|
Post by dToad on May 9, 2012 11:22:58 GMT -5
I'm a little anal about weights and measures. Using the right scale for the job is important, as is KNOWING that you can trust the scale.
I bought a DigiWeigh Chrome Scale 100g X 0.01g to measure nutrients, agar, and sugar for my media. It came with a 100g calibration weight. I also bought a test weight set with a 1g, 5g, 10g, 2 X 20g, and, a 50g weight.
Before using the weights I went to my local pharmacy where they have weights calibrated against our national standards. My calibration weight was off by 0.543g, and the test weights were within 0.2g. I adjusted all the weights so that they were within 0.005g of the value stamped on them. I drilled where needed, and added lead to bring them to that accuracy.
I also checked the scale with the pharmacist’s weights at 5g intervals from 5g to 125g to verify it's operation. A 50g tare setting was used to check from 100g to 125g.
I now can calibrate this scale, and verify its readings. I'll KNOW my measurements are accurate.
|
|
|
Post by dvg on May 9, 2012 14:10:33 GMT -5
dToad, you are obviously very particular about the accuracy of your weights and measures.
Best of luck with your tissue culture projects.
dvg
|
|
|
Post by Apoplast on May 9, 2012 14:52:40 GMT -5
Hi D'Toad - With tendencies like that, if you are not an engineer, you'd have made a great one! I'm very impressed you took the time and care to correct your weights.
The pharmacy idea is great. Although, I suspect if I tried it here in the States my request would be met by security, or a phone call to the police.
|
|
|
Post by dToad on May 9, 2012 16:05:36 GMT -5
My pharmacist has a set of class 1 weights that he has checked annually. He won't let anyone touch those weights I paid more than I did for the scale and weights for him to check them for me, and recheck after I modified the weights. I've been bitten before with equipment that was calibrated against bad standards. I was electronics technologist in the navy. I'd rather use a lower accuracy, well calibrated instrument than a poorly calibrated highly accurate one.
|
|
|
Post by lloyd on May 9, 2012 17:31:36 GMT -5
0.534 grams off on the 100 gm weight is only 0.00534 off. So the error in the calibration weight is probably only going to contribute 0.5% error. Your scale weighs down to 10 mg. So the calibration error on 10 mg would contribute maybe 0.05 mg error. That's 50 mcg. My homemade microgram scale can measure down to 100 mcg. These amounts are like small specks of dust. I know from experience that 100 mcg of plant hormone is hard to see or manipulate. I can see you had a jaunty time calibrating your weights. I, too, go on strange quests to accomplish strange aims like growing weird parasitic plants. So I'm not trying to belittle your heroic effort. However I think your scale is pretty accurate.
I have 4 scales at home (not counting the kitchen and bathroom one) so I also am a scale fanatic. :-)
|
|
|
Post by dToad on May 9, 2012 18:36:39 GMT -5
Jeweler's rouge to polish off those final thou's was fairly quick. It was easier to go slightly above, then remove material to bring them down to the desired weight.
|
|
ira
New Member
Posts: 6
|
Post by ira on May 14, 2012 11:14:26 GMT -5
scale accuracy test can be done with water. assuming room temperature, density of water is 1g/ml. So, 10 ml of water should give you 10g in your scale. This is usually how we check accuracy in a lab setting.
I have never done plant tissue culture (multicellular). But making media for bacteria and eukaryotic cells (unicellular), +/- .1 g to +/- 0.01g is more than enough for accuracy.
|
|
|
Post by lloyd on May 14, 2012 15:04:40 GMT -5
Actually for some hormones I go down to 100's of mcg.
|
|
|
Post by dToad on May 14, 2012 15:04:42 GMT -5
I used a volumetric flask to test my 2Kg scale. I find that 100g capacity is a little small for water tests. The way my 100g scale is calibrated, the total weight must be 100g, tare is not allowed.
|
|
ira
New Member
Posts: 6
|
Post by ira on May 14, 2012 15:48:32 GMT -5
Just been browsing the TC posts. Seems really interesting doing TC outside a lab setting and how most of the equipments used are improvised. Quite tempted to jump on the TC band wagon and apply my lab skills. Gotta go look more into this.
Lloyd: if you need to deal with less than 100 ug, cant you do you do a dilution instead of weighing?
|
|
|
Post by lloyd on May 14, 2012 18:17:16 GMT -5
Ira, you are correct, dilution is an excellent solution. The only problem is that some hormones are available in only small amounts (maybe a mg), are expensive and are not stable in solution.
For instance, when I wanted to try 2,4-epibrassinolide, it was about $25 for a mg. Three of us split it. I had to divide it into three parts which involved 100's of mcg. If I dissolved it, it would have deteriorated before use during shipping. Now you can buy the same amount of the chemical but in less pure form, so you can weigh 10's of mg which is much easier, and get the same amount of pure substance.
|
|