Weight - Good mg scales to buy

[Geofragment]

I just have a question about milligram scales. I need to buy some, and I was just wondering if anyone would be able to offer some advice on what scales are a good investment if they are being used for weighing research chemicals.
Thanks

[bl0whydr0420]

to what accuracy? and how many grams, maximum, would you need?

i personally use a "digiscale" that goes max 50grams, to a 0.01gram accuracy.
or 50g x 0.01.

they are easily obtainable through ebay. i got mine for like 25 after shipping and everything, and i know the person i got it from has bulk plans too. just do some research there.

found mine as a "jewelers scale" so i can weigh out my diamonds perfectly.

[Stimulants]

Originally Posted by bl0whydr0420

to what accuracy? and how many grams, maximum, would you need?

i personally use a "digiscale" that goes max 50grams, to a 0.01gram accuracy.
or 50g x 0.01.

they are easily obtainable through ebay. i got mine for like 25 after shipping and everything, and i know the person i got it from has bulk plans too. just do some research there.

found mine as a "jewelers scale" so i can weigh out my diamonds perfectly.

Accuracy is a misnomer.

Just because the scale can count to 1mg doesn't mean it is accurate to 1mg. One count is called 1d, meaning one division.

Many scales specify a repeatability of +/- 1 to 2d and linearity of 2-4d

Slightest vibration and draft will affect the measurement, so you can't realistically expect a reliable, stable mg scale that weighs less than 5 lbs

Accuracy of calibration weight is not THAT important since the skew is proportional. So, if you calibrate a 20g scale with a 19.900g mass, it will just read 19.9mg as 20mg, 1.99 as 2.00g and so on. It isn't going to cause a 0.1g error across the entire measurement.

To be accurate to nearest mg, then +/- 1mg repeatability is not acceptable. One should always have something with 10 times the resolution of the desired reading.

Analytical balances are almost always 0.1mg resolution with +/- 0.1mg repeatability. It should be adequate for measuring to nearest 1mg with a margin of error of 10 to 20%. Microrange scales that go into 1µg or 0.1µg range is not warranted unless the sample measured is say, a single dose of pure triazolam (125µg)

Scale should be line powered, should have a bubble level, glass draft cover and based on the magnetic force restoration sensing method or an old optical mechanical type.

Old optical mechanical type is affordable, however there's a steep learning curve. 0.1mg analytical balance is around US $1000.

Originally Posted by Alfa

To handle Research chemicals which often have dosages in the milligram(0.001) range, one needs a scale with a microgram (0.0001) range. But since scales in the microgram range are mega-expensive, most will settle for a milligram scale or even a two milligram scale (0.002). This means that the milligram scale will display a weight of 0.006 for both 0.0055 and 0.00649.

If a 0.01mg resolution scale is set to display only to 1mg, then that is what can be expected, for for a 1mg readability scale with 1mg internal resolution
that's not the way it works. For a 1mg readability scale with 20g capacity and 1mg repeatability, when you measure 0.50000g (+/- 0.025mg) OIML E1 calibration weight many times and take the standard deviation, it should be within 1mg. If the reproducibility is 2mg, then the scale may report the 0.50000g mass as 0.498g to 0.502g

There are some scales with internal resolution higher than display resolution and these scales will have a much better displayed value repeatability and it may have a spec like d=0.1g, reproducibility =0.03g, though such scales are not common. The region of up to about 5-10 counts from zero can not be used reliability as it is likely to get set back to zero as a part of internal zero drift corrective system.

With the two milligram scale this means that the scale will display a weight of 0.006 for both 0.005 and 0.0069.
To accurately measure weights of milligrams one needs sub-milligram scales, plus the function to adjust the feet of the scale, plus a cap to stop the influence of wind.

2mg with +/- 2-4mg repeatability would report 10mg actual weight as 6-14mg or 8-12mg. Unfortunately, readability does not equate accuracy. If the scale does not come with a detailed specifications, then it should be questioned.

Reputation Comments on this post:

Very sold knowledge of scales. Shared in a coherent and respectful manner. Thanks for the info.

[radiometer]

Tanita used to be the best price for performance, but they are no longer available. Look for scales made by Gempro or Acculab. For weighing individual doses with any degree of accuracy whatsoever you need to have a scale which is sensitive to .002 g or less. A .01 g scale is only good for weighing larger amounts such as 100 mg for further liquid measurement. The adage "you get what you pay for" applies to super cheap scales advertising this sort of accuracy costing under $100. Expect to pay $200 or more for a quality scale.

[Alfa]

To handle Research chemicals which often have dosages in the milligram(0.001) range, one needs a scale with a microgram (0.0001) range. But since scales in the microgram range are mega-expensive, most will settle for a milligram scale or even a two milligram scale (0.002). This means that the milligram scale will display a weight of 0.006 for both 0.0055 and 0.00649.
With the two milligram scale this means that the scale will display a weight of 0.006 for both 0.005 and 0.0069.
To accurately measure weights of milligrams one needs sub-milligram scales, plus the function to adjust the feet of the scale, plus a cap to stop the influence of wind.

Tanita scales are available.

Reputation Comments on this post:

I did not know that, good info

[jazzmetalguitar]

if one has known microgram weights couldn't they add these until the mg scale bumped up a notch to closer approximate the weight?

[anaesthetics]

A Tanita 1230 Professional Mini Diamond Scale would be ideal. SWIM obtained one on eBay for half its retail value and hasn't been disappointed in the slightest. Said scale is accurate to 0.002g. SWIM mentioned the importance of handling scale and product with latex gloves as oil and other residues will interfere with accurate calibration.

Reputation Comments on this post:

Useful information about handling and possible contamination.

[Pino]

Swim just bought a Proscale Gemological 10g/0.001g, which comes with a calibration set. Would this be appropriate to use for chemicals with dosages around 5 to 20 mg. Swim isn't really deep into the scale thing. He would say the scale has a precision of +/- 0.5 mg, which is an error of 10% in the smallest dose encountered. This should be enough, swim thought.

[skatardude10]

Swim just bought an AWM GEMINI-20 Milligram scale. Works great.

[hippie_lain]

swim needs a scale for doc, would it be ok to do the best he can on a milligram scale or would he need to go for a micro scale?

[trptamene]

Considering DOx's are active in the submilligram range, me thinks one should go for a micro scale or use the milligram in conjunction w/ a volumetric method.

[Pino]

^^^ Edit: You was faster than me, LOL

Probably better go for the micro scale. 0.5 mg can make a big difference with the stuff. Otherwise use one of the liquid measurement methods with your milligram scale. Eg: http://www.drugs-forum.com/forum/sho...0&postcount=17

And with more details: http://www.drugs-forum.com/forum/sho...ght=volumetric