I need to check the Heavy metal (lead) consumption assay using microbes at varying concentration in same media. ( 200mg/L to 2000mg/L).kindly help me to clear it.
The molecular mass you only need when you need molar concentrations. If the concentration is given in mg/L, just weigh the required amount (300 mg in your case) of the substance into a volumetric flask, add some medium to dissolve it and then fill up until the lower meniscus touches the 1 L mark. Note that many nitrates are hygroscopic, for precise results you need to dry them o/n under mild heat in an oven (or store them in a desiccator under vacuum over a drying agent).
Rinsila Kareem K.A Atomic weight of lead (Pb) is 207.2, lead (II) nitrate is 331.21
If you need 300 mg/L of Lead (Pb) only then
to prepare 300 mg/L of Pb
= 300 mg/L x (331.21/207.2)
= 479.55 mg/L i.e. dissolve 479.55 mg of Lead (II) nitrate per L of LB agar
if the purity is 98%
then you need
= 479.55 mg/L x (100%/98%)
= 489.34 mg of lead (II) nitrate per L of broth
since you need Pb from 200 to 2000 mg/L
better prepare a stock of Pb at 20,000 mg/L (lead nitrate is very soluble in water)
Stock at 20,000 mg/L (assuming 100% purity)
=31,970.08 mg or 31.97 g per L of deionized water (better 3.197 g per 100 mL to reduce volume of stock solution)
In theory the solubility of lead (II) nitrate is about 600 g per L
so you can even prepare 200,000 mg/L stock solution
After the experiment is done, dispose the waste properly. Pb is very toxic. I don't recommend working >20 mg/L for any experiments in my lab.
double check with someone else for the calcns. above.
Rinsila Kareem K.A and before I forget. metal ions t that high concentration may precipitate out of solution in complicated matrix such as LB broth and alkaline pHs as well. be careful!
M. Y. Shukor Thanks for the explanation sir,
I always add heavy metal after cooled the lb medium, but inspite there will be colour change in the medium, may be due to precipitaion.
Rinsila Kareem K.A Likely so as the Pb concentration you used may react with components in the broth leading to precipitation. measure soluble Pb after centrifugation of the broth
M. Y. Shukor yea, sure I will try with it.But is there any chance to reduce the media componants because that may affect bacterial growth right? ...i will check the growth by using this method by inoculating bacteria after centrifugation. Actually up till now Iam doing with the procedure as said by Engelbert Buxbaum ... now i am confused with the preparation of stock as you explained M. Y. Shukor . what will be better choice?
Rinsila Kareem K.A The stock preparation advised by Dr Buxbaum is based on lead (II) nitrate (the compound), whereas the stock I proposed is based on the metal Pb. If you are studying the effect of the compound then you should use the method of Dr Buxbaum, if you are studying the effect of the metal Pb, then you should use the method I suggested.
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