What is the difference between regular silica gel clean up and "ex-situ" silica gel clean up?

Modified on: Fri, 25 Jan, 2019 at 2:19 PM

Silica gel clean up is a required step in the process of preparing and analyzing Petroleum Hydrocarbons, particularly those in the C10 to C50 carbon chain range.

It is standard practice under CCME method guidance to include an in-situ silica gel clean up on every sampling being prepared for petroleum hydrocarbon (PHC) F2-F4 analysis.

This is where a polar compound is used to attract other polar compound in a sample (for example organic material), so that only non-polar compounds such as PHCs remain.  This ensures that what is being analysed is only the target compounds.

Historically, instances where repeat silica gel clean up would be requested to improve the potential removal of polar compounds from analysis.  This approach can be problematic as the level at which the process begins to strip target compounds out is difficult to determine and could have a potential to bias a result if continued past this point.

For particularly challenging sites that have high presence of organic materials such as peat, or samples taken near swamps an ex-situ silica clean up might provide some relief.  The process is similar to in-situ, in such that silica gel is used, but rather the gel being added to the sample extract, ex-situ clean up, involves running the sample through a silica column (vertical tube with silica).  

It is possible to split sample extracts and apply the separate clean up methods for comparison, however to apply one after the other is typically not allowable under most regulatory or methodology guidelines.

If you do expect your samples require additional silica gel clean up, please let one of our customer service team know prior to submission of your sample, or indicate it on the chain of custody.

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