achem noise and others

Chemical noise

random fluctuations in analye, unique to chemical measurments

Johnson noise

random thermal motion of electrons, does not depend on frequency

shot noise

fluctuations due to particle nature of electrons

environmental noise

characteristic but random, avoid measurements at 60hz

1/f, flicker noise

universal, constant frequency per decade of frequency. avoid measurements near DC

B or Δf

frequency bandwidth, depends on rise time.

rise time

time for output of instrument response to change from 10% to 90% after an abrupt change in input. can be reduced by

• narrower bandwidth

• reduce # of resistive components

• reduce temp of electronic components

electrodes of the 1st kind

pure metal electrode in equilibrium with its cation (ie. cu/cu2+)

electrodes of the 2nd kind

pure metal electrode in equilibrium with its cation that is sensing an anion that forms salts with its cation (ie. Ag/agcl)

electrodes of the 3rd kind

metal electrode that is made to respond to a differentcation. Example, use of a Hg electrode to detect Ca2+

glass membrane ph electrode sensing element

glass membrane tip

what ions in a glass membrane are responsible for conduction

calcium and lithium ions

junction potential error

ionic composition of buffer is different than analyte, changing junction potential

alkaline error

ph electrodes respond to both sodium and hydrogen ions in basic solutions, at high ph it will respond to both

acid error

not well understood, opposite of alkaline error

interfering species of f- electrode

oh-

range of nernstian response of f- electrode

10^-6 to 1M

low pass filter removes these types of noise

high frequency noise components of shot and thermal noise

high pass filter removes

flicker noise

why might a blank signal be different than the actual signal of the blank

drift, matrix effects

things that cause deviation from calculated E

mass transfer, charge transfeer polarization, electrode fouling, complex kinetics

ideal reference electrode

obeys nernst, doesnt undergo hysteresis, returns to original potential after small current changes, stable potential