Mercury is an ubiquitous element whose harmful effects on plants, animals and humans are well documented. The potential impact of mercury exposure on public health has recently prompted government regulators to set target levels of Hg in the sub part-per-trillion realm.

In order to achieve sub ppt levels of detection for mercury, analysts are turning to preconcentration techniques using gold amalgamation in conjunction with cold vapor atomic fluorescence detection.

The Hydra AF Gold Plus has been designed to maximize the analytical benefits of the gold amalgamation, atomic fluorescence approach, while minimizing the difficulties that can accompany sub ppt analytical measurements. From its continuous flow rinse feature to its ability to prescreen for high concentration samples, Hydra AF Gold Plus is designed to work for you.

Hydra AF Gold Plus combines the analytical capabilities of an advanced cold vapor atomic fluorescence analyzer with the ability to selectively preconcentrate Hg using gold amalgamation to enhance detection limits. By utilizing two independent fluorescence detection systems, this instrument maximizes analytical flexibility and provides an unparalleled working range (from <0.05 ppt with gold amalgamation to low ppm levels without gold amalgamation). This dual detector approach carries the added benefit of making Hydra AF Gold Plus compliant with both EPA Methods 1631 and 245.7.

Hydra AF Gold Plus is designed to automate all aspects of the fluorescence-based Hg measurement. Using its on-board 5 channel peristaltic pump and high capacity autosampler, it can process up to 10 standards, 7 check standards and 88 samples in a single unattended run. With this system, predigested sample is pumped together with stannous chloride during the reduction step. The mixture then flows into Hydra’s innovative gas/liquid separator where the analyte vapor then traverses a counter-flow Nafion™ dryer on its way to Hydra’s high sensitivity fluorescence detection system.

Hydra’s gas/liquid separator With this system, predigested sample is pumped together with stannous chloride during the reduction step. The mixture then flows into Hydra’s innovative gas/liquid separator which not only provides high throughput for routine samples, it also provides superior analytical recoveries for complex or poorly digested samples, and exceptional resistance to contamination from difficult foaming samples.

Dual Fluorescence Detection System Following the gas liquid separation step, analyte vapor is dried and then selectively directed into either of Hydra’s two fluorescence detection systems. One detector is high sensitivity detector used with the gold amalgamation system (typically used for Method 1631, or 0.05 ppt to low ppb determinations), the other is a lower sensitivity detector used for high concentration work (typically used for Method 245.7, or ppt to low ppm determinations).

Method Compliant Vapor Dryer
Regardless of which analytical mode is chosen, Hydra AF Gold plus operates in compliance with the associated EPA methodology by using appropriate vapor dryer and amalgamation system for the method. For example, when operating under the guidelines of Method 245.7, effluent from the gas/liquid separator is passed through a counter-flow Nafion™ dryer and then into Hydra’s fluorescence detector. When operating under the guidelines of method 1631, effluent from the gas/liquid separator is passed through a soda lime trap before flowing into the gold amalgamation system. Soda lime is important in the latter case, not only for removal of water from the analyte vapor, but also in protecting the gold traps from haloacid vapors (i.e., HCl, HBr).

Once through the dryer, analyte is passed through the first of two gold traps where mercury forms an amalgam; any residual water and/or organic vapors are vented from the system. Removal of water vapor from the measurement of mercury eliminates fluorescence light scatter and removal of organic vapors eliminates fluorescence quenching. Next, mercury is thermally desorbed from the first trap and swept onto the analytical trap. From there it is desorbed once again into the flowing gas stream and swept into Hydra’s high performance fluorescence detection system. The entire process takes about 4 minutes per sample.

This innovative dual detection feature not only provides compliance with both EPA methods 1631 and 245.7, it also eliminates the need for operator intervention and/or hardware changes when switching between modes.

Hydra’s proprietary high sensitivity detection system is designed to provide very high fluorescence collection efficiency while minimizing light scatter, giving exceptional signal-to-background and very low limits of detection.

High Concentration Protection System
The extremely low limits of detection of this approach (typically <0.05 ppt) make contamination a significant concern. This can be an issue when both blanks and with sample-to-sample carryover. Even when the analyst follows scrupulous analytical techniques, instrumental systems can inadvertently be contaminated by samples with unexpectedly high concentrations of mercury.

Hydra’s dual detector approach carries with it the unique ability to automatically prescreen samples for high concentrations of mercury. With this system activated, the operator is able to perform an automated, on-the-fly prescreen of each sample should there be concern about contaminating the high sensitivity detector and gold amalgamation system when operating with uncharacterized samples. When the prescreen mode is selected, output from the gas/liquid separator is briefly shunted to the low sensitivity detector (normally used for Method 245.7). If the concentration of mercury in the sample is below an operator selectable threshold, the instrument will switch modes and analyze the sample using the gold amalgamation/high sensitivity detector combination (normally used for Method 1631). If however, the sample exceeds the threshold concentration, the instrument will flag the result and proceed onto the next sample. By taking this approach, contamination of the gold amalgamation/high sensitivity detector combination is avoided, preventing costly downtime and loss of productivity.