When Does the Polyarc Need Replacement?
A Polyarc reactor has a limited lifetime. The lifetime is commonly 6 months or 5,000 injections. This can be heavily impacted by the type of analysis. Certain types of analytes can have a significant impact on the longevity of the Polyarc. This makes it difficult to predict how long a reactor will last without complete knowledge of the analysis. As a Polyarc user, it is important to understand what to avoid with the Polyarc and why.
The most common contaminants are silicon species. Given the inherent nature of silicon species under oxidative environments, exposure should be limited to preserve performance of the reactor. Silicon is commonly exposed to the Polyarc through column bleed from PDMS columns or residual derivatization reagents. Column bleed consists predominately of hexamethyl-cyclotrisiloxane and octamethyl-cyclotetrasiloxane, caused by a mechanism of “backbiting” at high temperatures in the column. These compounds will constantly elute during high temperature runs. Maintaining an oven temperature 30°C lower than the maximum temperature or using a low-bleed column can help extend the life of a Polyarc. The other way of introduction of silicon is from derivatized compounds. A trimethylsilyl group is commonly used to replace an active O-H bond to improve stability and volatility, and residual derivatization agent can be a large source of silicon. There is a possibility to use alternative methods (alkylation, esterification) to prevent premature replacement, or Deans switching can be used to divert the reactant.
The more damaging analytes are sulfur containing compounds. Exposure of sulfur will lead to irreversible damage to the catalyst. The reactor can tolerate up to 0.6 mg of sulfur before needing replacement. For a 0.1 uL splitless injection, the allowable concentration is approximately 1,000 ppm S, which allows for approximately 10,000 injections before deactivation. The Polyarc does allow for trace analysis of difficult to detect compounds such as carbonyl sulfide or carbon disulfide, which cannot typically be used with a GC-FID. Concentration and injection volume are the two important method restrictions. An accidental 1 uL splitless injection with DMSO as a solvent, can severely impact the lifetime of the Polyarc. This is why it is crucial for all users of a GC system with the Polyarc to understand the limitations. If a Polyarc is deactivated due to sulfur exposure, regeneration is possible, but the future sulfur capacity will be drastically reduced. Call ARC for instructions on the regeneration procedure.
BY CONNOR BEACH – SALES ENGINEER
April 20, 2022