Sumedh Phatak

Articles

This paper describes the challenges faced by labs analyzing mercury in fish samples when using conventional technologies such as CVAA and ICP and how direct mercury analysis can overcome these challenges.

Mercury Detection in Fish Samples by Direct Analysis

Direct mercury analysis is ubiquitous in analytical labs within the environmental, petrochemical, and specialty chemicals industry for analyzing mercury in solids and liquids. These labs are also required to test for mercury in gaseous samples, at times requiring specialty instruments. With the addition of Milestone's DMA-80 sorbent tubes, labs can utilize a single system and maintain the benefits of direct analysis.

Direct mercury analysis is a technique that is ubiquitous in analytical labs within the environmental industry, petrochemical industry, and specialty chemicals industry for analyzing mercury in solid and liquid samples. However, these labs are frequently required to test for mercury in gaseous samples in addition to utilizing specialty instruments. Most conventional systems do not offer the flexibility of analyzing for these samples, which has posed a problem for direct analysis. 

To address the need for a highly flexible system, Milestone Inc. offers sorbent tubes to trap mercury gases and subsequently analyze them on our standard Dual Cell (DL – 0.003 ng) or Tri Cell (DL – 0.001 ng) DMA-80 Direct Mercury Analysis Systems, offering a user the capability to directly analyze gases along with solid and liquid matrices without sample preparation. This flexibility translates into cost savings on the need for addition instrumentation, consumables and a time savings on the high throughput nature of the DMA-80.  

Figure 1: Sorbent tubes ready to be analyzed on the DMA-80 system.			

A certain pre-fixed volume of air is made to pass through a mass flow controller with the sorbent tube attached. The sorbent tubes contain a special mercury adsorbing material, which traps the mercury from the gases as they flow through the tubes. These mercury containing sorbent tubes can be directly placed on the autosampler tray and be directly analyzed along with the regular solid or liquid samples.  

Table I: Mercury analysis on gas standards			

Triplicates of two known gaseous standards having mercury concentrations of 0.1 μg/m

  were collected on sorbent tubes and analyzed on the DMA-80 Tri Cell system. Their average concentration, % recovery, and RSD were calculated. 

The sorbent tubes add tremendous flexibility to the DMA-80 direct mercury analysis system and enable a user to accurately and reproducibly analyze mercury in gaseous samples along with solid and liquid matrices without the need to invest in additional systems and while maintaining all the benefits of the direct mercury analysis technique. 

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Direct mercury analysis is ubiquitous in analytical labs within the environmental, petrochemical, and specialty chemicals industry for analyzing mercury in solids and liquids.

Direct Mercury Analysis of Gaseous Samples Using Sorbent Tubes

Single reaction chamber microwave digestion enables a chemist to digest up to 15 different specialty chemical samples simultaneously at temperatures as high as 300 °C, greatly simplifying the workflow while maintaining superior quality digestions.

The class of "Specialty Chemicals" encompasses a wide variety of chemicals ranging from single chemical entities to complex formulations. While some of these chemicals are easy to prepare for trace metals analysis, many others require extremely high temperatures for complete digestion, which is difficult to achieve even with conventional closed vessel microwave systems. Often chemists have to complement microwave technology with traditional tools like hot plates and Paar bombs to digest the highly stable matrices which in turn have their own set of limitations — large acid requirements, contamination, acid handling challenges, lengthy digestions cycles, and exposure of chemists to acid fumes. Finally, although multiple samples can be digested in closed vessel microwaves simultaneously, samples of similar matrices need to be batched and run separately to ensure complete control over the system. This can severely hamper the productivity of a lab testing specialty chemicals, as a wide variety of sample matrices often require preparation. 

Milestone's UltraWAVE SRC benchtop digestion system can digest up to 15 different samples simultaneously at temperatures and pressures as high as 300 °C and 199 bar. This high temperature and pressure capability enables a complete digestion of almost any specialty chemical that needs to be analyzed for trace metals. Samples can be directly weighed into disposable glass, autosampler type vials with the appropriate acid mixtures; no minimum acid quantity is required. Quartz and TFM vials can also be used depending on the user's application. This minimizes acid handling and transferring steps, which reduces errors due to contamination and the chemist's exposure to acids. It also completely eliminates the need to clean, assemble, and disassemble vessels used in conventional microwave systems. 

The reaction chamber was pre-pressurized to 40 bar to prevent the acids from boiling, which subsequently prevented cross-contamination and loss of volatiles. 15-position racks were used with disposable glass vials which were covered by loose fitting caps. This ensures pressure equilibrium on either side of the vial while preventing the condensation from the top of the chamber from dripping into the sample. 0.2g of ERM681 (low density polyethylene) and CRM8112A (ABS Resin) were simultaneously digested in 4 ml of 68% nitric acid. The samples were heated to 225 

C in 15 min and held at 225 °C for 15 min. The trace metals in the digested samples were analyzed using a PE Optima ICP-OES system. 

The data shows excellent DLs and recoveries. No loss of volatile elements (like Hg) or cross contamination was observed. Due to higher sample capacity, use of disposable vials and faster cool down time, the UltraWAVE sample throughput is 2–3 times higher as compared to closed vessel microwave digestions. Its lower consumables costs, simple operation, and superior digestion quality make Milestone's UltraWAVE a perfect choice for specialty chemical's sample prep. 

Single reaction chamber microwave digestion enables a chemist to digest up to 15 different specialty chemical samples simultaneously at temperatures as high as 300 ?C, greatly simplifying the workflow while maintaining superior quality digestions.

Sumedh Phatak

Articles

Mercury Detection in Fish Samples by Direct Analysis

Direct Mercury Analysis of Gaseous Samples Using Sorbent Tubes

Single Reaction Chamber Microwave Digestion for Specialty Chemicals