In part 1 of this series, I covered the issues of contamination and sample-to-sample memory effects in ICP-MS and how you can solve them. In part 2, I moved on to the challenge of interferences and how you deal with them. In this final part of the series, I’ll take you through the subject of sample preparation / handling and will describe how you can simplify and improve these processes.
The Perils of Manual Sample Handling
In the words of the pioneering French criminologist Edmond Locard, “Every contact leaves a trace.” This is as true for sample preparation as it is for forensic science, in that everything a sample, blank or calibration solution comes into contact with risks contaminating it. The basic rule is therefore to reduce manual sample handling steps as much as possible to minimise the risk, as well as using pre-cleaned labware as described in part 1 of this blog post series. As also mentioned in part 1, we humans are well known sources of trace element contamination (from hair, skin cells and dust from outside the lab carried in on our clothes), so performing as little manual sample manipulation as possible further helps reduce contamination.
Minimising manual sample handling has the added benefit of removing errors such as incorrect volume pipetting for sample dilution, random omission of internal standards from samples and mixing up stock solutions during calibration solution preparation (I have made all these mistakes at one time or another and I suspect (hope!) that I’m not alone).
Manual sample preparation is also a labour intensive process and is probably not the best use of your or your analyst’s time in the laboratory. Freeing up the time spent on this task enables your laboratory personnel to become both more efficient and more productive, allowing you to increase sample throughput, reduce analysis turnaround times and decrease your cost per sample.
How can you reduce manual sample preparation in your laboratory?
The majority of laboratories today use autosamplers for presenting samples to their ICP-MS instruments. Conventional autosamplers use a fairly long uptake tube in order to allow the sample probe to travel across a full rack of samples. This leads to long uptake and wash times which reduces the productivity of the instrument and increases the analysis cost. Using so-called ‘fast uptake and wash’, where the peristaltic pump of the instrument is accelerated during the sample uptake and rinse cycles, reduces the analysis time but increases wear on the pump tubing and can cause increased instability and drift during the run. A neater approach is to use an automatic valve based system where the sample is rapidly drawn into a loop using a vacuum pump (the Load step) before switching the valve to transport the sample into the instrument using a carrier stream pumped at a constant rate (the Inject step). Locating the valve close to the ICP-MS nebuliser allows this technique to achieve very short sample uptake times and by switching the valve back to its load position immediately after the sample acquisition finishes, rinse times are kept equally as short. If you’d like to learn more about these systems, your local ICP-MS sales representative will be able to help you.
Taking Automatic Sample Handling to the Next Level
Valve based systems don’t stop there. If you need to analyse medium to large numbers of samples every week and dilution of samples is a regular activity for you, the most effective way to minimise manual sample handling is to invest in a hands-free, valve-based autodilution system. There are a couple of major providers of such systems and a quick internet search or, as mentioned above, conversation with your local ICP-MS sales representative will highlight them. Autodilution systems not only take away the laborious task of fixed manual dilution of a set of samples (e.g. dilution by a factor of 10) using so-called prescriptive dilution, but also provide the ability to dilute intelligently by different amounts on a sample-by-sample basis, in accordance with rules such as ‘dilute if a result is above the calibration range’ or ‘dilute if the internal standard recovery is below an acceptable value.’ With the Thermo Scientific™ iCAP™ RQ and iCAP™ TQ ICP-MS instruments, the common software platform that operates them, Qtegra Intelligent Scientific Data Solution (ISDS), offers both prescriptive and intelligent dilution functionality as standard, giving you maximum flexibility for unattended, uncontaminated and error-free automatic analysis.
So, that’s it. Three challenges for accurate trace element analysis, and three blog posts from me on how you can overcome them. I hope you found it useful!
To learn more about our single, triple quadrupole, high resolution and multicollector ICP-MS instrument portfolio, take a look here. If you have any questions about how to solve your ICP-MS interference challenges, or if you’d like to learn more about how Thermo Scientific’s ICP-MS instruments can help meet your needs, let us know via the comments box below!