Pyxis SP-900 - Two-Vial Methods; Multiple Timing Steps; Figure 10 Concentration as a Function of Time

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Figure 10 Concentration as a Function of Time
4.5 Two-Vial Methods
Some colorimetric methods require using two vials. The water sample is added to two
identical vials. One vial is being used to zero the colorimeter, referred as to the
prepared blank. A reagent is added to the other vial, referred as to the prepared
sample. The absorbance value is determined from the prepared sample.
If the method requires two or more reagents, the prepared blank could be the resulting
solution after one or more reagents have been added to the sample.
The following procedure is typical for two-vial methods:
1. Place the prepared blank into the Pyxis SP-900 sample vial compartment and
press the ZERO button to zero the instrument.
2. Place the prepared sample into the Pyxis SP-900 sample vial compartment and
press the TMR1 button to start the method timer.
3. When the timing step is completed, the measured concentration will be displayed
on the top of the page. The timing step could be terminated earlier by pressing
STOP button.
4. Optionally, Pyxis SP-900 can be re-zeroed using the prepared blank after the
timing step is completed or terminated. The blank reading will be subtracted from
the measured concentration value, and the displayed concentration value on the
top-right corner will be updated. This step is optional. It is only necessary if the
prepared blank changes its color during the timing period.
5. Optionally, the prepared sample vial can be put back and read again by pressing
the READ button if the blank is re-zeroed after the timing step is completed or
terminated. A new concentration value based on the last absorbance value
measured will be calculated and displayed.
4.6 Multiple Timing Steps
Some colorimetric methods have two or three timing steps. Pyxis SP-900 shows a
count-down timer for the timing steps before the last timing step (Figure 10). During
these timing steps, one or more reagents are added to the sample, or operations such
as swirling the vial to mix the reagent and the sample are being performed. These