In the second part to my three-part series on trace elemental analysis, I want to address automated, intelligent liquid dilution that can provide two benefits, namely, a reduction in costs and a speeding up of analysis resulting in increased productivity. In my previous blog post, titled, Your Elemental Analysis is Costing You More Than You Think: Part 1, (link to post) , I discussed the advantages in using a switching valve to introduce samples using a segmented stream instead of a continuous flow stream.
Whether you’re preparing samples for analysis, making blanks and standards or restocking the rinse solution for your autosampler, you are spending many hours each day with a pipette in your hands. And what if you’re using an internal standard? That’s yet another solution to prepare and manually add to each and every blank, standard and sample (if you’re not utilizing a mixing tee). I have no doubt that you’ve mastered the use of adjustable volume and Class A pipettes to accurately dilute and prepare any solution that comes across your lab bench. But why would you want to? Performing manual dilution is tedious, time-consuming and introduces the risk for contamination. If you’re analyzing elements that are relatively unstable in solution, your calibration and check standards must be prepared on a regular basis, possibly daily.
And, what happens if you start your measurement sequence and results for one of your unknown samples gets flagged for being over-range? You’ll need to stop what you’re doing to pull that sample from the autosampler rack, dilute it to a volume you hope is sufficient to reduce the elemental concentrations to within the range of your calibration curve, then add it to your sample sequence for analysis with the new dilution factor.You did calculate and record the new dilution factor, correct? In your haste to get the sample re-prepared, you forgot to record the additional sample prep in your lab notebook? That’s a shame. You’d better pull that sample from the autosampler rack and prepare it a third time.
Wouldn’t it be nice if there was a device to help you perform some of these routine tasks? Wouldn’t it be even better if that same device performed these tasks while minimizing consumable and chemical waste costs, eliminating the potential for errors and cross contamination and recording all solution preparation in compliance with FDA 21 CFR Part 11 requirements? Our Inductively Couple Plasma Mass Spectrometry (ICP-MS) instruments (Thermo Scientific iCAP Q ICP-MS) offer an in-line, intelligent dilution module (Elemental Scientific prepFAST 2). The module is mounted directly to the instrument for minimal impact to your valuable bench space and is fully controlled through the ICP-MS software (Thermo Scientific Qtegra Intelligent Scientific Data Solution software) which allows for easy method setup and seamless operation. The system is so intuitive that even entry-level users can operate it and produce high-quality data with minimal training.
There are a number of advantages in utilizing an in-line dilution module including:
Entire calibration curves can be produced from a single stock standard.
Each unknown sample can be diluted in real-time using any dilution factor it requires.
On-line addition of internal standards.
Samples flagged as being over-range are automatically diluted and re-run.
Samples are automatically diluted if internal standard signals are suppressed due to high matrix samples.
Now, I know what you’re thinking. Aren’t there instrument vendors that manufacture an ICP-MS with a built-in aerosol dilution feature that’s integrated into the hardware, fully controlled through the software, and designed to provide on-line dilution? And, wouldn’t this built-in feature perform most of the tasks of the above mentioned in-dilution module? The answer to this question is, in my opinion, a whole-hearted, emphatic NOT EVEN CLOSE!
This aerosol dilution feature has a number of inferior performance aspects:
Loss of the ability to prepare standards. Everything must be prepared manually.
Loss of custom dilution factors. All solutions will be diluted by the same amount.
Loss of the ability to dilute over-range samples.
Loss of the ability to dilute samples to bring their internal standard recoveries into range in real-time, if needed.
And, if that’s not enough, using a gas aerosol to perform on-line dilution is a far inferior approach to using liquid dilution due to the following drawbacks:
To avoid excess salt deposition, an argon humidifier often has to be added to moisten the argon being used for dilution.
Samples are diluted after they’ve passed through the nebulizer and spray chamber which means high matrix samples will produce more severe memory effects.
In addition to memory effects, salt deposition and build-up from these high matrix samples will produce mass-dependent drift.
Introducing extra argon reduces the ionization energy of the plasma. which lowers the sensitivity of elements with high ionization potentials (As, Se, Zn, Cd).
Have I piqued your interest in in-line intelligent dilution to speed analysis and reduce costs? If so, then put down your pipette and check out our Productivity Portal and the valuable resources listed below.
On-demand webinar: Speed and Cost of Ownership (link to webinar), which looks at optimizing sample throughput and laboratory productivity using a low-cost benchtop ICP-OES with turn-key instrument methods and superior sensitivity and stability.