Probe analysis, direct

Purification of the radioactive tracer was modified to include a fractional sublimation before a single extraction—recrystallization cycle to conserve the tracer material. Microgram samples were prepared in melting point capillaries for assay by mass spectroscopic analysis (Table III), made by direct probe injection of the sample into the ion source (18). The probe was heated rapidly to 200°C, and mass spectra were obtained during vaporization of the sample. Tri-, tetra-, and pentachlorodibenzo-p-dioxins vaporized simultaneously with no observed fractionation. 

Identification. One compound isolated by TLC was found to be very inhibitory to morningglory seed germination and was identified using mass spectrometry. A LKB 2091 GC-MS was used for GC-MS analysis. In addition to GC-MS, the sample was also analyzed by direct probe. 

Plasticiser/oil in rubber is usually determined by solvent extraction (ISO 1407) and FTIR identification [57] TGA can usually provide good quantifications of plasticiser contents. Antidegradants in rubber compounds may be determined by HS-GC-MS for volatile species (e.g. BHT, IPPD), but usually solvent extraction is required, followed by GC-MS, HPLC, UV or DP-MS analysis. Since cross-linked rubbers are insoluble, more complex extraction procedures must be carried out. The determination of antioxidants in rubbers by means of HPLC and TLC has been reviewed [58], The TLC technique for antidegradants in rubbers is described in ASTM D 3156 and ISO 4645.2 (1984). Direct probe EIMS was also used to analyse antioxidants (hindered phenols and aromatic amines) in rubber extracts [59]. ISO 11089 (1997) deals with the determination of /V-phenyl-/9-naphthylamine and poly-2,2,4-trimethyl-1,2-dihydroquinoline (TMDQ) as well as other generic types of antiozonants such as IV-alkyl-AL-phenyl-p-phenylenediamines (e.g. IPPD and 6PPD) and A-aryl-AL-aryl-p-phenylenediamines (e.g. DPPD), by means of HPLC. 

It is of interest to examine the development of the analytical toolbox for rubber deformulation over the last two decades and the role of emerging technologies (Table 2.9). Bayer technology (1981) for the qualitative and quantitative analysis of rubbers and elastomers consisted of a multitechnique approach comprising extraction (Soxhlet, DIN 53 553), wet chemistry (colour reactions, photometry), electrochemistry (polarography, conductometry), various forms of chromatography (PC, GC, off-line PyGC, TLC), spectroscopy (UV, IR, off-line PylR), and microscopy (OM, SEM, TEM, fluorescence) [10]. Reported applications concerned the identification of plasticisers, fatty acids, stabilisers, antioxidants, vulcanisation accelerators, free/total/bound sulfur, minerals and CB. Monsanto (1983) used direct-probe MS for in situ quantitative analysis of additives and rubber and made use of 31P NMR [69]. 

Although the feasibility of direct probe MS for the analysis of additives in complex polymeric matrices has been demonstrated (Section 6.4), application is limited, difficult and requires above-average mass-spectroscopic expertise. Direct desorption in the MS probe is usually limited to screening of volatile components. Direct multicomponent spectroscopic analysis has other hurdles to overcome (UV/VIS lack of spectral discrimination IR/R functional-group recognition only, with no discriminative power for additives with similar functionalities NIRS unsuitable for R D problems NMR sensitivity). 

If we consider only a few of the general requirements for the ideal polymer/additive analysis techniques (e.g. no matrix interferences, quantitative), then it is obvious that the choice is much restricted. Elements of the ideal method might include LD and MS, with reference to CRMs. Laser desorption and REMPI-MS are moving closest to direct selective sampling tandem mass spectrometry is supreme in identification. Direct-probe MS may yield accurate masses and concentrations of the components contained in the polymeric material. Selective sample preparation, efficient separation, selective detection, mass spectrometry and chemometric deconvolution techniques are complementary rather than competitive techniques. For elemental analysis, LA-ICP-ToFMS scores high. 

