Common Problems with Ag, As, S, Ba, Pb and Cr

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.

• 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 (Ag⁰). When intentionally working in HCl minimize exposure to light.
• Many analysts experience low Ag recoveries when working in HNO₃ 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

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