ASXPRESS PLUS Rapid Sample Introduction System Operator’s Manual
Chapter 10: Using the Rapid Sample Introduction System
113
Developing a Method
This is an outline for method development which has worked well for many
laboratories. If you need further assistance, CETAC Technologies is happy to
help.
1 Determine the approximate volume of sample to be consumed during analysis
and at what pump speed.
2 Choose a loop of appropriate size.
3 Adjust the ASXPRESS PLUS parameters to completely fill the loop. The loop
should be overfilled slightly. This can be seen as some sample going into the
restrictor line just before the valve switches. For a description of each function
and parameter, see “Timing Parameters” on page 99.
4 The loop evacuation delay, probe rinse and rinse station refill parameters can
all be set to 1.0 initially.
5 The rinse pump speed is approximately half of what it would be without the
ASX
PRESS PLUS system, because two channels are to be used (air and carrier)
effectively doubling the flow rate.
6 In the ICP software, turn any rinse parameters off and adjust the “effective read
delay.” OEM software platforms call these parameters by different names.
7 In the ICP software, turn off any fast flush parameters or plasma stabilization
times so that only one pump speed and one read delay is to be dealt with, at
least at first. On rare occasions, a fast flush option may be used.
8 In the ICP software, incrementally adjust the read delay. Usually, a significant
amount of time can be cut from this parameter, perhaps a quarter at first. After
this, make fine adjustments to delay timing and or pump speed, making sure to
have the spray chamber wet with sample on the front side of integration for
about 5-9 seconds.
9 On the back side of the analysis, make sure that the loop has not been depleted
of sample before the integration is complete. It is important to use the worst
case sample for this purpose. Some OEM software platforms perform preshots
and then adjust integration times depending upon the information that is
obtained during this process. For some OEM instruments, the lowest
concentrated samples take the most time, but for others, the most highly
concentrated ones, and some use user-specified integration times no matter
what the concentration.
10 After the instrumentation is set up as described, look to the RSD’s to make fine
adjustments. One second of read delay or a very slight change in pump speed
can yield major differences in precision.
11 Finally, adjust the configuration parameters of probe rinse and refill to a higher
number. Make sure that the overall ASX
PRESS PLUS macro time is less than the
instrument's analysis time. If this condition is not met, samples will be skipped
and the system will appear to not function correctly.
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