Californium plasma desorption

Californium plasma desorption ( Cf-PD) dates back to 1973 [4-6,22,147-149] and was the first method to yield ions of bovine insulin [150]. Practically, Cf-PD served for protein characterization, an application which is now fully transferred to MALDI or ESI (Chaps. 11, 12) [151]. 

Deposition of the analyte on nitrocellulose films instead of metal foils allows the removal of alkali ion contaminations by washing of the sample layer which results in better PD spectra [156]. Further improvements can be achieved by adsorption of the analyte molecules on top of an organic low-molecular-weight matrix layer [157,158]. 

Benninghoven, A. Kiichner, F. The Energy Distribution of Atomized Neutral and Charged Products. Z. Natiaforsch. 1963,18A, 1008-1010. 

The Development of Secondary Ion Mass Spectrometry (SIMS) a Retrospective. Int. J. Mass Spectrom. Ion Proc. 1985,66,31-54. 

Stone-Age Mass Spectrometry the Begirmings of SIMS at RCA Laboratories, Princeton. Int. J. Mass Spectrom. Ion Proc. 1995,143,1-10. Macfariane, R.D. Torgerson, D.F. Cali-fomium-252-Plasma Desorption Time-of-FUght Mass Spectrometry. Int. J. Mass Spectrom. Ion Phys. 1976, 21, 81-92. 

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There are other MS ionization techniques applied to analyze pyrolysates such as secondary ion mass spectrometry (SIMS) [66], californium plasma desorption [67], fast atom bombardment (FAB) [68]. 

Sundqvist B, Roepstorff P, Fohlman J, Hedin A, Hakansson P, Kamensky M, Lindberg M, Salehpoour M, Save G (1984) Molecular Weight Determinations of Proteins by Californium Plasma Desorption Mass Spectrometry. Science 226 696... 

Saponins are too polar, too thermally unstable and not volatile enough to directly provide ions that are suitable for analysis. Until recently, derivatives (Me or TMS ethers) had to be prepared in order to obtain spectra. In the past ten years however, new techniques of soft ionization have emerged which have proved useful in the analysis of saponins. They are Field Desorption (FD), Fast Atom Bombardment (FAB), Laser Field Desorption (LD) and Californium Plasma Desorption (CPD). 

The technique of laser desorption/ionization (LDI) was introduced in the late l%Os [1-3], long before the advent of field desorption (FD, Chap. 8), californium plasma desorption ( Cf-PD, Chap. 10.7) or fast atom bombardment (FAB, Chap. 10). While low-mass organic salts and light-absorbing organic molecules are easily accessible by LDI [2,3], it takes a serious effort to obtain useful mass spectra of biomolecules [4], in particular when the mass of the analyte exceeds 2000 u [5,6]. FAB and Cf-PD therefore represented the standard in biomolecu-lar and biomedical mass spectrometry until the late 1980s, while LDI was regarded rather exotic [7]. 

Sundqvist, B. Macfarlane, R.D. Californium-252-Plasma Desorption-MS. Mass Spectrom. Rev. 1985, 4, 421-460. 

The application of molecular SIMS as a sensitive ionization source for nonvolatile and thermally labile molecules compares favorably with other new ionization methods in mass spectrometry such as field desorption (FD), Californium-252 plasma desorption (PD), fast heavy ion induced desorption (FHIID), laser desorp-... 

The rarest of these specialized techniques, californium-252 plasma desorption mass spectrometry, has not been applied extensively to inorganic systems, though in a 1983 review (115) Macfarlane quotes several examples, such as polymeric platinum blue, with molecular ions extending to m/z 3000. At present there are only 10 functioning systems and this certainly limits its growth. 

Mass Spectrometiy. Samples were introduced into a Californium-252 time-of-flight plasma desorption mass spectrometer in a 1% TFA solution applied to a nitrocellulose-covered aluminized Mylar foil. TTie samples were run at 15 kV accelerating volts with a 30-cm flight path, and the signal was accumulated for 19 hr (1),... 

Californium-252 time-of-flight plasma desorption mass spectrometry performed on 30 pmol of Hez-PbAN indicated two molecular ion peaks (Figure 4). The first peak at m/z 3934 [(M+ ) ], presumed to be the singly charged molecular ion, and a second broader peak centered at m/z 1966 [(M+2H) ], assumed to be the doubly-charged molecular ion, corresponded to molecular weights of 3933 and 3930, respectively. 

