Science & Research
Volume IV - 1.8 Orientation Exercises
Orientation and Training
|VERSION NO.: 1.3|
Section 1 - Laboratory Orientation
|EFFECTIVE DATE: 10/01/2003||REVISED: 02/14/2013|
- 1.8.1 Analytical Balances
- 1.8.2 pH Meters
- 1.8.3 Volumetric Glassware
- 1.8.4 Standard Solutions
- 1.8.5 Thermometers (optional)
- 1.8.6 Microscopes (optional)
The analyst becomes familiar with laboratory apparatus and glassware, preparation of standard solutions, and proper techniques that are common to many analytical procedures.
The completion of all or only parts of the orientation exercises listed in this section is left to the discretion of local management. Many of these exercises may not be applicable to the scientific discipline to which analysts are assigned. Therefore, these orientation exercises may be modified to meet the needs of the local laboratory.
- To determine how different laboratory balances function, their weight ranges, and their limitations.
- To develop techniques for accurate weighing.
- To determine which balances to use for a defined purpose (i.e. top-loader vs. analytical vs. microbalance).
- Determine the sensitivity at maximum load and at half maximum load of each type of balance assigned. Determine the minimum mass detected by balance(s).
- Weigh a nickel coin on the balance, remove the coin, and re-zero the balance. Repeat this process three times. Then repeat the process using another similar balance as well as a different type of balance. How do the weights compare? Repeat the process using a 100 mL beaker.
- Weigh five different nickels. Determine the average mass, the standard deviation (SD), the % relative standard deviation (%RSD), and the % error assuming that a standard nickel should weigh 5.000g.
- Obtain a standard set of weights and calibrate a top-loader balance using 0.5, 1, 5, 10 25, 50, and 100g weights. Plot the percent error against each weight tested. Are these errors within the limits set by the balance manufacturer?
- American Society for Testing and Materials International. (2003). E 617-97 Standard Specification for Laboratory Weights and Precision Mass Standards. Retrieve from http://www.astm.org.
- U.S. Pharmacopoeia and National Formulary (current ed.). (General Chapters, section 41, Weights and Balances, pp. 1689-1681). Gaithersburg, MD: Association of Official Analytical Chemists International.
- Skoog, D. A., West, D. M., Holler, F. J. (1990). Analytical chemistry an introduction(5th ed., p. 514). Philadelphia: Saunders College Publishing.
- USP General Notices and Requirements.
- Define precision. How is it related to accuracy? How does one measure precision?
- What is the USP definition of “accurately weighed” and how does it relate to “measurement uncertainty”. How is the measurement uncertainty of a balance determined?
- What do values of +/- 1 SD, of +/- 2 SD, and of +/- 3 SD tell us?
- What is the relationship between SD and % RSD. What is the benefit of using %RSD?
- Describe two possible ways in which samples could be contaminated during weighing.
- What are some of the common errors in weighing and describe how to minimize them?
To identify the principles involved in conducting an accurate potentiometric test by:
- Studying the operating principles of a pH meter and its electrodes.
- Examining the various electrodes and their use as well as examining other ways of determining pH.
- Carrying out simple determinations of pH.
- Review references, SOPs and operating manuals for each type of pH meter in the laboratory.
- Prepare and measure with a pH meter the pH of one or more of the buffers described in AOAC or USP/NF as directed by the trainer. Compare each measured pH to the theoretical value of the buffer(s). Plot buffer value versus measured pH.
- List and describe several electrodes in the laboratory. Discuss the use and proper care of each.
- List and describe each type of pH-indicating test paper used in the laboratory. What is the range of each? What is its accuracy? What are the storage parameters?
- List and describe several common pH end-point indicators in the laboratory.
- Draw and label a simplified schematic of a pH meter with reference and indicating electrodes.
- Measure the pH of deionized water. Why is the pH reading unstable? Why is the pH reading different than 7.00?
- AOAC official methods of analysis. (current ed.). Sections on "Buffer Solutions for Calibration of pH Equipment" and "Standard Buffers and Indicators for Colorimetric pH Comparisons" in Appendix: "Standard Solutions and Certified Reference Materials." Gaithersburg, MD: Association for Official Analytical Chemists International.
