subject: Borosilicate Sight Glasses Essential For Parenteral Drug Process Monitoring [print this page] An Ohio pharmaceutical processing facility specializes in converting daily-dose oral drugs into their longer-acting parenteral equivalents. Its technicians monitor the process fluid visually in order to maintain strict control of the transformation process. This is done through the use of sight glasses installed in process vessels. Without this type of gauge glass monitoring, a costly batch of health-saving product could become a very expensive effluent.
The process equipment at this plant was originally equipped with glass/metal fused sight glasses that the equipment manufacturer described as a proprietary design. The manufacturer claimed that the glass formula used in this design was equivalent to the industry gold standard, borosilicate glass. Generally, the accepted standard for glass used in pharmaceutical processes is a borosilicate formulation with no less than 12 percent boron.
The specifier of the pharmaceutical firms original equipment was concerned about the reliability of the glass to metal fusion in the sight glass assembly. This glass-metal interface is crucial in pharmaceutical applications to ensure that materials are not contaminated during processing. In the case of the Ohio parenteral drug company, their batch cost is more than a million dollars, so an added measure of security is well worth a marginal increase in the cost of gauge glass assemblies.
Still, the focus on glass to metal fusion, and an attractive price, may have obscured the importance of the glass formulation. Initially, the less expensive sight glasses performed well, but over a period of time the glass became increasingly cloudy. Eventually, it got to the point where it became difficult, if not impossible, to accurately monitor the process. The reason was obvious: the glass was being etched by process fluids.
An independent laboratory examination of glass elements in these sight glasses revealed that they were not borosilicate glass at all. In fact, the glass contained no boron. In its conclusion, the lab report described this as a common non-parenteral glass of a low-grade soda-lime formulation. As such, it would be unsuitable for many pharmaceutical applications, and certainly not for use in a parenteral drug process.
U.S. Pharmacopeia (USP) standards forbid the use of this soda-lime glass in containers for parenteral applications because of the risk of the glass leaching into the process material. In addition, soda-lime glass lacks the thermal shock resistance, heat resistance and, in this case, resistance to chemical etching required for many applications.
The failed sight glasses were removed and replaced with Metaglas brand sight glasses from L.J. Star, Inc. (www.ljstar.com), which are formed by fusing borosilicate glass with a stainless steel ring. During cooling, differing coefficients of thermal expansion between the solidifying borosilicate glass and the steel ring places the glass element under powerful compressive force, giving the completed component extraordinary strength while retaining all the other desirable characteristics of borosilicate glass.
The Ohio parenteral processing plant has been up and running for some time now with full visibility through the new sight glasses. Unlike the earlier products, Metaglas sight glasses provide the added benefit of allowing removal and reinstallation during routine maintenance. It is entirely reasonable to expect that the new sight glasses will remain in service throughout the life of the process system. The net result is a lower total cost of ownership while avoiding product contamination and process anomalies.
