Chromatography Forum

hi guys,

I having difficulties in preparing stock solution (500ug/1ml) for tocols. The standard is in high viscous liquid form and comes in a very vial (100mg). I weighed 2mg standard using metter toledo balance with accuracy up to 2ng and it is really difficult to do it. The standard tends to stick on spatula and cant transfer to weighing paper. if managed to transfered, the weigh either high or low that desired amount. Anyone who always deal with viscous standard can suggest me ways to overcome this.

Thanks in advance

Dealing with viscous liquids is the subject of two other current threads, have a look around on the forum.

Are you sure that you balance can weigh to 2 ng , 2 ug I can believe.

How close can you get to your target weight ? If you can get within a sensible margin (what sensible is will depend on the details of your application) then you can either calculate the volume of solvent required to make the solution to the target concentration, or you can use whatever convenient voloume of solution is in the method, and calculate the actual concentration from the accurate mass that you measured.

You can also weigh the solvent and do everyting by mass fraction.

I wouldn't use a spatula for this, and certainly not weighing paper - how do you propose to get the sticky liquid off the paper ? 2 mg is probably around 2 ul (depending of course on density). Do you have Microcaps or similar, or can you improvise using short pieces of fine glass tube ?. Weigh and tare a glass vessel with a microcap or fine tube, get some tocol std into and onto the tube, drop it back into the vessel and take the difference in weight.

Peter

sorry, it suppose to be ug and not ng.

i need about 2mg to be diluted in 100ml and it really difficult to hit the target.
I was thinking about the idea u mentioned. Tare a fine glass tube, calculate weigh changes after tube with tocol and mix with calculated amount of solvent.
actually i searched for the thread but couldn't find it, that the reason why I post this.
Thanks mike for ur information

viewtopic.php?f=19&t=15463&hilit=weighing

Sometimes browsing works better than search functions.

Peter