Volatilization from water error analysis

Many of the tests described involve physical properties such as refractive index, viscosity or melting point of the fat, of the fatty acids or of the lead salts of the fatty acids. However, there were also many chemical tests such as Reichert, Polenske, iodine, saponification and acetyl values. These all gave information as to the composition of the fat, some information as to fatty acid composition, others as to other non-glyceride components of the fat. Thus the iodine value is a measure of unsaturated fatty acids in the fat, now obtainable in more detail from a fatty acid profile. Similarly the Reichert value is a measure of volatile fatty acids soluble in water. For most purposes this means butyric acid, and so the modem equivalent is the determination of butyric acid in the oil. The modem method for milk-fat analysis is thus carrying out the analysis in a similar way to the Reichert determination, but uses a technique that is less dependent on the exact conditions of the analysis and is thus less likely to be subject to operator error. The Reichert value could be useful, in theory, even if milk fat was not present. Lewkowitsch notes that some other oils do give high values. Porpoise jaw oil has a value almost twice that of milk fat, while some other oils also have significant values. It is unlikely that one would have come across much porpoise jaw oil even in 1904, and even less likely today. 

Preconcentration of analytes in aqueous solution may be performed by a miscible organic phase followed by salting out. Thus, microextraction of anionic solntes snch as phenol, cresols and xylenols in industrial effluents can be carried ont with a small amonnt of isopropyl alcohol, followed by demixing of the phases with ammoninm snlfate. End analysis of the extract by GC-MS in the selected ion monitoring (SIM) mode allowed a LOD of 1 ppb for 50 mL samples . The best conditions for eliminating petrolenm prodncts from the concentrate were found for the GC determination of volatile phenols in natnral waters. Losses of volatile phenols due to preconcentration were insignificant and cansed no increase in the relative error of determination by the internal-standard method. The concentration of phenol in the atmosphere can be determined by sorption on Chromosorb 102, desorption with benzene and 0.1 M NaOH and GC nsing a capillary colnmn. LOD was abont 1 p,gm, with accuracy within 15% . 

The two techniques discussed above indicate that the combined application of GC and chemical methods of analysis is promising and can be used to develop commercial instrumentation. It must be pointed out, however, that these methods are not free from disadvantages (1) water is converted into acetylene, which complicates the analysis and is a source of unnecessary errors (2) the use of a nitrogen ooled trap to collect and concentrate volatile products resulting from oxidation and other chemical conversions also complicates the analysis and is a source of unnecessary errors (3) the dynamic conditions of combustion necessitate a rapid and complete oxidation reaction. The chemical aspects of combustion under dynamic conditions have been discussed [41,42]. 

Errors of initial data spread through the computation procedure and affect modeling results. Input data accuracy usually is presented as confidence interval with acceptable confidence level of not lower than 95%. However, usually as initial data are used results of water analyses conducted for other purposes and with insufficient accuracy. Such data often suffer from incompleteness and low accuracy. Concentration values with 2 or 3, sometimes 4 or 5 significative digits, without confidence interval, may contain false information. Their analytical correctness and precision usually are in the range of 2 - 10% and depend on utilized testing methods and analysis of their sensitivity and also of the analyst qualification. These notes most of all pertain to such values as pH, Eh and content of volatile components, first of all CO (see Tikhomirov, 2016, v. 1, pg. 41-76, and pg. 91-95,106-107 here). 

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