The Laboratory Instrumentation Effect

At Centek, we perform compound analysis of Fixed Gases, Sulfurs, VOC’s, and Siloxanes. From an analytical standpoint, the type of instruments used for analysis can make quite a difference. For example, commonly ASTM D5504 - 08 Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels uses Gas Chromatography and Chemiluminescence is used to analyze sulfurs from biogas. At Centek, we utilize EPA method TO15 and GC/MS instrumentation to analyze for sulfurs. Now I would like to break down why Centek uses GC/MS rather than GC and Chemiluminescence. With GC/MS technology, we achieve positive confirmation, better linearity, and lower detection limits. Yet, there is no ASTM method written for GC/MS detection of sulfur compounds. The GC is an older technology. It requires dual column confirmation and is not as stable.

Sampling Techniques – Suggestions?

The most successful way to achieve reproducibility is the sampling technique. I have been hired to visit several testing sites by companies needing to train their samplers. In the process, I have seen old tubing being used, open systems being tested and sampling valves that use siloxane base valves. These practices will inevitably affect reproducibility of results. At Centek, we strongly suggest utilizing trained samplers to ensure sampling is occurring using the same process to avoid variability from sampling techniques. This is something the laboratory cannot QC.

Why do you Recommend Fixed Gases (Methane, Oxygen, Nitrogen, Carbon Monxide, Carbon Dioxide) to be analyzed?

I would always recommend that fixed gases be done on every sample; you can get a lot of good information on sampling techniques off of it. For obvious reasons, fixed gases are used to derive methane content, specific gravity, and BTU value (gross and net). Centek can also tell if sampling techniques are satisfactory from the results of a fixed gas analysis. Low methane and high oxygen numbers will bias results low. Landfill or WWTP oxygen levels (normally) are at or below 1%. The results from a fixed gas analysis will indicate whether outside air has affected the results.

Why is Siloxane Analysis so Important?

There are many methods to perform analysis for major constituents of biogas. Siloxane analysis is important (when analyzing biogas) due to the fouling potential caused to Internal Combustion (IC)engines, micro turbines, boilers and SCR catalysts. Once heated, siloxanes form silica, sand like material. Silica deposits are known to cause engine seizure. We have found siloxane results via method TO-15 the most consistent and reproducible. Sampling in a tedlar bag is our most common sampling media for biogas. This method will analyze biogas as a whole air method in the gas phase. Several other testing methods try to capture it in a solvent or oil then convert to a solid and test as an inorganic compound. The problem is you are looking at the end product of what has now taken down your engine instead of analyzing the gas causing failure.

Capabilities & Services

Soil Gas Vapor Intrusion

Biogas Matrix Analysis

• Q&A with Laboratory Director

IH / IAQ

LEED IAQ Testing

Chinese Drywall

Product Testing

Sampling Services