Cadmium
Cadmium
Cadmium_UniCell_Other_CAD_Eng_Ody.fm Page 3 of 4
Total cadmium, including undissolved cadmium and complexed cadmium can
only be determined after digesting with the Metal Prep Set, HCT 200.
Note: The total cadmium measuring range is 0.02–0.36 mg/L.
Sample Collection, Storage, and Preservation
Collect samples in acid-cleaned glass or plastic containers. No acid addition is
necessary if analyzing the samples immediately. To preserve samples, adjust the
pH to 2 or less with concentrated nitric acid (about 2 mL per liter). Preserved
samples may be stored up to six months at room temperature.
Before analysis, adjust the pH to between 3 and 6 with 5.0 N Sodium Hydroxide
standard solution. Water samples which are free from complexing agents and
organic compounds can be analyzed directly. Other water samples have to be
digested with the Metal Prep Set in order to bring undissolved or complexed
cadmium compounds into solution.
Accuracy Check
Standard Additions Method (Sample Spike)
1. Touch
Options. Touch Standard Additions. A summary of the standard
additions procedure will appear.
2. 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.
3. Prepare three sample spikes. Fill three mixing cylinders with 250 mL of
sample. Use a pipet to add 0.1 mL, 0.2 mL, and 0.3 mL of 100-mg/L Cd
standard, respectively, to each sample and mix thoroughly.
4. 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.
5. 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 0.20-mg/L Cd standard solution by pipetting 0.20 mL of 100-mg/L
Cd standard into a 100-mL volumetric flask. Dilute to the mark with deionized
water. Stopper and invert to mix. Prepare this solution daily. Perform the
cadmium procedure as described.
To adjust the calibration curve using the reading obtained with the
0.20-mg/L Cd standard solution:
1. Touch
Options on the current program menu. Touch Standard Adjust.
2. Touch
On. Touch Adjust to accept the displayed concentration. If an alternate
concentration is used, touch the number in the box to enter the actual
concentration, then touch
OK. Touch Adjust.
See Section 3.2.4 Adjusting the Standard Curve on page 40 for more information.
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