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Parts-per-quadrillion sensitivity reveals miniscule markers, from those created by nuclear blasts to trace impurities in pharmaceuticals
To analyze trace elements—metals and nonmetals—in a sample, scientists often turn to inductively coupled plasma/mass spectrometry (ICP/MS). Under the best conditions, ICP/ MS detects elements down to the parts-per-quadrillion level. Within an ICP/MS system, an electromagnetic coil provides the required energy to form plasma from argon gas, and the sample is subsequently brought into the plasma to be decomposed and ionized. The ionized gas can be analyzed with MS. “ICP/ MS is used in a variety of industries, including environmental testing, food and agricultural studies, and pharmaceutical work,” says Dan Davis, atomic spectroscopy product manager at Shimadzu Scientific Instruments (Columbia, Md.). “For instance, ICP/MS is specified in EPA Method 200.8, Determination of Trace Elements in Waters and Wastes.”
According to Shona McSheehy Ducos, ICP/MS product manager, chromatography and mass spectrometry, Thermo Fisher Scientific (Waltham, Mass.), “The big up-and-coming opportunity for ICP/MS is in the pharmaceutical/ nutraceutical industry.” She says, “The new United States Pharmacopeia guidelines are supposed to be implemented in January 2018, and the sensitivity requirements will dictate that an ICP/MS will have to be used for most applications.”
Some organizations also use ICP/MS to accurately and reliably monitor the contents of consumer products. “The U.S. Food and Drug Administration (FDA) and the Nutrient Data Laboratory (NDL) of the USDA Agricultural Research Service have worked independently on determining the concentration of iodine in foods and dietary supplements and are now harmonizing their efforts,” write U.S. government scientists.1 The team noted: “The NDL recently qualified a commercial laboratory to conduct iodine analysis of foods by an … [ICP/ MS] method. Co-analysis of a set of samples by the commercial laboratory using the ICP/MS method and by the FDA laboratory using its standard colorimetric method yielded comparable results.”
Measuring through matrices
ICP/MS can detect tiny quantities of many materials, including trinitite, which can be used in forensic studies. (Image courtesy of Los Alamos National Laboratory.)When asked about an interesting new application of ICP/MS, McSheehy Ducos says that one “is our ability to analyze extreme high matrix samples—semi-saline solutions containing 25% NaCl.” She adds, “This is an unprecedented level of dissolved solids for an ICP/MS to handle, but our new robust interface and argon gas dilution feature allow us to measure elemental impurities in samples with dissolved solid levels that high.”
To deal with such high levels of dissolved solids, the technology must be modified. “We have interface setups for really high levels of dissolved solids, for high flexibility and for high sensitivity,” McSheehy Ducos says. “Each interface installs in just seconds and has automatic tune files to allow the instrument to optimize its own performance for the application you’re about to tackle.”
The new interface, McSheehy Ducos explains, “allows us to lengthen the central channel through which the ions from the plasma pass.” She adds, “Depending on the application and the specific sample matrix you’re trying to tackle, you may sacrifice a small amount of sensitivity, but you gain the ability to determine trace elements in matrices with levels of dissolved solids that, to date, have been too challenging for commercially available ICP/MS instruments.”
Enhancing health
Pharmaceutical companies analyze medicines and their raw materials for impurities with ICP/MS. (Image courtesy of Michael J. Ermarth, U.S. Food and Drug Administration.)Various segments of the healthcare industry already use ICP/MS. “In the pharmaceutical industry, companies are required to analyze for elemental impurities in pharmaceuticals that remain with the active pharmaceutical ingredients’ raw materials or are inadvertently introduced during the formulation and packaging processes,” Davis explains. “Their presence, even in small quantities, can influence the efficacy and safety of the product.”
Trace levels of substances in the environment can also impact human health. Copper mining from 1956 to 1982 in Kilembe, Western Uganda, released the metal in a mountain river valley, and scientists recently used ICP/MS on aciddigested samples to analyze soil, food, drinking water, human biomarkers and more.2 The scientists wanted to “assess the nature and extent of risk to local populations from metal contamination arising from those mining activities.” They found contamination in 51% of the agricultural soils, 25% of the drinking water and 40% of the river samples. In addition to copper, the ICP/ MS in this study revealed zinc and lead in some samples. The investigators reported that “risk assessment of local foods and water, based on hazard quotients (HQ values) revealed no potential health effects.” Still, they concluded: “Any mitigation of Kilembe mine impacts should be aimed at remediation of agricultural soils, regulating the discharge of underground contaminated water but also containment of tailing erosion.”
Metals and us
“One new and interesting application is metallomics,” says Davis. “It’s the study of metal and metalloids in biological systems and their interactions with proteins, genes and metabolites.” Work in this area depends on some technological advances. “Combining chromatography separation techniques, typically HPLC, with ICP/ MS to create hybrid systems results in highly sensitive analysis that provides precise identification and quantitation of metals,” Davis explains.
Shimadzu’s ICPMS-2030 includes software assistants that help scientists customize experiments. “The ‘Development Assistant’ automatically selects the optimal mass and internal standard for the target elements, and suggests concentration ranges for calibration curves, which allows any user to develop reliable methods with ease,” Davis notes. “The ‘Diagnosis Assistant’ identifies the presence or absence of mass interference based on qualitative analysis to quickly generate reliable results.”
Shimadzu’s HPLC platform can be combined with the ICPMS-2030 for metallomic studies. Combining these technologies can be complex enough, but Davis points out: “Shimadzu offers LabSolutions ICPMS TRM—time-resolved measurement—software, which controls the LC—Shimadzu Prominence Inert LC System—from the ICPMS-2030, allowing for one smooth platform that automatically detects and measures analyte peaks.”
Testing for trinitite
In 1945, the Trinity nuclear bomb test created a glassy material now known as trinitite. This material can be used to confirm that a nuclear explosion has occurred, or in forensic studies of what might be illegal nuclear materials, say, intended for a dirty bomb. University of Notre Dame (Ind.) scientists developed an ICP/MS-based approach to test for trinitite3 using solution mode (SM) and laser ablation (LA).
“The trace-element concentrations obtained by individual LA/ICP/MS analyses indicate a large scatter compared to the corresponding bulk-sample SM/ICP/MS results for the same sample,” the scientists noted, but the “favorable comparison reported here validates and confirms the use of the LA/ICP/MS technique in obtaining accurate forensic information at high spatial resolution in nuclear materials for source attribution purposes.”
From defending human health through defending one’s country, ICP/MS can reveal and quantify dangerous trace elements. In some circumstances, very small elements of something can be deadly. Adding various processes upstream—from HPLC to LA—provides even more applications of this technology. The parts-perquadrillion sensitivity of ICP/MS lets scientists explore some of the slightest samples—even those that may represent significant dangers.
References
- Pehrsson, P.R.; Patterson, K.Y. et al. Iodine in food- and dietary supplement-composition databases. Am. J. Clin. Nutr. 2016; doi: 10.3945/ajcn.115.110064.
- Mwesigye, A.R.; Young, S.D. et al. Population exposure to trace elements in the Kilembe copper mine area, Western Uganda: a pilot study. Sci. Total Environ. 2016; doi: 10.1016/j.scitotenv.2016.08.125.
- Dustin, M.K.; Koeman, E.C. et al. Comparative investigation between in situ laser ablation versus bulk sample (solution mode) inductively coupled plasma mass spectrometry (ICP-MS) analysis of trinitite post-detonation materials. Appl. Spectrosc. 2016; doi: 10.1177/0003702816662597.
Mike May is a freelance writer and editor living in Florida. He can be reached at [email protected].