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Heavy metals affect the stability and safety of drugs
1.
(1) Heavy metals
Heavy metals refer to metal impurities that can interact with color-developing agents under the experimental conditions of the pharmacopoeia (general rules) method
(2) Experimental conditions
Due to different experimental conditions, there are 3 methods listed in the general rules, the first method and the second method are commonly used for medicinal materials
(3) Results
The results shown by the inspection method are all the colors that the sulfide particles of trace heavy metals are evenly suspended in the solution; if the concentration of heavy metal ions is large, the sulfide will aggregate and sink after adding the color developer for a long time
(4) pH value
The optimal pH value for the formation of heavy metal sulfides is 3.
2.
(1) The first method
1.
2.
3.
4.
5.
7.
8.
(2) The second law
1.
2.
3.
Compare and then add 2ml each of thioacetamide test solution to the two tubes A and B respectively , shake well, place for 2 minutes, put on a white paper, see through from top to bottom, the color displayed in tube B is the same as tube A Compare, not go deeper
.
(3) Matters needing attention
1.
Freshly diluted stock solution The prepared solution should be prepared by accurately measuring the standard lead stock solution freshly diluted before use to prevent errors caused by the hydrolysis of lead nitrate; the glass containers used for preparation and storage must not contain lead
.
2.
Thioacetamide test solution The optimal pH value for the reaction of thioacetamide test solution with heavy metals is 3.
5, so when preparing acetate buffer (pH3.
5), use a pH meter to adjust, and thioacetamide test The color is the deepest when the added amount of the solution is 2.
0ml; the best color development time of the thioacetamide test solution color reagent is 2 minutes
.
3.
The dosage of standard lead solution is 2.
0ml (equivalent to 20ug of Pb) in order to facilitate visual comparison, less than 1.
0ml or greater than 3.
0ml, the color is too light or too dark, which is not conducive to visual inspection Compare
.
4.
Ignition temperature If the residue left under the item of Ignition Residue needs to be inspected for heavy metals, the Ignition temperature must be controlled at 500~600℃
.
5.
Ignition residue treatment Ignition residue is treated with nitric acid.
It must be evaporated to dryness until the nitrogen oxide vapor is exhausted.
Otherwise, the hydrogen sulfide generated by the hydrolysis of thioacetamide will precipitate milk sulfur due to oxidation, which will affect the inspection
.
After evaporating to dryness, the residue is treated with hydrochloric acid to convert heavy metals into chlorides, and then evaporate to dryness on a water bath to remove excess hydrochloric acid.
Add water to dissolve, add 1 drop of phenolphthalein indicator solution, and then add ammonia test solution drop by drop, stirring while adding.
Until the solution just turned light red, add acetate buffer (pH 3.
5) to adjust the pH of the test solution to 3.
5
.
(4) Calculation
1.
Calculating the standard lead solution concentration , the mass of 1 mol of lead nitrate [Pb(NO 3 ) 2 ] is 331.
2g, and the content of lead (Pb) is 207.
2g; weigh 0.
1598g of lead nitrate to make 1000ml stock solution, the content of Pb is:
The concentration of the standard lead solution obtained after the stock solution is diluted 10 times according to the law is 10ug of Pb per 1ml
.
2.
During the calculation and inspection of the heavy metal limit, if you take 1.
0g of the test product, compare it with the control solution made of 2.
0ml of standard lead solution to calculate the heavy metal limit
.
3.
The calculation of the standard lead solution sampling volume is calculated based on the amount and limit of the sample to be tested.
If 2.
0g of the sample is taken, it shall be inspected in accordance with the law, and the content of heavy metals shall not exceed 5 parts per million.
The standard lead solution (10ug/ml) should be taken.
How many milliliters?
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