The effect of sodium chloride concentration on the assay of LAS in seawater by MBAS methods

Kartal Çetintürk, Kasım Cemal Güven

Institute of Marine Science and Management, Istanbul University,  34470, Vefa, Istanbul, TURKEY
Present address: TUDAV (Turkish Marine Research Foundation) Beykoz, Istanbul, TURKEY


The effect of salinity in seawater on methylene blue active substance (MBAS) method for LAS determination was investigated. To reproduce the salinity of the Black Sea (18 ‰), Sea of Marmara (24 ‰) and Mediterranean Sea (34 ‰), we used sodium chloride from Aegean Sea, Merck and Baker products. Standard curve of LAS was drown in seawater reproduced in the same salinity. It was found that the purity and concentration of sodium chloride have an effect on the LAS level determined by Standard Methods in sample tested. Merck and Baker sodium chloride give similar results but using common salts, the results are more reliable.
In this work we proposed a modification improve MBAS assay in seawater as follows:
1. Standard LAS solution must be prepared with common salts with the same concentration as seawater tested.
2. The blank chloroform used was prepared applying the procedure of calibration curve of LAS determination by MBAS method omitting LAS.
3. The extraction with chloroform was made 6 times instead of 3 times.
4. The calibration curve of LAS was plotted using common salts instead of distilled water, with the same salinity of seawater examined.
5. Correlation equation were calculated from the equations of different salinity of seawater (18, 24, 34 ‰).

Keywords: LAS, sodium chloride, MBAS method

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