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Capillary GC Column Killers – Part 3

24 May 2012

Elemental Sulfur

Part 3 of my installment of Capillary GC Column Killers includes a compound known to just about everyone, sulfur. Either analysts have been aware for years that this compound has been in their samples/extracts, or they are surprised when they eventually find out that this compound has been causing their poor chromatography.

Many sample extracts, especially those from petroleum products, can contain elemental sulfur. This is not very surprising since the main source of sulfur today is derived from natural gas and petroleum products ( Sulfur ).  Other common environmental samples which may contain high levels of sulfur are from marine sediments and industrial wastes.


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Photo from Wikipedia

While elemental sulfur will not damage a column’s phase in the strictest sense, it can, however, contaminate the phase, and is very difficult to remove. Once it has contaminated the column’s phase, because sulfur is very reactive, it can cause adsorption and/or breakdown of active compounds in succeeding samples. This is especially true with pesticides.

The EPA has known for years that samples containing elemental sulfur can cause problems with sample analysis. Three of the common methods where they mention it are 8081A, 8082A, and 8141A. For samples suspected of containing elemental sulfur, they recommend that the sulfur be removed by using activated copper or tetrabutylammonium sulfite. Details covering sulfur removal from samples are presented in US EPA Method 3660B.

Please note that performing sulfur cleanup on a sample may remove one or more compounds of interest. It is always wise to perform some preliminary testing before using this method on all of your samples.  In addition to this method,  my co-worker Nancy pointed out to me that EPA Method 3640A (GPC Cleanup) can also be used to remove sulfur from samples, and in many cases doesn't have unwanted chemical reactions.  However, if the compound(s) of interest elute from the GPC column at the same time as the sulfur, other cleanup procedures need to be considered.

 

Below is an example chromatogram showing a sulfur peak (graciously provided by Jack Cochran). The red chromatogram shows the sample before clean-up, and the blue after clean-up. He informed me that the compounds were organochlorine pesticides and the detector was an ECD. As you can see, not only may this huge sulfur peak make quantitation difficult for compounds of interest, but as mentioned earlier, it may leave your column very reactive.


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Of course there are situations where the purpose of the analysis is to look for and quantitate elemental sulfur. Several ASTM methods were written to determine the amount of elemental sulfur in petroleum products. More recently, methods were developed to look for elemental sulfur, and other sulfur-containing compounds, in drywall. 

 

So, in summary, if you are having chromatography issues such as tailing peaks, loss or reduction of active compounds, and unexplained contamination “humps” in your chromatogram after analyzing samples from petroleum products, marine sediment or industrial waste, you may be experiencing the negative effects of having elemental sulfur in your samples/extracts. To keep your chromatography looking sharp, and possibly help your column last longer, spending some time removing this compound from your sample/extract prior to its analysis may be well worth the extra time and effort.