PFTBA

Resolution does not affect the accuracy of the individual accurate mass measurements when no separation problem exists. When performing accurate mass measurements on a given component in a mixture, it may be necessary to raise the resolution of the mass spectrometer wherever possible. Atomic composition mass spectrometry (AC-MS) is a powerful technique for chemical structure identification or confirmation, which requires double-focusing magnetic, Fourier-transform ion-cyclotron resonance (FTICR) or else ToF-MS spectrometers, and use of a suitable reference material. The most common reference materials for accurate mass measurements are perfluorokerosene (PFK), perfluorotetrabutylamine (PFTBA) and decafluorotriph-enylphosphine (DFTPP). One of the difficulties of high-mass MS is the lack of suitable calibration standards. Reference inlets to the ion source facilitate exact mass measurement. When appropriately calibrated, ToF mass... 

Mass spectrometers must be regularly tuned or calibrated against a known standard, e.g. perfluorotributy-lamine (PFTBA). The trend is towards miniaturisation (10 x 24 x 14 in.). A concept for a micro mass spectrometer, with potential applications in process monitoring, has been presented [167]. Mass-spectrometry instrumentation (1997) has been reviewed [166]. 

Diffusivities of xylene isomers in MCM-41 samples are of the same order of magnitude as in NaX zeolite indicating the existence of additional microporous structure in MCM-41 materials. On the other hand diffusion of bulkier 1-3-5 triisopropylbenzene (1,3,5 TIPB) is about one order of magnitude faster than in NaX indicating that diffusion of this sorbate, and of the bulkier perfluorotributylbenzene (PFTBA), occurs in the MCM-41 cylindrical mesopores. 

Figure ]. Effect of the nature of the purge gas on ZLC desorption curves for PFTBA on Al-MCM-41 sample (SiCVAfeO =19.7) at 100 °C.

The bulkier 1,3,5 TIPB showed about one order of magnitude faster diffusion in Si-MCM-41 than in NaX zeolite (16). Moreover, contrary to prevalent expectation, this molecule shows higher diffusivity than the smaller xylene isomers. These observations are indicative of the diffusion occurring in larger cylindrical pores (mesopores) of the Si-MCM-41 sample. However, diffusivity values of 1,3,5 TIPB, as well as PFTBA, are of the 10 9 cm2/s order, which is more typical of diffusion in zeolites and other microporous materials. The relatively slow diffusion of these molecules in the larger mesopores could be related to some hindrance effects resulting from structural defects and/or from the presence of extra-framework materials in the cylindrical mesopores. 

Before beginning ary analysis, an instrument must be checked for its performance. Every factory-built GC/MS instrument is equipped with a tuning substance, such as perfluorotributylamine (PFTBA). The characteristic mass ions of this compound (or any other tuning compound) and the relative area response corresponding... 

The two most widely used reference compounds for El are heptacosafluoro-tributylamine (PFTBA, (C4F9)3N) and perfluorokerosene (PFK, CF3-(CF2)n-CF3). 

Mass Spectrometer. The mass spectrometer was a Hewlett-Packard 5988A quadrupole mass spectrometer with a dual EI/CI source and positive and negative ion detection. The system was controlled by a Hewlett-Packard 1000 computer. The mass spectrometer was periodically tuned manually using perfluorotributylamine (PFTBA) on ions m/z 69, m/z 214, and m/z 502 in El and PCI modes, and on ions m/z 245, m/z 414, and m/z 633 in NCI mode. 

Accurate mass scales (or calibration curves) are generally established by measuring the mass spectrum of a reference compound simultaneously with the spectrum of the sample. The precise mass of every ion in the spectrum of the reference compound is known, so a precise mass correlation is thereby provided. Common reference materials are perfluorokerosene (PFK) and perfluorotributylamine (PFTBA), the mass spectra of which are shown in Figures 3.1 and 3.2, respectively. Since all the ions formed from these compounds contain several fluorine atoms (18.9984) and no hydrogen atoms (1.0078), they have negative mass defects and are well separated from organic ions that normally have positive mass defects. Of course, other chemicals may be used to provide reference masses, as long as the exact masses in its spectrum are known. 

Usually, ions of tn/z 69 and 414 from the calibration chemical PFTBA are used to find the values for the two parameters, A and B. The trapping frequency calibration is carried out near = 0.845 at a fixed RF trapping field. A linear relation between q xm and RF c is true only under ideal conditions but, as a first-order approximation, it works well for this two-step isolation method in a non-ideal quadrupole ion trap. Typically, in an ion trap for which the oscillation frequency of the RF potential is 1 MHz, the frequency error of the calibration is less than 1 kHz, which corresponds to an error of < 1 Th in the high-mass isolation step. The amplitude of the broadband waveform is determined empirically by the manufacturer and can be accessed by users. 

FIGURE 15.18 Top, a pseudo-product ion mass spectrum of m/z 264 of PFTBA but without collision-induced dissociation (CID) the mass spectrum was acquired with default isolation parameters and isolation window of 1 Th. Bottom, a full scan mass spectrum of PFTBA obtained with the same duration of ionization and showing both the m/z 264 peak and the C-isotopomer peak at m/z 265. By comparison, loss of the m/z 264 ion during the isolation process is essentially zero for this chemically-stable ion. For chemically-unstable ions, loss of precursor ion during mass-selective isolation can be minimized by using an isolation window of 3-5 Th. 

Figure 9 Mass spectra obtained from PFTBA with two miniature CiTs. (A) A iower mass range obtained with version 5 miniature CiT. (B) A higher range mass spectrum, aiso of PFTBA, obtained with version 7miniature CiT. (Reproduced with permission from Patterson GE, Guymon AJ, Riter LS, ef a/. (2002) Miniature cyiindricai ion trap mass spectrometer. Analytical Chemistry 74 6145-6153. Copyright 2002, by American Chemicai Society.)...

TRMS can provide information about possible artifacts related to the operation of standard analytical equipment (including ion sources and mass analyzers). Perfluorotri-n-butylamine (PFTBA) is often used as a calibration standard in EI-MS. Greaser et al. [206] observed products of the reaction of PFTBA ions with neutral species (residual water) in an ion trap. They monitored the buildup of the product of this reaction on a... 

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