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MLAB 2401:Clinical Chemistry

Chapter 3: Basic Principles and Practice of Clinical Chemistry, part 1

UNITS OF MEASURE

Measurement requires a numerical value and a unit

SI units: length ( meter ) mass ( gram ) quantity ( mole ) Volume ( liter ) Time ( second )

Basic units describe unrelated physical quantities

Laboratory results almost always have units of measurement associated with them

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Unit of Measure: Prefixes

Common prefixes that are added to units of measure: deci (d) 10-1

centi (c) 10-2

milli (m) 10-3

micro ( μ) 10-6

nano (n) 10-9

pico (p) 10-12

femto (f) 10-15

Example: A common unit of liquid measurement is a deciliter( dl ), or one – tenth of a liter

Combine a prefix with a basic unit results in a statement of a specific length, weight or volume Reporting clinical chemistry results may be in units such as :

mg / dL g / dL mEq / L

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Conversions

Most conversions within the metric system occur in units of TEN where changing a unit of measure to a higher or lower designation requires moving the decimal one place either to the left or to the right.

When converting measures in either the high end of the scale (example kilo to mega) or the low end of the scale (examples milli to micro, micro to nano, etc.) the decimal must be moved three places right or left as the prefix designations are assigned only to every third unit in the extreme ends.

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Example of a conversion

How many mls are there in 2.5 liters?

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The question you have to ask yourself is, what is the relationship between liters and mls? The answer : 1 liter = 1000 ml But now what?

We want to get rid of the “liters’ units and end up with “mls” … Right ?

mls 2500 Liter 1

mls 1000Liter 2.5

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1 2 51 0 0 0

11 2 5 0. L iters

m ls

L iterm ls

1.25 liters = _____ mls ? Remember, write a fraction that does two things:

1. Equals 1 2. Gets rid of unwanted units and / or adds needed units

100 mg = _________ ug ?

1 0 01 0 0 0

11 0 0 0 0 0mg

ug

mgug

,

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Another conversion example

“Physiological Saline” is used in Blood Banks and Hematology to prepare Red Blood Cell suspensions.

Physiological Saline is usually listed as being 0.9 % NaCl 0.9 grams of NaCl is added to 100 mls deionized water to make

physiological saline What is the Normality (N) of physiological saline?

0 9

1 0 0

1

5 8

1 0 0 0

10 1 5

..

gram s NaC l

m ls w ater

EqW t N aC l

gram s

m ls

L iterN

Fraction = 1 Fraction = 1

Conversions are manipulations of the units – not the values !!!

Unwanted units cancel outleaving EqWt / Liter = N

Scientific Notation

True scientific notation format: 1.22 X 104

BUT in hemo, for example a hemoglobin result would look like = 12.2 X 103

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Temperature

Scientific measurement of temperature is always expressed in the Celsius ( C) scale , not Fahrenheit ( F )

Measurement of temperature is an important component of the clinical lab. Instruments, refrigerators and incubators are required to operate within specific temperatures that must be maintained and monitored.

Each laboratory must have a NIST calibrated thermometer in order to ensure the accuracy of other thermometers in the laboratory

Celsius scale: 0 degrees = freezing point of water

100 degrees = boiling point of water

Conversion of Celsius to Fahrenheit and Fahrenheit to Celsius

F° = ( C ° x 1.8 ) + 32

C° = ( F ° - 32 ) 1.8

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Conversion: Temperature

Conversion of Celsius to Fahrenheit and Fahrenheit to Celsius

F° = ( C ° x 1.8 ) + 32

C° = ( F ° - 32 ) 1.8

For example: Your refrigerator at home is probably around 40 ° F. What is that in Celsius?

Celsius= 40-32 = 4.4 1.8

Water boils at 100 ° C. What is that expressed in Fahrenheit?

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Fahrenheit 1 8 1 0 0 3 2 2 1 2.

Solutions

The clinical lab almost always uses solutions. A solution means that something has been dissolved in a liquid. In the clinical laboratory the solvent we measure most of the time is human plasma. The solute is whatever the substance is we want to measure.

Mixtures of substances – the substances in a solution are not in chemical combination with one another.

Dispersed phase - the substance is dissolved (the solute) The substance in which the solute is dissolved is the solvent. Solute + Solvent = Solution

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Concentration

Concentration – refers to the amount of one substance relative to the

amounts of the other substances in the solution. Expressing Concentration

Percent solution (parts/100) % w/w – percentage weight per weight

Most accurate method of expressing concentration, but can be cumbersome (especially with liquids), not often used in clinical labs.

Example :mg/gm

% w/v – percentage weight per volume Easiest & most commonly used, very accurate if temperature controlled. Example : mg/dL

% v/v –percentage volume per volume Least accurate, but used when both substances are liquids Example : mL/L

Note: volumes of liquids are not necessarily additive.

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Solution Properties

Concentration can be measured in many different units

% Solutions: w/w, v/v , w/v (parts of solute / 100 totals parts ) Note: liquids + liquids and solids + solids alters the total parts, but solutes + solvents does not

Molarity: Moles / Liter

Molality: Moles / 1000 grams solvent

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What is a Mole?

