Hardness, Total
Hardness, Total
Page 4 of 6
Hardness_PT_ULow_CPZ_Eng_Ody.fm
Treating Analysis Labware
Clean all containers used in this test thoroughly to remove any traces of calcium
or magnesium. If possible, use plastic containers for all analysis and storage.
Clean containers by normal means, then rinse with ultra-pure (aldehyde-free)
water. Fill and soak for 10 minutes with a 1:25 dilution of Chlorophosphonazo
Reagent in ultra-pure water. Rinse well with ultra-pure water. Keep containers
tightly closed and dedicate them for ULR Hardness only. If containers are rinsed
and capped after each use, only occasional soaking is necessary. Fill the Pour-
Thru cell with this same mixture of chlorophosphonazo and water and let stand
for several minutes. Rinse with ultra-pure water.
Avoid contamination of the Chlorophosphonazo Reagent bottle when placing
the Repipet dispenser on the bottle. Rinse the inlet tubing and inside of the
dispenser cap with copious amounts of ultra-pure water using a wash bottle.
Place the inlet tubing into a beaker of ultra-pure water and depress the plunger
10–15 times to rinse the inside of the dispenser. (For best results, pour a small
amount of reagent into the beaker of rinse water.) Remove the dispenser from
the water and depress the plunger until all of the water has been expelled.
Shake off any excess water on the dispenser, place the dispenser on the bottle,
and tighten.
Sampling and Storage
Do not use glass containers. Collect samples in clean plastic containers,
preferably with screw-type closures. Rinse containers several times with the
water to be analyzed before capturing the final sample. Seal to avoid
contamination during transport. Analyze as soon as possible.
Accuracy Check
Standard Additions Method (Sample Spike)
1. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
2. Touch
OK to accept the default values for standard concentration, sample
volume, and spike volumes. Touch
Edit to change these values. After values
are accepted, the unspiked sample reading will appear in the top row. See
Standard Additions in the instrument manual for more information.
3. Obtain a Calcium Chloride Standard Solution, 20-mg/L (20,000-µg/L) as
CaCO
3
.
4. Prepare three sample spikes. Use a TenSette
®
Pipet to add 0.2 mL, 0.4 mL, and
0.6 mL, of a 20-mg/L as CaCO
3
Calcium Chloride Standard to three 50-mL
samples, respectively.
5. Analyze each sample spike as described in the procedure above, starting with
the 0.2 mL sample spike. Accept each standard additions reading by touching
Read. Each addition should reflect approximately 100% recovery. Each 0.2 mL
addition of standard should cause an increase of 80 µg/L hardness as CaCO
3
.
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