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Improving Sample Throughput

CompuChem, a division of Liberty Analytical based in Cary, North Carolina, recently improved sample delivery, measurement protocol and rinse-out times by coupling a rapid sampling system with an ICP-MS system, reducing the time required to analyze a typical CLP sample by 80 percent.

by Kenneth Grzybowski
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Rapid Sampling System Coupled with ICP-MS Reduces Analysis Time of Typical CLP Sample by 80 Percent

CompuChem, a division of Liberty Analytical based in Cary, North Carolina, analyzes samples under the Superfund Analytical Services Contract Laboratory Program (CLP). In the 27 years CompuChem has been involved with the program, we have probably analyzed more CLPtype samples than any other lab in the U.S.

The company recently improved sample delivery, measurement protocol, and rinse-out times by coupling an SC-FAST autosampler from Elemental Scientific with a PerkinElmer SCIEX™ ELAN® DRC-e inductively coupled plasma mass spectrometer (ICP-MS). We have reduced the time required to analyze a typical CLP sample by 80 percent.

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ICP-MS offers detection limits that, on average, are 1/1000 of those provided by inductively coupled plasma optical emission spectrometry (ICP-OES) and about 1/10 to 1/100 of graphite furnace atomic absorption (AA) spectroscopy. As a result, most labs use ICP-MS for analyzing samples with very low analyte levels and are not overly concerned about sample throughput. A typical ICP-MS user would likely be satisfied with a 10-minute-per-sample analysis time for the determination of 22 elements in triplicate. In fact, many analysts would probably accept much longer analysis times, especially if they had previously been forced to use two or three techniques to determine all 22 elements.

However, environmental laboratories carrying out high-volume CLP-type analysis have much more demanding throughput requirements. The major reason for this kind of productivity demand is the EPA’s need for a vast amount of data in support of the investigation and cleanup of contaminated hazardous waste sites under the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). The methodology that describes the determination of inorganic contaminants in these kinds of samples is outlined in the IlM05.3 (2004) and the updated IlM05.4 (2007) Statement of Work (SOW), which defines the analytical methods accepted by the CLP for the quantitation of 24 inorganic analytes, including mercury and cyanide, in water, soil, and sediment samples using ICP-OES, ICP-MS, cold vapor (CV) AA, and colorimetric techniques

The Superfund CLP program can generate extremely large numbers of samples because the data is critical for determining the extent of contamination at hazardous waste sites, assessing the response based on risks to human health and the environment, deciding on appropriate cleanup actions, and making determinations as to when remedial actions are complete. In addition, the data may also be used in litigation against responsible parties in the enforcement of Superfund legislation, which means the contract lab that carries out these analyses may be required to testify in court as to the integrity of its results. The bottom line is that the amount of data generated under this contract is exhaustive and must be of the highest quality because it is used to make major decisions regarding public health and environmental safety issues.

CompuChem has been carrying out continuous and uninterrupted contract work with the EPA since the CLP was initiated in 1981. Back in September 2008, the company’s existing 10-year-old ICP-MS had a catastrophic failure and was unable to run any samples until it was fixed or replaced. After a cost-benefit analysis, it was determined that repairing the instrument was not an option. CompuChem contacted all the major vendors and chose an ELAN® DRC-e. All the vendors were telling us it would take eight to ten weeks to get an instrument, which was unacceptable and would have cost us numerous contracts and revenue. PerkinElmer, after initially quoting us eight weeks, was able to readjust their time frame and have the instrument “Most labs use ICP-MS for analyzing samples with very low analyte levels and are not overly concerned about sample throughput.” delivered to us in three weeks.

Ron Buchanan, senior ICP-MS service engineer for PerkinElmer, installed the DRC-e instrument and provided the company with basic training, all in a few days. Even though we were not familiar with the software, after the instrument was installed, it took us only one week for training and method development before we were running samples again. We were very impressed that we could get back online so quickly.

By coupling the PerkinElmer SCIEX™ ELAN® DRC-e (shown here) with an SCFAST autosampler, CompuChem has significantly increased its sample throughput.

Since then, CompuChem has coupled an SC-FAST autosampler to its ICP-MS and by optimizing sample delivery, measurement protocol and rinse-out times, the lab is now analyzing a CLP sample for 30 elements in triplicate in one minute and 30 seconds. We had no idea that we could have increased our sample throughput by this much. The same analysis on our previous instrument took us nine minutes and 53 seconds, which translates into more than a fivefold improvement in sample throughput. There is no doubt in my mind that the ELAN® DRC-e will be critical to our mission.

SC-FAST is a rapid-sampling approach that significantly reduces the pre- and post-measurement times involved with delivering a new sample to and removing the previous sample from the ICP-MS. The autosampler probe is moved to the next sample while the previous sample is being analyzed, saving considerable time. A small vacuum pump rapidly fills the sample loop, which is positioned in proximity to the nebulizer, minimizing sample uptake time. Little or no signal stabilization is required, because the pump delivering the sample to the plasma remains at a constant flow rate and the injection valve ensures that no air is introduced into the sample line.

Improved productivity, combined with the recognized interference reduction capabilities of the ELAN DRC technology for the more difficult environmental analytes like selenium and arsenic, is helping the lab achieve its goal. The instrument is able to keep up with the current demands of the EPA Contract Laboratory Program and other environmental test methods and is also capable of testing based on future EPA trace element regulations as they inevitably will require detection of lower levels.