Hach DR2400 - Page 243

Cobalt
Cobalt
Cobalt_PP_Other_PAN_Eng_Ody.fm Page 3 of 4
Interferences
Sample Collection, Storage and Preservation
Collect samples in acid-washed plastic bottles. Adjust the sample pH to 2 or less
with nitric acid (Cat. No. 2540-49) (about 5 mL per liter). Preserved samples can
be stored up to six months at room temperature. Adjust the sample pH between
3 and 8 with 5.0 N Sodium Hydroxide Standard Solution (Cat. No. 2450-32) just
before analysis. Do not exceed pH 8 as this may cause some loss of cobalt as a
precipitate. Correct test results for volume additions; see Section 3.1.3 Correcting
for Volume Additions on page 29 for more information.
Accuracy Check
Standard Solution Method
Prepare a 1.0 mg/L cobalt standard solution as follows:
1. Dilute 10.0 mL of a 10-mg/L working stock solution to 100 mL in a
volumetric flask. Prepare the 10-mg/L working stock solution daily by
diluting 10.00 mL of Cobalt Standard Solution, 1000-mg/L as Co, to 1000 mL
with deionized water.
2. To adjust the calibration curve using the reading obtained with the 1.0-mg/L
standard solution, touch
Options on the current program menu. Touch
Standard Adjust.
3. 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.
Interfering Substance Interference Levels and Treatments
Al
3+
32 mg/L
Ca
2+
1000 mg/L as CaCO
3
Cd
2+
20 mg/L
Cl
–
8000 mg/L
Cr
3+
20 mg/L
Cr
6+
40 mg/L
Cu
2+
15 mg/L
F
–
20 mg/L
Fe
2+
Interferes directly and must not be present
Fe
3+
10 mg/L
K
+
500 mg/L
Mg
2+
400 mg/L
Mn
2+
25 mg/L
Mo
6+
60 mg/L
Na
+
5000 mg/L
Pb
2+
20 mg/L
Zn
2+
30 mg/L
Highly buffered samples or
extreme sample pH
May exceed the buffering capacity of the reagents and require
sample pretreatment; see Section 3.3 Interferences.