DILUTING SOLUTIONS,Diluting from One Strength to Another, Single Dilutions & Serial Dilutions

DILUTING SOLUTIONS

Diluting from One Strength to Another

Single Dilutions & Serial Dilutions

 

DILUTING SOLUTIONS

It is frequently necessary to dilute solutions during various laboratory investigations. To dilute a solution is to reduce its concentration, i.e., make a weaker solution from a stronger one. It is therefore necessary for a laboratory worker to be capable of solving simple dilution problems. The dilutions can be single or in series.

Diluting from One Strength to Another

A weaker solution can be prepared from a stronger solution by using the following formula: = RV/O

Where

 R = Required concentration

V = Volume of solution required

0 = Original concentration

Examples 

1. To make 1 litre of 0.1 mol/L solution of sodium hydroxide (NaOH) from 0.5 mol/L solution. 

R = 0.1 mol/L 

V = 1000 ml 

0 = 0.5 mol/L

Therefore, measure 200 ml of 0.5 mol/L NaOH and make it up to 1000 ml with

distilled water. 

2. Given 30 % solution, prepare 500 ml of a 9% solution.

Therefore, measure 150 ml of 30 % solution and make it up to 500 ml with distilled water.

3. Make 15 ml of 1:50 dilution of blood. In this case R = 1/50

V=15 ml

0 = 1

Therefore, to prepare 15 ml of 1:50 dilution, add 0.3 ml of blood to 14.7 ml of diluent.

Single Dilutions

Single dilutions are required when (1) the concentration of a substance in a solution is too great to be accurately determined, (2) the amount of specimen is less than the procedure requires.

Single dilutions are usually expressed as a ratio such as 1:2, 1:5 or 1:10, or as a fraction 1/2, 1/5 or 1/10.

To prepare 1:2 dilution, take 1 volume of original solution and add to 1 volume of diluent.

To prepare 1:5 dilution, take 1 volume of original solution and add to 4 volumes of diluent.

To prepare 1:10 dilution, take 1 volume of original solution and add to 9 volumes of diluent. 

Dilution factor When the diluted sample is used for an estimation instead of undiluted sample, a dilution factor is used to correct for the final result of estimation.

For example, 1:10 dilution of a specimen is used for the estimation of a substance, the concentration of the substance in the dilution should be multiplied by 10 to obtain the final concentration in the original specimen.

Serial Dilutions

Many laboratory procedures such as serological methods, make use of a series of dilutions which are referred to as serial dilutions. A complete dilution series may consist of 5 to 10 tubes. A fivetube two fold or doubling dilutions may be performed as follows (Fig. 4.2):

Place 1 volume of diluent in tube number 2 to 5.

Add I volume of specimen in tube numbers 1 and 2.

Mix the contents of tube number 2 and transfer 1 volume to tube number 3.

Repeat the same procedure up to tube number 5 and discard I volume from the fifth tube.

Thus the specimen in tube number 1 is undiluted.

Tube 2 contains 1 vol. of specimen and 1 vol. of diluent, therefore, the dilution is 1: (2 x 1), i.e., 1:2

Tube 3 contains 1 vol. of 1:2 dilution and 1 vol. of diluent, therefore, the dilution is 1: (2 x 2), i.e., 1:4.

Tube 4 contains 1 vol. of 1:4 dilution and 1 vol. of diluent, therefore, the dilution is 1:(2 x 4), i.e., 1:8.

Tube 5 contains 1 vol. of 1:8 dilution and 1 vol. of diluent therefore, the dilution is 1: (2 x 8), i.e., 1:16.

Serial dilutions may also be 5 fold or 10 fold in which case the original specimen is diluted 5 or 10 times. It is important that all the tubes in the serial dilutions must have equal final volume.