Dose - Research Chemicals Weighing Methods for Beginners

[Nagognog2]

I agree with radiometer: A set of calibration weights (masses) is an invaluable investment with any electronic balance that claims to weigh in the low milligrams. And the Ohaus set, containing weights from 1mg up to 500mg, is an excellent choice. If your lab rat is going to shell out for a good electronic balance, then I suggest the rat keep his paper route an extra week and spring for the Ohaus set of masses.

[kemistudent]

Does anyone have any blueprints for building a scale similiar to the one in the corner of of each of our posts?

[ecblunt]

i need something clarified if a take 100mg of something and mix it with 100ml of water. one ml of that water will contain 1mg of my something?

[deadsunrise]

Originally Posted by ecblunt

i need something clarified if a take 100mg of something and mix it with 100ml of water. one ml of that water will contain 1mg of my something?

Yes if that substance can be disolved in water. You can also do stronger ratios like 200mg/100ml or much more. The more mg you put water in the harder it will be to get everything disolved but you can do very concentrated solution with 2C's so 1/1 or 2/1 is not any problem.


If you are thinking about ordering 100mg and mixing with water instead of buying a scale be very careful because vendors usually send more or less than what you paid for. Some people have even received twice the amount they ordered. It can be a problem to drink 20ml thinking that you are having 20mg and having 40mg instead.

[London_Bloke]

SWIM finds advantages to having a daughter majoring in chemistry at university. SWIM has an AWS CV-10 milligram scale and felt she could not get the consistency she desired. So she asked her college-student offspring how it's done in the lab and she explained vacuum boxes to SWIM. But what well-educated offspring recommended to SWIM was to turn a glass mixing bowl or the glass lid to a pot over the scale and it's contents to prevent hand movements and air stirrings from causing wild fluctuations. It works very well.

However, because SWIM is a little on a overly-cautious side, she elected to use a similar technique as the original author of this post, but also chose to not attempt to measure smaller amounts. 100mg weighed out several times, then suspended in 50ml everclear seemed much safer in the long run. SWIM is very glad she did so.

Reputation Comments on this post:

	good post! Informative and intelligent
	good safe advice

[_caesar_]

Guys I know SWIM might be shunned for this but he's been eyeballing his RC doses. I know this is completely irresponsible and want to rectify it before something goes wrong.

I'm about to place an order for a Acculab VIC-123 and have just been reading illuminati boy's very informativeSafer Research Chemical User's Guide.Now with the VIC-123 will SWIM still have to use the volumetric technique for doses, or will it be able to precision weigh them. If not can someone recommend a scale that can.

Also can anyone else recommend any other equipment I might need for handling/storage etc.



Thanks.

[rodent]

SWIM just got his VIC123 and so far, is very satisfied with it.

As some have mentioned, he has noticed that the slightest air currents in the room will have it wandering many milligrams. Turn off all fans of any type and it's pretty stable.

What's sad is a friend 'invested' in a cheap $50 milligram scale and sent SWIM a sample of 2c-type substance. Now SWIM's not sure if he was skimpin a little or what but, his measured 25mgs was half that on the Acculab.

You get what you pay for I guess....

Reputation Comments on this post:

Good reply to question.

[radiometer]

^ That's supposed to be a very good scale. I'd still be leery of trying to weigh doses under, say, 10mg with it - in that case, it would still be safer to use liquid measurement. But one could do this with a fairly low amount, maybe something like 15-20mg.

Get yourself a set of calibration masses to go with the scale - you can get a decent set for about $40, which will contain various weights from 1mg to 100mg with which you may check the accuracy of the scale throughout its life.

Reputation Comments on this post:

Good reply to question.

[bearded]

I just have a real quick question, I don't know if anyone has mentioned it. Say you're dealing with the salt version of any chemical. Let's say Hcl.

You have 100mg in a bag, you dissolve that 100mg into 100ml(cc) of dH2o.

If you make sure all the chemical is dissolved, take 1cc and drop it onto a glass mirror and allow it to evaporate...will you have 1mg of chemical Hcl?

[Nagognog2]

Yes and no. One would not use 100ml of H2O. One would wash and place said contents into a proper container (graduated cylinder comes to mind) and then add H2O until the total solution comes to 100ml - measuring correctly from the bottom of the miniscus* at the 100ml graduation. Then you would have very close to 1mg/ml. Assuming that there was actually 100mg to begin with.

* Don't know what miniscus means? Pour some H2O into a glass and look at the surface. See how the surface of the liquid is low in the center and bends up towards the edges of the glass? The low center is the bottom of the miniscus. This is how you measure most liquid solutions. That will be $20. Pay up. LOL!

