1. Boric acid – API analysis 2. Aluminium hydroxide tablets
Case
studies
Boric acid is known to have antifungal and antimicrobial
properties and therefore has a clinical use. Typical pharmaceutical analysis of
boric acid as an API includes its reaction with a known amount of mannitol and
subsequent titration of unreacted mannitol.
(a)
Research the chemical structure of mannitol
including its stereochemistry.
(b)
Describe the reaction of boric acid and
mannitol, including relevant chemical equations.
(c)
For the analysis of boric acid as an API, 1.0
g of the acid is typically dissolved in 100 ml of water, and 15.0 g of mannitol
is added. The solution is then titrated with 1 M sodium hydroxide (NaOH)
solution using phenolphthalein as indicator.
Calculate the volume of NaOH needed in this titration if the API
has a purity of 99%.
(d)
Research the typically accepted error margins
for the purity of boric acid as an API.
Your pharmaceutical analysis company has been contacted by an
important client and asked to analyse a batch of aluminium hydroxide tablets.
The description of your brief states that you are supposed to analyse the API
in these tablets following standard quality assurance guidelines.
Typical analysis methods used for quality purposes are often
based on titration reactions, but also a variety of other quantitative analysis
methods such as gravimetric analysis can be used. Typically, a certain amount
of the tablet powder is dissolved in water, and hydrochloride acid (HCl) is
added. An excess of the precipitation reagent is added, and the solution is
stirred until precipitation is completed. The precipitate is then filtered,
dried to constant weight and weighed.
(a)
Draw the chemical formula of aluminium
hydroxide.
(b)
Research the type of analysis used. Within
your studies, you should look at a variety of precipitation reagents and understand
how different factors can influence this method.
(c)
Formulate the relevant chemical equations.
(d)
The package states that each tablet contains
475 mg aluminium hydroxide. For the experiment, 20 tablets are weighed (total
weight 12.5 g) and powdered. An amount of powder containing 0.4 g aluminium
hydroxide is dissolved in water and HCl, and reacted with excess 8-hydroxy
quinolone. After stirring this solution for 2 h near the boiling point, the
precipitate is filtered and dried overnight in the oven at 100 ∘C.
The precipitate weighs 2.0 g.
Calculate the amount of aluminium hydroxide 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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