On rare occasions, heavy metal contamination (e.g. Fe) of a solution in contact with stainless steel can be a problem. In such cases we recommend using stretched PE-50 tubing in the SH-27B or SF-28 inline solution heaters.  The fact that the stainless steel tubing inside these heaters is a straight tube makes this a viable option.  However, the tubes inside the SC-20 are coiled, which means it is not possible to push PE-50 tubing through this heater/cooler.