# My brain hurts...(help needed)

Rich H richh6109 at remove-this.yahoo.co.uk
Sun May 6 17:06:08 EST 2001

```OK, I'll start by apologising for going a bit OT but.....

I wonder if someone can help me with this simple problem (I think I know the
answer, but I would like someone to confirm this).

I'm currently doing a lactate assay, which normally wouldn't be a problem, I
just get the readings from a spectrophotometer, compare them against a
standard and get the reading in mg/dL (or mmol/L by multiplying by 0.111).
The problem is I'm helping a microbiologist calculate the amount of lactate
in an agar core (which is dissolved in 1ml deionised water)and I'm
struggling to work out the answer.

I've got the lactate reading of the solution (1.18 mmol/L), but this is the
reading for the dissolved core + water, so I thought I'd better work out the
volume of the core.  To work this out I need to find the volume of the
cylinder, yes? This was 2.5mm radius by 7mm height. Using pi x radius (2.5mm
sq) x height (7mm) gave me a volume of 137mm cubed.  So I divided the
lactate reading by the volume and then multiplied by the dilution factor
(1000).  Is this correct?  Do I need to include the mass of the cylinder in
there somewhere?

Apologies to newsgroup regulars who don't want to read this simplistic
drivel, but I'm a middle-aged molecular biologist who remembers little of
his chemistry calculations all those years ago!

R.

```