Solutions:- Part 1 – Solutions Preparation used in Clinical Laboratory, and Dilution Formula

Definition of the solution:

A solution is a homogenous mixture of one or more substances called solutes dispersed molecularly in a sufficient quantity of dissolving medium called solvent.

• When a solution holds as much as a dissolved solute as it can at a specific temperature, it is called a saturated solution.

Saturation of the solution depends upon:

1. Temperature.
2. Atmospheric pressure.
3. Nature of the solute.
4. Nature of the solvent.

The following are the type of solutions commonly used in the clinical laboratory.

Percent solution

1. This is defined as parts per 100, which represents the percent (%).
   1. This is independent of the molecular weight of the substance.
   2. This is expressed as a solute concentration as a percent % (per hundred parts of the total solution).
2. If you want to make a 5% glucose solution, you will add 5 grams of glucose in 100 ml of distal water.

Percent solution types are:

1. Weight/weight (weight per unit weight)
   
   1. The % of a solute or grams of solute per 100 grams of the final solution.
      1. Example:
      2. To make a 100 G of a 5% of an aqueous solution of HCl (using 12 M HCL).
   2. Calculation =
      1. 5 % = 5/100 = 0.05
      2. Therefore 0.050 x 100 = 5 grams of HCL.
         

         Solution weight/weight example

   3. Another example is:
      1. 5 grams Na₂SO₄ dissolved in 95 grams of water (roughly 95 mL). Total weight of 100 grams (solute + solvent).
2. Weight/volume (weight per unit volume):
   1. This is an expression of weight (mass) per unit volume. This W/V is used most often when the solid chemical is diluted in liquid. Weight per unit volume is as grams per liter (g/L) or milligram per milliliter (mg/mL).
   2. Examples:
   3. This is usually expressed as gram/100 mL of diluent.
      1. To make a 10 % solution, add 10 grams of the substance to a final volume of  100 mL of liquid.
      2. If a solution with a concentration of 10 mg/mL is required, and 100 mL of this solution is to be prepared, the use of a proportional formula can be used  as follows:
         

         Solution weight / volume example

3. Volume/volume (volume per unit volume V/V): 
   1. This is convenient for the composition of two liquids.
   3. Example:
   4. if you want to make 50 mL of 2% HCl.
      1. Calculation:
         1. 0.20 x 50 = 1 mL
         2. Therefore add 49 mL of water to 1 mL of HCL. 
            

            Solution volume by volume example

   5. 5% of the glacial acetic acid solutions:
      1. 5 mL of glacial acetic acid diluted with distal water to a volume of 100 mL.

Molar solution

1. 1. This is defined as units of moles per liter (mol/L).
   2. The symbol M indicates molarity is replaced by mol/L
      1. or millimoles/millimeter (mmol/mL).
   3. 1 Mol of a substance = gram molecular weight of that substance.
      1. Example:
         1. Makeup 250 mL of a 4.8 molar solution of HCl.
         2. HCL molar weight = 36.5 g.
         3. 36.5 HCL/mol x 4.8 mol HCL/L x 250/1000 mL = 43.8 g HCL
         4. 250 mL H2O + 43.8 = 4.8 Molar solution.
      2. The One molar solution of H2SO4:
         1. It contains 98.08 g/L of the solution.

Normal solution

1. 1. Normality (normal solution) is defined as gram equivalent weight per liter (eq.wt/L).
      1. OR milliequivalent weight/milliliter (meq / mL).
   2. Equivalent weight = gram weight/valency.
   3. Example: 
      1. NaCl gram weight = 58 gram and valency = 1
      2. 58/1 = 58 grams equivalent weight per liter.

Simple Dilution

1. 1. This is defined as the total volume desired and the amount of stock needed.
   2. Example:
   3. 1: 10 dilution = ratio of 1 : 9 = 1 : 10 = one part of serum + 9 parts of diluent.
      1. 100 μL + 900 μL of saline.
      2. 1 mL serum + 9 mL of saline.
      3. 2 mL serum + 18 mL of saline.

Serial Dilution

1. This is defined as multiple progressive dilutions ranging from a more concentrated solution to a less concentrated solution.
2. Serial dilutions are useful in a small quantity of serum and to find the titer of antibodies.
3. The first dilution is made just like the simple dilution.
4. Now subsequent dilutions are made from each preceding dilution.
5. If you want to make a serial dilution of 1: 2, 1: 4, 1: 8, 1: 16, and so on.
   1. The total volume is fixed; suppose it is 1 mL.
   2. (Initial dilution factor) (next dilution factor) = final dilution factor
   3. 1 : 2 x 1 : 2 = 1 : 4.
6. Procedure
   1. First tube = (1 mL serum + 1 mL diluent) = 1 : 2
   2. Second Tube = 1 mL from from ist tube + 1 mL diluent = 1 : 4
   3. Third tube = 1 mL from tube 2 + 1 mL diluent = 1 : 8
   4. Fourth tube = 1 mL from tube 3 + 1 mL diluent = 1 : 16

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