proudly sponsored by
|
archiving of SOWACS proudly sponsored by |
|
Hello sowacs list members, I have just received a very exciting update on the "Dasgupta" Voltammetric sensor from Sandy Dasgupta. Included is a pdf of the paper published in Talanta journal in 2002: see abstract below. The type of sensor is one that has not seen any discussion on sowacs. I tried in the past to seed discussion - but no-one appeared to know about it. I had even gone so far as to remove the category from the list on sowacs!:( but now it appears I need to revisit this. With your help we can succinctly describe this sensor type and how it works... Sandy comments that: "We are presently testing a Rhodiated version of this sensor encased in a porous enclosure and thermostated " (photos are up on the page below).. and that this sensor is STILL looking for commercial backing! I have updated the Voltammetric page http://www.sowacs.com/sensors/voltammetric.html which until now only contained this description from 1996 correspondence: " The sensor consists of a blunt ended hypodermic needle cathode containing concentric PTFE insulating tube and therein, a Pt-wire anode. The sensing film is formed by dip-coating a 1:7 blend of a perflourosulfonate and a polyestersulfonate ploymer at the tip of the needle. Atop this sensing film is a composite protective film of cellulose acetate and nylon that inhibits the passage of ionic or low MW constituents and allows the transport of water...." More descriptive text is taken from the introductory text of the current paper: "In comparison to capacitance or ac impedance based sensors that probe water content based on how sorption of water changes the capacitance or impedance of silica, Al2 O3 or a polymeric substrate, electrolytic sensors for water are in principle capable of faster response. This is because the sorbed water is electrolytically decomposed and the response to decreasing moisture content does not have to be limited by the rate of desorption from the substrate. At the minimum an electrolytic moisture sensor is composed of two electrodes, at least one of which is composed of a noble metal to resist anodic oxidation. The electrodes are in contact with an electrolyte that has high affinity for moisture and that becomes conductive upon sorption of moisture." This is still not simple enough for me... please could someone explain??? The full abstract follows: A microfabricated amperometric moisture sensor Xiao-Li Su, Xiong Xingguo, Tim Dallas, Shubhra Gangopadhyay, Henryk Temkin, Xuejun Wang, Richard Walulu, Jianzhong Li, Purnendu K. Dasgupta, * Received 4 April 2001; received in revised form 12 July 2001; accepted 16 July 2001 Talanta 56 (2002) 309-321 Abstract We describe a microfabricated moisture sensor with interdigitated Au or Pt electrodes on a silicon substrate. The sensor active area is covered with a spin-coated, baked-on layer of Nafion ® perfluorosulfonate ionomer of submicron thickness. The sensor responds to moisture with a 10-90% rise time of 50-100 ms and a 90-10% fall time of 20-30 ms, faster than any other presently available sensor. The logarithm of the sensor current is related to the cube root of the moisture level at a given temperature. At 23 °C, the sensor easily measures relative humidities as low as 10%. The sensor response at a given absolute humidity level decreases exponentially with increasing temperature. The film is stable up to a temperature of 150 °C, permitting elevated temperature moisture measurement. Since sorbed water is actively decomposed electrolytically, the sensors exhibit negligible hysteresis. Response reproducibility of an individual sensor is <1%, that between identically made sensors is <5%, suggesting mass production techniques without individual calibration will be acceptable for all but the most demanding situation. © 2002 Elsevier Science B.V. All rights reserved. Bruce Metelerkamp Sowacs owner, chief enthusiast (and list Moderator) -- *************************************************** NOTE: To get off this list, send an email to list@sowacs.com with the subject line: unsubscribe_sowacs For full instructions see this page: <http://www.sowacs.com/subscribe/index.html>