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* Visit
inorganicventures.com/tech/icp-operations/for additional information from this link
28
• The use of nitric acid and/or HF is preferred for preparation of samples for Ag analysis. Solutions of Ag in either acid are
stable for extended periods.
• Trace levels of HCl or Cl
-1
must be eliminated otherwise a fixed error due to AgCl precipitation will result.
• If the sample preparation requires the use of HCl, attempt to keep the HCl content high (10% v/v) in an attempt to keep the
Ag in solution as the AgCl
x
1-x
anionic chloride complex. In addition, the concentration of Ag should be ≤ 10 μg/mL Ag. In
short, keep the HCl concentration high and the Ag concentration low.
• Solutions containing suspended AgCl and/or the AgCl
x
1-x
anionic chloride complex are photosensitive. The Ag
+1
will
undergo photo-reduction to the metal (Ag
0
). When intentionally working in HCl minimize exposure to light.
• Many analysts experience low Ag recoveries when working in HNO
3
media. The problem is due to trace chloride
contamination. Although analysts are aware of the problems with precipitation as the chloride, they are puzzled because no
AgCl is observed. However, the metal has already photo-reduced onto the container walls.
Ag elemental data*
Arsenic (As)
• Avoid using dry ashing for sample preparation. Loss during sample preparation as the volatile oxide (As
2
O
3
bp 460 °C)
or chloride (AsCl
3
bp 130 °C) can be avoided by performing closed vessel digestions (EPA Methods 3051 and 3052), acid
digestions under reflux conditions (EPA Method 3050B, Nitric and Perchloric Acid Digestions) or by caustic fusion
using either sodium carbonate or sodium peroxide/sodium carbonate fluxes.
• Approach ICP-OES and ICP-MS determinations with caution. ICP-OES suffers from poor sensitivity and spectral
interference issues and ICP-MS from the
40
Ar
35
Cl mass interference (other interferences include
59
Co
16
O,
36
Ar
38
Ar
1
H,
38
Ar
37
Cl,
36
Ar
39
K,
150
Nd
2+
, and
150
Sm
2+
) on the monoisotopic
75
As. The use of atomic absorption using either the hydride generation
or the graphite furnace techniques is very popular, although the use of ‘reaction cells’ that appear to eliminate the
40
Ar
35
Cl
interference in ICP-MS is an option worth exploring.
As elemental data*
Common Problems with Ag, As, S, Ba, Pb and Cr
13
This part of our ICP Operations guide provides some suggestions that you may find useful when attempting to work with
silver, arsenic, sulfur, barium, lead, or chromium.
Silver (Ag)
Ag forms more insoluble salts than any other metal, although Pb and Hg are not far behind. For an overview of Ag stability
please our article entitled Silver Chemical Stability.*
Acetate
Arsenate
Arsenite
Borate
Bromate
Bromide
Carbonate
Chloride
Chromate
Cyanide
Ferricyanide
Fluoride
Iodate
Iodide
Nitrate
Oxalate
Oxide
Phosphate
Sulfate
Sulfide
Tartrate
Thiocyanate
1.04
0.085
0.00115
0.905
0.196
0.014
0.105
0.0154
0.00256
0.022
0.066
172
0.00503
0.028
216
0.00378
0.00248
0.064
0.83
0.0174
0.0201
0.025
Salt
Salt
Solubility in g./100g. H
2
O
Solubility in g./100g. H
2
O
Table 13.1:
Solubility of common silver salts at room temp. (~22 C°)
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