Because C-terminal amides have often been reported in insect neuropeptides (8), a 33 residue C-terminal amide consistent with the sequence data was synthesized by solid-phase methods. The peptide was purified by HPLC and its structure confirmed by automated Edman degradation. Californium-252 time-of-flight plasma desorption mass spectrometry provided additional evidence for the structure via a very broad peak for the singly-charged molecular ion at m/z 3902-3906. Because the calculated MW of Hez-PBAN (3899.6, based on the most abundant ion in the isotope cluster) was seen to differ from that observed in the mass spectrum of the isolated native peptide by ca. 32, it was presumed that the native peptide had undergone oxidation of both its methionines to their respective sulfoxides during the course of its isolation and purification. 

Figure 4. Partial Californium-252 time-of-flight plasma desorption mass spectrum of Hez-PBAN.

R. D. Macfarlane and D. F. Torgerson, Californium-252 plasma desorption mass spectroscopy, Science 191 (1976), 920-925. 

Macfarlane, R. D. and Torgerson, D. F. Californium-252-plasma desorption time-of-flight mass spectrometry. Int. ]. Mass Spectrom. Ion Phys. 21 81-92, 1976. 

Becher <90JA3709> has studied by californium-252 plasma desorption mass spectrometry the alkali metal ion complexation of a crown ether containing two pyrazole subunits. Rebek <93RTC330> prepared one of his famous molecular clefts with two 3-/-butylpyrazol-l-yl substituents. 

In 1980, using plasma desorption mass spectrometry with californium ( Cf), the exact molecular weight of PTX (1) was established as 2680 for the first time [13]. The planar stracture of 1 was eventually clarified in 1981 [14-16], and its complete stereostructure was elucidated in 1982 [17-20]. Finally, the true stereostructure of 1 was established by an overall degradation reaction and chemical synthesis in 1982. Kishi and his coworkers completed the total synthesis of palytoxin carboxylic acid (3) in 1989 [21, 22], and of PTX itself in 1994 (Figure 30.2) [23,24]. 

Californium-252 ( Cf) plasma desorption (PD) ionization, introduced in 1974 by Torgerson and co-workers [15], soon found applications for the analysis of large nonvolatile, polar, and thermally labile molecules [16,17]. Because of the pulsed nature of the plasma beam, PD is well adapted to TOF mass spectrometry. The basic concept of PD-TOFMS is illustrated in Figure 2.5. In this technique, the sample is deposited as a solid film on a thin aluminum foil or other suitable... 

B. Sundqvist and R. D. Macfarlane, Californium-252-plasma desorption mass spectrometry, Mass Spectrom. Rev. 2, 421-460 (1985). 

Another early desorption technique is that of plasma desorption mass spectrometry (PDMS). The sample is deposited onto a thin aluminum or aluminized polyester foil (0.5-1 pm in thickness) and placed just in front of a californium-252 emitter which is located in a time-of-flight (TOF) mass spectrometer (Figure 7). Californium is an a-emitter that decays into two highly energetic a-particles that are expelled in diametrically opposite directions. One of these particles collides with and ionizes the sample while the other hits a collection plate and triggers the timing circuit for the TOF mass spectrometer. 

Every 2 years, a special issue of Analytical Chemistry is published with a literature survey on the MS of polymers [10-12]. At least two other literature surveys are worthwhile to mention here because they provide a more in-depth review on specific topics than this review. One survey focuses exclusively on copolymers (i.e., with polymers in which two or more repeat units are found along the macromolecular backbone) [13]. A large part of this review deals with the determination of an important quantity, namely the relative abundance of the monomers (usually referred to as copolymer composition). A review by Klee [14] appeared in 2005 that deals exclusively with step-growth polymers. A section describes poly(imide)s in detail, especially with those made of PYM (pyromellitic anhydride), and PYM derivatives (even highly fluorinated, such as hexafluoro-PYM). Other sections of the review discuss plasma desorption MS experiments using a radioactive Californium nuclide, namely Ca. 

Aduru S, Chait BT. Californium-252 plasma desorption mass spectrometry of oligosaccharides and glycoconjugates control of ionization and fragmentation. Anal Chem. 1991 63 1621-5. 

McNeil CJ, Mac rlaine RD. Observation of a fully protected oligonucleotide dimer at m/z 12637 by californium-252 plasma desorption mass spectrometry. J Am Chem Soc. 1981 103 1609 10. 

Several recently developed techniques to enhance sample desorption capitalize on the transfer of kinetic energy to the sample through molecular collisions to produce desorbed positive and negative ions as well as desorbed neutral molecules. The more useful of these bombardment techniques include secondary ion mass spectrometry (SIMS), fast atom bombardment mass spectrometry (FAB-MS), and californium-252 plasma desorption mass spectrometry (252 Cf-MS). The sample can be deposited on an inert surface and directly bombarded in the solid state, or more commonly it is dissolved (or suspended) in an inert and nonvolatile medium such as glycerol. 

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