Metrohm 837 IC Degasser - Manual (Page 25)

4.4 Carry-over with sample degassing
837 IC (Eluent/Sample/Combi) Degasser/ Instructions for Use 8.837.1003
19
Liquid is leaking from the
exhaust opening (15) • Leak in the instrument • Contact Metrohm Service
LED "Abs <65" (4) does not
light up (while pump is run-
ning)
• Leak in vacuum chamber
• Vacuum pump does not work
properly
• Contact Metrohm Service
• Contact Metrohm Service
4.4 Carry-over with sample degassing
If you work with sample degassing (837 IC Sample/Combi Degasser),
you should rinse longer (with the succeeding sample) because of the
longer "Transfer time" (The time the sample needs to flow from the sam-
ple vial through the degasser till the end of the sample loop). The rinse
time should be at least 2-3 longer than the "Transfer time", to minimize
carry-over effects. The "Transfer time" itself depends on pumping
capacity, total capillary volume and volume of the gas removed by the
degasser (thus on the amount of gas in the sample).
4.4.1 Determination of the "Transfer time"
To determine the "Transfer time", the system (pump tube, tubing con-
nections, Degasser capillary, sample loop) should be emptied. Pump
air through the system for some minutes, until all liquid is displaced by
air. Then, aspirate a typical (for your later application) sample, and
measure the time the sample needs to flow from the sample vial till the
end of the sample loop. The migration of the top of the sample flow can
be observed with the eye. The measured time is the "Transfer time". The
rinse time should be at least 2-3 times longer (Check carry-over, see
section 4.4.2).
4.4.2 Check sample carry-over
Sample carry-over and required rinsing time can be checked by spiking
a sample with an ion (which is not or only in small amounts contained
by the original sample); for example phosphate for mineral water sam-
ples. Procedure:
1. Prepare two samples:
a. Sample A: a sample, typical for your application
b. Sample B: Sample A - spiked with a "Spike-Ion"
2. Let sample A flow through the sample flow path (for the duration
of the rinsing time), inject it and measure
3. Let then flow sample B through the sample flow path (for the du-
ration of the rinsing time), inject it and measure
4. Then let again sample A flow through the sample stream (for the
duration of the rinsing time), inject it and measure
The ratio of the peak area of the "Spike-Ion" in the second measurement
of sample A to the peak area in the measurement of sample B reflects
the extend of the sample carry-over. The smaller that ratio is, the