Sulfite-sensitive solvent/polymeric-membrane electrode based on bis(diethyldithiocarbamato)mercury(II)

A new solvent/polymeric-membrane electrode which exhibits significant potentiometric response toward sulfite ion in the 1 x 10-6-1 x 10-3 M range is described. The membrane is prepared by incorporation of neutral bis(diethyldithiocarbamato)mercury (II) in a thin film of plasticized poly (vinyl chloride). In sharp contrast to classical Hofmeister behavior, the resulting membrane displays little or no response to a wide range of anions (log Kpoti,j [les] -4, i being sulfite) including sulfate, nitrate, nitrite, chloride, perchlorate, salicylate, and alkylsulfonates. Bromide and thiocyanate are moderate interferents, while significant response to iodide, thiosulfate, and sulfide is observed. These selectivity data, along with other response characteristics of the membrane, are used to postulate the mechanism by which the electrode responds to sulfite. Preliminary studies demonstrate that the electrode can be used in conjunction with an outer gas-permeable membrane for highly selective detection of total sulfite species in the form of sulfur dioxide.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28138/1/0000589.pd

Advances in potentiometric gas sensing: Continuous monitors for ambient ammonia and sulfur-dioxide.

Two advances in the technique of potentiometric gas sensing are introduced. A novel approach to collecting gases in a recipient solution is used to devise a continuous monitor for atmospheric ammonia, and a new sulfite-sensitive solvent/polymeric potentiometric membrane is developed and found suitable for sulfur dioxide measurements. An introduction to the state of gas monitoring in general, and potentiometric gas sensing in particular, is given in Chapter 1. In Chapter 2 a simple yet new way of collecting analyte gas into a suitable recipient stream is described. Continuously-flowing recipient buffer (pH 7) is exposed directly to the gas sample to be analyzed via a microporous sniffer tube. The collected ammonia converts to ammonium in the buffer and is pumped through an established flow-through ammonium-selective electrode. The optimized sensing arrangement is capable of continuously monitoring sub-ppbv levels of atmospheric ammonia. The Chapter describes the response time, detection limits, stability, and selectivity characteristics of the new system. The theoretical foundations for the behavior of the sniffer design are discussed in Chapter 3, accounting for the observed detection limits and response behavior. Chapter 3 also predicts the sniffer's response to changes in sample temperature, as well as the effects of modifications to the present design for faster response and/or better detection limits. In Chapter 4, a new solvent/polymeric electrode membrane based on bis(diethyldithiocarbamato)mercury(II) is introduced. The membrane is highly sensitive to sulfite-ion activity, displaying a lower limit of detection below 1 $\mu$M sulfite. It is found to exhibit selectivity towards sulfite over most common ions (iodide, bromide, and reduced-sulfur anions interfere). The selectivity of the potentiometric sensor is enhanced by its incorporation into a flow-through gas sensing arrangement, providing selective determination of sulfite in liquid samples even in the presence of the above interferents. In conjunction with the new sniffer, this membrane can also provide continuous measurement of gas-phase sulfur dioxide at parts-per-billion levels.Ph.D.Analytical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128283/2/8907128.pd