In a lot of the scientific literature, dissolved organic carbon (DOC) is given in microMolar units of carbon. Modern instruments give DOC in parts per million (ppm). I'm trying to figure out how to convert uM to ppm. Since uM is dependent on the molecular weight, I already have a problem. DOC is actually a distribution of dissolved compounds so there is no single molecular weight. I do know that approximately 65% of the DOC in seawater is <1000 Daltons, but what is an appropriate value to use for molecular weight in this case? Values for DOC in seawater range, but blanks are often reported around 25-30 uM C. Blanks are the measurement of DOC on a sample that has no dissolved carbon in it, so it represents the contribution from the measurement method. I'm trying to convert this value into ppm so I can compare it to a modern system blank which is reported in ppm. Once I decide on a molecular weight to use, what is the actual calculation to convert from uM to ppm? Is this correct? [tex]ppm = MW \times \mu M \;C[/tex] where ppm is parts per million (mass), uM C is microMolar carbon, and MW is molecular weight in grams/mole. Any help is much appreciated.