Exercises and Case studies - Chelation Therapy

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Chapter: Essentials of Inorganic Chemistry : Chelation Therapy

Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch of solutions for infusion containing disodium edetate.


Exercises

 

1. Sodium calcium edetate is usually administered by intravenous infusion. A 5 ml ampule con-tains 200 mg/ml sodium calcium edetate.

(a)        What is the number of moles of calcium sodium edetate present in one ampule? Express your answer in moles.

(b)       What is the concentration of calcium sodium edetate in one ampule? Express you answer in moles per litre.

 

2. Dimercaprol is usually administered by intramuscular injection. A 2 ml ampule typically con-tains 50 mg/ml dimercaprol.

(a)        What is the number of moles of dimercaprol present in one ampule? Express your answer in moles.

(b)       What is the concentration of dimercaprol in one ampule? Express you answer in moles per litre.

 

3. Draw the structure of all enantiomers of DMSA and discuss which one is used clinically.

 

4. Draw the chemical structure of the cobalt(II)–EDTA complex ion.

 

5. Draw the chemical structure of Hg2+ coordinated by dimercaprol.

 

Case studies

 

1. Disodium edetate

Your pharmaceutical analysis company has been contacted by an important client and asked to analyse a batch of solutions for infusion containing disodium edetate. According to your brief, you are supposed to analyse the active pharmaceutical ingredient (API), following standard quality assurance guidelines.

Typical analysis methods used for quality purposes are based on titration reactions. A certain amount of the solution is diluted in water and hexamethylenetetramine together with HCl is added. The resulting solution is titrated against a solution of lead nitrate using xylenol orange triturate as indicator .

(a)    Research the type of titration described. Describe the chemical structure and mode of action of the indicator.

(b)   Formulate the relevant chemical equations.

Typically, disodium edetate is dispensed as 5 ml ampules containing 200 mg/ml of the API. For the analysis, an amount of solution containing theoretically 0.3 g disodium edetate × 2H2O is dissolved in water. Hexamethylenetetramine (2 g) and dilute HCl are added to this solution, which is then titrated against 0.1 M lead nitrate solution in the presence of xylenol orange triturate as the indicator .

(c)    How many milligrams of the API are there in one ampule?

For each titration, the following volume of lead nitrate has been used:

9.0 ml 8.8 ml 8.6 ml

Calculate the real amount of disodium edetate × 2H2O present in your sample. Express your answer in grams and moles.

(e)    Critically discuss your result in context with the stated value for the API.

(f)     Research the typically accepted error margins.

 

2. Dimercaprol

Dimercaprol injections can be used as for the treatment of heavy-metal poisoning. Your pharmaceutical analy-sis company has been contacted by an important client and asked to analyse a batch of solutions for injections containing dimercaprol. The chelating agent is typically dispensed in 2 ml ampules containing 50 mg/ml of dimercaprol. According to your brief, you are supposed to analyse the API, following standard quality assur-ance guidelines.

Typical analysis methods used for quality purposes are based on titration reactions. A certain amount of injection is dissolved in methanol. Diluted HCl and an iodine solution are added and the resulting solution is titrated against sodium thiosulfate .

(a)    Research the type of titration described and how the endpoint is detected.

(b)   Formulate the relevant chemical equations.

According to its label, a 2 ml ampule of dimercaprol contains 50 mg/ml. An amount of solution theoret-ically containing 0.10 g dimercaprol is dissolved in methanol. Dilute hydrochloric acid (20 ml, 0.1 M) is added together with 50.0 ml of a 0.05 M iodine solution. After 10 min, the solution is titrated against a 0.1 M sodium thiosulfate solution .

How many milligram of the API are there in one ampule?

For each titration, the following volume of sodium thiosulfate has been used:

16.95 ml 17.10 ml 17.00 ml

Calculate the real amount of dimercaprol present in your sample. Express your answer in grams and moles.

(e)     Critically discuss your result in context with the stated value for the API.

(f)      Research the typically accepted error margins.

 

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