Wlist (1932) has discussed the effect of storage on the chlorinity of samples. He compared the results from samples examined almost immediately at sea with those titrated in the shore laboratory after a considerable period of time. He concludes that there is a definite tendency for the chlorinity to increase on storing. The effect was largest with sample bottles that had been previously titrated and, therefore, no longer full; and least with full bottles on which the stoppers had been covered with paraffin wax. In the case of the incompletely full bottles the mean increase of chlorinity was 0.011 %0 while in the case of the full bottles with paraffined stoppers it was only 0.002%0. For many purposes, as, for instance, the exploration of relatively unknown waters, such small differences can be of little importance but in the investigation of well known areas and, particularly, in cases where the seasonal and long period changes of the physical characters are sought, even such small effects may be of the same order of magnitude as those which are being examined.
Thompson, E. F.. 1940. "Effect of delayed titration on the salinity determination." Journal of Marine Research 3, (3). https://elischolar.library.yale.edu/journal_of_marine_research/576