1.1 Methods
Notes:
1. When testing chlorinated water the residual chlorine contents can influence the colour
reaction of the liquid reagent. This can be avoided (without interfering with the pH
measurement) by adding a small crystal of Sodiumthiosulfate (Na
2
S
2
O
3
· 5 H
2
O) to the
sample before adding the PHENOL RED solution. PHENOL RED tablets already contain
Thiosulfate.
2. Due to differing drop sizes results can show a discrepancy in accuracy by comparison
with tablets. This can be minimised by using a pipette (0.18 ml PHENOLRED solution is
equivalent to 6 drops).
3. After use replace the bottle cap securely.
4. Store the reagent in a cool, dry place ideally at between 6°C and 10°C.
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