Hach DR/700 Procedures Manual page 180

BARIUM,
continued
SAMPLING AND STORAGE
Collect samples in an acid cleaned glass or plastic container. Adjust the
pH to 2 or less with nitric acid (about 2 mL per liter). Preserved samples
can be stored up to six months at room temperature. Adjust the pH to 5
with 5.0 N sodium hydroxide before analysis. Correct the test result for
volume additions; see Sampling and Storage, Volume Additions,
(Section I) for more information.
ACCURACY CHECK
Standard Additions Method
a) Snap the neck off a Barium Voluette Ampule Standard, 5000 mg/L Ba.
b) Use the TenSette Pipet to add 0.1 mL, 0.2 mL and 0.3 mL of standard,
respectively, to three 25-mL samples and mix each thoroughly (for
AccuVac ampuls, use 50-mL beakers).
c) Analyze each sample as described above. The barium concentration
should increase 20 mg/L for each 0.1 mL of standard added.
d) If these increases do not occur, see Standard Additions (Section I) for
more information.
CALIBRATION
A new calibration is necessary for each new manufacturing lot of
BariVer 4 Reagent Powder Pillows or AccuVac Ampuls. A new
calibration is also needed when the water sample to be tested has a
barium concentration which is not between that of the standards used to
calibrate the DR/700.
To perform a calibration, make 2 barium standards using the technique
described in Step 4 of the method. Make them so that one has a slightly
lower and the other a slightly higher barium concentration than that
anticipated to be in the water sample. Process each in the same way as
the "displayed standard" described in this method.
Next, perform paragraph 3.2.4.1, Calibration Using Two Prepared
Standards, in the DR/700 instrument manual. Either standard can be
used as Standard 1 or Standard 2.
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