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GC contamination on Agilent 6890 - 2005/11/28 18:24
Recently my lab has had some difficulties with an unknown peak that appears on instrument blanks. This peak occurs at around 180 degrees C and with a flow of around 10ml/min using helium it appears around 20 minutes into the run. Heating the inlet and column at 280 appreciably reduces the peak but if the instrument is allowed to cool down and set for a period of time, it recurs larger. Our helium lines are stainless steel, certified clean, with stainless steel regulators and gauges and we also support a getter system. We have 18 GCs, nine of which are on one gas system and nine on a separate gas system. However, this peak occurs on GCs from both systems. Our gas is chromatographic grade helium. We have baked the septa at high temps before use. When we inject a solvent, doesn't matter which kind, the peak gets bigger. We have tried different and new columns and it still appears. We are concerned that there may be something within the GC inlet inside that is contributing to this, such as O rings in the EPC unit. Has anyone else suffered this problem? Please advise.
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GC contamination on Agilent 6890 - 2005/11/28 18:25
It sounds to me as if your clean stainless steel has become contaminated. It only takes one bad cylinder of gas. A fast way to check if it is contamination from the stainless steel gas supply tubing is to do the following. Hold your oven above 180 to establish a baseline. Then with matches or a lighter heat up the stainless steel column. Start close to the cylinder and work toward the GC. If there is anything in the column it will be carried to and through the column producing a large peak. If that happens your gas supplier at some time in the past, sent you a GC helium tank filled with party ballon grade helium. Do you use filters between your cylinder and injector? If you do, replace them. There are external multiple filter systems that have cartidges to remove water, oxygen and organic. Some are indicating for additional protection.
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