Mole = 6.022 X 1023 number of atoms or molecules

Molecular Weight

The molecular weight( MW ) of hydrogen = 1.0 That means that 6.022 X 1023 hydrogen atoms weighs 1.0 gram

The MW of H2O = (1)(2) + (16) = 18 1 mole of water weighs 18 grams That means that 6.022 X 1023 H2O molecules weigh 18.0 grams

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Solution Properties

Normality (normal solutions): Equivalents Weights / Liter Working with normality, is most important when

dealing with acid or bases in neutralization reactions.

Equivalent Weight = MW / Valence

Valence = the electrical charge of an ion, or the number of moles that react with 1 Mole H+

Equivalent Weight

Equivalent Weight = Molecular Weight / Valence

The valence is the electrical charge of the substance 1 Equivalent weight of any substance reacts with 1 Equivalent Weight

of hydrogen ions

Example

The MW of calcium = 40 grams Calcium ions carry a +2 electrical charge ( valence = 2 ) Equivalent Weight of calcium = 40 / 2 = 20 grams

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Solution Properties

Normality N = M x valence M = N / valence M is always < N

Calculation tips Use ratio and proportion when NOT changing concentration. For calculations changing concentrations (as in titrations), use:V1C1

= V2C2 Important to remember that you cannot make a solution more

concentrated.

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Solution Properties

Titration – Method of measuring concentration of one solution by comparing it with a measured volume of a solution whose concentration is known

General formula: when you have a volume and concentration of one, and either the volume or the concentration of the other: V1 C1 = V2 C2

For Example:

How many mls of 1.0 N HCl is required to prepare 25 mls of 0.5 N HCl ?

( 1.0 N ) ( ? mls ) = ( 0.5 N ) ( 25 mls )

? mls = 12.5 mls

You would need to add 12.5 mls of 1.0 N HCl to 12.5 mls of deionized water

( a total volume of 25 mls ) to prepare 25 mls of 0.5 N HCl

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pH and Buffers

Buffers resist change in acidity Buffers are usually weak acids ( or bases) and their salts

pH is the unit used to measure acidity ( Hydrogen ion concentration ) “p” = “negative log” of the concentration of a substance in solution. Example: pH = - log [H+]

The Hydrogen ion concentration of deionized H2O is 1 x 10-7 M The negative log of 10-7 = 7. The pH of H2O is 7.0

The pH scale ranges from 0 - 14 pH 7 = neutral pH > 7 = alkaline (basic) pH < 7 = acid

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H

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Dilutions

A ratio of the concentrate to the total (final) volume. A 1:4 dilution has a 1 volume of sample and 3 volumes of diluent mixed

together.

Any volume can be used to create this dilution, but it must be the same unit of volume

Keep in mind the sample size when making your dilution For example: a 2:3 dilution could contain:

2 mL serum: 1 mL pure water 20 µL of serum: 10 µL of pure water 0.2 mL of serum: 0.1 mL of pure water

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Dilutions

Find the dilution factor:

0.1 mL serum 0.1 mL serum = 1 2.9 mL DI water 5.0 mL total X 1.0 mL reagent A 1.0 mL reagent B 5.0 mL total volume

X = 50 (that is the dilution factor) Dilution is 1/50

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Examples of dilutions and dilution factors

Parts Parts Total Dilution Dilution Specimen Diluent Volume Factor

1.0 1.0 2.0 1 : 2 2

1.0 2.0 3.0 1 : 3 3

1.0 3.0 4.0 1 : 4 4

1.0 9.0 10.0 1 : 10 10

0.5 4.5 5.0 1 : 10 10

0.2 1.8 2.0 1 : 10 10

0.2 9.8 10.0 1 : 50 50

Serial Dilutions

In these types of questions, you are given a series of tubes. Each tube having a measured amount of a diluent. You are instructed to add a specified amount of specimen into the first

tube, mix well and transfer a specified amount of the mixture to the next tube, etc.

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Serial Dilutions

Example: 6 tubes, each with 0.5 mL DI water Add 0.2 mL serum to first tube and serially dilute Find the dilution in tube # 6

Find the dilution factor (will be the same in each of these tubes)

1/dil factor x 1/dil factor x 1/dil factor (etc. 6 times) Result multiplying the numerator 1x1x1x1x1x1x1x = 1 Multiplying the denominators

Will give the result as 1 / 838

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Resources

http://www.youtube.com/watch?v=ZqdU3VfQ_Tc

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Solution Properties

Density – An expression in terms (usually) of a mass per unit of volume

Many examples - including specific gravity, osmolality

Water Specifications

Tap water is unsuitable for lab use (too many impurities)

Types of water purification techniques Distillation – removes most organic matter Reverse osmosis Filtration Deionization – ions removed

Reagent Grades of water Type I Purest – Required for sensitive tests Type II Acceptable for most uses Type III OK for washing glassware

CAP - QC of water : pH, electrical resistance, bacterial culture

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Water filtration system forAutomated chemistry analyzer.