Composition, elemental

Micro Limiting Dilution Composition (% by wt) Empirical Formula 

Multienzyme complexes, Ribosomes, Chromosomes, Membranes, Structual elements. Contractile systems 

A typical molecular analysis of various micro-organisms is shown in Table 5.9U ) Most of the elemental composition of cells is found in three basic types of materials—proteins, nucleic acids and lipids. In Table 5.10, the molecular composi-tion of a bacterium is shown in more detail. Water is the major component of the cell and accounts for 80-90 per cent of the total weight, whilst proteins form the next most abundant group of materials and these have both structural and functional properties. Most of the protein present will be in the form of enzymes. Nucleic acids are found in various forms—ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). Their primary function is the storage, transmission and 

Microorganism Protein Composition (% dry wt) Nucleic acid Lipid Population in Dry weight culture in culture (numbers ml ) (g (100 ml) ) Comments 

Fungi (filamentous) 10-25 1-3 2-7 3-5 Some Aspergillus and Penicillium species contain 50% lipid 

In the present context, petrolenm composition is defined in terms of (1) the elemental composition, (2) the chemical composition, and (3) the fractional composition. All three are interrelated, althongh the closeness of the elemental composition makes it difflcnlt to relate precisely to the chemical and fractional composition. The chemical and fractional composition are somewhat easier to relate becanse of the qnantities of heteroatoms (nitrogen, oxygen, snlfnr, and metals) that occnr in the higher-boiling fractions. 

The elemental composition of petrolenm varies greatly from crude oil to crude oil. Most compounds in petrolenm (nsnally more than 75%) are types of hydrocarbons, and the majority of the chemical components in petroleum are made 

The set-up of elemental and enthalpy balances constitutes the basis for the consistency check of experimental data from biotechnological processes. For that purpose, the exact composition and physico-chemical characterization of all species involved in the process under study has to be determined including biomass. Another use is the design of the growth medium or the investigation of possible stoichiometric limitation by the medium supply. We chose to take into account all atoms bound in the main macromolecules whereas other atoms, mainly present as ions in biomass (K, Ca, Na. ..), are not incorporated in the elemental formula [28]. One C-mol of biomass is defined as C.H, O, N S, R 

Except in gas-phase processes (not discussed here), carbons derive mostly from thermal conversion of macromolecules (or polymers) either present in nature as biomass (coalification) or industrially available from heavy oil or coal derivatives 

Examples of Coalification and Carbonization of Various Substances (Main Parameters Given Are Local Molecular Orientation [LMO] Occurrence, Solidification, and Elemental Analysis [C, mo]) 

Notes Asphaltenes IC7, heptane insoluble IC5, pentane insoluble refinery residues AR, atmospheric residue VR, vacuum residue. HV Vickars microhardncs.s measurement for solidification tempara-ture. If LMO occurrence is obtained by Fourier transform infirared (FUR), electron spin resonance (ESR), reflectance, or viscosity measirrements, an asterisk ( ) is used. 

FIGURE 1.27 van Krevelen diagram for carbonaceous materials carbonization steps for kerogens and coals. (Adapted from D.W. van Krevelen. Coal. 3rd ed. Elsevier, Amsterdam 1993, 979 pp. (a) see pp. 173-332 (b) see pp. 627-658. With permission.) 

Attempts to include heteroatom contribution in the crystallographical calculations, or at least in texture and structure evaluations, began with the pioneering papers by Warren [71,72] and Ergun [12,13] on coals, but they were restricted to hydrogen. 

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The determination of the elemental composition of a petroleum cut is of prime importance because it provides a quick means of finding out the quality of a given cut or determining the efficiency of a refining process. In fact, the quality of a cut generally increases with the H/C ratio and in all cases, with a decrease in hetero-element (nitrogen, sulfur, and metals) content. 

A microbe employs a focused beams of energetic ions, to provide infomiation on the spatial distribution of elements at concentration levels that range from major elements to a few parts per million [27]. The range of teclmiques available that allowed depth infomiation plus elemental composition to be obtained could all be used in exactly the same way it simply became possible to obtain lateral infomiation simultaneously. 

The quantitative imaging capability of the NMP is one of the major strengtiis of the teclmique. The advanced state of the databases available for PIXE [21, 22 and 23] allows also for the analysis of layered samples as, for example, in studying non-destmctively the elemental composition of fluid inclusions in geological samples. 

What particularly seemed to excite Wohler and his mentor Berzelius about this experiment had very little to do with vitalism Berzelius was interested m cases m which two clearly different materials had the same elemental composition and he invented the term isomerism to define it The fact that an inorganic compound (ammonium cyanate) of molecular formula CH4N2O could be transformed into an organic compound (urea) of the same molecular formula had an important bearing on the concept of isomerism... 

Quantitative Calculations When needed, the relationship between the analyte and the analytical signal is given by the stoichiometry of any relevant reactions. Calculations are simplified, however, by applying the principle of conservation of mass. The most frequently encountered example of a direct volatilization gravimetric analysis is the determination of a compound s elemental composition. 

