[sodakrugby]

I'm attempting to make a 50 ppm standard of K in 1000 mL. The pre-made standard solution is approximately 10000 +/- 60 μg/ml with a density of 1.025 g/ml. By volume I believe I would have to convert the 10000 μg/ml to μg/g by dividing by the density 1.025 g/ml to get 9756.1 μg/g which is equivalent to ppm. Then to get 50 ppm it would be (ml)(9756.1 μg/g) = (1000 ml)(50 μg/g) and solve it to be 5.12 ml. So I would add 5.12 ml of my 10000 μg/ml standard in 1000 ml to get 50 ppm. Am I doing this right? Should I being doing it by weight with a scale? I feel like it would be more accurate. We have a scale that goes to 0.0000 g. How would I do it by weight? Thanks!!!

[Borek]

Looks OK to me. Question is - how precise does your standard need to be? You have assumed density of 1 g/mL for water - could be that's OK, could be that adds to the error.

Weighing small volumes is never simple, as they quickly dry pout, often quickly enough for the weight changes to be observed as a drift on the scale. I would prefer to measure the volume.