Yes, we call it our Salinity Test Strip. This test strip measures the level of chloride present and can be used as an indirect indicator of sodium when the sodium is present due to sodium chloride salt.
If the sodium is due to NaCl and not from other sources, a ppm level of 500 ppm Cl would be equivalent to a ppm level of about 320ppm sodium based on the differences in molecular weight. A 1000ppm chloride result would therefore be about 640ppm sodium.