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Lab Skills Recap Biotech II

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

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Units of Measurement Units define measurements & give the numbers value

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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

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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

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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)

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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

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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

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

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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

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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 g 10 mM = 0.01 moles/L 1L = 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

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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

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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

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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)

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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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