Chlorine, Total
Chlorine, Total
Page 8 of 10
ChlorineTot_PT2_ULow_DPD_Eng_Ody.fm
5. Prepare three sample spikes. Fill three mixing cylinders (Cat. No. 1896-41)
with 50 mL of sample. Use the TenSette
®
Pipet to add 0.1 mL, 0.2 mL, and
0.3 mL of standard, respectively, to each sample and mix thoroughly.
6. Analyze each sample spike as described in the procedure above, starting with
the 0.1 mL sample spike. Accept each standard additions reading by touching
Read. Each addition should reflect approximately 100% recovery.
7. After completing the sequence, touch
Graph to view the best-fit line through
the standard additions data points, accounting for matrix interferences. Touch
View: Fit, then select Ideal Line and touch OK to view the relationship between
the sample spikes and the “Ideal Line” of 100% recovery.
See Section 3.2.2 Standard Additions on page 32 for more information.
Method Performance
Precision
Standard: 290 µg/L Cl
2
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 for more information.
Summary of Method
It is essential that interfering sample turbidity is removed using a 3-micron
membrane filter. To avoid chlorine loss, the filtration is done after reacting the
DPD with the chlorine in the sample. The filter used has been specifically
selected to avoid retention of the colored product. Sample color is compensated
by zeroing the spectrophotometer on a filtered sample.
Several modifications to the normal DPD chlorine method are necessary to
measure trace levels of chlorine. The Pour-Thru Cell must be used in the
spectrophotometer. Liquid reagents are also required. The reproducible optics of
the Pour-Thru Cell give more stable readings than is possible with movable
sample cells, resulting in more stable measurements.
The reagents are packaged in ampules and sealed under argon gas to ensure
stability. Use of liquid reagents eliminates any slight turbidity that might be
caused by using powdered reagents. Due to the possible oxidation of the
reagents (which could give a positive chlorine reading in the blank), a reagent
blank must be determined at least once a day for each lot of reagent used. This
reagent blank value is subtracted from the sample result and the corrected value
is the actual chlorine concentration. Test results are measured at 515 nm.
Program 95% Confidence Limits of Distribution
86 287–293 µg/L Cl
2
Portion of Curve ∆Abs ∆Concentration
Entire range 0.010 2 µg/L Cl
2
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