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Instrumental Test 1

UW-Platteville Instrumental with Dr. Cornett Exam 1

three types of error determinate, indeterminate, and gross errors
determinate error bias; definite and identifiable causes; distribute symmetrically about the mean, determinate errors have a single direction and are not affected by averaging.
three types of determinate error method, operator, equipment/environment
indeterminate error stats; ex. they just happen but manifest in Gaussian curve; due to the many uncontrollable variables that are an inevitable part of any physical measurement and due to the chaotic nature of the universe
gross errors depends on your level of carefulness; generally personal errors attributable to carelessness, laziness, or ineptitude; ex. math miscalculation by the experimenter
wet ashing nitric acid; use on oxyacid to break matricies
dry ashing cook things down
2 ways to screw up lose analyte; add analyte
Is HCl an oxy-acid? no
qualitative method yields info about the identify of atomic or molecular species or the functional groups in the sample; is it there?
quantitative method numerical info about the amount of a species; how much is there
ways to determine a sample quantitatively gravimetric or volumetric
instrumental methods of analysis newer methods for separating and determining chemical species
instruments can be viewed as a communication device between the system under study and the investigation
the stimulus elicits a response from the system under study whose nature and magnitude are governed by the laws of physics and chemistry
data domains various modes of encoding info; 2 categories: electrical & non-electrical
what are the divisions nonelectrical domains physical and chemical domain; scale position; numbers
electronic instruments acquire information in which domain the nonelectrical domain
which domain does an electronic instrument process information in electrical domain
in what domain do electronic instruments present information a nonelectrical domain
what are the divisions of electrical domains analogue, time, and (most) digital
what are the divisions of analogue domains current, voltage, charge
what are the divisions of time domain frequency, pulse width, phase
what are the divisions of the digital domain and are they electrical or nonelectrical domains count (electrical), serial (electrical), parallel (electrical), and numbers (nonelectrical)
analogue domain signals are encoded as the magnitude of either voltage, current, charge, or power (electrical qualities)
electrical noise affects the magnitude of the electrical signals
time domain information is stored as a time relationship of signal fluctuations (not amplitudes of the signal)
frequency the number of cycles of the signal per unit time
period time required for a full cycle (aka time between LO to HI, or vice versa, transition)
pulse width the time it takes for a wave to go from a LO to HI to LO signal
digital domain has how many levels 2: on or off (only has two possible states)
in the digital domain you have to define a signal as a high or a low state; these states definitions depend on the experiment
when an experimenter reads and interprets a number representing a measured quantity it is in what sort of domain nonelectrical domain
bit binary digit of information; fundamental unit of info in digital domain
how is a bit transmitted along a single electronic channel or wire and counted by a person or instrument (called count digital data-is not super efficient)
a more efficient way to read bits is in binary numbers which base 2 numeral system (usually 0 and 1); ex. (2^2 + 1) 3 = 0011 and (2^1) 2 = 0010; (2^2) or 4 = 0100
detector a mechanical, electrical, or chemical device that identifies, records, or indicates a change in one of the variables in its environment
example of a detector pressure, temperature, electrical charge, electromagnetic radiation, nuclear radiation, particulates, or molecules
detection system the entire assemblies that indicate or record physical or chemical quantities
a UV detector is an example of a detection system
transducer devices that convert info in nonelectrical domains to electrical domains and vice versa
examples of transducers photodiodes, photomultipliers and other electrical photodetectors that produce current or voltage proportionally to radiant power of electromagnetic radiation that falls on their surface
transfer function (of the transducer) mathematical relationship between the electrical output and the input radiant power, temperature, force, or magnetic field strength
sensor a class of analytical devices that are capable of monitoring specific chemical species continuously and reversibly
examples of sensors glass electrode and ion-selective electrodes, Clark and fiber-optic sensors (optrodes)
a sensor is a what plus a what transducer plus chemically selective recognition phase