In general terms, the main function of the magnetic/electric-sector section of the hybrid is to be able to resolve m/z values differing by only a few parts per million. Such accuracy allows highly accurate measurement of m/z values and therefore affords excellent elemental compositions of ions if these are molecular ions, the resulting compositions are in fact molecular formulae, which is the usual MS mode. Apart from accurate mass measurement, full mass spectra can also be obtained. The high-resolution separation of ions also allows ions having only small mass differences to be carefully selected for MS/MS studies. 

In one instrument, ions produced from an atmospheric-pressure ion source can be measured. If these are molecular ions, their relative molecular mass is obtained and often their elemental compositions. Fragment ions can be produced by suitable operation of an APCI inlet to obtain a full mass spectrum for each eluting substrate. The system can be used with the effluent from an LC column or with a solution from a static solution supply. When used with an LC column, any detectors generally used with the LC instrument itself can still be included, as with a UV/visible diode array detector sited in front of the mass spectrometer inlet. 

High-Resolution, Accurate Mass Measurement Elemental Compositions... 

There is a more important use. Suppose a mass spectrometer has accurately measured the molecular mass of an unknown substance as 58.04189. Reference to tables of molecular mass vs. elemental composition will reveal that the molecular formula is CjH O (see Table 38.2). The molecular formula for an unknown substance can be determined which is enormously helpful in identifying it. 

A Listing of Elemental Compositions vs. Accurate Mass at Nominal Integer Mass of 58... 

By high-resolution mass spectrometry, ions of known mass from a standard substance can be separated from ions of unknown mass derived from a sample substance. By measuring the unknown mass relative to the known ones through interpolation or peak matching, the unknown can be measured. An accurate mass can be used to obtain an elemental composition for an ion. If the latter is the molecular ion, the composition is the molecular formula. 

Gases and volatile materials can be swept into the center of an argon plasma flame, where they are fragmented into ions of their constituent elements. The m/z values of ions give important information for identification of the elemental composition of a sample, and precise measurement of ion abundances is used to provide accurate isotope ratios. 

This hybrid is used in one form to measure highly accurate m/z values to obtain excellent elemental compositions of ions and therefore molecular formulae from molecular ions in the other form, it is used to obtain MS/MS data at high resolution. 

In theory, this process can be reversed in that any measured mass leads to an elemental composition. For example, a measured value of 17 would imply the composition, NH3. 

In practice, other elemental compositions could add up to 17. For example, OH (oxygen = 16, hydrogen = 1), CDHj (carbon = 12, deuterium = 2). 

For larger masses, the possibilities increase enormously. At mass 100, there would be literally thousands of possible elemental compositions so that, although integer mass can be measured mass spectromet-rically, attempts to obtain elemental compositions will not lead to a definite answer. 

Even for large molecules, the ability to measure accurate mass means that elemental compositions can be obtained from the accurately measured molecular mass. 

Accurate mass measurement on a molecular ion of any substance gives directly the molecular formula for fragment ions, similar measurement gives their elemental compositions. 

The double-focusing mass spectrometer is arguably the finest instrument for obtaining molecular and elemental compositions. 

A double-focusing mass spectrometer can mea.sure mass accurately to several decimal places, thus enabling the determination of molecular formulae and elemental compositions of fragment ions. 

Emission spectroscopy is a very useful analytical technique in determining the elemental composition of a sample. The emission may be produced in an electrical arc or spark but, since the mid-1960s, an inductively coupled plasma has increasingly been used. 

Fig. 4. Scanning electron micrograph of 5-p.m diameter Zn powder. Neck formation from localized melting is caused by high-velocity interparticle coUisions. Similar micrographs and elemental composition maps (by Auger electron spectroscopy) of mixed metal coUisions have also been made.

Other techniques in which incident photons excite the surface to produce detected electrons are also Hsted in Table 1. X-ray photoelectron Spectroscopy (xps), which is also known as electron spectroscopy for chemical analysis (esca), is based on the use of x-rays which stimulate atomic core level electron ejection for elemental composition information. Ultraviolet photoelectron spectroscopy (ups) is similar but uses ultraviolet photons instead of x-rays to probe atomic valence level electrons. Photons are used to stimulate desorption of ions in photon stimulated ion angular distribution (psd). Inverse photoemission (ip) occurs when electrons incident on a surface result in photon emission which is then detected. 

Analysis of Surface Elemental Composition. A very important class of surface analysis methods derives from the desire to understand what elements reside at the surface or in the near-surface region of a material. The most common techniques used for deterrnination of elemental composition are the electron spectroscopies in which electrons or x-rays are used to stimulate either electron or x-ray emission from the atoms in the surface (or near-surface region) of the sample. These electrons or x-rays are emitted with energies characteristic of the energy levels of the atoms from which they came, and therefore, contain elemental information about the surface. Only the most important electron spectroscopies will be discussed here, although an array of techniques based on either the excitation of surfaces with or the collection of electrons from the surface have been developed for the elucidation of specific information about surfaces and interfaces. 

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

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