In a previous blog post, we wrote about Cold Vapor Atomic Absorption Spectroscopy, a primary technique for mercury analysis. In this post, we will describe Teledyne Leeman Labs’ instruments that facilitate the process.
Leeman Labs offers two CVAA systems; the Hydra IIAA, an entry-level CVAA system that can detect mercury limits of less than 5.0 ng/L with a usable range of 5 ng/L to 1 mg/L; and the QuickTrace M-7600 CVAA Mercury Analysis System, which is a dual beam system capable of ultra-trace detection limits of less than 0.5 ng/L.
Hydra IIAA Mercury Analyzer
The Hydra IIAA design was based on the US EPA method 245.1, which allows for determination of total mercury in drinking, surface, ground, sea and brackish waters and industrial and domestic wastewaters. Method 245.1 typically requires sample digestion techniques that produce liquid samples with mercury present in the +2 valence state. The Hydra IIAA system can be converted to a direct analysis combustion mercury analyzer by quickly changing the analyzer’s module.
The system works as an acidified digested aqueous sample from an autosampler is introduced via the peristaltic pump as Hg2 dissolved in a solution of stannous chloride (10% w/v) in 10% hydrochloric acid. A sodium or potassium borohydride solution will also work. At the same time, a reducing agent (10% SnCl2 in 7 – 10% HCl) is introduced via another parallel peristaltic pump channel.
The sample and the reagent streams meet at the mixing tee and then enter the mixing tube where the stannous chloride (Sn2+) reduces Hg2+ into Hg0 while the mixture is on its way to the Gas Liquid Separator (GLS). At this stage, the analyte is present as a finely dispersed emulsion of liquid (metallic) Hg0 micro-droplets, in excess SnCl2 solution medium.
Visit our website for more information on the Hydra IIAA Mercury Analyzer.
QuickTrace M-7600 CVAA Mercury Analysis System
The design of the QuickTrace M-7600 is based on the US EPA method 245.1, but provides the ability to also analyze samples using performance-based US EPA 245.7, which was develop by the EPA to address address State needs for measuring toxic metals at ambient water quality criteria (WQC) levels, when such measurements are necessary to protect designated uses. The methods typically require sample digestion techniques that produce liquid samples with mercury present in the +2 valence state.
The carrier gas (Ar or N2) enters the reference cell of the spectrometer to facilitate measurement of the incident radiant power (P0) at 253.7 nm, and then continues on to the GLS. Meanwhile, an acidified digested aqueous sample from the autosampler is introduced via the peristaltic pump as Hg2+ dissolved in solution. Simultaneously, a reducing agent (10% SnCL2 in 7% HCl) is introduced via a parallel peristaltic pump channel. The sample and reagent (SnCl2) streams join at the mixing tee, and immediately enter the liquid mixing tube. Stannous chloride (Sn2+) reduces Hg2+ in solution to Hg0 while the mixture is en route to the GLS. At this stage the analyte is present as a finely dispersed emulsion of liquid (metallic) Hg0 micro-droplets, in excess SnCl2 solution.
Visit our website for more information on the QuickTrace® M-7600 CVAA Mercury Analyzer
For more details about how the QuickTrace M-7600 works beyond this stage, review Teledyne’s Practical Guide for Selecting the Best Technique for Mercury Measurement.