CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
FIGURE 9-8 Refractometer that compares solutions with air.
Source: Delmar/Cengage Learning.
FIGURE 9-9 Refractometer scale showing a specific gravity of
1.034; note the scale for serum or plasma protein.
Source: Delmar/Cengage Learning.
Preparing Solutions from a More Concentrated
Strength to a More Dilute Strength
Some reagents are labeled as dilute, concentrated, saturated, or supersaturated.
This does not indicate a definitive measure as to the concentration of
a reagent. Temperature, presence of other ions (charged particles), and other
factors greatly affect the amount of solute that can be dissolved in a solution.
These terms are more qualitative than quantitative in nature. A dilute
specimen contains little solute, while a concentrated solution contains much
more. A supersaturated solution contains a great deal of undissolved solute
particles. Physical tests (also called colligative properties) may also be used in
diagnosing the disease state of a patient. For example, the osmolality or high
level of ions that are present in urine or plasma is determined by the effect
they have on the temperature at which the solution freezes.
Calculations for Obtaining the Desired Solution Strength
Most solutions can be bought from commercial suppliers. However, some solutions
come as concentrates, and it is necessary to prepare them according to
the strength needed. In addition, some solutions must be prepared as “working
reagents” by adding two or more solutions together. These reagents may be
required to be fresh, as the reactivity may be lost on standing for a period of time.
In Figures 9-10 and 9-11, two methods of preparing solutions are provided.
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