In my previous blog post, I established a set of key terms that are relevant when discussing elemental analysis. Here, I will use those terms to discuss a topic that must be addressed when tackling a new application: which instrument technique is best to use for your application? In some cases, a regulatory body will direct you toward a particular technique for your analyses. For example, if you’re in a drinking water lab and you’re reporting to EPA Method 200.7, you’ll need to use an ICP-OES (link to product page) to satisfy the requirements of the method. If you’re in a pharmaceutical lab and you’re reporting data under the new USP guidelines (Chapters <232>, <233>, <2232>), you’ll be encouraged to use an ICP-OES or an ICP-MS (link to product page) to quantify elemental impurities.
In other cases, the instrument selection isn’t made based upon regulatory requirements. However, the decision is relatively straightforward, based upon the needs of your particular application. For example, if your laboratory’s only focus is to determine trace levels of lead in whole blood samples, a graphite furnace-AAS (link to product page) instrument would be optimal. If your laboratory is responsible for quantifying mercury species in fish, an ion chromatograph (link to product page) coupled to an ICP-MS will provide you with the speciation capability and sensitivity required for this application.
How to Choose the Best Technique for the Task at Hand
For applications in which instrument selection isn’t obvious, how do laboratories choose which technique is best? The first and, in my opinion, the most important question to ask is: What are the detection limit requirements for this application? There’s no sense in considering an instrument if it doesn’t provide you with the sensitivity you need to accurately measure the lowest concentrations you’re expecting to encounter in your samples.
Once you’ve determined your detection limit requirements, additional questions to ask include:
What is the range of concentrations you expect to encounter in your samples?
How many elements do you need to measure in your samples?
How many samples do you need to measure per day or per week?
Do the sample matrices contain challenging components (high levels of dissolved solids, volatile organics)?
A Thought Process to Consider
When evaluating your instrument options, consider the following flow chart to help guide your selection. Keep in mind that this is a general guide to get you started. If your laboratory must analyze hundreds of samples a day, you’ll want to carefully consider your options for automating your instrument and maximizing its sample throughput ability.
A selection can also be guided based on your laboratory requirements as well as your application requirements. For example, what kind of bench space do you have available in your laboratory? There’s no sense in purchasing an instrument if you don’t have space for it in your lab, right?
Hopefully you find this information useful when tackling your next application challenge. Stay tuned for future posts that will discuss method optimization and strategies for analyzing challenging samples. If you have topics you would like addressed, please let me know in the comments section.