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Inst. Analysis

Exam 1

Analytical Method types(2) Classical or instrumental
Classical Analytical Method accurate mass/volume measurements. Ex)gravimetric or volumetric measurements
Instrumental Analytical Method (aka wet-chemical mthods) some physical property is measured. Ex)conductivity, electrode potential, light absorption, emission, mass to charge ratio, and fluorescence
Machine device, having, a unique purpose, that augments or replaces human or animal effort for the accomplishment of physical tasks. Ex) Simple devices such as lever, wedge, wheel, axle, pulley and screw as well as complex mechanical system such as automobile
Instrumentation in tech, the development & use of precise measuring equipment.
Difference between instrument & Machine machine:does work Instrument: some kind of measuring device ex) IR: electromagnetic radiation
Characteristic Property: Emission of Radiation ?: Instrumental Method Emission spectroscopy (X-ray,UV, visible, electron), fluorescence, phosphorescence, and luminescence (X-ray, UV, and visible)
Characteristic Property: Absorption of Radiation ? Instrumental Method Spectrophotometry and photometry (X-ray, UV, visible, IR);nuclear magnetic resonance, electron spin resonance spectroscopy
Stimulus Energy source
Response Analytical information
Instrument of chemical analysis converts information about the physical or chemical characteristics of the analyte to info that can be manipulated & interpreted by a human.
Analytical Instrument communication device between the system under study and the investigator
Measuring extent of absorption by analyte in a solution passing a narrow band of wavelengths of visible light through a sample.Intensity of light is determined before and after interaction with the sample, ratio of intensities provides measure of analyte concentration
Attenuated becomes less
photodiode absorbs light & produces current--> gets translated into some kind of reading a humna being can understand
Encoding Instruments function by converting diff type of info form one form to another
Electrical Signals current, voltage, & charge
Data domains: 2types: ? various modes of encoding information. 1. Nonelectical domain 2. Electrical domain
Nonelectrical domain: human reading, what humans can understand. All measurements begin & end in a nonelectrical domain.Physical & chemical information that is of interest resides in these domains. (length, density, chemical composition, intensity of light, & pressure)
Modes of encoding information as electrical quantities can be subdivided into 3 Domains 1.Analog Domains 2. Time Domains 3. Digital Domains
Analog Domain: 3 main things to remember information is encoded as the magnitude of an electrical signal vs. time (electrical quantities: current, charge, voltage or power) 1. Continuous 2. Inherently more susceptible to electrical noise 3. Not as reliable (in comparison to Digital)
Time Domain (E) Time relations of signal fluctuations Ex) Furrier Transform (FT) Horizontal dashed lines are arbitrary analog signal threshhold that is used to decide whether signal is high or lo Ex) Raman spectroscopy,& instrumental neutron activation analysis
Digital Information Data are encoded in the digital domain in a two-level scheme 1. Descrete 2. On/Off similar to Hi/ Lo <- arbitrary signal is defined. Most digital info is encoded, transferred, processed, an decoded in binary form.
Interdomain concversions Any measurement process
Optical filter removes radiation from beam of light that is unrelated to the concentration of specific analyte
Input transducer f
Parallel Digital data desired information is presented in simultaneous
Analog vs. Digital signal Comparison Characteristic Continuous vs. Discrete
Analog vs. Digital signal Comparison how is it measured meter vs. counter counter counts # of signals occurring with in specific boundary conditions ex) time & change in wavelength
Analog vs. Digital signal Comparison examples pH measurement: using glass electrode responds to the aH3O+ by changing voltage (or F measurement) Atomic emission: atoms in excited state return to ground state via emission of a photon E=hv
Analog vs. Digital signal Comparison Advantages/disadvantages More susceptible to electrical noise vs less susceptible to electrical noise, more stable & less "drift" over time
Detectors, Transducers, sensors do similar things but some are more specific than others, convert one signal to another
Detector mechanical, electrical or chemical device that identifies, records or indicates a change in one variable in the environment ex)Gas chromatography detector, liquid detector, ionization detector
Transducer converts nonelectrical to electrical domains (slightly more specific)
Sensor device capable of monitoring a specific species continously
Detection system entire assemblies that indicate or record physical or chemical quantities. (UV detector used to indicate & record presence of eluted analytes in liquid chromatography
Transducer function the mathematical relationship between the electrical output and the input radiant power, temperature, force, or magnetic field strength
Quartz crystal microbalance (QCM) device is based on the piezoelectric characteristics of quartz. Electric potential difference develops across its surface when quartz is mechanically deformed
Readout Device something so a human being can read/interpret. Transducer that converts electrical signal into a signal that an observer can understand.
Difference between absorption spectroscopy and emission/fluorescence absorption spectroscopy: laser beam is in line with detector; E/F: laser is not in line with detector
