Phosphorus, Reactive (Orthophosphate)
Phosphorus, Reactive (Orthophosphate)
PhosphorusReac_UniCell_Other_Asc_Eng_Ody.fm Page 3 of 4
Sample Collection, Storage, and Preservation
Analyze samples within 3 hours after collection for best results. Store in a cool
dry place in plastic or glass bottles that have been acid cleaned with
1:1 Hydrochloric Acid Solution and rinsed with deionized water. Do not use
commercial detergents containing phosphate for cleaning glassware used in
this test.
If prompt analysis is impossible, preserve samples up to 48 hours by filtering
immediately and storing at 4 °C. Do not use mercury compounds as
preservatives. Warm samples to room temperature before analysis.
Accuracy Check
Standard Additions Method (Sample Spike)
1. Clean glassware with 1:1 Hydrochloric Acid Solution. Rinse again with
deionized water. Do not use phosphate detergents to clean glassware.
2. After reading test results, leave the sample cell (unspiked sample) in the
instrument. Verify the chemical form.
3. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
4. 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.
5. Snap the neck off a Phosphate 10-mL Ampule Standard, 500-mg/L as PO
4
3–
.
6. Prepare three sample spikes. Fill three 25-mL mixing cylinders with 25 mL of
sample. Use a pipet to add 0.1 mL, 0.2 mL, and 0.3 mL of 500-mg/L PO
4
3–
standard, respectively, to each sample and mix thoroughly.
7. 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.
8. 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.
Standard Solution Method
1. Use a 30-mg/L Phosphate Standard Solution listed under Optional Standards.
Perform the phosphate procedure as described.
2. To adjust the calibration curve using the reading obtained with the
30-mg/L PO
4
3–
Phosphate Standard Solution, touch Options on the current
program menu. Touch
Standard Adjust.
3. Touch
On. Touch Adjust to accept the displayed concentration (the value
depends on the selected chemical form). If an alternate concentration is used,
touch the number in the box to enter the actual concentration, then touch
OK.
Touch
Adjust.
For more information, see Section 3.2.4 Adjusting the Standard Curve on page 40.
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