a readout device is a transducer that converts info from an electrical domain to a form that is understandable by a human observer (usually a nonelectrical domain)
calibration determines the relationship between the analytical response and the [analyte]; usually determined with chemical standards
direct comparison of standards for calibration comparing a property of the analyte (or the product of a reaction with the analyte) with standards such that the property being tested matches or nearly matches that of the standard
null comparison or isomation method calibration [analyte] = [standard after dilution]
titrations and calibration one of the most accurate of all analytical procedures; the analyte reacts with a standarized reagent (the titrant) in a reaction of known stoichiometry; amount of standard needed to reach equivalence can be related to [analyte]
external-standard calibration external standard is prepared separately from the sample; used to calibrate instruments and procedures when there are no interference effects from matrix components in the analyte solution
internal standard is added to the sample itself
calibration is accomplished by obtaining the response signal as a function of known [analyte] then form a calibration curve
ideal blank identical to the sample but without the analyte
external calibration curve uses what method least squares method
solvent blank contains some solvent as the sample
reagent blank contains solvent and all other reagents used in sample prep
once prepared the concentration of the standards can change because of decomposition, volitilization, or absorption onto container walls
multivariate calibration the process of relating multiple instrument responses to an analyte or a mixture of analytes (also used to identify interferences not identifiable in a univariate calibration)
standard addition methods alioquots, spiking, single-addition method
spiking adding one or more increments of a standard solution to sample aliquots containing identical volumes
single-addition method assumes a linear relationship which isn't always true
internal-standard method substance that is added in a constant amount to all samples, blanks, and calibration standards in an analysis
internal-standard method calibration plot plot analyte signal: internal standard vs. [analyte] standard; may compensate for several types of both random and systematic errors (ex. matrix effects)
an amount added to a sample must be known to be absent from the sample's matrix so that the only source of the standard is the added amount
what 6 questions should you ask for selecting an analytical method 1. how accurate? 2. how much sample is available? 3. what is the concentration range of the analyte? 4. what components of the sample might cause interference? 5. what are the physical and chemical properties of the sample matrix? 6. how many samples?
selectivity definition the degree to which the method is free from intereference by other species contained in the sample matrix
selectivity figure of merit coefficient of selectivity from 0 to infinity
precision definition degree of mutual agreement among data that have been obtained in the same way
precision figure of merit absolute standard deviation, relative standard deviation
bias definition popular mean - true value = bias
bas figure of merit absolute systematic error, relative systematic error
sensitivity definition a measure of its ability to discriminate between small differences in [analyte]; 2 factors: slope of the calibration curve and the reproducibility or precision of the measuring device
sensitivity figure of merit calibration sensitivity, analytical sensitivity
detection limit definition the minimum concentration of mass of analyte that can be detected at aknown confidence level (limit depends on ratio of magnitude of analytical signal to the size of statistical fluctuations in the blank signal)
detection limit figure of merit blank + three times standard deviation of the blank
dynamic range definition the lowest concentration at which quantitative measurements can be made {limit of quantitation (LOQ)} to the concentration at which the calibration curve departs from linearity by a specified amount (LOL, limit of linearity)
dynamic range figure of merit LOL to LOQ (should be least a few orders of magnitude)
usually in developing an analytical method, we attempt to identify the source of bias and eliminate it or correct for it by the use of blanks and by instrumental calibration
calibration sensitivitiy the slope of the calibration curve at the concentration of interest (doesn't take into account precision of individual measurements)
analytical sensitivity slope of calibration curve/std deviation of measurement; disadvantage: often concentration dependent
detection limit's value of k is generally argued to be k=3 so detection will be 95% in most cases
what is a transducer in an analytical instrument devices that convert info in nonelectrical domains to info in electrical domains and vice versa
