The ICP-MS technique is the method of choice in many routine and research laboratories because of its wide range of applicability, lowest detection limits, and short measurement time. Contract and other routine laboratories seek to continuously increase their sample throughput, as this increases revenue and profit. The ICP-MS detection technology is based on counting ions of target elements generated from the sample in the plasma. Performance criteria, such as detection limit and precision, greatly depend on counting statistics, for example the signal-to-background ratio. At this point the instrument's sensitivity is key, which is the count of ions detected per time interval at a given concentration. The higher the sensitivity, the shorter the time required for reaching a certain counting statistic, and therefore the shorter the measurement time per sample. Drinking water analysis according to EPA method 200.8 will serve as an example of maximizing sample throughput by using the industry-leading sensitivity of the PlasmaQuant® MS Elite ICP-MS in combination with discrete sampling as a further performance enhancement.
Drinking water samples and certified reference materials (CRM) were diluted 1:2 with a 1% nitric acid solution and subsequently analyzed on the PlasmaQuant® MS Elite ICP-MS with a standard sample introduction system, oneFAST sampling valve (Elemental Scientific), and autosampler ASPQ3300.
Instrument parameters were tuned for maximum sensitivity, and measurement times for all isotopes were optimized for fastest measurements, while maintaining the required performance criteria (detection limit, precision, recovery, long-term stability). All 21 analyte isotopes and four internal standards were measured using helium as a collision gas in the iCRC integrated collision–reaction cell to remove potential interferences by kinetic energy discrimination (KED).
A discrete sampling valve was used to shorten the rinse time between samples, which typically reduces the total time per sample by about 80%.
Two water CRMs (NIST 1640a, NIST 1643f) were analyzed to verify the accuracy of the method. Results were within 91–103% of certified values, therefore within the ±10% recovery range specified by EPA 200.8. Analysis of two laboratory-fortified matrices (LFM, +1 ppb and +10 ppb) resulted in 91–104% recovery, well within the specification of 70–130%.
The relative standard deviation (RSD) was used to assess method precision at different parameter settings. An excellent average RSD of 1.5% was obtained at a sample throughput of 60 samples per hour, surpassing the requirements of EPA 200.8 by far.
Figure 1: The Analytik Jena PQMS Elite
If high precision is not the main priority, sample throughput can further be boosted to >80 samples per hour by using a shorter measurement time. Under these conditions, the instrument delivers a competitive precision of 2.2% average RSD, which is still within the requirements of the EPA method.
A long-term stability evaluation resulted in <10% drift for all isotopes over seven hours of continuous operation.
Thanks to its industry-leading sensitivity, the PlasmaQuant® MS Elite demonstrates excellent precision and accuracy at an unmatched sample throughput. The analytical method developed surpasses all performance requirements of EPA 200.8 and other regulations by far, and the long-term stability proves the method's robustness.
Besides allowing laboratories to analyze more samples per day, the PlasmaQuant® MS also reduces argon consumption by 50% compared to a conventional ICP-MS instrument, and therefore has the lowest running cost on the ICP-MS market.
The combination of minimal running cost and highest sample-throughput results in the lowest cost per sample-overall cost savings of more than 30% have been reported by laboratories that replaced their ICP-MS with a PlasmaQuant MS Elite.
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