BUFFERS IN

CHEMICAL

ANALYSIS

Chirag Patel

an unbuffered solution

or a buffered solution

acid added base added

acid added base added

What exactly is a buffer?

A buffer solution is a solution which resists changes in pH when a

small amount of acid or base is added.

The resistive action is the result of equilibrium between the weak acid

(HA) and its conjugate base (A-).

HA(aq) + H2O(l) → H3O+

(aq) + A-(aq)

• A buffer works best in the middle of its range, where the amount of

undissociated acid is about equal to the amount of the conjugate

base.

• Commonly used in biological systems.

• Enzyme-catalyzed reactions depend on pH.

When an acid is added, the conjugate base converts the excess H3O

+ ion into its acid (conjugate base removes excess H3O+)

H3O+

(aq) + A-(aq) → HA(aq) + H2O(l)

When a base is added, the acid converts the excess OH- ion into its conjugate base and water (acid removes excess OH- ion)

HA(aq) + OH-(aq) → A-

(aq) + H2O(l)

Buffer with equal concentrations of conjugate

base and acid

OH-H3O+

Buffer after addition of H3O+

H2O + CH3COOH H3O+ + CH3COO-

Buffer after addition of OH-

CH3COOH + OH - H2O + CH3COO-

In actual fact, the pH changes but very slightly

Large amounts of added H3O+ or OH- may overcome the buffer action

and change pH of solutions

Buffers are most effective when the ratio of acid to conjugate base is 1:1

Buffers are less efficient in handling acids if the acid is more than the conjugate base

Buffers are less efficient in handling bases if the acid is less than the conjugate base

There are two kinds of Buffer Solutions:

I. ACIDIC BUFFER: A Weak Acid and the Salt of Its Conjugate

Base (useful in the acidic range)

• eg. 1.0 M CH3COOH & 1.0 M CH3COONa

II. BASIC BUFFER: A Weak Base and the Salt of Its Conjugate Acid

(useful in the basic range)

• eg. 1.0 M NH3 & 1.0 M NH4Cl

- A measure of how well a solution resists changes in pH

- Increases with increasing concentration of buffer

- Maximum when pH = pKa

- The greater the buffer capacity the less the pH changes upon addition

of H+ or OH-

-Choose a buffer whose pKa is closest to the desired pH

- pH should be within pKa ± 1

The buffer range is the pH range over which the buffer is effective.

Buffer range is related to the ratio of buffer component concentrations.

[HA]

[A-]The closer is to 1, the more effective the buffer.

If one component is more than 10 times the other, buffering action is

poor. Since log10 = 1, buffers have a usable range within ± 1 pH

unit of the pKa of the acid component.

• Calibration of pH meters

• Control of pH in industrial reactions

• Used in maintaining water quality

• Pools and hot tub

• Wine making

• pH balanced shampoos and deodorants

• Soil pH

• Minimizing effects of acid rain

Borax Neutraliser

• Boric Acid Neutraliser is an easy to use saturated solution

• usable at room temperature without precipitating out.

• Creates a boric acid/potassium borate buffer solution

Borax Decahydrate ( Powder )

[Na2B4O7 : 10H2O]

• Borax dissolves to form a boric acid/sodium borate buffer solution

• will not allow pH to be reduced too much, avoiding clouding.

• when using Borax to neutralise, although minimum pH achieved is

not quite as low as with other neutralisers.

• Cleopatra used raw milk which has the lactic acid in it.

• This is because it is unpasteurised and thus poses a potential health

risk.

• AHAs most commonly used in cosmetic products are glycolic acid

and lactic acid.

• AHAs function as pH adjusters, these are materials added to

products to make sure they are not too acidic or basic and are

therefore mild and non-irritating.

Alpha Hydroxy Acids(AHA)

• Triethanolamine, Diethanolamine and Ethanolamine are clear,

colourless, viscous liquids with ammonia-like odours.

• Triethanolamine is used in makeup products such as eyeliners,

mascara, eye shadows, blushers, etc. as well as in fragrances, hair

dyes, wave sets, sunscreens, skin care and skin cleansing products.

The carbonic acid-hydrogen carbonate buffer system.

Human blood plasma needs to have a pH between 7.35 and 7.45.

Acidosis and alkalosis.

The pH of blood is controlled by a mixture of buffers.

• The carbonic acid-hydrogen carbonate ion buffer is the most

important buffer system.

• Carbonic acid, H2CO3, acts as the weak acid

• Hydrogen carbonate, HCO3-, acts as the conjugate base

• Increase in H+(aq) ions is removed by HCO3-(aq)

• The equilibrium shifts to the left and most of the H+(aq) ions are

removed

• Any increase in OH-(aq) ions is removed by H2CO3

• The small concentration of H+(aq) ions reacts with the OH-(aq) ions

• H2CO3 dissociates, shifting the equilibrium to the right, restoring

most of the H+(aq) ions

• Most materials released into blood are acidic

• The HCO3- ions removes these by being converted into H2CO3

• This acid is converted into CO2(aq) through the action of an enzyme.

• CO2(aq) is converted into CO2(g) in the lungs, which is then exhaled

• The amount of CO2(aq) in the blood can be regulated by changing

breathing rate

• Heavy breathing removes more CO2(g)

• Breathing less quickly removes less CO2(g)

• The Chemistry of Natural Rainwater

• The Chemistry of Acid Rain

• The Buffering Capacity of Limestone Chemistry of Acid Rain

• During electrophoresis, the electric field electrolyses the water

molecules into H+ and OH- ions that migrate to the respective

migrate to the respective electrodes.

Glycine as buffer

• Unlike most other buffering compounds, which are capable of

stabilizing pH in only one pH range, glycine has two pH buffering or

stabilizing regions.

• The accompanying graph illustrates the change in pH after addition

of acid (HCl) or base (NaOH) to glycine. As you can see, glycine

exhibits excellent buffering action between pH 1.5 to 3.0 and

between pH 9.0 to 13.0.

Soft drinks, Lozenges and tablets

Syrups

Mouthwashes

Livestock feed

Antacids

Analgesics

Cosmetics

Antiperspirants

Toiletries

Pharmaceuticals

Agricultural chemicals

• Always buffer the aqueous component of the mobile phase

separately7. pH of the mobile phase and pKa of Analyte will change

in the presence of organic solvents

• High buffering power at prescribed pH.

• Does not damage column or equipment.

• It seems that using Ca(OH)2 resulted in steady hydrolysis due to its

buffering property.