Midterm 1 Review

Question 1

Define Accuracy?.

Answer 1

A measurement of closeness of a measured value to the true value

Question 2

Define Precision.

Answer 2

A measure of reproducibility. The agreement between replicate measurements of the same quantity

Question 3

Random Error?

Answer 3

Affects precision. usually small human error. The random nature of indeterminate errors makes it possible to treat these effects by statistical methods.

Question 4

Systematic/Determinate Error?

Answer 4

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

Question 5

Confidence Interval?

Answer 5

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.

Question 6

Confidence limit?

Answer 6

The numbers at the upper and lower end of a confidence interval.

Question 7

Null Hypothesis?

Answer 7

There is no significant difference

Question 8

Selectivity?

Answer 8

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)

Question 9

Sensitivity?

Answer 9

Instruments response to change in analyte concentration. Affected by slope and precision of cal curve.

Question 10

Calibration Sensitivity?

Answer 10

For two method with equal precision, the one with streeper cal curve is more sensitive.
S = mc + Sblank

Question 11

Analytical Sensitivity?

Answer 11

If two calibration curves of equal slope the one with higher precision is more sensitive.
Y = m/s

Question 12

Limit of Detection (LOD)

Answer 12

The smallest analyte that can be detected with statistical confidence

Question 13

Limit of Quantification (LOQ)

Answer 13

The smallest analyte that can be quantified with statistical confidence

Question 14

Limit of Linearity (LOL)

Answer 14

The point where signal is no longer proportional

Question 15

Matrix?

Answer 15

The component of the sample other than the analyte of interest.

Question 16

Matrix Matching?

Answer 16

Used in analysis to compensate for matrix effects that influence analytical response.

Question 17

What is Standard Addition?
Advantages & Disadvantages?

Answer 17

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

Question 18

What is Internal Standard?
Advantages & Disadvantages?

Answer 18

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

Question 19

Enhancing S/N?

Answer 19

Shielding electronics, cooling instruments, low pass filters

Question 20

Software improvements for S/N

Answer 20

Signal averaging, digital filtering, fourier transform

Question 21

Transmittance?

Answer 21

Amount of light that passes through

Question 22

Absorbance?

Answer 22

Amount of light absorbed

Question 23

Double Beam Spectrophotometer

Answer 23

Allows you to cope beam of light and deflect rapidly to get more accurate %transmittance

Question 24

Continuum Source Examples?

Answer 24

Tugsten, D2 lamps, IR- uses globar

Question 25

Line Source Examples?

Answer 25

Hollow cathode tubes, lamps, lasers

Question 26

Lasers?

Answer 26

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

Question 27

4 processes of a laser

Answer 27

1. 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.
2. Spontaneous Emission, a species in an excited electronic state may lose all or part of its excess energy by spontaneous emission of radiation.
3. 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.
4. Absorption, two photons with energies exactly equal are absorbed

Question 28

Flame structure?

Answer 28

1. Primary combustion zone (blue luminescence)
2. Interzonal Region: Hottest part of flame (rich in atoms, used in spec)
3. Secondary combustion zone: atoms and other species converted

Question 29

XRF
Advantages and Disadvantages

Answer 29

1. An incoming x-ray knocks out an electron from an inner atomic orbital
2. An unstable electron configuration is produced
3. 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,

Question 30

How to get molecules to excited state?

Answer 30

Absorb visible or UV light
Absorb a photon
Collide with atoms or particles
Heat, light or electricity

Question 31

Why use narrow bandwidth?

Answer 31

Lowers interference signals

Question 32

ICP vs emission Spectroscopy

Answer 32

Has a more stable heat source
Sample is able to stay in longer to completely atomize