81-29
PHOSPHORUS, REACTIVE, continued
9) Press ZERO. The display will count down and then show another
four-digit concentration value. The S2 annunciator will begin flashing.
10) Press the
RIGHT ARROW key. The left digit will begin flashing.
Press the arrow keys to edit the display to read 5.000 for PO
4
3-
.
11) Press
READ. The display will count down and then show a relative
absorbance near zero. This step enters the upper limit (S2) value. The
S2 annunciator will flash.
Note: The colorimeter will display measurements above the upper limit,
but the accuracy is questionable.
12) Press the
RIGHT ARROW key. The left digit and the S2
annunciator will flash. Use the arrow keys to enter the correct
absorbance difference. If a negative number appears, continue to press
the
UP ARROW key until a positive 0.570 appears.
13) Press
READ. This enters the calibration curve. The S2 annunciator
will flash.
14) Press
CAL. The calibration is automatically completed and stored
in the filter module memory under program number 81.000. The display
will show the concentration value for demineralized water and the
ZERO indicator will be flashing.
SAMPLING AND STORAGE
Collect samples in plastic or glass bottles that have been acid cleaned
with 1:1 Hydrochloric Acid Solution and rinsed with demineralized
water. Do not use commercial detergents containing phosphate for
cleaning glassware used in this test.
Analyze samples immediately after collection for best results. If prompt
analysis is impossible, preserve samples up to 24 hours by storing at
4 °C. For longer storage periods, add 4.0 mL of mercuric chloride to
each liter of sample and mix (use of mercuric chloride is discouraged
due to health and environmental concerns). Sample refrigeration is still
necessary. Samples preserved with mercuric chloride must have a
sodium chloride level of 50 mg/L or higher to prevent mercury
interference in the test. Spike samples low in chloride with 0.1 g sodium
chloride per liter of sample.
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