Hach DR/850, Procedures Manual, Page: 23 / 460

23
CHEMICAL ANALYSIS INFORMATION
, continued
Hach 1:1 Nitric Acid Pillows contain 2.5 mL of acid; correct for this
volume. The addition of a Sodium Carbonate Power Pillow (neutralizes
the 1:1 Nitric Acid Solution Pillow) does not need to be corrected for.
Boiling Aids
Boiling is necessary in some procedures. Using a boiling aid such as
boiling chips (Cat. No. 14835-31) helps reduce bumping. Bumping is
caused by the sudden, almost explosive conversion of water to steam as it
is heated. Avoid bumping; it may cause injury or sample loss.
Make sure the boiling aids will not contaminate the sample. Do not use
boiling aids (except glass beads) more than once. Loosely covering the
sample during boiling will prevent splashing, reduce the chances of
contamination and minimize sample loss.
Sample Filtration
Filtering separates particles from the aqueous sample. Filtration uses a
medium, usually filter paper, to retain particles but pass solution. This is
especially helpful when sample turbidity interferes with analysis. Two
general methods of filtration are gravity and vacuum. Gravity filtration
uses gravity to pull the sample though the filter paper. Vacuum filtration uses
suction and gravity to move the sample through the filter. An aspirator or
vacuum pump creates the suction. Vacuum filtration is faster than gravity
filtration. Vacuum filter (see
Figure 1 ) as follows:
1. Using tweezers, place a filter paper into the filter holder.
2. Place the filter holder assembly in the filtering flask. Wet the filter
with deionized water to ensure adhesion to the holder. Empty the
flask before filtering the sample.
3. Position the funnel housing on the filter holder assembly.
4. While applying a vacuum to the filtering flask, transfer the sample to
the filtering apparatus.
5. Slowly release the vacuum from the filtering flask and transfer the
solution from the filter flask to another container.
Figure 1 Vacuum Filtration