To determine the Total Chlorine Concentration in given sample of water
Note: DPD Total Chlorine Reagent Powder Pillows contain a buffer formulation, which will withstand high levels of hardness (at least 1000 mg/L) without interference.
Reagents:
- DPD Total Chlorine powder pillows
- Distilled water
Apparatus:
- Direct Reading Spectrophotometer,
- 25-ml or 10-ml sampling cells 2-Nos.
- Beakers 50-ml
Procedure:
- Enter the stored program number for free and total chlorine (Cl2)-powder pillows, Press Enter; the display will show Dial run to 530.
- Rotate the wavelength dial until the small display shows: 530 nm
- 3 – Press enter, the display will show. mg/L Cl2
- Fill a sample cell with 25-ml of sample.
- Add the contents of one (DPD Total chlorine) Powder Pillow to the sample cell (the prepared sample). Stopper the sample call and shake for 20 seconds. Remove stopper. Note: A pink color will develop if chlorine is present.
- Press Shift/Timer, A 3-minute reaction period will begin.
- When the timer beeps, the display will show, mg/L Cl2, fill another sample cell (the blank) with 25 ml of sample, Place into the cell holder.
- Press Zero, the display will shows: Wait thon, 0.00 mg/L
- Within three minutes after the timer beeps, place the prepared sample into the cell holder. Close the light shield.
- Press Enter, the display will show: Wait, then the result in mg/l. chlorine (C12) will be displayed.
Note: If the sample temporarily turns yellow after sample addition, or shows Over Range, dilute a fresh sample and repeat the test. A slight loss of chlorine may occur because of the dilution. Multiply the result by the appropriate dilution factor.
Summary of Method:
Chlorine can be present in water as free available chlorine and as combined available chorine. Both forms can exist in the same water and be determined together as the total available chlorine Free chlorine is present as hypochlorous acid and/or hypochlorite ion. Combined chlorine exists as monochloroamine, dichloramine, nitrogen trichloride and other chloroderivatives. The combined chlorine oxidizes iodide in the reagent to iodine: The iodine reacts with DPD (N, N-diethyl-p-phenylenediamine) along with free chlorine present in the sample to form a red color, which is proportional to the total chlorine concentration. To determine the concentration of combined chlorine, run a free chlorine test. Subtract the results from the results of the total chlorine test to obtain combined chlorine.