Midterm 1 Review Flashcards
Define Accuracy?.
A measurement of closeness of a measured value to the true value
Define Precision.
A measure of reproducibility. The agreement between replicate measurements of the same quantity
Random Error?
Affects precision. usually small human error. The random nature of indeterminate errors makes it possible to treat these effects by statistical methods.
Systematic/Determinate Error?
Have a definite value and an assignable cause and are of the same magnitude for replicate measurements made
in the same way. Systematic errors lead to bias in measurement results
Confidence Interval?
Provides an expected range in which the true mean is in. An interval surrounding an experimentally determined mean x within which the population mean m is expected to lie with a certain degree of probability.
Confidence limit?
The numbers at the upper and lower end of a confidence interval.
Null Hypothesis?
There is no significant difference
Selectivity?
Refers to the degree to which the method is free from interference by other species contained in the sample matrix. (How a method is influenced by other species in the sample)
Sensitivity?
Instruments response to change in analyte concentration. Affected by slope and precision of cal curve.
Calibration Sensitivity?
For two method with equal precision, the one with streeper cal curve is more sensitive.
S = mc + Sblank
Analytical Sensitivity?
If two calibration curves of equal slope the one with higher precision is more sensitive.
Y = m/s
Limit of Detection (LOD)
The smallest analyte that can be detected with statistical confidence
Limit of Quantification (LOQ)
The smallest analyte that can be quantified with statistical confidence
Limit of Linearity (LOL)
The point where signal is no longer proportional
Matrix?
The component of the sample other than the analyte of interest.
Matrix Matching?
Used in analysis to compensate for matrix effects that influence analytical response.
What is Standard Addition?
Advantages & Disadvantages?
The sample itself is used as the matrix for calibration, by spiking the samples.
High quality measurements, determines concentration and chemical species
Need high amount of sample. Hard to make cal curve
What is Internal Standard?
Advantages & Disadvantages?
A compound that is not analyte is added to the unknown.
Compensates for both random and systematic errors, simple and accurate
Must be similar to analyte, and IS must be absent from the sample. Must know Relative Response Factor
Enhancing S/N?
Shielding electronics, cooling instruments, low pass filters
Software improvements for S/N
Signal averaging, digital filtering, fourier transform
Transmittance?
Amount of light that passes through
Absorbance?
Amount of light absorbed
Double Beam Spectrophotometer
Allows you to cope beam of light and deflect rapidly to get more accurate %transmittance
Continuum Source Examples?
Tugsten, D2 lamps, IR- uses globar
Line Source Examples?
Hollow cathode tubes, lamps, lasers
Lasers?
Light amplification by stimulated emission of radiation. Have high intensities, and narrow bandwidths. The process of stimulated emission, produces a beam of highly monochromatic and remarkably coherent radiation
4 processes of a laser
- Pumping, a process by molecules in ground state of a laser is excited to E3 by means of an electrical discharge, passage of an electrical current, or
exposure to an intense radiant source. - Spontaneous Emission, a species in an excited electronic state may lose all or part of its excess energy by spontaneous emission of radiation.
- Stimulated emission, the excited
laser species are struck by photons that have precisely the same energies. Collisions of this type cause the excited species to relax to the lower energy state and to simultaneously emit a photon. The stimulated emission is totally coherent with the incoming radiation. - Absorption, two photons with energies exactly equal are absorbed
Flame structure?
- Primary combustion zone (blue luminescence)
- Interzonal Region: Hottest part of flame (rich in atoms, used in spec)
- Secondary combustion zone: atoms and other species converted
XRF
Advantages and Disadvantages
- An incoming x-ray knocks out an electron from an inner atomic orbital
- An unstable electron configuration is produced
- An electron from a higher energy orbital fills the hole and excess energy is emitted as a fluorescence x-rays which can be measured
Fast, no limits on measurements, simple sample preparation.
Hard to measure light molecules,
How to get molecules to excited state?
Absorb visible or UV light
Absorb a photon
Collide with atoms or particles
Heat, light or electricity
Why use narrow bandwidth?
Lowers interference signals
ICP vs emission Spectroscopy
Has a more stable heat source
Sample is able to stay in longer to completely atomize
