I'm also a little bit confused by your application. For example, I've done automated potentiometric titrations in the 100-500 ppm range. I've used Farjan's method to determine the titer of a chloride solution, using 0.5 g of chloride. I found it in the US Pharmacopeia, you may find it in another pharmacopeia. The solid is for sale, as is the indicator solution
You'll notice I'm analyzing very small amounts, of very pure chloride. If you want to analyze the total chloride ion of a salt lake sample or evaporated salts, you will have to dilute. Not that none of these methods are selective for sodium chloride, so if this is a salt lake sample, I'm not surprised you're finding interference giving you false high levels.