Page 376 - The Veterinary Laboratory and Field Manual 3rd Edition

Clinical chemistry 345

2 To make 1 l hydrochloric acid (HC1), 0.01 mol/1 volume of serum required: 5/2 = 2.5 ml.
from a 1 mol/1 solution:
Therefore, to prepare 5 ml of a 1 : 2 dilution add
C = 0.01 mol/1 2.5 ml of serum to 2.5 ml of physiological saline.
V = 1 l
S = 1 mol/l 3 Calculate the dilution of blood when mixing
0.05 ml of blood and 0.95 ml of diluting fluid:
Volume of stronger solution required (X):
total volume of body fluid and diluting fluid:
0.01 × 1000/1 = X = 10 ml 0.05 + 0.95= 1.0 ml.

Therefore, measure 10 ml of HC1 (1 mol/1), and Therefore, dilution of blood: 1/0.05 = 20, that
make up to 1 l with distilled water. is, 1 : 20 dilution.

4 Calculate the dilution of urine using 1 ml of
Saturated solutions
urine and 9 ml of diluting fluid (that is, physi-
Saturated solutions are solutions which con- ological saline):
tain the maximum amount of solute which can
be dissolved in a given solvent at a given tem- total volume of urine and diluting fluid:
perature and pressure. Supersaturated solutions 1 + 9 =10 ml.
are those in which more solute is added than
can be dissolved. Salt crystals from saturated Therefore, dilution of urine 10/1 = 10, that is,
solutions may form around the neck of glass 1 : 10 dilution.
stoppered bottles causing the lid to stick, so it
is advisable to use screw capped Borex bottles Diluting techniques
instead.
Diluting techniques are simple but must be
dILutInG body FLuIdS and caLcuLatInG done with due care and with thorough mixing
dILutIonS between steps. The easiest method is to perform
Samples such as body fluids may need to be a stepwise dilution from the original solution
diluted in specific solvents for biochemical tests. into a series of containers containing diluent,
These need to be prepared carefully and handled see Figure 7.12.
according to the relevant laboratory protocol.

ExaMPLES Examples of simple qualitative tests
1 To make 10 ml of a 1 : 20 dilution of blood: for district laboratories

volume of blood required: 10/20 = 0.5 ml. Although most of the common biochemical
screening tests are now done using automated
Therefore, to prepare 10 ml of a 1 : 20 dilution, systems or simple dip-stick kits there can still
add 0.5 ml of blood to 9.5 ml of diluting fluid. be occasions where these are not available. The
following are five simple manual tests that can
2 To make 5 ml of a 1 : 2 dilution of serum in be performed in small district veterinary labo-
physiological saline: ratories, and which we have found useful, for

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