- U.S. Pharmocopeia and National Formulary (current ed.). (General Chapters, Section 791, "pH.", "Indicator and Test Papers." and "Buffer Solutions." ). Gaithersburg, MD: Association for Official Analytical Chemists International.
- Beyon, R. J., Easterby, J. S. (1996). Buffer solutions(ISBN 0199634424). Oxford, UK: BIOS Scientific Publishers.
- Calculate the pH of a 0.075 M solution of acetic acid; assume the Ka = 1.8x10-5 for acetic acid. Prepare such a solution and measure the pH, calculate the % error, and give at least three reasons for the error.
- Would a pH measurement in MeOH or in 50% MeOH - H2O be accurate? Why or why not?
- Define buffer capacity.
- List several factors involved in selecting a buffer for a given procedure.
- What is the useful range in buffering capacity about the pKa of the weak acid?
- Describe how to prepare a liter of 0.0100 M phosphate buffer at pH = 8.00 using only 10.0 M H3PO4 and a concentrated NaOH solution.
- Discuss the use of an "equivalent weight" of an acid or base.
- What kinds of determinations, other than pH, may be made using a pH meter? Give two examples.
- To develop good technique in the handling and use of volumetric glassware.
- To calibrate one or more pieces of laboratory volumetric equipment, to review National Institute of Standards and Technology (NIST) and USP/NF requirements for volumetric glassware, and compare these to the calibration values obtained.
- Review references.
- Obtain a density vs. temperature table for water and accurately calibrate each piece of volumetric glassware supplied by the trainer (e.g., volumetric pipet, volumetric flask, buret). Calculate the % error for each measurement and compare to stated accuracy.
- Measure the delivery times of two or three pipets of assorted volumes using a stopwatch. Compare with NIST, USP. etc., standards and manufacturers' specifications.
- Convert the volume of one of the measurements at temperature of measurement to the volume at 20°C and 25°C.
- Be prepared to explain the complete calibration operation, including all steps in the calculation, the use of significant figures, precision, and accuracy.
- Harris, D.C. (August 1998).Quantitative chemical analysis (5th. ed.).
- U.S. pharmacopoeia 25 and national formulary 20. (General Chapter, Section 31, “Volumetric Apparatus.”). Taunton, MA: Rand McNally.
- Leveson, D. J. (2002). Rounding of Numbers, How, When and Why. Retrieve version from http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/roundoff.html.
- Can all volumetric glassware be NIST certified?
- What do the letters "TC" and "TD" signify?
- Why should freshly boiled water be used in calibrating glassware?
- How would someone know when a piece of volumetric glassware is not clean? What method would be used to clean it?
- List the manufacturer’s % accuracy of the following types of volumetric equipment: Class A 10 mL pipette, Class A 100 mL volumetric flask, 10 mL Mohr pipette, 1 mL Auto Pipette, 10 uL Auto Pipette, 100 mL graduated cylinder, 250 mL graduated beaker.
- List several of the variables involved in correctly using a 10 mL volumetric pipette.
To identify the principles and techniques involved in conducting a successful, accurate standardization by:
- Using one or more official methods for standardization of volumetric solutions.
- Preparing one or more standard laboratory solutions for later use or for other analysts.
- Preparing an accurate dilution of a standard solution.
- Review references.
- Prepare a solution of 0.1 N NaOH, 0.1 N HCl, or other solutions as assigned by the trainer. Using an official method (AOAC or USP/NF), standardize the solution. Perform the analysis in triplicate and calculate the %RSD.
- Prepare100 mL of 0.01N NaOH from the standardized 0.1N NaOH to within 1% accuracy.
- AOAC official methods of analysis. (current ed.). (Appendix: “Standard Solutions and Certified Reference Materials.”). Gaithersburg, MD: Association of Official Analytical Chemist International.
- U.S. Pharmocopeia 25 and National Formulary 20 (current ed.). (General Chapters, Section on “Volumetric Solutions.”). Taunton, MA: Rand McNally.
