c. Limits of Performance
(1) Temperature Limits
Most manufacturers of electrochemical sensors specify the lower temperature limits, usually 32 to 50 F (0 to 10 C), and upper limits, typically 120 to 140 F (50 to 60 C). These do not present a problem for most applications, but the user should be aware that lower temperatures tend to result in longer response times. When used outdoors in cold climates, ambient temperatures should be monitored to assure that the lower limits are not exceeded.
Since many electrochemical sensors are battery-operated, it should be noted that temperature extremes can adversely affect the performance or life of the batteries used in these devices [5,6].
(2) Interferences
Electrochemical sensors designed to measure toxic gases may be non-specific (i.e., cross-sensitive to other compounds). Response specificity is determined by the semi-permeable membrane selected, the electrode material, and the retarding potential (the potential used to retard the reaction of species other than the analyte). Filtering or pre-scrubbing of the sampled atmosphere is also an effective method that has been employed by some manufacturers for some applications. However, not all interferences have been eliminated.
5. MANUFACTURERS
Manufacturers of electrochemical sensors are too numerous to list. For example, there are at least 16 companies that manufacture oxygen monitors with electrochemical sensors. Consult current publications in the field of industrial hygiene and safety for manufacturers of specific sensors [7,8].
6. REFERENCES
[1] Woodfin, W. J. and M. L. Woebkenberg. An Evaluation Of Portable Direct-Reading Oxygen Deficiency Monitors, (NIOSH, unpublished, 1984).
[2] Air Sampling Instruments, 7th ed., Ch. V, ACGIH, Cincinnati, OH (1989).
[3] Methods of Air Sampling and Analysis, 2nd ed., Morris Katz, Ph.D., Editor, Library of Congress No. 77-6826, American Public Health Association (1977).
[4] NIOSH Criteria for a Recommended Standard...Working in Confined Spaces, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 80-106 (1979).
[5] Parker, C. D., et al. An Evaluation of Personal Sampling Pumps in Sub-Zero Temperatures, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 78-117 (1978).
[6] Evaluation of Rechargeable Batteries Used in Industrial Hygiene Equipment, Final NIOSH Contract Report No. 210-78-0090 (1980).
[7] American Laboratory 1993 Buyers Guide, Am. Lab., 25(5) (February 28, 1993).
[8] Pollution Equipment News 1993 Catalog and Buyers Guide, Rimbach Publishing, Inc., 25(6) (November, 1992).
