Instrumental Analysis Exam 1

What is Analytical Chemistry?

improving/extending analytical methods and/or developing new analytical tools/methods

Analysts/enablers

build instruments, devise procedures for obtaining information

Determinators/exploiters

Concerned only with end result

Analyte

chemical species we are looking for

matrix

everything else present in the sample

Classical Methods

Physically separate components of interest

Instrumental Methods

Using physical properties of analyte as distinguishing characteristic

Instrument

Produces measurements

Machine

Produces products

Transduction

Change in form of information

Systematic/determinate error

comes from flaw in equipment or experiment design, error is consistant/reproducibl.

Detection of systematic error

analyze known sample, use different method to measure same quantity, round robin, analyze blank

correction of systematic error

Calibrate glassware and instrumentsm use standard addition/internal standard to correct matrix effects

Random/indeterminate error

Comes from. uncontrolled variables in measurement, equal chance of being above or below true value

Ways to correct random error

can’t be totally eliminated

Precision

Describes reproducibility of result

Accuracy

how close the measurement is to the true value

uncertainty

degree of variability within a dataset

Experiment repeated multiple times and errors purely random, results will appear as

gaussian distribution

standard dev describes

level of random error

smaller standard deviation=

better precison

calibration/working curve

response vs quantity

Selectivity

ability to distinguish analyze from other species in sample, to the degree of which the analyte is free from interference

Sensitivity

ability to respond measureable and reliably to change in analyte concentration (slope of calibration curve)

Blanks

sample not intended to contain analyte, accounts for interference by other species in sample

A method is specific if

responds to only one analyte without interferances

Detection limit (LOD)

Smallest quantity of analyte that is significantly different from the blank k=3

Quantitation limit (Lower Limit of Quantitation)

smallest quantity of analyte that can be quantified with reasonable accuracy (IUPAC k=10)

Linearity

measures how well a calibration curve follows straight line, response proportional to analyte quantity

Bias

degree of systematic error

LOD

IUPAC, k=3, smin=sblank+kstdevblank

linear Dynamic Range

rage of analyte concentrations where quantification is possible (LOQ to LOL)

Limit of linearity (LOL)

response deviates from best fit line by 75%

transducer

changes form of information

processor

separates, correlates, processes info

Why are electrical measurements common?

fast acquisition, rapid and complex processing possible, inexpensive

analog electrical measurements

continuous in amplitude and time, directly measure current, voltage, charge, power, more susceptible to electrical noise

Time electrical measurements

information stored in time domain, measures frequency, duration (pulse width), phase, less susceptible to electrical noise

Digital electric measurements

Information quantized in levels, measure by counting/discrite value, least susceptible to electronic noise

Analog Measurements

current, voltage, charge

time measurements

frequency, pulse width, phase

Digital measurements

count, serial, parallel, number

Signals that can be both analog and digital

Photomultiplier, Tachometer, Geiger counter

Ohm’s Law

V=iR

Power Law

P=iV

DC Power suppy

AC Power Supply

Resistors

Ground

Kirchoff’s Law

all in=all out

Voltage Divider (Resisters in series)

Current Divider (resistors in parallel

Voltage Divider Equation

For voltage measurments, to prevent loading error

internal resistor (RM ) large compared to load resistor (Rl)

Load Resistor

what voltage is measured across

For current measurements

want Rm (internal resistor) small to RL (Load resistor

AC voltage quanitifcation

peak to peak or RMS

Capacitance

ability to store charge with potential

Capacitor

Twi netak okates with non-conductor between

Capacitor

Potentiometer

Capacitance relation

Q=C*V

Voltage and current across capacitor

time dependent, takes time for capacitor to charge/recharge

RC time constant

t=R*C (in s)

in AC, increasing frequency results in

decreasing resistance

Low Pass Filter

Resistor and capacitor in series

Low Pass Filter

Diode

conducts current in only one directions (semiconductor

Zener Diode

semiconductor that conducts in only reverse direction once threshold voltage is reached

Diode

zener diode

Converting AC to DC

Transformer, rectifier, filter/regulator

What does a transformer do

decreases voltage amplitude

Rectification

With diode, makes everything positive

Filtering/smoothing

With RC together, smooths out the distance between peaks

Regulate/stabilizer

With Zener diode with zero breakdown voltage

Amplification

increasing electronic signal

PNP Amplifier

NPN Amplifier

Gain

Signal out/signal in

Operational Amplifier (op amp)

complex arrangement of transistors

Issues with Basic amplifiers

Fragile, provide limited gain

Op amp

Op amp properties

High gain (10^4-10^6), doesn’t draw much power from input, produces a ton of current, adjustable gain with feedback, can perform math operations

Positive feedback loop (less preferred)

Negative Feedback Loop

Comparator

Comparator Equation

Current follower/current-to-voltage converter

Current follower/current-to-voltage converter equation

Voltage Follower

Voltage Follower Equation

What does a voltage follower do mathematically?

Multiplication/division

What does this do mathematically?

Addition or subtraction

What does this do mathematically?

integration

What does this do mathematically?

Differentiation

Binary System

Two states: on/off

Components of digital system

Signal shaper, internal clock, gates

Signal Shaper

Comparator, differential amplifier with high gain