Option
Description
Program name
Enter a name for the user program, (e.g., the name of the parameter).
Program type
Select single wavelength (for applicable spectrophotometers).
4.
Enter the settings for the user program:
Option
Description
Units
mg/L
Wavelength
520 nm
Concentration resolution
0.001
Chemical form
As
Upper limit
0.220
Lower limit
–0.020
Timer 1
15:00
Timer 2
15:00
Timer 3
15:00
Calibration
Read standards
5.
Select
CALIBRATION: C = A + BA.
Push
EDIT
.
6.
In the Read Standards menu, enter the concentration of the prepared standard
solutions.
7. Prepare the blank solution:
Use a 25-mL sample cell that only contains unreacted
arsenic absorber solution.
8.
Insert the blank solution into the cell holder and push
ZERO
.
9.
Insert the first prepared standard solution into the cell holder. Make sure that the
standard solution concentration is selected on the display and push
READ
.
10.
Continue to measure the remaining standard solutions.
11.
Push
GRAPH
. Make sure that
FORCE ZERO
is off.
12.
If the graph is acceptable select
DONE>EXIT
.
13.
Save (store) the user program. When the user program is selected in the test
procedure, the calibration curve is used to measure the sample concentration.
Summary of Method
A mixture of zinc, stannous chloride, potassium iodide and hydrochloric acid reduces the
arsenic into arsine gas in a specially equipped distillation apparatus. The arsine goes
through a scrubber that uses a cotton ball soaked with lead acetate for sulfide removal.
Then the arsine goes into an absorber tube that contains a solution of silver
diethyldithiocarbamate in pyridine. The arsenic reacts to form a red complex that is read
colorimetrically. A manual calibration is necessary for this procedure. The measurement
wavelength is 520 nm.
Consumables and replacement items
Required reagents
Description
Quantity/test
Unit
Item no.
Arsenic Standard Solution, 1000-mg/L As
varies
100 mL
1457142
Hydrochloric Acid, ACS
25 mL
500 mL
13449
Lead Acetate Solution, 10%
1 mL
100 mL
1458042
Potassium Iodide Solution, 20%
3 mL
100 mL
1456842
Pyridine, ACS
50 mL
500 mL
1446949
6
Arsenic Silver Diethyldithiocarbamate Method (0.200 mg/L)
