Tackling Unresolved Problems in ICP-MS

Inductively coupled plasma–mass spectrometry (ICP-MS) is a powerful analytical technique. But like any other analytical techniques, there are challenges involved. We recently asked ICP-MS experts what unresolved problems exist-especially with samples in complex matrices-and how ICP-MS methods or technologies can be developed to attack them.   Steve Ray, an assistant professor of chemistry at the University at Buffalo, responded with a wise reminder: "Very rarely is there ever a silver bullet solution to complex analytical problems."   Collision cell technology has helped immensely, he said, but as certain problems are solved, the remaining problems become progressively more difficult and less tractable. "Oddly, the solution to many problems with ICP-MS likely falls not on the MS portion, but in the source itself," he said. "More study of ICP-MS as an ionization source is required, particularly as it will be applied in laser-ablation and nanoparticle applications."   Craig Westphal, a principal investigator at Chemours Analytical, a subsidiary of DuPont, pointed back to sample handling. "It's now possible to use ICP-MS to analyze high total dissolved solids samples directly at levels on par with ICP-OES, but carryover and subsequent raised instrument background levels mean we can't analyze percent and low parts-per-trillion levels easily on the same instrument, even with dedicated sample introduction systems," he said. Nevertheless, he feels that for most applications in his industrial R&D environment, existing instrumentation has sufficient detection limits. "Although I'd always want it to be faster, better, and cheaper," he added.   The majority of remaining unresolved problems relate to interference removal, with multiply charged interferences remaining an inherent problem of ICP, said Traci A. Hanley, is a chemist at the United States Food and Drug Administration (US FDA). Although the introduction of the collision–reaction cell greatly enhanced the ability to reduce isobaric interferences, interference removal with the CRC is matrix-dependent in single-quadrupole ICP-MS instruments, she noted-anything ionized that enters the CRC will affect the reproducibility and robustness of the cell reaction.   "As a result, the introduction of the triple-quadrupole ICP-MS system has been revolutionary in combating doubly charged, isobaric, and background noise interferences without losing sensitivity," she said. In a triple-quadrupole ICP-MS instrument, she explained, ionized matrix is removed in the first quadrupole, and isobaric and multiply charged interferences can be removed or reduced in the CRC, leaving the second quadrupole as a mass filter.   Triple-quadrupole ICP-MS instrumentation has its place, but it likely won't be the ultimate panacea, said David Koppenaal, the chief technology officer for the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory. "New, integrated methods for sample preparation and instrumental analysis must be developed," he said. "For too long, instrument manufacturers have approached this issue as two separate problems, and have treated them as such-letting smaller, independent companies handle the sample handling issues while they focus only on the instrumentation itself."  

  This article is an edited excerpt of “

Analysis of the State of the Art: ICP-MS

.”    The article is part of a special group of six articles covering the state of the art of key techniques, also including

laser-induced breakdown spectroscopy (LIBS)

,

X-ray fluorescence (XRF) spectroscopy

,

infrared (IR) spectroscopy

,

near-infrared (NIR) spectroscopy

, and

Raman spectroscopy

.