Hi. I am trying to cultivate microalgae heterotrophically and want to measure the glucose concentration of the medium during periodic sampling. (I presume there are no other sugars in the medium since I prepared it with glucose only). I would like to use the DNS (Miller) method as I have seen it referenced frequently. However, I have some questions on the details of the procedure. First, is the Rochelle salt (tartarate) required in the reagent? A colleague said they used it without the tartarate but I am having trouble getting consistent results – I have tested the same standard solutions a few times and gotten different values. Also, I have noticed that the color of my reagent has changed slightly. In the original publication it mentions that the sulfite oxidizes over time and should be replenished… but how am I to confirm that this is the case? Does anyone using this procedure have this issue of having to re-add sulfite after some time? Also, in what concentration range are you able to use this method? If anyone can share from their experience and enlighten me I would be very greatful.