In the final post to my three-part blog series on trace elemental analysis, I want to discuss the importance of proper sample preparation. In my previous blog posts (see links to posts at end of this post below), I described the advantages in using a segmented carrier stream for sample introduction and automated, intelligent liquid dilution for streamlined sample preparation and sample handling. However, I have yet to address the first step in the elemental analysis workflow: sample preparation.
Whether you are analyzing drinking water, lubricating oils, geological materials or refractory metal oxides, proper sample preparation is essential in producing quality results.
If your samples are in liquid form and can be analyzed directly or with little modification prior to analysis, count your blessings. Your sample preparation requirements are about as minimal as they can get. If your samples are in solid or liquid form, but are readily soluble in an aqueous or organic solvent, you’re still in luck. You can follow the dilute-and-shoot method of sample preparation which is only slightly more involved than the protocol required for samples that can be analyzed neat.
If your samples are in solid form and aren’t readily soluble, you’ll need to be more creative about getting your samples into solution. The bad news is that your sample preparation will have to be carefully planned and executed to make sure the samples are properly dissolved and remain as stable as possible once in solution. The good news is that there are many laboratories facing similar challenges, so you’re not alone. The other good news is that there are well-established digestion methods for almost every sample matrix so you won’t get stuck creating a method from scratch.
Your first option is to digest your samples using a hot plate. The benefit to this technique is that hot plates are relatively inexpensive and easy to operate, and flasks of any size can be used to accommodate a variety of sample masses. Downsides to this approach are that hot plates tend to heat unevenly, they can’t accommodate more than a couple of flasks at a time, and volatile elements will likely be lost during the digestion.
Your second option is to digest your samples via fusion using proper flux material. Fusion digestions are great at tackling even the most challenging sample matrices; however, the procedures can be somewhat time-consuming and require multiple steps, expensive flux material and crucibles must be purchased, and a special fusion instrument or high-temperature furnace is required in order to heat the flux material to its melting point temperature.
Your third (and best) option for getting your sample into solution is to use closed vessel microwave digestion. This technique utilizes the power of microwave radiation to thermally decompose samples in the presence of strong acids. In a closed vessel, volatile elements are prevented from escaping and high temperatures and pressures can be used to increase the rate of the digestion reaction. Acids can be raised to temperatures above their boiling points which increases their oxidative potential and drives the reaction to completion, often without the use of harsh acids such as perchloric acid.
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Microwaves can accommodate dozens of samples simultaneously and the temperature inside each reaction vessel is carefully controlled to produce highly reproducible conditions. Vessels are fully heated and cooled while still inside the microwave cavity, eliminating the need to handle hot acids and increasing the safety of the digestion procedure.
If you’re looking to streamline your sample preparation workflow and improve the overall productivity of your laboratory, check out our Productivity Portal which provides a selection of materials to describe proper sample preparation.
By, the way, my previous two posts can be found here:
- Your Elemental Analysis is Costing You More Than You Think: Part 1
- Your Elemental Analysis is Costing You More Than You Think: Part 2
If you have questions or concerns about maximizing the efficiency and productivity in your laboratory, let us know in the comments box below. Looking forward to your questions.