Date of Award

Spring 1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Environmental Science - (Ph.D.)

Department

Chemical Engineering, Chemistry and Environmental Science

First Advisor

S. Mitra

Second Advisor

Barbara B. Kebbekus

Third Advisor

Joseph W. Bozzelli

Fourth Advisor

Richard B. Trattner

Fifth Advisor

Pradyot Patnaik

Abstract

Continuous analysis allows a representative portion of a sample to flow continuously through an analytical instrument, which gives analytical information with little or no delay in time. A microtrap is a small diameter tube packed with adsorbents in series. When a gaseous sample containing volatile organic compounds (VOCs) flows through the microtrap, the VOCs can be trapped selectively by adsorbents. Then a pulse of electrical current is applied to the microtrap. This rapid heating results in a desorption that can act as a sharp injection for GC separation. Thus the microtrapped sample is the total amount of VOC present in the sample stream during the time period between two sequential injections.

Three injection systems: the gas sampling valve, the sequential valve microtrap (SVM) and the on-line microtrap-backflushing system (OLMT-BF) were compared for response characteristics and detection limits. Both SVM and OLMT-BF systems were shown to have low detection limits, and the OLMT-BF system can obtain information almost continuously even during the time period between the pulses. A microtrap based nonmethane organic carbon (NMOC) analyzer was also developed for continuous monitoring of a gas stream. In the NMOC analysis, the microtrap served to separate all permanent gases from the organics as well as an on-line preconcentrator for NMOC. The microtrap based NMOC analyzer has low detection limits and low interference from CO2 and H2O.

A method for continuous monitoring of VOCs in water has been developed using on-line membrane extraction and microtrap GC system. Aqueous sample containing VOCs is passed through a hollow fiber membrane. The VOCs selectively permeate across the membrane into an inert gas stream. The VOCs are concentrated and injected into GC column using the microtrap. Continuous monitoring is achieved by making a series of injections.

A minitrap-canister system has been studied for analysis of VOCs in ambient air. An ambient air sample was collected in a Summa canister. Then the sample was concentrated using a multibed minitrap. The trapped VOCs were released rapidly by an electrical pulse and injected on to a GC column without any focusing. The detection limits for hexane and toluene are 0.02 ppb.

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