all parts to make sure that all fragments are removed.

Insert the column ends into a septum to prevent stationary phase oxidation during storage. Always store the column in the original box away from sunlight or fluorescent lights to avoid polymer damage. In particular, Rtx-Wax, Rtx-624, Rxi-1301Sil MS, Rxi-624Sil MS, Stabilwax, Rtx-1301, and Rtx-1701 columns (polyethylene glycol and cyanosilicone polymers) are especially susceptible to UV-induced degradation and should be shielded from light.

 

C. Protection Against Dirty Samples

Samples that contain nonvolatile or high molecular weight residue can contaminate the stationary phase, decrease quantitative accuracy, and cause a loss of peak resolution after a limited number of injections. Using an inlet liner with wool and installing a guard column are two specific precautions recommended to help increase the number of analyses performed before column and inlet liner maintenance is required.

The first precaution involves the use of an inlet liner packed with wool to trap sample residue and prevent it from entering the capillary column. Prepacked liners are generally recommended because they are more consistently packed and in situ deactivation removes active sites, making them highly inert. Alternatively, liners may be manually packed by inserting a loosely packed 2 cm wool plug approximately 1 cm below the maximum penetration distance of the syringe needle. Too much packing material can detrimentally affect the performance of the column. Refer to the instrument manual for specific inlet packing instructions.

Stationary phase coated packings are not recommended because they tend to be adsorptive and can bleed stationary phase onto the column. This problem is particularly damaging if a methyl silicone inlet packing is used with a Carbowax PEG-type capillary column.

The second precaution involves using a guard column, which prolongs the analytical column’s life by trapping nonvolatile contaminants. Integra-Guard columns contain a guard column section that is manufactured within the same tubing as the analytical column. The guard is the initial 5- or 10-meter section of the capillary tubing that has been deactivated but not coated with stationary phase. Because it is integrated into the same tubing as the analytical column, it has been tested for bleed and inertness along with the analytical column (phase coated section of the column). Another advantage of using Integra-Guard columns is that because the guard section is built in, there is no connection to make to the analytical column and, therefore, no risk of connection-related leaks.

Traditional guard columns are 5- or 10-meter sections of deactivated, uncoated tubing that are attached to a separate analytical column inlet using connectors, such as SilTite µ-Union or Press-Tight connectors. Restek offers a wide variety of connectors for this purpose. Whether you choose an integrated Integra-Guard or traditional separate guard column, the inlet end should be trimmed periodically to remove the initial segment when it becomes contaminated with sample components. Restek can also factory-connect guard columns and analytical columns for you. To order, contact Customer Service or visit www.restek.com and enter the analytical column catalog number in the cart and then add the suffix under Special Instructions.

Suffix#

Guard and Analytical Column Preassembled with SilTite µ-Union Connector

-370

5 m, 0.18 mm Rxi guard column connected to 0.18 mm ID analytical column

-371

5 m, 0.25 mm Rxi guard column connected to 0.25 mm ID analytical column

-372

5 m, 0.32 mm Rxi guard column connected to 0.32 mm ID analytical column

-373

5 m, 0.53 mm Rxi guard column connected to 0.53 mm ID analytical column

-374

10 m, 0.18 mm Rxi guard column connected to 0.18 mm ID analytical column

-375

10 m, 0.25 mm Rxi guard column connected to 0.25 mm ID analytical column

-376

10 m, 0.32 mm Rxi guard column connected to 0.32 mm ID analytical column

-377

10 m, 0.53 mm Rxi guard column connected to 0.53 mm ID analytical column

 

D. Connecting Fused Silica Tubing

Connectors are necessary to attach guard columns and restrictors or to repair broken analytical columns, and Restek offers several choices. The Defined PressFit connectors and Press-Tight connectors are glass connectors with a tapered internal diameter at each end and are the quickest and least expensive option. Polyimide resin (cat.# 20445) can be used to strengthen and create permanent press-tight connections, preventing the possibility of premature separation. The SilTite μ-Union connectors are another alternative; these connectors are constructed of deactivated metal and provide easy installation and a zero-dead-volume, permanent leak-tight connection, which makes them ideal for use with mass spectrometers. A popular and effective option is the MXT-Union connector, which will not break and ensures low dead volume. Our Vu2 Union connector and SeCure "Y" connector combine the simplicity of a Press-Tight connector with the strength of a metal union and can be used to a temperature of 400 °C. When connecting fused silica columns, it is essential to make a clean, square cut so a good seal can be obtained. Always leak check new connections using a Restek electronic leak detector.

 

E. Connecting Stainless-Steel Tubing

In order to connect MXT columns, special connectors must be used. The MXT low-dead-volume connector and MXT low-dead-volume "Y" connector are Siltek treated and deactivated to make them inert to active compounds. They will not cause peak tailing or affect system inertness and can be used up to 430 °C without degrading the deactivation layer. Stainless-steel replacement ferrules are available to fit 0.28 mm ID MXT columns (cat.# 20398), 0.18/0.25/0.32 MXT columns (cat.# 20535), and 0.53 mm ID MXT columns (cat.# 20399). An MXT connector can also be used with special Vespel/graphite ferrules to connect an MXT column to a fused silica column. A fused silica Press-Tight connector cannot be used with MXT columns because without polyimide coating on the outside of the tubing, a leak-free connection cannot be obtained.

 

F. Column Maintenance

Maintenance is necessary if a column experiences high bleed (that cannot be decreased by overnight conditioning), adsorption of active components, peak tailing, or changes in relative retention times. Cutting two loops (approximately one meter) from the column inlet is often sufficient to restore a contaminated column. Closely examine the inlet end of the column to make sure that all contaminated tubing has been removed. Occasionally, it becomes necessary to remove more than two loops from a heavily contaminated column to restore it to acceptable performance.

 

G. Injecting Water and Other Solvents

In general, injecting water and other solvents will not damage bonded or nonbonded phase capillary columns provided that the solvent is vaporized before it reaches the front of the column (i.e., when split, splitless, or direct injections are performed). However, if operating the capillary column in cold or heated on-column modes, some damage may occur. To reduce the risk of damage, avoid using water and methanol with Rt-2560 Stabilwax, Stabilwax-DB, Stabilwax-DA, Rtx-2330, and Rtx-225 phases when using cold or heated on-column injection techniques. Alternatively, avoid damage from water and methanol by attaching a 5-meter Hydroguard guard column to the capillary column inlet. This allows the solvent to vaporize before reaching the capillary column. Injecting water, methanol, or other solvents will not damage the other phases Restek offers, regardless of the injection mode.

 

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