Nitrogen compounds soil extractions

We first deal with humic substances extracted from soils formed under different climates because climate, as will be shown later, has a profound effect on the types and concentrations of nitrogen compounds present in humic substances. 

Generally amino acids are extracted from the soil by refluxing in 6M HCl for up to 24h. The conditions for maximal extraction have been thoroughly investigated. Once extracted, the amino acids are usually estimated by reaction with ninhydrin. Ammonium ions and amino sugars in the hydrolysate react with ninhydrin, but non-nitrogenous compounds such... 

The aroma compounds from the tropical fruits described in this chapter can be very important for consumers and industry as they are exotic and extremely pleasant however, the production of these compounds by biotechnological processes should be emphasised since the extraction from the fruits is a hard task. Many tropical soils contain less nitrogen and phosphorus, have lower capacity to absorb fertilisers, and therefore have lower conventional productive capacity, but some tropical soils have been very intensively farmed and further intensification is possible in other areas. Thus, the evaluation of a sustainable agriculture in tropical regions requires a sophisticated approach including the estimation of the risk of microbial or insect infestations. As many fruits go directly to fresh markets or to immediate processing, a continuing supply of the flavour manufacturers in the future is not completely assured. 

Roche and Miller [192] have shown that ultrasonic extraction gives more accurate results when compared with a heated nitrogen purge in the determination of volatile organic compounds in soils. 

Greco [40] determined optimal extraction conditions for the recovery of nitrogen-containing aromatic compounds from soil. 

Purines and pyrimidines are components of nucleic acids and are known to occur in soils. According to Bremner (1967), the nitrogen in purines and pyrimidines accounts for less than 1% of the total soil nitrogen. Much of the earlier information on the presence of these compounds comes from G. Anderson (1957, 1958, 1961) who identified guanine, adenine, cytosine, thymine, and traces of uracil in acid hydrolyzates of humic acids extracted from three Scottish soils. Anderson used paper and ion-exchange chromatography to detect and estimate the concentrations of nucleic acid bases. More... 

HSs can be purchased from a few commercial chemical companies (Aldrich, Fluka, etc.). The origin of these compounds or the method of extraction is unknown, but are probably derived from soil, coal or peat. Characteristics and quality varj from batch to batch and the colour of these products is very dark. Commercial HAs often have a high ash content. HA and FA from soils and waters are usually very different from the commercial ones (Malcolm and MacCarthy (1986)). Commercial products are often much larger in size and need to be purified. They were also found to be very similar to peat and should not be used to simulate water HSs behaviour (Malcolm and MacCarthy (1989)). Other authors found that commercial HS contain a large amount of residual components and a much lower nitrogen content than typical aqueous HS. Their use for studies has not been recommended (Legube et al. (1990)). 

Studies involving bile salts in EKC separations include (i) determination of i -triazines and quats in well water samples (ii) separation of the 16 priority pollutant PAHs for inspection in ambient air samples (iii) characterization of the electrophoretic behavior of 56 aromatic compounds (phenoxy acid herbicides, phenylalkanoic acids, aromatic carboxylic acids, aromatic sulfonic acids, azo and other dyes, and nitrogen-containing aromatic acids) for further assessment of extraction and sample clean-up procedures using spiked water and soils and (iv) recovery of synthetic dyes from spiked water and soil matrices. Another interesting application of MEKC with diverse bile salts is the prediction of ecotoxicity of aromatic compounds. ... 

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