CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
1. What dilution factor would be needed to prepare a 50 mEq/L solution of NaOH (sodium
hydroxide) from a 2,000 mEq/L stock solution by diluting with distilled water?
Solution: 50 mEq/2,000 mEq = 5/200 or 1-to-25 dilution factor or 1:25
2. If 100 mL of the 50 mEq solution is needed, the dilution ratio of stock concentrate to total
volume must be observed. The ratio of the dilution needed is 1 mL of stock to 25 mL of
the diluent.
Solution:
1
= x
25 100
Therefore, 25x = 100, so x = 4. In order to maintain a total volume of the desired 100 mL,
96 mL of diluent would be added to 4 mL of the stock concentrate.
Serial Dilutions of Sample
It is sometimes necessary to quantitate the level of a component of the blood
serum or plasma by diluting the sample and then reacting the diluted samples.
For example, to quantitate the level of antibodies against a certain antigen, a
serum sample would require serial dilutions growing less and less concentrated,
and then reacting the diluted samples with the antigen. The last tube showing
a reaction would be the end-point and the results would be a semi-quantitative
result. The increasing dilution levels must be consistent, e.g., they must increase
from 1:2, 1:4, 1:8, etc., or 1:10, 1:20, 1:40, etc. See Table 9-9 for an example of
the dilutions for a two-fold dilution series.
Procedure for Serial Dilution
From Table 9-9, the procedure is as follows:
1. 1.0 mL from tube 1 mixture will be added to tube 2.
2. After mixing, 1.0 mL from tube 3 will be added to tube 4, and so on, until
all tubes have been treated. Note that each tube will contain 1 mL when the
mixture from the preceding tube is added.
Table 9-9 Serial Dilution Starting with a 1:2 Dilution
Table shows dilution factors when diluted specimens from previous tube are added to the next tube.
Tube 1 Tube 2 Tube 3 Tube 4 Tube 5 Tube 6 Tube 7 Tube 8 Tube 9*
Resulting ratio 1:2 1:4 1:8 1:16 1:32 1:64 1:128 1:256 1:512
Serum 1.0 mL … … … … … … … …
Diluent 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL
Diluted sample—from previous tube … 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL 1.0 mL
*The last tube will contain 2 mL, so 1.0 mL must be discarded.
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