Diode array spectrophotometer

July 2010 Analytical Instrumentation & Environmental Monitoring

Online monitoring of bisphenol A in polymer plants.

Bisphenol A (BPA) is a chemical building block that is used to make polycarbonate plastic and epoxy resins. Polycarbonate is a lightweight, high-performance plastic that is used for products such as electronics, automotive and sports safety equipment. Epoxy resins are used for paints and adhesives as well as a variety of protective coatings.

Although most of the Bisphenol A is consumed in the polycarbonate and epoxy manufacturing processes, low level releases of residual Bisphenol A are possible. The level of Bisphenol A present in the process effluent must be measured to ensure that it meets environmental regulations. A typical range for BPA in the effluent is 0-25 ppmw, although a 0-100 ppmw measurement range is often used to monitor possible process upset conditions.

The IPS-4 diode array from Ametek Process Instruments is a cost-effective UV spectrophotometer for the measurement of low ppmw Bisphenol A in effluent water. A major advantage is the rapid scan time of the diode array. Typically a full spectrum is scanned in less than one second. This fast optical response allows for rapid corrective action when an upset condition occurs.

An important consideration when measuring Bisphenol A in effluent is the pH of the aqueous stream. BPA exists as an acid in acidic streams and as a phenate salt in alkaline streams. The UV absorption band for phenol at 265 nm shifts to 285 nm for the phenate absorption. In most Bisphenol A applications, the pH of the effluent is adjusted with caustic and the phenate is measured at 285 nm. There is less susceptibility to interfering components at the 285 nm wavelength for the phenate absorption band.

The IPS-4 has no moving parts in the optical bench, which provides excellent wavelength stability. It has an easy-to-use, multilanguage LED display, a Xenon flash lamp source for long service life, typically greater than two years, and auto zero and auto calibration capabilities. If required, an optional heated sample cell enclosure is available for operation up to 150°C.

For more information contact Jan Pretorius, OEN Enterprises, +27 (0)11 675 4447, [email protected], www.oenenterprises.co.za

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