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Lab Skills Recap
Biotech II
Metrology Vocabulary
Unit of measurement
 Accuracy
 Precision
 Standards
 Calibration

Verification
 Traceability
 Tolerance
 Errors
 Uncertainty

Units of Measurement

Units define measurements & give the
numbers value
Accuracy vs Precision


Accuracy is how close an individual value is to the
true or accepted value
Precision is the consistency of a series of
measurements
From Basic Laboratory
Methods for
Biotechnology:
Textbook and
Laboratory Reference,
Seidman and Moore,
2000
Expressions

Accuracy

% error = True value – measured value X 100%
True value
Precision
Expression of variability
 Take the mean (average)
 Calculate how much each measurement
deviates from mean
 Take an average of the deviation, so it is the
average deviation from the mean

Recording Measurments




With analog values, record all measured values
plus one that is estimated
Scientific Notation
Rounding
Significant Digits




The digits 1 - 9 always count. (51 has 2)
Zeroes between the digits 1 - 9 always count. (501 has 3)
Zeroes in the beginning of a number never count. (0.00501 only
has 3)
Zeroes at the end of a number count only if there is a written
decimal point. (5010 has 3, 501.0 has 4)
Validity of a Measurement





Measurements should be made in accordance with
an external authority
A standard is an external authority
Verification is the checking of the performance of
an instrument or method without adjusting it.
Calibration is the bringing of a measuring system
into accordance with external authority, using
standards
Tolerance is the amount of error that is allowed in
the calibration of a particular item
Error

Error is responsible for the difference
between a measured value and the “true”
value
Gross (blunders)
 Random - errors that cannot be eliminated
 Systematic - measurements that are consistently
too high or too low, bias


Estimate of the inaccuracy of a
measurement that includes both the random
and systematic components
Lab Equipment

Volumes
Large volumes
 Small to medium volumes
 Very small volumes.


Mass
Table top balance
 Analytical balance (<10 mg)

Solution Prep




Solution: a homogeneous mixture in which
one or more substances are dissolved in
another.
Solute: substances that are dissolved;units
are often g, mg, or µg
Solvent: substances in which solutes are
dissolved (often times this is water or a buffer); units are
often L, ml, or µl
Concentration: amount per volume mass/vol;
units are g/L, g/ ml, mg/ml, molar
Ways to express solutions
Mass per volume (mg/ml)
 % mass/volume (5% = 5g/100 ml)
 Molarity (moles/Liter)
Make 100 µl of a 100 mg/ml solution

100 µl = 0.100 ml
Make 100 ml of a 10 mM NaOH
1 mole of NaOH = 40 g
10 mM = 0.01 moles/L
1L = 1000 ml
0.100 ml x 100 mg = 1mg = .001 g
ml
Make 1 L of 10% NaOH
1 L = 1000 ml
100 ml x 0.01 moles x 40g =
1000 ml mole
.04g
1000 ml x 10 g = 100 g
100 ml
Acids, Bases







Acids
Produces H+ ions in
solution
H2CO3
pH less than 7
Sour tasting
Corrosive
Conducts electricity
Neutralized bases







Bases
Produces OH- ions in
solution
Mg(OH)2
pH greater than 7
Bitter tasting; slippery
Corrosive
Conducts electricity
Neutralizes acids
pH
Measurement of H+ion concentration
 -log of H+ ion concentration
 1 x 10 -4 H+ is equal to a pH of 4
 1 x 10 -1 H+ is equal to a pH of 10
 pH can be measured with a pH meter

Spectrophotometry
Spectrophotometers are instruments that
measure the interaction of light with
materials in solution
 Spectrophotometers compare the light
transmitted through a sample to the light
transmitted through a blank.
 The blank contains everything except the
analyte (the material of interest)

Quantitative Spectrophotometry




Measure the absorbance of standards
containing known concentrations of the
analyte
Plot a standard curve with absorbance on
the X axis and analyte concentration on the
Y axis
Measure the absorbance of the unknown(s)
Determine the concentration of material of
interest in the unknowns based on the
standard curve