6 Figures of Merit: MUST KNOW ALL OF THESE aka quantitative performance criteria 1. Precision 2. Bias 3. Sensitivity 4. Detection limit 5. Dynamic Range 6. Selectivity
Precision Degree of mutual agreement among data that have been obtained the same way. Provides measure of random, or indeterminate, error of analysis. Ex)absolute standard deviation, relative standard deviation, coefficient of variation, variance
Bias provides a measure of absolute systematic, or determinate error of an analytical method. Difference between mean and known analyte concentration of standard reference material
Sensitivity ability to differentiate between small differences in analyte concentration.
2 factors that limit Sensitivity 1. Slope of calibration curve 2. Precision of a measuring device: reproducibility
2 factors that limit Sensitivity if the two methods have... 1. Equal precision: the method with the "steeper" calibration curve is more sensitive 2. Identical calibration curves: the more precise method is more sensitive
2 types/definitions of Sensitivities 1. Calibration Sensitivity 2. Analytical Sensitivity
Calibration Snsitivity slope, m, of calibration curve at concentration of interest. - Calibration ignores precision of a method attain precision through analytical sensitivity Equation: S=mc+S(bl)
Analytical Sensitivity: includes precision in a meaningful mathematical way. Tells how calibrated it is. - advantage: it is relatively insensitive to amplification factors - another advantage is that it is independent of the measurement units for S - disadvantage: depends on
Detection limit: minimum concentration or weight of analyte that can be detected at a KNOWN CONFIDENCE LEVEL. - Limit depends on ration of magnitude of analytical signal to the size of the statistical fluctuations in the blank signal. Accepted value for K=3
Dynamic Range over what range of concentrations can instrument take reasonable readings. Extends from the lowest concentration at which quantitative measurements can be made to the concentration at which the calibration curve departs from linearity by specific amount.
LOQ limit of quantitation: start above minimal concentration.
LOL limit of linearity
C(min) just because it can be read, does not mean it will have same precision. It's precision varies and it is not quite quantifiable
Instrument Calibration: calibration of instrumental methods We talked about 3 1. Calibration curve 2. Standard Addition Method 3. Internal Standard Method
Instrument Calibration: 1. Calibration Curve Make standrd sol->msr inst response->plot results->msr unknown-> ex)F- concentration in quant Success of method depends on 1.accuracy of standard concentrations(usually ok) 2. Accuracy of "matrix" of standard approx matrix of samples to be measured
Matrix: all components comprising the analytical sample (making) F-: stock sol, ukn sol had same matrix; tap wtr had things we knw & things we didnt knw of; this was ok bc detectro was specific for F- * When detector is not specific this is not the best metho
Instrument Calibration: 2. Standard Addition Method add 1 or + increments of a varied stndrd sol to ukn sample aliquots of sample size: "spiking sample" * useful for analyzing complex samples in which the likelihood of matrix effects is substantial. same stndrd sol,diff amts of stndrd, dilutd to same vol
Instrument Calibration: 3. Internal Standard Method standard added in constant amount to all samples, blanks, & calibration standard. Used for gas chromatography. Mesaure peak area, of known same amount in ea. specific sample ( known material)
Chapter 2 Electrical components & Circuits 1. Recorders A. Analog B. Digital C. computer monitor/printer
1. Analog Recorder pen responded to pulley system
2. Digital Recorder pen responded to digitized voltages by moving a specific amount--> has been replaced by computer (interface)
Computer monitor/printer instrument manufacturers tried to build their own computers but weren't good at it.
Chapter 5: Signals & Noise
Definitions of: 1. Noise 2. Signal 1. s (standard deviation) of measured signal 2. x(w line on top) avg value of measurement.
Signal to noise ratio S/N= inverted relative standard deviation RSD: standard deviation/avg value of msrment
Noise spurious signal components limits our ability to take measurements to minimize noise --> increase S/N ratio
Sources of Noise: (4) 1.Thermal (Johnson) Noise 2.Shot Noise 3.Flicker Noise 4.Environmental Noise
Source of Noise: 1. Thermal Noise due to thermal agitation of charge carriers (usually electrons). don't have to worry about this with a super conductor RMS * can reduce noise by: 1.cooling down 2.lowering resistance 3.decreasing bandwidth of msrmnt
Source of Noise: 1. Thermal Noise - White Noise Noise is independent of absolute frequency but dependent on frequency bandwith
T(r) from Change in frequency equation: D(F)= 1/3T(r) "Rise of time" of instrument: how fst the instrument responds to an abrupt change inpact * T & D(f) are inversely proportional
Source of Noise: 2. Shot Noise when electrons go across a junction due to movement of charge particles across a junction Involves IRMS * can be decreased by decreasing bandwidth
IRMS: definition &units Root mean square noise current: Square root of: 2IeD(f) where I is current & e is a constant [microA]
Source of Noise: 3. Flicker Noise does depend on magnetic frequency FN=1/f aka: one over f noise
Source of Noise: 4. Environmental Noise good quiet region is a good region Due to metal & magnet interactions Ex) NMR could not be too close to elevator due to magnet interactions
Source of Noise: 4. Environmental Noise a) Shimming changing currents through coils, moving the magnetic field
Created by: 1642230524



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