- Volumetric Solutions: Preparation and Standardization
- General Information: http://pubs.acs.org/reagents/reagent2000/sec_e000.html
- Preparation and Standardization: http://pubs.acs.org/reagents/reagent2000/sec_e001.html
- What is a primary standard? What are its essential properties? Why was the standard dried?
- What conditions are to be met to maximize the accuracy of a standardization?
- Define the normality factor and discuss its use.
- Why couldn’t one accurately weigh out solid NaOH to make the 0.1 N standard NaOH solution?
- Define a "1 in 2" solution; a "(1 + 2)" solution; a 10% W/W KI solution; a 10% V/V methanol - water solution; a 5% W/V acetic acid solution; a saturated solution. Calculate the normality and molarity of a 10% H2SO4 solution.
This exercise is to be modified for different analytical disciplines and may be integrated with other exercises.
- To familiarize the analyst with different types of liquid-in-glass thermometers.
- To establish the proper use of each type of thermometer.
- To familiarize the analyst with the methods used to calibrate thermometers.
- Review references for care, handling, and calibration of liquid-in-glass thermometers.
- Calibrate one each of the following (if the laboratory uses them): partial immersion, total immersion, complete immersion, and maximum recording thermometers using two standards for each thermometer.
- American Society for Testing and Materials International. (1984, March). E 77-84 Standard ( pp. 59 – 72).
- Wise, J. A. NIST Special Publication 819, A procedure for the Effective Recalibration of Liquid-in-Glass Thermometers.
- Define partial immersion, total immersion, and complete immersion as related to thermometers.
- How can an analyst recognize the different types (partial, total, or complete) of immersion thermometers?
- How does a maximum recording thermometer differ from a complete immersion thermometer?
- What is the best method for reuniting a separated mercury column?
- Why should an open flame not be applied to a thermometer to raise the temperature?
- Why are two or more standards generally used to calibrate a thermometer?
- Why is the boiling point of pure H2O generally not used as one of the two calibrating standards?
- How many significant figures can be obtained from the temperature reading of a normal thermometer at room temperature?
- List another typical device for measuring the temperature besides a glass thermometer.
This exercise is to be modified for different analytical disciplines and may be integrated with other exercises.
- To acquaint the analyst with the proper care and use of the light microscope, i.e.:
- Study the operation of the microscope parts.
- Learn the correct procedures for cleaning the microscope.
- Learn the procedure for light alignment of the microscope.
- Learn the method for determining the microscope factor of the microscope.
- Learn the method of calibrating an ocular micrometer.
- Review reference material found in the lab on the microscope.
- Clean the objectives, condenser, and oculars.
- Properly align the microscope.
- Determine the microscope factor of the microscope. Prepare a slide and determine the microscopic count of a food sample.
- Calibrate an ocular micrometer. Measure the length and width of some stained bacteria.
- (1998). Bailey and Scott's diagnostic microbiology (10th ed., chap. 11, pp.134-150). St. Louis, MO: Mosby Co.
- Goldstein, D. J. (1999). Understanding the light microscope, a computer-aided introduction (1st ed.). Academic press.
- Manuselis, G., Mahon, C. R. (2000). Textbook of diagnostic microbiology (2nd ed.). AACC press.
- Burrells, W. (1977). Microscope technique: a comprehensive handbook for general and applied microscopy. New York: John Wiley & Sons.
- Murphy, D. B. (2001). Fundamentals of light microscopy and electronic imaging (1st ed.). Wiley-Liss.
- American Public Health Association. Standard methods for examination of dairy products. (current ed.). Washington, DC: American Public Health Association.
- Murray, P. (1995). Manual of clinical microbiology (6th ed., chap. 4) Washington, DC : American Society of Microbiology Press.
- Define the following types of illumination: bright field, dark ground, phase contrast, and fluorescence.
- Where is each form of illumination used?
- What are the two ways someone can tell an oil immersion lens from a high dry lens?
- List and describe each objective in the nosepiece.
- List and describe the ways the light source may be used to gain the best resolution.
- List and describe the cleaning procedure for each microscope used in the laboratory.