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Lab Skills Recap
Biotech II
Metrology Vocabulary
Unit of measurement
 Accuracy
 Precision
 Standards
 Calibration
 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
From Basic Laboratory
Methods for
Textbook and
Laboratory Reference,
Seidman and Moore,
% error = True value – measured value X 100%
True value
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
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
Tolerance is the amount of error that is allowed in
the calibration of a particular item
Error is responsible for the difference
between a measured value and the “true”
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
Large volumes
 Small to medium volumes
 Very small volumes.
Table top balance
 Analytical balance (<10 mg)
Solution Prep
Solution: a homogeneous mixture in which
one or more substances are dissolved in
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
Make 1 L of 10% NaOH
1 L = 1000 ml
100 ml x 0.01 moles x 40g =
1000 ml mole
1000 ml x 10 g = 100 g
100 ml
Acids, Bases
Produces H+ ions in
pH less than 7
Sour tasting
Conducts electricity
Neutralized bases
Produces OH- ions in
pH greater than 7
Bitter tasting; slippery
Conducts electricity
Neutralizes acids
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
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
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