what is the info processor in an instrument for measuring the color of a solution visually? human brain; spectrophotometers; colorimeter
what is the detector in a spectrograph where spectral lines are recorded photographically? a photoelectric to convert light intensity into a resistance
what is the transducer in a smoke deterctor? input transduer (nonelectrical to electrical domain)
what is a data domain? various modes of encoding information (electrical and nonelectrical)
name electrical signals that are considered analogue. How is the info encoded in an analogue signal? current, voltage, charge; coded as the magnitude of one of the electrical qualities-voltage, current, charge, or power
increasing sensitivity (or increasing slope) can help increase signal
how to increase sensitivitiy (increase slope) get the analyte away from the matrix; concentrate the analyte; react it w/ something that is easier to see (measure the tag & pray for a linear relationship); do a reaction & derive something (as long as a linear relationship)
noise definition "everything that bugged you"' as soon as you turn on an instrument you create an antenna
signal is additive but noise is not; noise is random
thermal noise/Johnson noise cause by thermal agitation of charged particles (random); if the temperature is 0K there is no energy; present even w/o current in a resistive element; "white light"
temperature and thermal noise are related how directly
equation for thermal/Johnson noise Vrms = (4kT(ohm)(deltaf))^1/2
bandwidth delta f; 1/3tr
rise time tr; lag for quantum mechanics;the time it takes to go from 10% of the signal to 90%
shot noise jumping the valence band of a semi-conductor; "white noise"; happens whenever an e- jumps a junction
shot noise is reduced if bandwidth is reduced
shot noise equation i(rms)=(2I(e-)(deltaf))^1/2
whenever you move between AC and DC you lose some of the precision; elmininating conversions helps eliminate the amount lost; manifests as drift (unidirectional) (can be considered a bias); reduce drift with wire wound resistors
flicker noise equation 1/frequency
hardware and S/N filtering low pass filter; high pass filter; band-pass filter
low pass filter removes higher frequencies (thermal and shot noise)
high pass filter removes low frequencies such as flicker and drift
band pass filter combines high and low pass filters
hardware and S/N shielding grounding
modulation is hidden in electronics boards
software and S/N ensemble averaging ex. run 10 samples, add together then add & you get a signal but noise is random it could happen 1 run or all 10 but that will also be divided by 10
software and S/N boxcar averaging "more pts undder the curve to integrate" idea-ish; focused on pts in the box cars; average everything in the box; the narrower the box the better you are as long as you can have as many data points as possible; you want the most points as fast as possible
software and S/N digital filtering "play games with your computer"; weighted digital filtering; ex. 2 chromatography peaks that aren't completely resolved where the computer estimates where the peak "should" end; Fourier transform
signal carries info about the analyte that is of interest to the scientist
noise made up of extraneous info that is unwanted because it degrades the accuracy and precision of an analysis and also places a lower limit on the amount of analyte that can be detected
you can never be free of noise in an experiment; in most measurements N's magnitude is basically constant; how do we compare Signal and Noise S/N
the effect of noise increases as the quantity being measured decreases
S/N is a more useful figure of merit than noise or signal alone
for a DC signal the magnitude of the noise equals the standard deviation; S/N =mean/std dev
standard deviation can be estimated at a 99% confidence level by (max-min)/5
it be comes impossible to detect a signal when S/N is less than 2 or 3
at the smaller S/N only a few peaks can be recognized with certainty
two types of noise chemical noise and instrumental noise
types of instrumental noise thermal/Johnson noise, shot noise, flicker noise, and environmental noise
chemical noise arise from uncontrollable variables that affect the chemistry of the system being analyzed; ex. variations in temperature, or pressure that affect equilibrium; ex. humidity that changes moisture content
what is noise that associated with each component of an instrument (with the source, the input transducer, all signal-process elements, and the output transducer) instrumental noise
it rise time increases what happens to bandwidth it decreases but that also makes the run time slower and longer
what is the effect on thermal noise of decreasing the response time of an instrument from 1s to 1 micros? a 1000x increase in noise; bandwidth increases
how is thermal/Johnson noise related to frequency it's not
Created by: 530848841



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