4-2
Once past the polycarbonate membrane, the substrate encounters an extremely thin layer of the
appropriate oxidase enzyme. There the following reaction occurs:
Substrate + O
2
oxidase
H
2
O
2
+ Byproduct
Although oxygen is consumed in this reaction, the buffer is not seriously depleted of oxygen,
nor is the rate of enzyme reaction very sensitive to small changes in oxygen concentration.
Therefore, it is not necessary to measure or control the oxygen content in the sample chamber.
Hydrogen peroxide diffuses toward the platinum anode in the probe assembly. This gives rise to
the probe signal current.
The platinum anode is protected from other oxidizable substances by a thin layer of cellulose
acetate. This makes the anode specific for hydrogen peroxide. Low molecular weight, reducing
compounds can interfere. Typical interferences include phenols, hydrazine, hydrogen sulfide
and mercaptans.
A variety of sample types can be analyzed with the 2700 SELECT. Generally, the only sample
preparation that
may
be required is dilution of the sample to bring the substrate concentration
within the linear range of the instrument. (see Section 1.4 for the working range of each
chemistry).
Neither color nor turbidity interferes with measurements.
Small particles do not affect the reaction in the sample chamber that houses the probes, but
samples with particles large enough to clog the sipper should be avoided.
Further information and specific procedures for determining the concentration of chemical
analytes in many products or specimens are available in YSI Application Notes. If you would
like to discuss your application or inquire about other uses for the 2700 SELECT, contact YSI
Technical Support (address and phone information on the back cover of this manual).
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