Instrumental Analysis Exam 1 Questions With 100% Correct Answers

Instrumental Analysis Exam 1 Questions With 100% Correct Answers classical analytical method - answermass and volume (gravimetric chloride, titration) instrumental analytical method - answerinstrument used to measure a property (nickel determination) instruments function by converting - answerinformation from one data domain to another encoding - answerinformation is transformed from one form to another. usually involves electrical domains electrical domains - answeranalog, time, digital ex: FT-NMR analog domain - answermagnitude/amplitude of electrical signal vs time, wavelength, frequency, temperature ex:voltage, charge time domain - answertime relationship of signal fluctuations vs x ex: frequency, pulse width, phase digital domain - answer2- level encoding: on or off more usually Hi or Lo count, serial, parallel analog means - answercontinuous digital means - answerdiscrete how is analog measured? - answermeter ex: pH measurements with glass electrode how is digital measured? - answercounter- counts # of signal within specified boundary condition ex: atomic emission- atoms in excited state return to ground state, emitting a photon disadvantage of analog - answermore susceptible to electrical noise advantage of digital - answerless susceptible to electrical noise -more stable/less drift over time detector - answermechanical, electrical, or chemical device that identifies, records, or indicates a change in one of the variables in the environment transducer - answertype of detector that converts between the nonelectrical domain and the electrical domain sensor - answertype of detector capable of continually monitoring a specific species readout device - answertransducer that converts electrical signal into something understandable by an observer quantitative performance criteria for instruments - answer1. precision 2. bias 3. sensitivity 4. detection limit 5. concentration range 6. selectivity criteria: precision - answerhow determined: standard deviations and other "figures" derived from it criteria: bias - answerhow determined: systemic error bias= population mean-true value criteria: sensitivity - answerhow determined: calibration and analytical sensitivity criteria: selectivity - answerhow determined: coefficient of selectivity- for ion sensitive electrodes sensitivity - answerability to differentiate between small differences in analyte concentration factors important for sensitivity - answer1. slope of calibration curve 2. precision of measuring device *if 2 methods have = precision, the method with steeper calibration curve will be more sensitive *if 2 methods have same calibration curve, the more precise method will have greater sensitivity calibration sensitivity - answerslope, m, of calibration curve at concentration of interest s=mC + sBL s=mC + sBL - answerequation of calibration curve. s=instrument signal for analyte sBL=instrument signal for blank c=concentration m=calibration sensitivity analytical sensitivity, γ - answerγ= m/ss where ss = standard deviation of signals detection limit - answerminimum concentration of analyte that can be detected at a known concentration interval -analytical signal must be greater than variation in blank minimum distinguishable analytical signal - answerSmin= Sbl + ksbl Sbl= AVG signal due to blank k=constant, accepted # is 3 sbl= standard deviation of blank signal dynamic range/concentration range - answerconcentration range over which measurements can be reliably taken LOL= limit of linearity