Oscillatory shear experiments are the preferred method to study the rheological behavior due to particle interactions because they directly probe these interactions without the influence of the external flow field as encountered in steady shear experiments. However, phenomena that arise due to the external flow, such as shear thickening, can only be investigated in steady shear experiments. Additionally, the analysis is complicated by the different response of the material to shear and extensional flow. For example, very strong deviations from Trouton s ratio (extensional viscosity is three times the shear viscosity) were found for suspensions [113]. 

Reactor vessels range in volume from 1.2 to 2.5 liters. The size used may be dependent on the pressure application requirements. A high-pressure reactor can run up to about 60 bar. Porting is provided on the reactor vessel for auxiliary probes (e.g, oxygen sensors, pH measurement, and on-line analysis). These probes may be inserted directly into the reactor contents. Porting is also available for the controlled addition of gas, liquid, or solid materials. 

Direct probe mass spectrometry. Glycosphingolipids (30-100 pg) were permethylated as described (12). The samples (less than 5 p g) were subjected to electron impact/desorption analysis with a Varian MAT CH-5 DF mass spectrometer under the following conditions emission current, 300pA electron energy, 70 eV acceleration voltage, 3KV ion source temperature, 160° C emitter wire current, programed from 0 to 35mA. 

Direct probe analysis. The spectra of the methylated derivatives of fractions I-IV are shown in Figure 2 (a-d), together with abbreviated structured formulas and indications of some fragments (Refs. l-6 were consulted for comparison). Only fraction I gave ions indicative of the entire molecule at m/z 894 (M-l) and m/z 863 (M-32) for a monoglycosyl-ceramide containing Cj6>q fatty acid and Cjg.j long chain base. 

The FAB ionization technique was originally described by Barber et al. in 1981 (3). FAB is a direct probe technique suitable for the analysis of high molecular weight polar organic compounds. In FAB the sample is dissolved in a matrix such as glycerol or thioglycer-... 

In contrast to the mass spectrum of a compound obtained by direct probe measurement, the spectrum of the same compound obtained by GC-MS analysis does not contain meta-stable ions. The absence of these ions makes the interpretation of mass spectra obtained by GC-MS analysis more difficult than those obtained by direct probe measurement. In addition, during editing of mass spectral data (see Sect. 9.1.3.4), the ratio of the relative intensity of an ion fragment at m/z p to its naturally occurring 13C isotope ion peak at m/z (p + 1) may be distorted. 

Physical and spectral properties of batrachotoxins are presented in Table I. Mass spectra have been presented and interpreted (3,13,14). The parent ion of batrachotoxin is virtually nondetectable by direct probe methods, and instead an apparent molecular ion of miz 399 is seen, probably because of pyrolytic elimination of the pyrrole carboxylate moiety. Batrachotoxin alkaloids do not chromatograph on capillary gas chromatographic columns, but a pyrolysis product has been detected at 280°C on the temperature-programmed, packed OV-1 columns used for analysis of other dendrobatid alkaloids (see Appendix). The pyrrole carboxylate moiety is responsible for major ions of C7H9N02 (m/z 139), C6H9N ... 

We have already seen that, depending on the values of the reactivity ratios, there is a tendency to get random, alternating, blocky, etc., types of copolymers. Probability theory allows us to quantify this in terms of the frequency of occurrence of various sequences, like the triads AAA or ABA in a copolymerization of A and B monomers. The value of this information is that such sequence distributions can be measured directly by NMR spectroscopy, thus allowing a direct probe of copolymer structure and an alternative method for measuring reactivity ratios. As mentioned above, there are problems, as some spectra can be too complex and rich for easy analysis, as we will see in Chapter 7. 

Furthermore, we have shown that oxidation in air can also be used to control the average crystal size in ND powders with subnanometer accuracy. Three different characterization techniques were used for measuring the crystal size because such analysis is very complex for nanocrystals. While HRTEM is able to visualize ND crystals, the calculated size distributions are statistically not reliable and the average size is often overestimated. Agglomeration and difficulties in sample preparation do not allow accurate estimates on average crystal size values. XRD, which directly probes the crystalline structure of a material, is more reliable in terms of statistics and average values, but lattice distortion and strain can interfere with size effects in XRD pattern and lead to an incorrect interpretation of the results. 

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