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2008 vol. 1

Tech Tip

HPLC guard columns (cartridges) are installed in front of an analytical col-

umn in order to protect it from strongly retained impurities. Understanding

the significant factors that affect guard column performance can help you pro-

tect your analytical column and save money by extending column lifetime.

Packing & Dimensions

It is best to use a guard column that contains the same packing material as the

analytical column. In other words, the best guard column for a Pinnacle™ II

C18 analytical column is a Pinnacle™ II C18 guard column. Trident guard car-

tridges come in two lengths, 10mm or 20mm. The 10mm length is adequate

for most applications, but a 20mm guard should be considered for samples

that contain a lot of impurities, such as crude extracts. Regarding internal

diameter (ID), the general rule is that the guard column ID should be the same

as, or one size smaller than, the ID of the analytical column to prevent a loss

of efficiency.

Cartridge Holder Options

Trident guard cartridges can be used with three different styles of Trident

guard holder: integral, in-line, and direct. Note that guard cartridges from one

manufacturer should never be used in another manufacturer’s holder.

The Trident Integral guard system is a cost-effective, low dead volume option

that is recommended when purchasing a guard and analytical column at the

same time. This system includes an analytical column, a guard cartridge, and

extra frit, all of which are integrated into a single unit. The advantages of the

Trident Integral Guard column system are that it has the lowest dead volume

of any of the holders and is also the most cost effective option.

Restek also offers in-line and direct holders. Trident In-Line holders are tradi-

tional stand-alone style holders that require an additional piece of HPLC cap-

illary tubing to connect the guard holder to the analytical column. The Trident

Direct Holder differs in that it contains a threaded PEEK™ tip. The threaded

tip allows the holder to screw directly into the analytical column’s inlet end fit-

ting, eliminating the need for any additional tubing. The Trident In-Line and

Trident Direct holders both can be connected to any HPLC column, even

those from other manufacturers. Both these holders are available in either a

“with filter” or “without filter” version. The “with filter” versions have an XF

(extra filter) fitting that contains a cap frit that can be changed independently

of the guard cartridge.

Filters

The ID of the cap frit should match the ID of the guard cartridge; however, frit

porosity is largely a matter of preference. The smaller porosity will provide the

greatest protection against particles, but also may mean that the frit needs to

be changed more frequently. Choosing a filter porosity that matches the

porosity of the analytical column protects against particles lodging in the col-

umn inlet frit.

Restek offers a wide selection of HPLC guard options. An understanding of

the significance of different guard column parameters, including dimensions,

holder styles, and extra filters, can simplify the selection process. Choosing the

proper guard column will maximize the lifetime of your analytical column by

effectively protecting it from sample contaminants.

Selecting the Right HPLC Guard Column

By Terry Reid, Technical Service

Trident Direct 10mm guard

cartridge holder with filter

Trident In-Line 10mm guard

cartridge holder with filter

fitting

XG-XF

Fitting

Guard

Cartridge

Body

Components

Assembled

Installed onto column