L J single shot or up to 50 automatic multi sequential runs H improved static or dynamic combustion at selectable oxygen concentration H sample amount up to 100 mg Q extreme compactness no gaschromatographic column separation of the combustion products
thermal focusing and programmed tem perature desorption PTD technique* * patent pending
THE NEW ELEMENTAL ANALYZER
DANI CHΝ89.00
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DANI S.p.A. • I 20052 MONZA (Ml) • VIALE ELVEZIA 42 • ITALY • TEL. (039) 323993 - 324448 • TELEX 332280 DANI I • CIRCLE 34 ON READER SERVICE CARD 702 A · ANALYTICAL CHEMISTRY, VOL. 59, NO. 10, MAY 15, 1987
FOCUS (TOF-MS). According to Jack Holland of Michigan State University, "Timeof-flight has always been appealing be cause of the simplicity of the mass spectrometer and a linear ion flight path that accommodates a virtually unlimited mass range. "Two drawbacks have so far prevent ed time-of-flight from being a domi nant type of mass spectrometry," Hol land continues. "First, space and ener gy defocusing impede the resolution of time-of-flight instruments tremen dously. Second, because time-of-flight MS involves measurement of a timed event, there is a duty cycle to contend with. In other words, the instrument can only be 'on' for about l/10,000th of the time as ions are being extracted from the source. The rest of the time it's not extracting ions for subsequent measurement." Of course, intermittent operation is not always a disadvantage. As Fred
Time-of-flight MS and FT-MS both involve multichannel detection, in which all of the ions are detected simultaneously, without having to scan the spectrum. %% McLafferty of Cornell University points out, "A number of ionization methods only operate in a pulsed mode or provide better sensitivity if operated in a pulsed mode. These include the Cf-252 plasma desorption source, pulsed SIMS [secondary ion MS] sources, and pulsed laser sources. This then suddenly becomes an advantage instead of a disadvantage for time-offlight MS." McLafferty sees a number of other advantages that account for increasing scientific and commercial interest in TOF-MS: "Time-of-flight MS and FTMS both involve multichannel detec tion, in which all of the ions are detect ed simultaneously, without having to scan the spectrum. On top of that, for high molecular weight species, there is the advantage afforded by the virtually unlimited mass range of time-of-flight instruments. The only real drawback is that time-of-flight is not very good for tandem MS." "People are delighted with desorp tion modes such as laser desorption
