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