Functional group analysis indirect methods

This chapter examines the fundamental structural properties of organic molecules that directly or indirectly affect pKa values of organic acids, making it possible to estimate theoretical upper limits for concentrations of common acidic functional groups, to assess methods of quantitative analysis of acidic functional groups in humic substances, and to examine several models that have been proposed for the description of proton binding by humic substances. Some of the concepts that appear obvious in the context of this chapter have been included for the simple reason that the literature on acidity of humic substances reveals that these points have frequently been either misunderstood or neglected. 

An indirect method for the determination of amino groups from the excess of unreacted reagents, namely, acrylonitrile [59, 113, 114] and benzaldehyde [115], has been developed and is based on converting the amines into volatile and stable derivatives. These indirect methods, although developed for GC analysis, are of interest as methods of functional group analysis. 

Organic Analysis Several organic functional groups or heteroatoms can be determined using gravimetric precipitation methods examples are outlined in Table 8.5. Note that the procedures for the alkoxy and alkimide functional groups are examples of indirect analyses. 

NADH, containing a tertiary amine functional group, has been readily determined by Ru(bpy)32+ ECL. However the oxidized form, NAD+, containing an aromatic secondary amine group produces virtually no ECL signal. This had led to a variety of indirect enzymic methods of analysis, where the activity of the enzyme results in the conversions between NAD+ and NADH. These are discussed in Sec. 8. 

Numerous descriptions of methods of analysis of the acidic functional groups of humic substances have been published (e.g., Stevenson and Butler, 1969 Schnitzer and Khan, 1972 Stevenson, 1982). The published methods include direct titrations, discontinuous titrations, indirect titrations, indirect titrations coupled with either a distillation or ultrafiltration step, thermometric titration methods, nonaqueous titrations, irreversible reactions of acidic hydrogens with various organic and inorganic reagents, and so on. The two most commonly described methods are the barium hydroxide... 

Due to the lack of suitable functional groups in steroid hormones, titrimetry has never played an important role in steroid hormone analysis. Of the several indirect methods, however, one is still widely used all pharmacopoeias contain methods for the determination of ethinyl steroids on the basis of the exchange of the acetylenic hydrogen for silver ions and the titration of the liberated acid with standard sodium hydroxide. 

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