Diethanolamine (DEA) is manufactured in huge quantities and is used in a wide range of processes and products. E.g., it is used as a surfactant, corrosion inhibitor, and to scrub hydrogen sulfide from refinery process gases. It is also used as a wetting agent in shampoos, lotions, creams and other cosmetics.
DEA is usually measured using chromatography, such as HPLC or IC. This instrumentation is expensive, maintenance intensive, and has low sample throughput. In response to a customer request, we developed a Zone Fluidics method which is simple, fast, and uses relatively low cost instrumentation.
Our method is based on the reaction of DEA with a reagent, NBD-Cl (7-chloro-4-nitrobenzo-2-oxa-1,3 –diazole), to form a highly fluorescent derivative which emits at 525nm when excited at 475 nm. The ZF sequence consisted of the following steps: aspirate µL sized zones of sample, reagent, and buffer sandwiched between two air bubbles; dispense the zone stack through our Superserpentine reactor to produce mixing; dispense the mixed zones to a flow through heater; stop the flow and heat at 60 deg. C. for 120 sec; dispense the mixed zones through our bubble tolerant fluorescent flow cell equipped with an ET photon counter. The measured peak is linearly dependent on DEA concentration as seen in the following calibration curve. All fluidics operations as well as data acquisition, processing, and reporting is performed by our FloZF software.
The quantitation limit is about 5 ppm, although this could be lowered with further refinement of the method. There is no upper limit of quantitation as samples can readily be diluted with ZF sequences. Sample throughput is approximately 3 per minute.
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