ICP_Operations_Guide_2016

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.*

Table 13.1: Solubility of common silver salts at room temp. (~22 C°)

Salt

Solubility in g./100g. H 2 O

Salt

Solubility in g./100g. H 2 O

Acetate Arsenate Arsenite Borate

1.04 0.085 0.00115 0.905 0.196 0.014 0.105 0.0154 0.00256

Fluoride Iodate Iodide Nitrate Oxalate Oxide Phosphate Sulfate Sulfide Tartrate Thiocyanate

172 0.00503 0.028 216 0.00378 0.00248 0.064 0.83 0.0174 0.0201 0.025

Bromate Bromide Carbonate Chloride Chromate Cyanide Ferricyanide

0.022 0.066

• 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) 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* or chloride (AsCl 3

* Visit inorganicventures.com/tech/icp-operations/ for additional information from this link

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