Laboratory Techniques

• Types of samples: qualitative and quantitative
• Qualitative– determination of identity of the chemical species
• Quantitative– determination of the relative amount of the chemical specie in each amount of sample
• Macro analysis – amount of analyte is more than 0.10 grams (100 mg)
• Semimicro analysis – amount of analyte is between 0.010 – 0.10 grams
• Micro analysis – amount of analyte is 10-4 to 10-2 grams
• Ultramicro analysis – amount of analyte is less than 10-4 grams
• An example of micro analysis is the determination of creatinine in a urine sample
• An example of ultramicro analysis is the determination of arsenic, boron, nickel or silicon in the body through urine test
• Reagent Grade- Confirms to the minimum standards set forth by the Reagent Chemical Committee of the American Chemical Society (ACS)
• Primary-Standard Grade- Chemicals with extraordinary purity prepared by National Institute of Standards and Technology (NIST)
• Special-Purpose Grade -Chemicals prepared for a particular or specific applications
• Select the best grade of chemical available for analytical work. Whenever possible, pick the smallest bottle that is sufficient to do the job.
• Replace the top of every container immediately after removing reagent. Do not rely on someone else to do.
• Never return any excess reagents to a bottle.
• Hold the stoppers of reagent bottles between your fingers. Never set a stopper on a desktop.
• Never insert spatulas, spoons, or knives into a bottle that contains a solid chemical.
• Keep the reagent shelf and the laboratory balance clean and neat.
• Follow local regulations concerning the disposal of surplus reagents and solutions.
• Wash properly apparatuses before using by washing with a liquid detergent (preferably as it will not leave solid residues in the glass)
• Wash it with tap water then several small portions of distilled water (usually with the use of wash bottle). Properly cleaned water will show uniform and unbroken film of water.
• Drying is usually a waste of time and is always a potential source of contamination. So, unless you instructed to do so, drying is not necessary
• Rinsing with acetone may help for drying and removing grease films.
• Some procedures will tell you to reduce volumes of your samples containing nonvolatile solutes by evaporation
• chlorides and nitrates can be evaporated by adding sulfuric

  acid
• nitrate ion and nitrogen oxides by adding urea
• Evaporate Ammonium chloride by adding concentrated Nitric acid
• Supernatant Liquid is the resulting liquid after a mixture of liquid and solid has been left to settle out or centrifuged to separate the two
• medical definition of supernatant liquid is referred to as centrifugate
• To remove the supernatant, carefully pour or pipette the

  solution away from the solid. If the solid becomes resuspended as the supernatant is removed, centrifuge the sample again.
• clear centrifugate is usually transferred to another test tube
• Pouring- Turn the test tube so that the highest level of solid is away from the vessel to which you are transferring the supernatant, then carefully pour out the liquid.
• Pipetting- Remove the supernatant with a pipet or medicine dropper. Squeeze the bulb to expel air, and place the tip of the

  pipette into the solution. Be careful to keep the tip of the

  pipette away from the solid. Slowly release pressure from

  the bulb to draw the supernatant into the dropper.
• When removing the supernatant using suction, be careful

  to:

  ■ avoid expelling air bubbles into the solution and

  ■ keep the tip of the dropper away from the solid
• The purpose of washing precipitates is to ensure that all interfering ions will be washed away from the sample.
• Centrifuge is a device by which a centrifugal force produced by an electric motor speeds up the rate of setting of a precipitate.
• The test tube containing the solution to be centrifuged should

  always be balanced by placing another test tube, containing an equal volume of water in the centrifuge opposite the solution
• When reading volume in an apparatus, always read in eye

  level at lower meniscus
• Apparatuses used in analytical chemistry forprecisely measuring volume are the following:

  1. Volumetric Pipet
  2. Mohr Pipet
  3. Serological Pipet
  4. Eppendorf Micropipet
• Add one drop of acid or base to the sample then stir. Drop a sample solution to the litmus paper to check any change

  in color