Metrohm 881 Compact IC pro – Anion – MCS - Manual (Page 93)

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5 Operation and maintenance
881 Compact IC pro – Anion – MCS
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5.9 Rinsing the sample path
Before a new sample can be measured, the sample path must be rinsed
with it so that the measuring result is not falsified by the previous sample
(Sample carry-over).
In the case of automated sample feeding, the rinsing time should be at
least 3 times the transfer time.
The transfer time is the time required by the sample to flow from the sam-
ple vessel to the end of the sample loop. The transfer time depends on the
pump capacity of the peristaltic pump or the Dosino used, the total capil-
lary volume and the volume of the gas removed by the sample degasser (if
used) - in other words the amount of gas in the sample.
Ascertaining the transfer time
To ascertain the transfer time, proceed as follows:
1 Emptying the sample path
Pump air through the sample path (pump tubing, tubing connec-
tions, capillary in the degasser, sample loop) for several minutes until
all liquid is displaced by the air.
2 Aspirating the sample and measuring time
Aspirate a sample typical for the later application and use a stop
watch to measure the time required by the sample to travel from the
sample vessel to the end of the sample loop.
The time measured corresponds to the "transfer time". The rinsing
time should be at least 3 times the transfer time.
Checking the rinsing time
It is possible to determine whether the rinsing time is adequate via a direct
measurement of the sample carry-over. Proceed as follows:
1 Preparing two samples
￭ Sample A: A typical sample for the application.
￭ Sample sample B: Ultrapure water.
2 Determining "Sample A"
Let "Sample A" pass through the sample path for the duration of the
rinsing time, then inject and measure.