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:
- Temperature.
- Atmospheric pressure.
- Nature of the solute.
- Nature of the solvent.
The following are the type of solutions commonly used in the clinical laboratory.
Percent solution
- This is defined as parts per 100, which represents the percent (%).
- This is independent of the molecular weight of the substance.
- This is expressed as a solute concentration as a percent % (per hundred parts of the total solution).
- 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:
- Weight/weight (weight per unit weight)
- The % of a solute or grams of solute per 100 grams of the final solution.
- Example:
- To make a 100 G of a 5% of an aqueous solution of HCl (using 12 M HCL).
- Calculation =
- 5 % = 5/100 = 0.05
- Therefore 0.050 x 100 = 5 grams of HCL.
- Another example is:
- 5 grams Na2SO4 dissolved in 95 grams of water (roughly 95 mL). Total weight of 100 grams (solute + solvent).
- The % of a solute or grams of solute per 100 grams of the final solution.
- Weight/volume (weight per unit volume):
- 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).
- Examples:
- This is usually expressed as gram/100 mL of diluent.
- To make a 10 % solution, add 10 grams of the substance to a final volume of 100 mL of liquid.
- 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:
- Volume/volume (volume per unit volume V/V):
- This is convenient for the composition of two liquids.
- Example:
- if you want to make 50 mL of 2% HCl.
- Calculation:
- 0.20 x 50 = 1 mL
- Therefore add 49 mL of water to 1 mL of HCL.
- Calculation:
- 5% of the glacial acetic acid solutions:
- 5 mL of glacial acetic acid diluted with distal water to a volume of 100 mL.
Molar solution
-
- This is defined as units of moles per liter (mol/L).
- The symbol M indicates molarity is replaced by mol/L
- or millimoles/millimeter (mmol/mL).
- 1 Mol of a substance = gram molecular weight of that substance.
- Example:
- Makeup 250 mL of a 4.8 molar solution of HCl.
- HCL molar weight = 36.5 g.
- 36.5 HCL/mol x 4.8 mol HCL/L x 250/1000 mL = 43.8 g HCL
- 250 mL H2O + 43.8 = 4.8 Molar solution.
- The One molar solution of H2SO4:
- It contains 98.08 g/L of the solution.
- Example:
Normal solution
-
- Normality (normal solution) is defined as gram equivalent weight per liter (eq.wt/L).
- OR milliequivalent weight/milliliter (meq / mL).
- Equivalent weight = gram weight/valency.
- Example:
- NaCl gram weight = 58 gram and valency = 1
- 58/1 = 58 grams equivalent weight per liter.
- Normality (normal solution) is defined as gram equivalent weight per liter (eq.wt/L).
Simple Dilution
-
- This is defined as the total volume desired and the amount of stock needed.
- Example:
- 1: 10 dilution = ratio of 1 : 9 = 1 : 10 = one part of serum + 9 parts of diluent.
- 100 μL + 900 μL of saline.
- 1 mL serum + 9 mL of saline.
- 2 mL serum + 18 mL of saline.
Serial Dilution
- This is defined as multiple progressive dilutions ranging from a more concentrated solution to a less concentrated solution.
- Serial dilutions are useful in a small quantity of serum and to find the titer of antibodies.
- The first dilution is made just like the simple dilution.
- Now subsequent dilutions are made from each preceding dilution.
- If you want to make a serial dilution of 1: 2, 1: 4, 1: 8, 1: 16, and so on.
- The total volume is fixed; suppose it is 1 mL.
- (Initial dilution factor) (next dilution factor) = final dilution factor
- 1 : 2 x 1 : 2 = 1 : 4.
- Procedure
- First tube = (1 mL serum + 1 mL diluent) = 1 : 2
- Second Tube = 1 mL from from ist tube + 1 mL diluent = 1 : 4
- Third tube = 1 mL from tube 2 + 1 mL diluent = 1 : 8
- Fourth tube = 1 mL from tube 3 + 1 mL diluent = 1 : 16
Good