YSI 2700D, Руководство пользователя

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6-4
The 2700 SELECT employs a steady state measurement methodology. A typical sensor
response is shown in Figure 6.3.
Figure 6.3
Typical Sensor Response
When sample or calibration standard is dispensed into the chamber, it is diluted into 600
microliters of buffer. The sensor response increases and plateaus. After several seconds, the
buffer pump flushes the chamber and the sensor response decreases.
The net response is the difference between the plateau current (i
plat
) and the initial baseline
current (i
ib
). Typical net responses for the 2700 SELECT are between 10 and 25 nA
(nanoamps) for YSI calibration solutions. The maximum net probe current is about 500
nanoamps.
!
The 2700 SELECT monitors the probe baseline current for nA activity and stability. If an
unstable baseline is detected, the buffer pump will continue to flush the sample chamber with
buffer. When a stable baseline is established, an automatic calibration is initiated.
After every calibration and sample, the final baseline current (i
fb
) is compared to the initial
baseline current (i
ib
) during the flush cycle. If a significant shift is detected, the buffer pump
continues to flush. As soon as the baseline recovers, buffer flushing ceases and the instrument
performs its next command. There is a limit of about 3 minutes, at which time the instrument
displays a baseline error message.
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