Intact sampling

Electron ionization occurs when an electron beam crosses an ion source (box) and interacts with sample molecules that have been vaporized into the source. Where the electrons and sample molecules interact, ions are formed, representing intact sample molecular ions and also fragments produced from them. These molecular and fragment ions compose the mass spectrum, which is a correlation of ion mass and its abundance. El spectra of tens of thousands of substances have been recorded and form the basis of spectral libraries, available either in book form or stored in computer memory banks. 

Lately, electrospray ionisation technique (ESI-MS) which is compatible with RP-HPLC has been routinely used. This allows labile molecules to be studied intact. Sample molecules are simultaneously nebulised and ionised at atmospheric pressure in the presence of several thousand volts. The resulting ions can be multi-protonated (multiply charged) and relatively stable. This mode of ionisation has recently been used in the development of RP-HPLC coupled with positive ion ESI-MS and ion-trap MS protocols for the identification and... 

Solid-state 13C NMR was employed to characterize intact samples of cutin and suberin biopolyesters. Although a considerable degree of structural heterogeneity was observed for both materials, it was possible nonetheless to resolve and assign many NMR peaks, even when the polyesters were accompanied by waxes or cell walls. Quantitative estimates for the various aliphatic, aromatic, and carbonyl carbon types indicated that cutin was primarily aliphatic in composition, whereas suberin had more aromatic and olefinic moieties. Additional analysis should be facilitated by the biosynthetic incorporation of selectively 13C-enriched precursors (26,27). 

FIGURE 2.36 " Al MAS NMR spectra at 104.2 MHz obtained on faujasite samples at various stages of the SiCU dealumination procedure (a) starting faujasite sample, (h) intact sample after reaction with SiCU before washing, (c) sample (b) after washing with distilled water, and (d) after several washings. 

FIGURE 3-27 Cleaving proteins and sequencing and ordering the peptide fragments. First, the amino acid composition and amino-terminal residue of an intact sample are determined. Then any disulfide bonds are broken before fragmenting so that sequencing can proceed efficiently. In this example, there are only two Cys (C) residues and... 

Figure 5.1.2 Matrix solid-phase dispersion (MSPD) extraction as a micro-preparative extraction technique for an on-flow LC-NMR-MS screening. Since the latter requires only sample amounts in the 0.5-2 mg range, the sample preparation can be achieved by fast small-scale extraction procedures, such as MSPD. This is a sample preparation technique that combines both sample homogenisation and extraction of compounds of interest in one single step starting from the intact sample material. Thus, it simplifies the extraction and clean-up steps, reduces the sample manipulation and is much faster than conventional techniques. It is therefore very well suited for a rough separation of extracts into classes of compounds of similar polarities, which can then be submitted to LC-NMR-MS analysis...

NMR spectroscopy, with its array of unique characteristics and capabilities, is playing a key role in the field of metabolomics. Specifically, the high reproducibility, excellent quantitation and ability to analyze intact samples offer numerous opportunities to understand systems biology, discover biomarkers,... 

The process involves the use enzymatic and chemical techniques to cut a second, intact sample into smaller and smaller pieces. Because these techniques cut heparin fragments at specific sites, each piece provides structural information at reducing and non-reducing ends. In addition, the mass of each of these... 

Other spectroscopic methodologies such as infrared and Raman spectroscopies should be developed to allow the determination of the presence of molecules in intact samples (Chenery and Bowring, 2003). 

The basic properties of the rock matrix were determined from laboratory tests on intact samples and were provided by JNC (2000). Typical values are effective porosity 0.379 % Young s modulus 61 GPa Poisson s ratio 0.303 coefficient of linear thermal expansion 8.21x 10 °C thermal... 

After the first 5700 years of decay, 50% of the original sample is left. After 5700 more years, 50% of that sample will have decayed, which means that there is now 25 % of the original intact sample. This is the amount of time that the question is asking for. To be clear about our analysis, let s rephrase what we have said. We have 25% of the original sample left at this point. Thus the decay of 75% of the original sample is complete. So the answer is 5700 x 2 = 11400 years. 

Simple lahoratory and field strength test. Useful aid to core logging Carried out on intact samples with no discontinuities and yields data on the rock material properties. The length to diameter ratio of 2 1 is a minimum for cylinders... 

Usually carried out on intact samples with no discontinuities and yield data on rock material properties. Larger samples may contain one or more discontinuities, in which case the data relates to the properties of the rock mass... 

In early mass spectrometry applications of lasers, the sample was irradiated directly by a laser beam to desorb intact sample-related ions [27]. In this direct mode, termed laser desorption/ionization (LDI), the extent of energy transfer is, however, difficult to control and often leads to excessive thermal degradation. Also, not all compounds absorb radiation at the laser wavelength and thus are not amenable to LDI. Only those compounds that have mass below 1000 Da can be analyzed by LDI. Analytical sensitivity is also poor. A key contribution of LDI experiments is the observation that the desorption efficiency of amino acids and peptides that absorb the laser fight beam is greater than those without the chromophore [28]. IR lasers (e.g., an Nd YAG laser at 1.06 p m and a pulsed CO2 laser at 10.6 pm) and UV lasers (frequency-quadrapled Nd YAG laser at 266 nm) have aU been used. The detection of malaria parasites in blood by LDI with an N2 laser has been demonstrated [29]. 

Fig. 2. The effect of the addition of 25 p,M DBMiB to D1/D2 reaction centres. (A) shows the fluorescence decay of an inactive sampie, with a Qy band absorption maximum at 672.9 nm, before the addition of the quinone. After the addition of 25 mM DBMiB there was no change to the fiuorescence decay, in (B) curve (1) shows a typicai fluorescence decay of an intact D1/D2 sample, with a Qy band absorption maximum of 675.9nm, before the addition of DBMIB. Curve (2) is the fluorescence decay of an intact sample containing 25 pM DBMIB. This sample had not previously been exposed to laser light.

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