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Units of Measurement Units define measurements & give the numbers value
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Lab Skills RecapBiotech 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)
100 µl = 0.100 ml
0.100 ml x 100 mg = 1mg = .001 g ml
1 L = 1000 ml
1000 ml x 10 g = 100 g 100 ml
1 mole of NaOH = 40 g10 mM = 0.01 moles/L1L = 1000 ml
100 ml x 0.01 moles x 40g = .04g 1000 ml mole
Make 100 ml of a 10 mM NaOH
Make 1 L of 10% NaOH
Make 100 µl of a 100 mg/ml solution
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