How does one prepare concentrations in the mass/volume (weight/volume) form, for substances like nucleic acids or in this case, proteinase? A detailed example would be helpful.
I need to prepare squishing buffer for a DNA extraction /PCR exercise to help me learn the materials better for a in class "internship".
The squishing buffer recipe I found from a laboratory class manual describes it as: 10 mM of Tris-Cl, pH 8.2, 1 mM of EDTA, 25 mM of NaCl , and 200 µg/ml of proteinse K (freshly diulted).
I understand molarity concentrations well enough. One only has to determine the total molar mass of a substance, in this case NaCl, and with that molar mass (g/mol) then use the given desired molarity (in this case 25 mM of NaCl, which equals 0.025 mol /one liters) to get the number of grams of the substance needed. In this case, since we need 0.025 moles / 1 Liter, we would need to multiply that by the molar mass to get: (g/mol) X (mol/l) = g/l of NaCl.
I understand percent solutions (to a degree) as well. If I needed 1% agrose gel, I would take 1 gram of agarose solid powder and bring that to 100 ml total to obtain a 1%, either using water or buffer?
I am having trouble understanding the concepts of concentration, in reference to mg/ml.
From what I understand, µg/ml is a weight (mass)/volume type of concentration. Therefore, should it be the case that if I wanted to prepare 200 µg/ml of proteinase (freshly diluted), how would I go about it? Would I add 5 ml of deionized water to get a working volume of 1000 µg of proteinase per 5 ml of water, which would be equivalent to 1 mg of proteinase per 5 ml of water. From that 1mg of proteinase to 5ml of water, should I then draw 0.2 µl (or 200 ml) of solution to then have the 200 µg/ml? Or am I totally wrong? I tried googling for more information, but I became more and more confused.