Amperometric method

#This application generally relates to subject matter disclosed in the following U.S. applications: Ser. No. 773,163, filed Mar. 1, 1977, issued as U.S. Pat. No. 4,096,047; Ser. No. 164,291, filed June 30, 1980, issued as U.S. Pat. No. 4,325,797; Ser. No. 319,708, filed Nov. 9, 1981, issued as U.S. Pat. No. 4,372,021; Ser. No. 345,536, filed Feb. 3, 1982, issued as U.S. Pat. No. 4,518,477; Ser. No. 493,316, filed May 10, 1983, issued as U.S. Pat. No. 4,563,249; Ser. No. 691,519, filed Jan. 14, 1985, issued as U.S. Pat. No. 4,585,542; Ser. No. 821,747, filed Jan. 23, 1986, issued as U.S. Pat. No. 4,711,703; Ser. No. 743,155, filed June 6, 1985; and Ser. No. 890,155, filed July 28, 1986.

#1. Field of the Invention

#The invention generally relates to amperometry, i.e. the art of quantitative electroanalysis; specifically, the invention relates to an amperometric method for quantitative determination of a first electroactive and normally gaseous species (termed "EAGS"), such as elemental oxygen, and of a second electroactive and also normally gaseous species (the second "EAGS"), such as elemental hydrogen, in a normally fluid medium that may be gaseous or liquid.

#The invention will now be explained in more detail with reference to the enclosed drawings in which:

#FIG. 1 is a diagrammatic illustration of an apparatus for carrying out the novel method;

#FIG. 2 is a diagrammatic illustration of a novel cell for use in the inventive method; and

#The diagram of FIG. 1 shows a first MEAC 1 of a generally conventional structure as disclosed, for example, in U.S. Pat. No. 4,096,047 having a sensing face 10 exposed to a fluid medium provided within enclosure 3, a working electrode (e.g. cathode) 11 being made of Au, Ag, Cu or an alloy of these metals, or having its active surface 110 made of these metals. A counter electrode (e.g. anode) 15, e.g. of the conventional Ag/Ag-Cl-type, is arranged within the electrolyte space 112 containing a convention al electrolyte (not shown) while a constant DC-voltage is maintained between the counter electrode and the working electrode in a manner known per se. Additional electrodes, e.g. guard electrodes for the sensing or working electrode, may be used but are not shown. The sensing face 10 of MEAC 1 is provided by the surface of a conventional semi-permeable membrane, i.e. one that is substantially impermeable to the electrolyte but is permeable to the first EAGS, but a masked sensor as disclosed in No. EP-A- 205,399 is suitable as well and may be preferred if no guard electrode is to be used.

#The second MEAC 2 has a structure similar to that or MEAC 1 except that the working electrode 21, or its active surface 210, is made of platinum, a platinum metal or an alloy of platinum group metals (platinum being considered to belong to the platinum group). The sensing face 20 of MEAC 2 again is a semipermeable membrane of the type known (e.g. as disclosed in No. EP-A- 124,818) and the sensing face 20 is exposed to the medium within enclosure 3. As shown, enclosure 3 may be provided with an inlet 31 and an outlet 32 both of which could also be the "ends" of a tubular enclosure 3 if the latter is a conduit or the like fluid-passing means. In other words, no particular diameters are critical for enclosure 3 and/or its feeding ends.

#Leads 28 are provided between working electrode 21 and counter electrode 25 to carry the amperometric signal generated at the working electrode 21 by reaction of both the first and the second EAGS to control instrument 8. The resulting signals may then be evaluated by an operator or fed, via conduits 79 and 89, to an evaluating device that converts the signals from instruments 7, 8 into a readout, monitoring signal, printer or the like output indicated schematically as output 91. A result obtained by a human operator from the readings of instruments 7 and 8 would also be considered as an "output 91".