Buffer Capacity Flashcards
Buffer capacity
The magnitude of the resistance of a buffer to pH changes is referred to as the buffer capacity ().
Buffer capacity is the amount of acid/ base that can be added to a buffer without causing a large change in pH.
Measure of the buffers’ ability to resist changes in pH
What is the buffer capacity known as
Buffer efficiency/ buffer index/ buffer value
True or False
Pharmaceutical solutions are buffered to a low capacity
True
To protect the drug
Effect of high capacity
In eye drops, if high capacity is used, it’ll try changing the pH of the eye, causing irritation
Relation between the buffer capacity and the concentration of the buffer components
Directly propotional
True or False
The smaller the pH change in a solution after the addition of a specific amount of acid or base, the smaller the buffer capacity of the solution.
False
The smaller the pH change in a solution after the addition of a specific amount of acid or base, the greater the buffer capacity of the solution.
True or False
buffer capacity of a solution is a fixed value
False
buffer capacity of a solution is not a fixed value
It will decrease with the external addition of acid or base
What’s more important in a drug is it the pH or the buffer capacity?
The buffer capacity
True or False
Each buffer works better at a certain pH range
True
Can we use phosphate buffers in the eye?
No
Prepare a buffer solution of pH 5.0 having a capacity of 0.02.
Slide 27/28
The selection of the buffer system depends on:
- pH range and buffer capacity required
- purpose of use (topical or IV)
- compatibility and level of toxicity
The borate buffer is used in the _______, and can’t be used in the _______.
Eye preparations, IV injections
Borate and phosphate buffers are incompatible with many compounds, including:
Salts of silver, iron, magnesium, and zinc
Borate buffers form complexes with many excipients, such as:
Glycerol and carbohydrates
Borate buffer is composed of
Boric acid
Sodium Borate
Difference between in vitro and in vivo
In vitro - in the lab
In vivo - inside a living organism
Buffers in the blood
Primary buffers
Secondary buffers
Primary buffers
In the plasma
Carbonic acid/ bicarbonate
Phosphoric acid/ sodium phosphate
Plasma proteins (such as glycoproteins)
How can the plasma proteins, such as glycoproteins, act as buffers?
They behave as acids in the blood and can combine with bases, which make them act as buffers
Secondary buffers
In the erythrocytes
Haemoglobin (acid)/ oxyhemoglobin(salt)
Phosphoric acid/ potassium phosphate
Minimum and maximum pH of the blood
6.9 - 7.8
What is the lachrymal fluid?
Tears
Lachrymal fluid buffer capacity
Have a great degree of buffer capacity
Dilution value of lachrymal fluid
15
a dilution of 1:15 with neutral distilled water is possible before an alteration of pH is noticed. This would be referred today as dilution value rather than buffer capacity.
pH of tears
7.4
7-8
However, CO2 in the air makes conjunctival fluid more acidic
Minimum and maximum pH of the lachrymal fluid
6.6 - 9
Effect of phosphate buffer on the eye
phosphate buffer produced irritation in the eyes, due to its high capacity
Buffers in the parenteral solution
Parenteral solutions for injection into the blood are usually NOT buffered or buffered to a low capacity so that the buffers of the blood may readily bring them within the physiologic pH range, due to the large volume of thhe blood
pH of the urine
6
Minimum and maximum pH of the urine
4.5-7.8
Response of the kidney to the pH of the urine
When the urine pH is below normal values, hydrogen ions are retained by the kidneys and when the urine pH is above 7.4, hydrogen ions are excreted by the kidneys to return the pH to its normal value.
What can alter the pH of the urine?
Some food and drinks
pH of the human body
7-8
Rrange of the pH in the body
1-10
HCl buffer consists of
Hydrochloric acid
Potassium chloride
Sodium chloride
Why is potassium chloride added to the HCl buffer?
Adjust the ionic strength
Influence of Buffer Capacity and pH on Tissue Irritation
•The lower the buffer capacity of the pharmaceutical solution.
•The smaller the volume of the pharmaceutical solution used.
•The larger the volume and buffer capacity of the physiological fluid where pharmaceutical solution is used..
Weak acidic drug ionise in which medium?
Basic medium
Which ffoorm of the acid is soluble
Ionic form
Which form of the buffer is soluble
Ionic form
Which form of the buffer will pass to the cells through the ppm
Non ionized
Ionized dissolve in water
True or false
The buffer stay non ionic at the same pH
True
True or False
it is important that the drug will be in unionized form in the part of the body where it is placed to be absorbed.
True
So it can pass through the cell
Choice of buffer depends on
the desired pH and buffering capacity, compatibility with other excipients, toxicity