[bearded]

I don't know if someone has ever posted this on the site before, or if it would have much us with RCs, but certainly someone friendly with cidley would find this of us.

http://www.sci-spot.com/Mechanical/balance.htm

You have to know a little something about electronics, but these are plans to make a scale capable of weighing from micrograms all the way up to a few milligrams.

Enjoy.

[anaesthetics]

So, it seems as though the Tanita 1210 has the best reputation from what I've read.. what about the 1230? Anyone used this model personally? SWIM's "source" claims .001 g readability, but SWIM would feel much more comfortable hearing some testimonials beforehand. Thanks...

[radiometer]

No one's tried one yet that I know of, but we're assuming it will be the same quality as the 1210. The 1230 features .002g readability, not .001g.

[rodent]

Something I noticed while precisely measuring sugar for my morning coffee was an annoying tendency with my Acculab VIC-123 to drift by about 1 mg per 3 seconds. Even after setting an ideal measuring environment (no drafts, steady table balanced out) and calibrating the scale, it would often read -10mgs within 30 seconds or so and keep going. You might imagine a little frustration here. I have always been very careful when moving/storing scale and taken good care of it.

After playing around with the removable tray and being careful not to use much force, I was able to get it to stay perfectly steady at zero. Don't know if this is a common issue with other scales but I just wanted to point that out to other owners of the same model. Hope it helps some SWIM out there.

[Nagognog2]

The Tanita stays at 0 with no load.

[radiometer]

rodent, have you tried using some of the different settings the acculab has? I read a post somewhere stating that the factory setting drifted, but one of the other ones worked perfectly for them. i may be able to find the post by searching if you want me to.

I should really redo this write-up, it was done in haste without expectation of its being a long-term sticky.

[rodent]

Yeah, Radiometer if you can find the post you speak of, that would be great. Did a quick search this morning and couldn't find much about it. Either way, I'll find the booklet that came with it and play around with the settings this weekend and see if that helps.

Thanks for the help!

[radiometer]

this scale does drift if you use the factory settings.

I use 1.1.4 and 1.3.4 (you'll know when you get it).

Also, it takes more than 3 seconds to stablize, and is very sensitive to temp fluctuations (don't keep your hands over the pan while waiting for your reading).

******** (damned message length, non-quote-reading forum setting)

Reputation Comments on this post:

very nice :-)

[London_Bloke]

SWIM was researching the possible purchase of a set of calibration masses. Who knew they varied so widely in price? SWIM certainly didn't. Looking at a set of brass Ohaus, all 100mg or smaller for about $40. Would this be a good investment or money flushed away? Some of those sets were over $800, and talk of traceable certificates made huge differences.

[radiometer]

Originally Posted by BadnessNeeds

SWIM was researching the possible purchase of a set of calibration masses. Who knew they varied so widely in price? SWIM certainly didn't. Looking at a set of brass Ohaus, all 100mg or smaller for about $40. Would this be a good investment or money flushed away? Some of those sets were over $800, and talk of traceable certificates made huge differences.

Yes, the cheap sets work just fine. I've checked some on an analogue scale which reads easily to .1mg, and they are all extremely close to the stated weights - if memory serves correct, they were all within .1mg. When placed on a Tanita scale, they all registered the stated weights. The set was advertised as being made of brass, but the weights received appear to be made of aluminum (they are silver and have not tarnished over time). The set I'm referring to is made by Ohaus, part no. 218-16.

The only use for these weights for the average user is to check whether their scale is reading properly, which is not really that technical an application, thus IMO there's no need for the expensive ones if the cheap ones are good enough. Everyone who weighs doses of chemicals should own them, otherwise there's no way to know that a 20mg reading (for example) truly means there's 20mg on the pan.

Reputation Comments on this post:

Excellent advice - all of it (the whole thread)

[London_Bloke]

SWIBadness knows how to take good advice. The part number was the same as the set SWIM was eyeballing. Within 5 minutes of reading this post, SWIM was confirming her purchase of one set of Ohaus 218-16 Calibration Mass Set, 500 mg

Valuable advice - thank you again SWIRadiometer!

[rodent]

Right on! You just saved me much frustration, Radiometer.
I settled for 1.1.3 and it works perfect

Thanks for digging that up!

I was noticing the same thing Badness but think I might go for one of the cheaper sets myself.

[Nagognog2]

Tell your Octopus to always handle the masses (weights) with the tongs provided. Even the little skin-oils from the tentacles will throw off the accuracy. Should they get dirty & need cleaning - use iso-propyl alcohol.

[London_Bloke]

Use of tongs will be a new house rule. SWIM's cavy always wears gloves when weighing and such. No small feat for a quadraped.

[Fresh]

Thanks for the info radiometer. SWIM just ordered a scale and was wonder how to go about weighing certain things. Hope it's a good scale. It was the cheapest mg scale available lol.