Chromium, Hexavalent
Chromium, Hexavalent
ChromiumHex_UniCell_Other_DCH_Eng_Ody.fm Page 3 of 4
Sample Collection, Preservation, and Storage
Collect samples in a cleaned glass or plastic container. Store at 4 °C (39 °F) up to
24 hours. Samples must be analyzed within 24 hours.
Accuracy Check
Standard Additions Method (Sample Spike)
1. After reading test results, leave the sample cell (unspiked sample) in the
instrument.
2. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
3. 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.
4. Pipet 0.1, 0.2, and 0.3 mL of 50-mg/L Cr
6+
standard solution, respectively, to
three 25-mL samples and mix thoroughly.
5. Transfer 4 mL of each solution to three sample vials and analyze as described
in the procedure. Accept each standard additions reading by touching
Read.
Each addition should reflect approximately 100% recovery.
6. 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
Prepare a 0.70-mg/L Cr
6+
Standard solution daily, as follows:
1. Using a pipet, transfer 1.40 mL of Hexavalent Chromium Standard Solution,
50-mg/L, into a Class A 100-mL volumetric flask.
2. Dilute to the mark with deionized water.
3. To adjust the calibration curve using the reading obtained with the
0.70-mg/L standard solution, touch
Options on the current program menu.
Touch
Standard Adjust.
4. 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.
Perform the hexavalent chromium procedure as described above. See Section
3.2.4 Adjusting the Standard Curve on page 40 for more information.
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