Lab 2: solutions - formulation and evaluation Flashcards
What are the advantages of solutions?
content uniformity
thermodynamically table
drug immediately available for absorption
easy to swallow
What are the disadvantages of solutions?
inconvenient to store and transport low stability requires preservative requires accurate measurement hard to mask bad taste of drugs
What are the 3 main types of solutions investigated in this lab?
aromatic waters
simple syrup
amaranth
what are aromatic waters?
A class of aqueous solutions containig saturated solutions of volatile oils or other aromatic substaces.
They are used in the pharmacy for their medicinal value as well as their flavouring agent
we used anise and peppermint
What is simple syrup?
a concentrated solution of sucrose in water. It is used as a sweetener
What is amaranth?
A commonly used colouring agent of pharmaceutical preparations
What is the aim of lab 2?
to prepare and evaluate the quality of
aromatic waters anise and peppermint
simple syrup
amaranth solution
What is the function of purified talc?
It is an adsorbent and is added to remove excess oil.
I.e a distributing agent which speeds up the mixing process
what is weight per volume of concentrated water?
density
What are the components of a polarimeter?
Polariser
Sample tube
Analyser/Analysing filter
What does the polariser do?
Filters out lightwaves so that only polarised light passes through the sample
What does the sample tube do?
Contains the optically active solution causing the plane of polarised light to rotate
What does the analyser do?
This filter is rotated until no light passes through
What does the viewer see in a polarimeter?
The viewer rotates the analysing filter to find optical zero. This is when both the circle and the line are white. The degree at which this occurs is noted.
The viewer then slowly rotates the analyser until the circle is white and the horizontal column is black. The degree at which this occurs is also noted
The optical rotation of the sample is the difference between the two degrees.
What is the optical rotation?
The angle through which the plane of polarisation rotates when a polarised light is passed through a substance.
Which sort of molecules do optical rotation occur in?
Chiral molecules
Solids with rotated crystal plates
What does a + value of optical rotation indicate?
the plane of polarised light is rotated clockwise
What does a - value of optical rotation indicate?
the plane of polarised light is rotated anticlockwise
What does the optical rotation of a sample depend on?
The number of optically active species through which the light passes.
i.e. depends on both the sample path length and the analyte concentration
What is the formula for the specific optical rotation measured at 589.3nm at 20 degrees?
1000a/lc
where
a is the degree of rotation (degrees)
l is the length of the polarimeter tube (dm)
c is the concentration of the sample (g/L)
D is the wavelength of the sodium D- line (589.3nm)
What does 1 dm equal?
10cm
What is specific gravity?
The ratio of density of the test substance to the density of a reference substance.
This measures the RELATIVE density
What are the reference substances to measure relative density for liquids and gases?
liquids = water gases = air
Why is the relative density of a syrup not measured with a pycnometer?
The syrup is too thick so its relative density must be measured using a hydrometer to a reference substance, water.
For the formulation of Amaranth solution (APF) why must the solution be immediately stirred after adding the compound hydroxybenzoate solution?
methyl and propyl paraben in propylene glycol is insoluble in water. hence the solution must be immediately stirred to avid precipitation.
What is weight per mL? (g)
the weight in grams of 1mL of liquid
What is density? (Kgm^-3, g/mL Kg/L)
the ratio of mass to volume AT A SPECIFIC TEMPERATURE
What is the relative density?
the ratio of the density of a substance to the density of a reference material (air or water)
What is apparent density?
the weight in air per unit volume
What is talc?
a purified, hydrated, magnesium silicate.
How does talc adsorb the excess oil?
It has a high surface area and aDsorbs excess oil.
This can then be filtered as filter pores are much smaller than the talc particles.
This leaves the solution free of the undissolved or excess oil.
What is invert syrup?
mixture of glucose and fructose prepared by hydrolysing a 66.7%w/w solution of sucrose with a suitable mineral acid
This is neutralised with calcium carbonate or sodium carbonate.
The degree of inversion is at least 95%
What is an example of a suitable mineral acid used in the formulation of invert syrup?
hydrochloric acid
How is a disaccharide formed?
when 2 monosaccharides undergo a condensation reaction resulting in the elimination of small molecule such as water.
What kind of a sugar molecule is sucrose?
a disaccharide comprising of glucose and fructose
Is sucrose optically active?
yes
What is a Hydrometer?
cylindrical glass with a bulb weighted with mercury or lead to make it float.
This is used to measure the relative density of syrup
What is Archimede’s principle?
that an object suspended in fluid causes the fluid to be displaced by the submerged part of the suspended object.
There is an upward force on the object that equals the weight of the displaced fluid
This causesthe object to float.
What does Archimede’s principle tell us about the density of a substance?
That the lower the density of the substance, the farther the hydrometer will sink
What is amaranth?
a short lived plant which blossoms densely packed flowers in the summer or autumn.
What are amaranth flowers a source of?
a deep red dye
What is synthetic amaranth?
The synthetic dye made similar to that of the amaranth flower dye
What chemical structure group does amaranth belong to?
polycyclic aromatic hydrocarbons
What is CHB?
compound hydroxybenzoate solution
This is a preservative effective over a wide pH range.
Its maximum chemical stability is at pH 4-5
What are parabens?
organic esters (e.g. methyl hydrozybenzoate, propyl hydroxybenzoate)
These are subject to degradation to form para acid and their corresponding alcohols
What conditions cause the degradation of parabens to para acids + their corresp. alcohols?
the combination of temperature, pH and time
What is the effect of pH and ionisation on the methyl and propyl hyroxy benzoate parabens?
MHB and PHB have a pKa of 8.5
In pH 4-5 they will be 99.9% unionised and are therefore able to passively diffuse into microbial cells to exert their effect.
They are also the most stable at pH 4-5
What is the effect of pH on the stability of lemon syrup?
A low pH such as 1.2, will cause hydrolysis of the lemon syrup. This will cause glycosidic bond to break resulting in glucose + fructose monosaccharides
Given that the optical activity is now -19° (not the range +56 to 60° expected for sucrose,) this also tells us that we do not have sucrose anymore.
NB: Glucose and fructose have optical activities of +52.3 to +53.3° and -91 to -93.5°, respectively.
Therefore, the -20° is the optical activity expected for the mixture of glucose and fructose. Note the mean of the two sugars is (+52º + (-92.25º)) / 2 = -20°
In the evaluation of aromatic waters such as concentrated anise water, why did the density of anise water not comply with the BP requirements?
We did not leave the talc to interact with the solution long enough so it did not absorb the excess oil.
This meant that filtering of the talc removed a lot of the oil resulting in a lower density than the BP requirements
