YSI 9300 Photometer - Manual (Page 52)

Reagents and Equipment
YSI DPD No 1 Tablets
YSI DPD Oxystop Tablets (Optional)
YSI DPD No 3 Tablets
YSI 9300 or 9500 Photometer
Round Test Tubes, 10 ml glass (PT 595)
Separation of Chlorine Residuals
The photometer is programmed for both free and total chlorine. Use program
Phot 7 Free Chlorine, then select the ‘Follow On’ option on screen to continue test
for program Phot 8 Total Chlorine.
Test Instructions
1 Rinse test tube with sample leaving two or three drops of sample in the tube.
2 Add one DPD No 1 tablet, crush tablet and then fill the test tube with
sample to the 10 ml mark. Mix to dissolve tablet.
3 Select Phot 7 on photometer.
4 Take photometer reading immediately (as result may drift on standing), in
usual manner - see photometer instructions.
5 The result represents the free chlorine residual as milligrams per litre. Stop
the test at this stage if only free chlorine determination is required.
6 If it is desired to measure combined or total chlorine residual continue the
test on the same test portion. Select the ‘Follow On’ from screen options to
continue the test program.
7 If shock treatment chemicals are present in the pool, add one DPD Oxystop
tablet, crush and mix to dissolve. Stand for one minute before proceeding.
8 Add one DPD No 3 tablet, crush and mix to dissolve.
9 Stand for two minutes to allow full color development.
10 Take photometer reading.
11 The result represents the total chlorine residual as milligrams per litre.
12 The combined chlorine residual is obtained by subtracting the free
chlorine residual result from the total chlorine residual result :-
ie Combined Chlorine = Total Chlorine - Free Chlorine
Note: A too high chlorine level (above 10 mg/l) can cause bleaching of the
pink coloration formed in the DPD test and give a false negative or lower than
expected result. If a colorless or pale pink test solution is obtained, then a
high level chlorine may be present, check for the possibility of bleaching by
repeating the test on a sample diluted with chlorine-free
water.
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