Other Instrumental Methods

7 OTHER INSTRUMENTAL METHODS 3.7.1 Atomic Eorce Microscopy 

As the preceding discussion of nitrogenase metal-sulfur clusters indicate, analysis of complex bioinorganic systems requires the use of multiple analytical techniques and the cooperative exchange of data and ideas of many researchers. The descriptions in this chapter have attempted to give students some idea of the scope and complexity of instrumental techniques available to the bioinorganic chemist. It has not been intended to be either comprehensive or theoretical in presentation. Students are encouraged to acquaint themselves further with the theory and practice of instrumental techniques, especially those that are important to their particular research interests. 

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Branching in the polymer chain affects the relationship between retention and molecular weight.83 Universal calibration has been used with some success in branched polymers, but there are also pitfalls. Viscosimetry84-91 and other instrumental methods have proved to be useful. A computer simulation of the effects of branching on hydrodynamic volume and the detailed effects observable in GPC is available in the literature.92 93 In copolymer analysis, retention may be different for block and random copolymers, so universal calibration may be difficult. However, a UV-VIS detector, followed by a low-angle light-scattering (LALLS) detector and a differential... 

Elemental composition (anhydrous salt) Co 32.33%, N 15.31%, 0 52.47%. The aqueous solution may be analyzed for cobalt by AA or ICP or other instrumental methods. The nitrate anion may be measured by ion chromatography or nitrate ion-selective electrode. The solutions may require sufficient dilution for all these measurements. 

Elemental composition Co 32.47%, C 28.10%, O 37.43%. Cobalt octacarbonyl may be digested with nitric acid, diluted appropriately, and analyzed by AA, ICP, or other instrumental methods (see Cobalt). The compound may be dissolved in methanol and the solution analyzed by GC/MS. 

Elemental composition Au 77.56%, F 22.44%. Gold(lll) fluoride may be characterized by x-ray techniques. The concentration of gold may be determined by AA and other instrumental methods following digestion in aqua regia and appropriate dilution. 

Elemental composition Hf 55.73%, Cl 44.27% The acid extract of hafnium tetrachloride may be analyzed for hafnium by AA or other instrumental methods (See Hafnium). 

Elemental composition Pb 64.11%, Cr 16.09%, O 19.80%. Lead chromate may be identified from its physical properties and x-ray crystallography. Lead and chromium can be measured in a nitric acid solution of the compound by AA, ICP, and other instrumental methods. (See Lead.)... 

Elemental composition Ni 78.58%, O 21.42%. Nickel may be analyzed in a diluted solution of the oxide in nitric acid by AA, ICP and other instrumental methods. The oxide may be identified from its physical properties and by x-ray diffraction. 

Elemental composition (in anhydrous NiS04) Ni 37.93%, S 20.72%, 0 41.35%. The water content in hexahydrate, NiS04 6H20, and heptahydrate, NiS04 7H20, are 41.12% and 47.98%, respectively. Nickel may be analyzed in aqueous solution by AA, ICP, and other instrumental methods (see Nickel). Sulfate may be analyzed in aqueous solution by ion chromatography. The compound may be characterized by x-ray methods. 

Elemental composition K 44.87%, S 18.40%, and O 36.73%. Potassium content may be determined by analyzing an appropriately diluted aqueous solution for the metal by AA, ICP, or other instrumental methods (see Potassium). The sulfate concentration may be measured by ion chromatography or gravimetry following precipitation with barium chloride. 

Elemental composition Ag 65.03%, Cr 15.68%, 0 19.29%. The salt is dissolved in nitric acid, diluted, and analyzed for silver and chromium by flame-and furnace-AA, ICP-AES or other instrumental method to measure the contents of these metals. 

Water of crystaUization in hydrated salts can be measured by thermo-gravimetric analysis. Zinc can be analyzed in an aqueous solution by AA or ICP. Sulfate can be identified by precipitation with barium chloride solution or by ion chromatography. The zinc content in the heptahydrate is determined by AA, ICP and other instrumental methods. 

Numerous methods have been published for the determination of trace amounts of tellurium (33—42). Instrumental analytical methods (qv) used to determine trace amounts of tellurium include atomic absorption spectrometry, flame, graphite furnace, and hydride generation inductively coupled argon plasma optical emission spectrometry inductively coupled plasma mass spectrometry neutron activation analysis and spectrophotometry (see Mass SPECTROMETRY Spectroscopy, OPTICAL). Other instrumental methods include polarography, potentiometry, emission spectroscopy, x-ray diffraction, and x-ray fluorescence. 

As with other techniques, a single instrument is usually not sufficient for full analysis of organophosphorus residues. HPLC is often combined with other instrumental methods, mostly GLC, TLC or mass spectrometry. A recently suggested procedure for the analysis of residues found in potatoes requires the use of three different HPLC and three different GLC instruments for the study of one sample183. 

ISO 1431-3 specifies that the calibration of the ozone meter is carried out in accordance with ISO 1396443 which is the general standard for determination of ozone concentration by UV photometry. The operation of UV meters is also to be in accordance with ISO 13964. The other allowed methods are electrochemical, chemiluminescence and wet chemical. Other instrumental methods are operated in accordance with the manufacturer s instructions (having been calibrated to ISO 13964) whilst the wet chemical methods are given in detail in an appendix. Although not referenced, there is also a general method using chemiluminescence44. 

More recently, enantiomer ratios have been used as evidence of adulteration in natural foods and essential oils. If the enantiomer distribution of achiral component of a natural food does not agree with that of a questionable sample, then adulteration can be suspected. Chiral GC analysis alone may not provide adequate evidence of adulteration, so it is often used in conjunction with other instrumental methods to completely authenticate the source of a natural food. These methods include isotope ratio mass spectrometry (IRMS), which determines an overall 13C/12C ratio (Mosandl, 1995), and site-specific natural isotope fractionation measured by nuclear magnetic resonance spectroscopy (SNIF-NMR), which determines a 2H/ H ratio at different sites in a molecule (Martin et al 1993), which have largely replaced more traditional analytical methods using GC, GC-MS, and HPLC. 

Once a separation is developed, several pieces of information about the sample can be ascertained from the chromatogram. First, by counting the peaks, one can estimate how many components are present in the mixture. Second, by the use of standards, both the identity and concentration of each compound present can be obtained. Lastly, if the mixture is totally unknown, the peaks can be collected and the identity confirmed by other instrumental methods of chemical analysis (e.g., infrared, nuclear magnetic resonance, or mass spectroscopy). 

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