CLINICAL LAB SCIENEC

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ESSENTIALS OF CLINICAL LABORATORY SCIENCE
process where water is passed through a semipermeable membrane under pressure,
which removes roughly 90% of the impurities from dissolved solids such
as minerals, and perhaps 98% of organic impurities, including microorganisms
and other undissolved materials. Reverse osmosis does not remove carbon dioxide
and other dissolved gases, and removes only a tenth of ionized particles.
Filtration removes insoluble materials, and activated charcoal, clays, and other
materials can be used to remove organic materials. These methods result in the
production of Type I water.
Measuring Solution Strength
A concentration of an analyte (material being tested for) is expressed in several
ways. The most common methods for measuring concentrations or strength of
the reagent’s active component would be expressed as a percent solution, either
molar, molal, or normal. These terms for measurement mainly relate to preparing
basic chemical solutions but are no less important when performing chemical
reactions on body fluids. The amount of specimen and the amount of analytes in
the specimen is based on concentration, and calculating the results often requires
a factor for the dilution of the ratio of sample and reagent.
Percent Solutions
Percent solutions refer to the amount of solute expressed as parts per 100 parts
of solution. As an example, a 10% solution would have 10 parts of solute and 90
parts of solvent, making a total of 100 parts. Rarely, one will have the situation
where there would be 10 parts in 100 parts of solvent. This situation would be
expressed as 10 in 100, as the total volume would then be 110 parts. Therefore,
this would be different from a 10% solution. For general laboratory use, percent
solutions are most often used in performing tests that require they be made fresh
by the laboratory worker. Figure 9-4 shows two methods of preparing percent
solutions. A is a weight-to-volume (w/v) problem, and B is a volume-to-volume
(v/v) problem.
Molar Solutions
A molar solution refers to a type of reagent sometimes prepared for use in the
clinical laboratory. Molarity refers to the number of moles (mol) of solute
per liter (L) that are dissolved in a solution. Commercially prepared chemistry
reagents for performing clinical chemistry tests are often made as a molar solution.
Test results may be based on the amount of solute called a substrate that
is found in specific amounts in the reagent. One mole of a substance, which is
its gram molecular weight (gmw), when dissolved in 1 liter (L) of solvent is a
molar solution of 1 mol/L, or 1 M. The SI unit of measurement for many chemistry
procedures is based on millimoles/L (10 –3 or thousandths). Sometimes, for
analytes found in very small amounts in the human body, the reagents will be in
micromoles/L (10 –6 or millionths), and nanomoles/L (10 –9 or billionths). Figure
9-5 shows the information needed and the calculations for preparing a molar
solution of sodium hydroxide (NaOH).
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