Quality means "characteristic element" and control is the "power to regulate or direct." Putting these two definitions together, quality control becomes "power to regulate or direct a characteristic element." This is a simple statement that carries a lot of impact. This definition says that you have the power to influence the test result.

Where does this power come from? How is this influence limited so that the test result reflects what is actually in a sample? What makes up quality control?

Quality control starts with sampling. After all, the test result is only as good as the initial sample. Errors made in sampling are the most influential part of a test outcome.

What type of sample is correct for the test — grab or composite? If the sample is for treatment plant information, then decide what information is required from the test result. If the test is specified by NPDES permit, the permit will specify the sample type. Sampling types, requirements, and other information related to sampling can be found in the following section on Sampling and Preservation.

It is good QC practice to keep a log for each piece of laboratory equipment. This log should include:

• Name, manufacturer, model and serial numbers
• Date received and date in service
• A copy of the purchase order and packing slip
• Maintenance schedule
• Warranty information
• Calibration schedule
• Manual

Update the log to show:

• Any repairs and cost
• The address and phone number of the repair company
• All routine maintenance such as:
• Changing batteries, light bulbs, electrolyte or membranes
• Adjustments in temperature settings
• Defrosting
• Cleaning of distillation units
• changing DI tanks and/or filters

This file shows that proper care of the equipment is occurring. The file is also useful when it comes time to prove to supervisors that equipment needs replacing, and it is helpful to part–time lab people who run into trouble when the full– time laboratory person is not available.

Keep a daily record on the temperatures of ovens, incubators, refrigerators, samplers, etc. Thermometers used to monitor incubators, refrigerators, and samplers are placed into a bottle containing water or glycerin. The liquid remains at the temperature of the equipment, giving a steady reading for recording. Periodically check the thermometer readings against a National Institute of Standards and Technology (NIST) certified calibrated thermometer. Record the readings of both thermometers on the daily equipment log.

There are several grades of chemicals available. To control errors introduced by chemicals, buy those that are referred to as "A.C.S." or "AR". The rating indicates that the chemical meets the minimum requirements of the American Chemical Society Committee on Analytical Reagents.

When the chemical is delivered to the laboratory, mark the label with the date it was received and note any expiration date. Read the material safety data sheet (MSDS) and place the sheet in a central location, for example in a marked notebook with other chemical MSDSs. Note the proper way to store the chemical and any chemicals that are incompatible. Do not store incompatible chemicals together. Also mark the label with the date opened. Learn from these notes how long it takes to use the chemicals. Then buy chemicals or prepare solutions in the most economical size. Remember that time, sunlight and extremes of heat and cold can shorten the shelf life of a chemical. Also, it is expensive to dispose of an expired or unneeded hazardous chemical.

When making solutions in the laboratory, always label the storage bottle with:

• Name of the solution
• Strength of the solution
• Who made it
• The date it was made
• Any expiration date
• Storage Conditions

Glassware performs three basic functions in the laboratory: storing of reagents, measurement of volume and confinement of reactions. Borosilicate glass, which features high chemical resistance, is the best type of glassware to perform these functions. Pyrex^® or Kimax^® are two brand names of glassware that meet this specification.

Glassware comes in three types of precision. Precise glassware includes volumetric flasks, volumetric pipettes and accurately calibrated burettes. Measuring glassware includes graduated cylinders and serological or Mohr pipettes. Approximate glassware includes beakers and Erlenmeyer flasks.

NIST has set tolerances, or error limits, for volumetric glassware. All volumetric glassware meeting the most stringent standards is marked "Class A" and should always be used when making standards, solutions, and dilutions.

Precise and measuring glassware are divided into two classes. TC or "To Contain" glass ware means that when liquid at 20˚C is poured to the set level, the vessel holds only that amount of liquid, but will not necessarily deliver the same quantity. TD or "To Deliver" glassware will deliver the volume poured to the set level because the calibrations account for the drainage film remaining on the glass wall after pouring.

Using each piece of glassware correctly is critical to accurate analytical methods. For instance, the amount of drainage film varies depending on the time allowed for the liquid to drain and on the cleanliness of the inner walls. Therefore, use uniform pouring and thorough washing techniques.

The following items need to be recorded:

• The date(s) analyses were performed;
• The individual(s) who performed the analyses
• The analytical techniques or methods used; and
• The results of such analyses.

Here are some other items to record on the benchsheet:

• Buffers or standards used to calibrate instrumentation.
• Instrument variables
• Date the sample was collected
• Time the analysis was started
• Time and date of completion of the test, if extended time is necessary to complete the analysis
• Result of quality assurance standard

Retain records for a period of at least 3 years from the date of the sample.