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A mass spectrometer in every hand
ZHENG OUYANG
call it ‘portable’,” says Ouyang. “It was Portable mass spectrometers have been portable for Olympic weightlifting atharound for decades but have never quite achieved their potential for several reasons. letes!” The new instrument consumes just 35 W of power, in contrast with the 150 Though the size and weight of these instruments have been inching steadily downward, only recently have the spectrometers reached a weight at which a typical scientist might be able to lift one (⬍10 kg). In addition, the amount of power consumed by previous models has made it difficult to run the instruments off of a battery for any length of time, and the types of samples that can be analyzed have been limited because only electron impact ionization sources could be coupled to portable mass specThe Mini 11 portable mass spectrometer with a trometers. Now, in a recent AC paper cell phone for scale. (2008, DOI 10.1021/ac801275x), Graham Cooks, Zheng Ouyang, and W required for the Mini 5. The most recolleagues at Purdue University have incent model, the Mini 10, was introduced troduced the smallest, lightest, and leastin 2006; it weighed 22 lb and consumed energy-consuming portable, autonomous ⬃70 W of power (Anal. Chem. 2006, 78, mass spectrometer to date. And, as an 5994⫺6002). added bonus, the new instrument is comBut perhaps the most significant patible with many ionization sources, inachievement of the Mini 11 is its disconcluding ESI and several atmospheric-prestinuous atmosphere-pressure interface sure ionization (API) sources. (DAPI). On previous miniature instruOuyang is a former student of Cooks ments, ions were introduced into the anaat Purdue (and is now a professor of biolyzer via a multiple-pumping-stage intermedical engineering at the same instituface, in which pressure is reduced stepwise tion), so he has been working on the porfrom ambient to the millitorr levels retable mass spectrometer project for years. quired for mass analysis. “The pumping “I remember at the beginning it started system is the most expensive, most heavy, because Graham saw this need for a perand the most-power-consuming part of sonal mass spec,” says Ouyang. “A small mass spec can be used for multiple applica- the whole system,” says Ouyang. In designing the DAPI system, “what we did tions, because MS technology is obviously instead of letting the ions go through the so useful for general purposes.” He adds multiple vacuum stages [is,] we let them that applications specific to portable mass jump from the air directly into the spectrometers include homeland security screening, environmental and quality-con- vacuum.” Rather than leaving the entry channel open all the time, as in the old trol monitoring, and some biomedical design, a DAPI interface opens for ⬃20 applications like analysis of tissues and ms and funnels the ions directly into the biofluids. ion trap. After the interface closes, a small The current instrument, which the repumping system reduces the pressure to searchers call the Mini 11, weighs in at the millitorr range in ⬃200 ms. just 9 lb, with dimensions of 22 ⫻ 12 ⫻ Besides reducing the size and power 18 cm. That’s a far cry from the Mini 5, requirements of the instrument, the the original portable instrument develDAPI interface allows the researchers oped by the researchers several years ago; to couple ESI and API ion sources, for it weighed ⬎100 lb. “You could barely 7904
ANALYTICAL CHEMISTRY /
NOVEMBER 1, 2008
example, DESI, to the Mini 11. With the previous generation of miniaturized mass spectrometers, the researchers were limited to analyzing volatile organic molecules by using electron impact ion sources; now, the applications can be expanded to the analysis of larger nonvolatile molecules like peptides and proteins. “It’s worth noting that while one has to be prepared to give up some performance [with a miniature instrument], we’ve been very surprised at how little we’ve had to give up,” says Cooks. “That includes being able to look at proteins. We really didn’t expect to be able to get reasonable protein spectra on these tiny instruments.” Although Cooks and Ouyang are happy with the Mini 11, they say that it could be even better. “We need to improve the performance of some of the ionization methods... We’ve got nanogram and subnanogram sensitivity in particular cases, but we would really like to get the performance improved in terms of lowering the detection limits,” says Cooks. “We don’t think that there’s any rational reason why you would stop where we are right now.” This paper appears in the October 1, 2008 issue of AC. —Jennifer Griffiths
10.1021/AC8019027 2008 AMERICAN CHEMICAL SOCIETY
Published on Web 10/04/2008
