Instrumental Methods and Statistical Terms

• TURBIDIMETRY

  • For measuring abundant large proteins and bacterial suspensions
  • Principle: it determines the amount of light blocked by a particulate matter in a turbid solution.
  • Use: protein measurements (CSF and urine); to detect bacterial growth in broth cultures; antimicrobial test (broth method); to detect clot formation.
• NEPHELOMETRY

  • For measuring the amount of antigen-antibody complexes (proteins).
  • Principle: it determines the amount of scattered light by a particulate matter suspended in a turbid solution
  • Components: light source (mercury-arc lamp, tungsten-filament lamp, light emitting diode, and laser), collimator, monochromator, sample cuvet, stray light trap, and photodetector
• Electrochemistry Techniques

  • The measure of current or voltage generated by the activity of a specific ion
• Electrochemistry Techniques

  1. Potentiometry - Ion Selective Electrode
  2. Coulometry
  3. Amperometry
  4. Voltammetry
• POTENTIOMETRY

  • The measurement of electrical potential due to the activity of free ions – change in voltage indicates activity of each analyte; and measures the differences in voltage at a constant current.

  ▪ Follows Nernst Equation

  ▪ Reference electrodes: Calomel and Ag-AgCl

  ▪ Use: pH and pCO2 tests
• ION SELECTIVE ELECTRODE (ISE)

  • An electrochemical transducer capable of responding to one given ion.
  • Very sensitive and selective for the ion it measures
  • Its ionic selectivity depends on the membrane/barrier composition used.
  • ISE membranes: glass aluminum silicate (sodium), valinomycin gel (potassium), organic liquid membrane ion exchangers (calcium and lithium), gas and enzyme electrodes.
• 2. COULOMETRY

  • Measurement of the amount of electricity (in coulombs) at a fixed potential.
  • Follows Farday's Law
  • Use: chloride test (CSF, serum and sweat)
  • Interference: bromide, cyanide and cysteine
• 3. AMPEROMETRY

  • Is the measurement of the current flow produced by an oxidation-reaction
  • Use: pCO2, glucose, chloride and peroxidase determinations

  a.) Polarography – measurement of differences in current at a constant voltage

  ▪ Follows Ilkovic Equation
• 4. VOLTAMMETRY

  • Measurement of current after which a potential is applied to an electrochemical cell.
  • Allows sample to be preconcentrated, thus utilizing minimal analyte
  • Anodic stripping voltammetry – for lead and iron testing
• STATISTICAL TERMINOLOGIES

  1. Central Tendencies

  -Mean

  -Median

  -Mode

  2. Other Terminologies

  - F-test

  - T-test

  - Range

  - Inferential Statistics

  - Standard Deviation Index
• Mean

  • associated with symmetrical and normal distribution
• Median

  • the value of the observation that divides the observations.
  • The midpoint of a distribution; and 50th centile.
• Mode

  • the most frequent observation
  • used to describe data with two centers (bimodal).
• F-test

  • used to determine whether there is a statistically significant difference between the standard deviation of two groups of data.
• T-test

  • used to determine whether there is a statistically significant difference between the mean of two groups of data.
• Range

  • simplest expression of spread or distribution; the difference between the highest and lowest score in a data
• Inferential statistics

  • used to compare the Standard Deviation or Mean of two groups of data.
• Standard Deviation Index

  • the difference between the value of a data point and the mean value divided by the group’s SD.