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Lab Skills Recap

Lab Skills Recap. Biotech II. Metrology Vocabulary. Verification Traceability Tolerance Errors Uncertainty. Unit of measurement Accuracy Precision Standards Calibration. Units of Measurement. Units define measurements & give the numbers value. Accuracy vs Precision.

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Lab Skills Recap

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  1. Lab Skills Recap Biotech II

  2. Metrology Vocabulary • Verification • Traceability • Tolerance • Errors • Uncertainty • Unit of measurement • Accuracy • Precision • Standards • Calibration

  3. Units of Measurement • Units define measurements & give the numbers value

  4. 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

  5. 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

  6. 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)

  7. 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

  8. 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

  9. Lab Equipment • Volumes • Large volumes • Small to medium volumes • Very small volumes. • Mass • Table top balance • Analytical balance (<10 mg)

  10. 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

  11. 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 0.100 ml x 100 mg = 1mg = .001 g ml Make 100 ml of a 10 mM NaOH 1 mole of NaOH = 40 g 10 mM = 0.01 moles/L 1L = 1000 ml 100 ml x 0.01 moles x 40g = .04g 1000 ml mole Make 1 L of 10% NaOH 1 L = 1000 ml 1000 ml x 10 g = 100 g 100 ml

  12. 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 Acids, Bases

  13. 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

  14. 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)

  15. 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

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