Measurement of total organic carbon (TOC) is one of the most critical tests performed in high purity water systems requiring accuracy at or near 1 ng/mL.  This is particularly true in the semiconductor industry, where any statistically sustained departure of The TOC content from the baseline (the best that can be attained) is generally enough to cause a call for abrupt system shutdown. Most analyzers rely on the complete oxidation of organic compounds and measurement of the CO2 produced by conductivity.  These systems are necessarily batch analyzers.  Oxidation can also produce a variety of conducting species that can lead to both over and under estimations of TOC.  We present a method capable of measuring TOC without digestion.  All compounds absorb to some varying degree in the deep UV, and we measure that absorbance using the 214 nm line from a zinc lamp using a fiber optic coupled CCD spectrometer.  Lamp drift correction is performed by referencing to the 468 nm zinc emission line.  Cavity enhanced absorption spectroscopy (CEAS) is used to increase the effective pathlength and increase the sensitivity of the device.  CEAS also results in nonlinear absorbance amplification such that at low absorbance values, a greater pathlength is observed leading to a greater dynamic range.  A diffuse reflective cell constructed of extruded Polytetrafluoroethylene, with physical pathlength of 25 cm, is used to achieve an effective pathlength of up to 280 cm.  Potassium hydrogen phthalate (KHP) and glucose were used to evaluate the system.  Limits of detection for KHP and glucose are 0.484 nM and 64 �M respectively, or 46.5 ng/L and 4.6 mg/L.  These values represent the likely upper and lower limits of the device with real samples falling somewhere in between.  When used in conjunction with other TOC analyzers such a device can prove useful in identifying potential sources of contamination.

Continuous total organic carbon monitoring by ultra-violet cavity enhanced absorption spectroscopy

247th National Meeting (2014)

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