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2007 vol. 4

Tech Tip

WarmUp Before You Run

Why conditioning your inlet parts after maintenance is good practice

By Scott Grossman, GC Accessories Chemist

• Eliminate background peaks and avoid

costly reanalysis.

• Improve reproducibility and system

performance.

• Demonstrate system cleanliness.

Every good coach tells athletes to warmup before

they run to make sure the body is primed for opti-

mum performance. The same principle applies to

maintaining your gas chromatograph—time spent

warming up the analytical system after mainte-

nance pays big dividends by improving accuracy

and reducing the need for reanalysis. No matter

whose products you purchase, inlet parts, just like

columns, require a brief conditioning before they

are ready for analytical work. Although it is tempt-

ing to save time by jumping directly into sample

analysis after maintenance, warming up your system

helps you ensure accurate results the first time. In

this article, we will highlight inlet liners as a perfect

example of the need to condition your inlet after

maintenance to avoid costly coelutions, irrepro-

ducible results, and avoidable reanalysis.

Sources of Contamination

Even the best liner can exhibit a small bleed pat-

tern if it is used immediately after installation.

Common sources of contaminants that can cause

bleed include plastic packaging (e.g. phthalates

used to make plastics more flexible) and fatty acids

from finger oils. To evaluate bleed from contami-

nated liners, we first established a clean baseline

with a control liner, then installed a test liner, and

ran the instrument without making an injection.

Figure 1 illustrates the effect of handling an inlet

liner with bare hands. Even some gloves will

impart hydrocarbon contamination that can be

very prominent and persistent (Figure 2). So, care

needs to be taken when handling your new liners.

Handling liners with clean forceps or lint-free

technical wipes is a good way to prevent liner

contamination.

Reduce Noise by Conditioning Your System

This contamination, also called background

“noise,” can be eliminated simply by conditioning

the GC system prior to use. You can condition the

entire inlet a variety of ways. One suggestion is to

make a few preliminary runs using the analytical

method parameters (inlet temperature, oven pro-

gram, etc.) to be used in the subsequent analyses.

We evaluated several commercially available liners

and determined that liner bleed generally will be

gone by the second or third run (Figure 3). An

Figure 2

Hydrocarbon peaks from nitrile gloves are another

example of contamination from maintenance activities that can

be eliminated by warming up the system.

Column:

Rxi

-5ms, 30m, 0.32mm, 0.25µm (cat.# 13424)

Sample:

no sample injected; instrument ran the method conditions with no injection.

Inj.:

no injection; splitless mode (hold 0.5 min., split flow 40mL/min.)

4mm single gooseneck liner with wool, IP deactivated (cat.# 22406).

Inj. temp.:

250°C

Carrier gas:

helium, constant flow

Flow rate:

5.0mL/min.

Oven temp.:

50°C (hold 5 min.) to 320°C @ 30°C/min. (hold 10 min.)

Det.:

FID @ 330°C

GC_EX00955

Figure 1

Eliminate contamination peaks from finger oils by

warming up the system prior to sample analysis.

First Analysis

Second Analysis