Solutions for trace metal analysis

Environmental metals testing is very common for analysis of drinking water, wastewater, solid waste, soils and compost due to metal toxicity and regulations. With the advanced technologies today, in one elemental analysis run, multiple metals are often analyzed in multiple samples. However, different metals have unique properties in terms of sample preparation, ionization conditions, and spectral interferences. Therefore, tips and tricks are often the most valuable information that help with individual metals analysis.

Choosing the right instruments

Atomic spectrometry instruments are the most popular instruments used for trace metal anlysis. Depending on the sample throughput, cost, sensitivity/detection limit, concentration range, matrices, and regulation requirments, different instruments can be chosen for different environmental applications. For instance, many metal elements can be analyzed easiliy and economically with ICP-OES but elements such as arsenic and lead are better analyzed by ICP-MS due to their low regulatory limit in drinking water.

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Sample preparation for metal analysis

Although metal analysis can be conducted directly from solid matrix through coupling of ICP-OES or ICP-MS with laser ablation instruments, the majority of the samples are analyzed in the liquid form. To make sure metal elements are totally dissolved in liquid samples, acid digestion  is often used. Depending on the matrix difference and analytes of interest, different acids or acid mixtures are used for the best digestion results and minimum interferences in downstream analysis. 

For water analysis, sample preparation can refer to EPA 200.7 and 200.8 methods; for soils, solid waste and sludges, EPA 3050B 3051A , and 3052  (total digestion) can be used for sample preparation. There are other quick methods for soil sample preparation, such as Mihlich-1 and Mihlich-3 methods that are not for total metal composition analysis in soils.

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Overcoming interferences

One of the biggest concerns using ICP-OES and ICP-MS is to overcome interferences. There are three types of interferences: physical, chemical and spectral.

Physical interferences occur when the physical properties of the sample is vastly different than the physical properties of the calibration standards. Examples of physical properties would include viscosity, density and surface tension. Physical interferences within the sample, injection and subsequently inside the plasma.

Chemical interferences occur when a sample matrix causes the standard to behave differently in the presence or absence of the matrix. Examples include ionization effects, molecular formation, and plasma loading.

Spectral interferences are the interferences generated either due to the simliar region of light emission between the analyte atoms and the interfering atoms (ICP-OES) or the analyte ions with similar mass and charge ratio with the interfering ions (for ICP-MS).

For more information 
  • View the webinar  on how to remove different interferences: Demystifying Interence Removal

Improving metal analysis productivity

When analyzing thousands of samples in a large contract lab, operators are often frustrated with low productivity and efficiency. There are multiple ways to improve productivity:

  • Fast sample introduction
  • Automated sample dilution including prescriptive and intelligent dilution
  • Integrated software with "get ready" functionality and more importantly,  highly stable performance

Tips and tricks:
Environmental samples analysis on ICP-OES and ICP-MS

Instrument operation may look simple and straight forward, but there are many tips and tricks for sample analysis precision. Both instruments and sample preparation methods play important roles in getting high precision results:

  • Sample preparation: precipitation
  • Sample preparation: gas production during the run
  • Sample preparation: plasma drift due to the sample matrix
  • Instruments: nebulizer type, gas flow rate, and peristaltic pump tubing
  • Instruments: extraction lens and mirror adjustment
  • Instruments: maintenance and use of skimmer cone inserts
For more information
  • Watch the on-demand webinar  on Improving Analysis Precision for ICP-OES and ICP-MS for Environmental and Geological Applications
  • Download technical notes TN43202 and  TN43208 to find solutions on improving matrix tolerance, which is important for ICP-MS for complex matrix samples. 

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Elemental speciation using IC-ICP-MS

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Nanoparticles analysis using ICP-MS

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Mercury analysis in trade effluent

Mercury is a toxic element and is regulated in drinking water, wastewater, soil, and air. Under the Clean Water Act (CWA), the U.S. EPA regulates wastewater effluent discharge into surface water under the National Pollutant Discharge Elimination System (NPDES) program. Municipalities and industrial users must obtain NPDES permits to discharge their treated wastewater. Mercury is one of the most important heavy metal element regulated under NPDES. The U.S. EPA approved multiple methods to measure the trace mercury concentration in effluent . EPA 200.8 is also an approved method that uses ICP-MS to determine the concentration of mercury.

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Related subtopics

Hydraulic Fracturing

The impact of hydraulic fracturing (fracking) on the environment has been a hot topic of discussion for many years. Currently, there is no federal regulation on fracking water analysis although there are some basic analysis requirements from a few states. It is critical to know the types of metals present in fracking flowback and/or produced water. We provide comprehensive solutions for the analysis of metals, anions, and organic compounds in fracking water.

The U.S. EPA requires specific analytical methods to be used for metals analysis in compliance with drinking water and solid waste regulations. For instance, for drinking water, the EPA methods 200.5 (Axial ICP-OES), 200.7 (ICP-OES), 200.8 (ICP-MS), and 200.9 (GFAA) are mandatorily used for different metals; for solid waste, SW846 methods 6010c (ICP-OES), 6020 (ICP-MS), and 6020A (ICP-MS) are used for metals analysis for groundwater, sludges, soil, and solid waste as a performance guidance. We have a regulatory guide and many applications for specific regulatory methods.

For metal analysis, other countries use different regulatory methods. For instance:

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