Hach-Lange BODTRACK II User Manual - Manual (Page 21)

Chlorine
Chlorine in the sample must be removed prior to testing. Keep the
sample at room temperature for 1 to 2 hours before a test to dissipate
low chlorine concentrations. If any chlorine remains after sitting for
2 hours, or if the chlorine concentration is high, add sodium thiosulfate to
remove the chlorine.
1. In a 250-mL Erlenmeyer flask, add 100 mL of sample.
2. Add 10 mL of 100 g/L potassium iodide solution and 10 mL of 0.02 N
sulfuric acid standard solution to the Erlenmeyer flask.
3. Add 3 droppers of starch indicator solution and swirl to mix.
4. Titrate from dark blue to colorless with 0.025 N Sodium Thiosulfate
standard solution.
5. Calculate the quantity of sodium thiosulfate standard solution
necessary to dechlorinate the remaining sample:
mL of sodium thiosulfate = (mL used)×(mL sample to be
dechlorinated)÷100
6. Add the necessary quantity of 0.025 N sodium thiosulfate standard
solution to the sample and mix fully. After 10 to 20 minutes, do the
BOD test.
pH effect
Low BOD test results occur when sample pH is outside the range of 6 to
8. Keep this pH to simulate source sample conditions or adjust the pH to
neutrality (buffered at pH 7). Use 1.0 N (or weaker) sulfuric acid to
neutralize caustic samples. Use 1.0 N (or weaker) sodium hydroxide to
neutralize acidic samples. When samples are pH adjusted, they should
also be seeded.
Supersaturation
Equilibrate supersaturated cold samples (samples that contain more
than 9 mg/L of dissolved oxygen at 20 ºC) to saturation.
1. Heat or cool the sample to approximately 20 ºC.
2. Half fill a sample bottle with sample.
3. Shake for 2 minutes or aerate with filtered compressed air for
2 hours.
Maintenance
D A N G E R
Multiple hazards. Only qualified personnel must conduct the tasks
described in this section of the document.
C A U T I O N
Chemical exposure hazard. Obey laboratory safety procedures and
wear all of the personal protective equipment appropriate to the
chemicals that are handled. Refer to the current material safety data
sheets (MSDS) for safety protocols.
Clean the instrument
Clean spills on the instrument with a soft cloth that has been dampened
with deionized or distilled water.
Clean the sample bottles
Clean the sample bottles and caps with a brush, water and a mild
detergent. Flush the containers with fresh water followed by a distilled
water rinse.
Clean the stir bars and seal cups
Clean the stir bars with hot water and soap. Use a brush to remove
deposits. Rinse with fresh water and then rinse with distilled water.
Carefully empty and rinse the seal cups with water. Invert to dry.
Storage
The bottle fences prevent tipping of the bottles and provide tubing
management in storage. For storage, put the tubing in the opening in the
English 19