Chlorinity high precision method

Salinity is presently determined by measuring the conductance of seawater by using a salinometer. The modem definition of salinity uses the practical salinity scale, which replaces the chlorinity-salinity relationship with a definition based on a conductivity ratio (Millero, 1996). A seawater sample of salinity S= 35 has a conductivity equal to that of a KCl solution containing a mass of 32.435 6g KCl in 1 kg of solution at 15 °C and 1 atm pressure. No units are necessary on the practical salinity scale however, in practice, one often sees parts per thousand, ppt, or the abbreviation psu. New salinometers using this method are capable of extremely high precision so that the salinity ratio can be determined to 1 part in 40 000. At a typical salinity near 35 this procedure enables salinities to be determined to an accuracy of 35.000 0.001. This is much better than most chemical titrations, which, at best, achieve routine accuracy of 0.5 parts per thousand. 

A specific reagent for the primary hydroxyl group determination is triphenylchloromethane [22], which has a very reactive chlorine atom and a bulky substituent (triphenylmethyl). Due to the high steric hindrance of triphenylchloromethane, a selective reaction with primary hydroxyl groups takes place. Unfortunately, the precision is not very high because the secondary hydroxyl groups react only to a very small extent (8-10%). In order to make it a more precise method, it is necessary that before the determination, a calibration curve should be done and the real primary hydroxyl content is corrected by the decrease in the quantity of secondary hydroxyl reacted. 

This chapter presents the analytical procedures for calcium, magnesium, potassium, chlorinity, sulphate, bromide, boron and fluoride, selected as the most interesting major constituents. (The methods for determination of the CO2 species are thoroughly outlined in Chapters 8 and 9.) It describes the methods, firstly from a theoretical and, secondly from a practical point of view. To make meaningful studies of the relative variations of these ions in the sea it is important to apply analytical procedures capable of high precision. The methods reported here have been tested by the author in large series and found to be among the most reliable. Most of the procedures have been subject to several modifications since their... 

Finally, treatment of amides with phosphorus oxychloride gives Vilsmeier complexes, which are often formulated as A-alkylated imidoyl chlorides (59). Irrespective of their precise nature, it has been found that they can be converted very efficiently to aldehydes by reduction with zinc followed by aqueous work-up (Scheme 17). Although the method has only been used for benzaldehyde and a number of chlorinated and brominated analogs, the yields reported are consistently high (87-97%). ... 

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