Acid-catalyzed hydration of alkenes
If you are certain that there are no other halogenated byproducts or reagents remaining in your solution, and that any levels of bromine and iodine would be negligible compared to chlorine (fluorine would not be detected), then one of the total halogen analysis (TX) methods would be a good choice.  

If this is an ongoing analysis that you need to set up, I suggest the Carius halogen method. Wikipedia gives a good overview here:  


  The Carius halogen method in analytical chemistry is a method for the
  quantitative determination of halogens in chemical substances. A
  known mass of an organic compound is heated with fuming nitric acid in
  the presence of silver nitrate contained in a hard glass tube known as
  carius tube, in a furnace. Carbon and hydrogen present in the compound
  are oxidised to carbon dioxide and water. The halogen present forms
  the corresponding silver halide (AgX). It is filtered, washed, dried
  and weighed.  


Alternatively, depending on the equipment available to you, you could also do an oxygen bomb combustion of the sample with a bicarbonate absorbant, followed by either titration of the resulting chloride or ion chromatographic (IC) analysis. In the case of the IC finish, you can usually just use the IC eluent as the adsorbant.   

If you are only going to do this analysis once, or only rarely, then I would strongly suggest a commercial TX anaysis using Standard Methods - For the Examination of Water and Wastewater, Method 9020. Method 9020B is for the analysis of total organic halogens (TOX) in water, which is not appropriate for your analysis as a whole because it includes a step for extracting trace amounts of organics from water onto activated carbon. But, then a TX analysis is performed on the activated carbon, which is what you would want to do for your compound rather than for the activated carbon. This is typically about an $80 analysis. 

Regardless of the TX technique used, you would of course then assume that all of the halogen came from the ethyl chloride and calculate the ethyl chloride concentration from there.