Hach DR/850, Procedures Manual, Page: 382 / 460

382
Sampling and Storage
Collect samples 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
phosphates for cleaning glassware used in this test.
Analyze samples immediately after collection for best results. If
prompt analysis is impossible, preserve the sample for up to 28
days by adjusting the pH to 2 or less with concentrated sulfuric
acid (about 2 mL per liter) and storing at 4 °C. Neutralize and
warm the sample to room temperature before analysis. Correct
test results for volume additions; see
Volume Additions in
Section 1.
Accuracy Check
Note: Clean glassware with
1:1 hydrochloric acid
solution. Rinse again with
deionized water. Do not use
detergents containing
phosphates to clean
glassware.
Standard Additions Method
a) Fill three 25 mL graduated mixing cylinders with 25 mL of
sample.
b) Snap the neck off a Phosphate PourRite Ampule Standard,
50 mg/L as PO
4
3- .
c) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL,
respectively, to the three 25-mL aliquots of sample
prepared in
step a . Mix well.
d) Analyze each sample as described in the procedure
using 5.0 mL of the prepared standard additions for
each test. The concentration should increase 0.2 mg/L,
0.4 mg/L, and 0.6 mg/L PO
4
3- , respectively.
e) If these increases do not occur, see Standard Additions
(Section 1).
Standard Solution Method
To check accuracy, use a 1.0 mg/L Phosphate Standard Solution
(see Optional Reagents). Or, prepare a standard by pipetting 2 mL
of solution a Voluette Ampule Standard for Phosphate Standard,
50 mg/L as PO
4
3- , into an acid-cleaned Class A 100-mL
volumetric flask. Dilute to the mark with deionized water.
Substitute this standard for the sample and perform the procedure
as described. The mg/L PO
4
3- reading should be 1.0 mg/L.
OR
Prepare a 2.5 mg/L standard solution by pipetting 5 mL of a
50-mg/L Phosphate Voluette Ampule Standard into an
PHOSPHORUS, TOTAL,
continued