Looks like you try to recover Ag from photographic fixer solution. This might be a good point to start:

http://www.kodak.com/ek/uploadedFiles/Content/NewCo/HSE/PDFs/Photochemicals/MeasuringSilver.pdf

People also coprecipitate Ag with mercury (II) sulfide (DOI: 10.1002/9780470027318.a0827) to get rid of high salt loads, but thats for trace amounts.

You likely have several g/l, so it might be enough just to dilute your sample to ppm levels with distilled water to minimize the matrix effects. BTW, it is probably the thiosulfate that causes your trouble.

Good day sir. There are two ways to solve it, either precipitating sodium from solution or precipitating out silver and redissolve it in other solution. 

Sodium precipitation can be done by bubbling carbon dioxide into your solution in presence of ammonia, which later precipitate out sodium as bicarbonate. But this might cause precipitation of silver our of solution as silver carbonate. 

Silver precipitation rather easier, you can add chloride into solution and dissolve the precipitated silver chloride with ammonia solution. However ICP will extinguish if you directly feed in this solution, so you need other treatment to remove ammonia (digest with acid etc). 

But as Thomas Fischer said, I think you need to worry thiosulfate more than sodium. Currently your sodium content is about 2.3% w/v, you will observe intense red orange plasma (through filter) but it shouldn't extinguish your plasma. 

From my experience with seawater the most simple way is diluting the solution. If the Ag signal is then too low, you can increase the integration time until you get a robust signal.

Good luck

Thank you Thomas, Ooi and Yitzhak.

I was not aware that thiosulfate would be a problem, I will further investigate this, Thomas and Ooi.

In a first attempt, I will try to dilute and increase the integration time as Yitzhak suggested.

You could try to establish your personal analytical protocol using cation-exchange resins. Good luck!