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A. General Information

B. Theory of Hg Analysis

C. Theory of Operation

A. General Information

The Tekran^® Series 2600 system allows the analysis of ultra-trace levels of total mercury in liquid samples.  It offers unparalleled sensitivity and flexibility for those who require truly sensitive total mercury analysis.

Series 2600 is capable of providing a fully automated implementation of the new US EPA Method 1631. This method is capable of measuring waters with a detection limit of much less than the required < 0.5 ng/L (ppt).

Key Features

• Sensitivity measured in parts per quadrillion. Typical MDL: <0.05 ppt
• Atomic Fluorescence based: Greater sensitivity, selectivity and dynamic range than AA based systems
• Unprecedented modularity and flexibility
• Capable of multiple methods:
  • Direct reading
  • Single stage gold pre-concentration
  • Dual stage gold pre-concentration
• Works with stannous chloride or sodium borohydride reduction

Total Mercury in Liquids

• Automates analysis of aqueous samples
• Dual stage gold pre-concentration
• Single stage gold pre-concentration
• Direct reading
• May be used with stannous chloride or sodium borohydride reductant

Mercury in Gases

• Automated analysis of adsorbent sample cartridges using dual stage pre-concentration with thermal desorption

B. Theory of Hg Analysis

All of the low level methods depend on pre-concentration of the mercury onto an absorbent cartridge of some type, generally for periods of 6 or 24 hours. This is usually followed by subsequent analysis in a laboratory. Adsorbents used have included hopcolite, silver, iodized carbon, gold coated sand, gold coated quartz wool or gold coated quartz beads.

Detection was formerly performed using cold vapor atomic absorption spectrophotometry (CVAAS), however, cold vapor atomic fluorescence spectrophotometry (CVAFS) is now the preferred method due to better sensitivity, specificity and linearity.

C. Theory of Operation

The theory of the method is that solid samples are digested, usually with Aqua Regia, to release Hg into solution.  The solution is then preserved with a very strong oxidant (BrCl, bromine monochloride) in order to keep Hg in solution as Hg²⁺, since it will not volatilize like Hg^o will.  Water samples are also oxidized with BrCl.  The purpose of this is to oxidize all the Hg (Hg^o, HgCl₂ complexes Hg⁺, Hg bound to organics, Hg bound to minerals, etc.) in the sample to Hg²⁺.  The machine then takes the sample with Hg²⁺ and reacts it with a very strong reductant, Stannous Chloride (SnCl₂), to produce Hg^o, which is then stripped from the solution as a gaseous phase with Ar gas.  Since Hg amalgams with Au, the machine uses Au coated quartz sand to trap the Hg.  The Au is then heated and pushed onto a second Au trap.  The point of these traps is to concentrate the gaseous Hg so that when the Hg reaches the analyzer it is a spatially small concentrated pulse of Hg.  The analyzer is a UV source that causes fluorescence of the Hg in the analyzer chamber, which is then detected using a photo multiplier tube.

      The Tekran 2600 CVAFS is a high precision instrument that is capable of running numerous samples quickly and accurately.  The general working range for the machine is 0.5-100 ng/L, but the machine is capable of measuring 0.1-400 ng/L (samples above 100 ng/L should be diluted to avoid carryover).  The machine uses about 35mL of solution (use either 60mL centrifuge tubes, not recommended or 40mL borosilicate I-chem vials with Teflon lined lids, highly recommended) and is an automated process taking ~4 minutes per sample.  Though the machine is automated it should be checked periodically, once every 45 minutes or so.