Instrumental Analysis Exam 1

Charge-Coupled Device (CCD) - Diagram

(A) SiO2 insulators (B) Si electrode (C) Light (D) electrons stored beneath the positive electrode (E) Electron and hole generated by a photon (F) n-doped Si substrate

Charge-Injection Device (CID) - Diagram

(A) Charge formation and integration (B) Measure V1 (C) Measure V2 (D) Remove Charge (E) Substrate (F) n-type Si (G) SiO2 Insulator (H) Nondestructive readout mode (I) Destructive readout mode

Charge Transfer Device - Diagram

(A) Substrate (B) n-doped silicon (C) SiO2 insulator (D) electrodes

Photodiode-Array (PDA) - Diagram

(A) Clock (B) Start (C) Switch 1 (D) Switch 2 (E) Switch N (F) Photodiodes (G) Reset (H) Output (I) Integrator (J) Integrator reset Switch (K) Common

Photomultiplier Tube - Diagram

(C) Quartz envelope (D) Anode (E) Photoemissive cathode (F) Grill (G) Radiation (H) Dynodes

Photomultipler Tube Electrical Diagram

(A) Quartz envelope (B) Amplifier (C) To readout (D) Cathode

Phototube - Diagram

(A) Electrons (B) Wire anode (C) Photon Beam (D) power supply (E) Cathode

Photovoltaic Cell - Diagram

(A) Glass (B) thin layer of silver (C) Selenium (D) Iron (E) Plastic Case

Silicon Diode - Diagram

(A) pn junction (B) Metal contact (C) Hole (D) Electron (E) Wire Lead (F) p region (G) n region (H) Depletion layer (I) Reverse bias

Photovoltaic Cell - Definition

radiant energy generates a current at the interface of a semiconductor layer and a metal

Phototubes - Definiton

radiation causes emission of electrons from a photosensitive solid surface

Photomultipler - Definition

Contains a photoemissive surface and several additional surfaces which emit a cascade of electrons when struck by electrons from the photosensitive area

Photoconductivity - Definition

transducers in which absorption of radiation by a semiconductor produces electrons and holes, thus leading to enhanced conductivity

Silicon photo diodes - Definition

photons cause the formation of electron and hole pairs and a current across a reverse biased pn-junction

Charge-transfer transducers - Definition

the charges developed in a silicon crustal as a result of absorption of photons are collected and measured

A number of cycles per unit time is called

frequency

Amperometry is based on what principle?

Electrical properties

Atomic absorption spectroscopy is based on what principle?

interaction with electromagnetic radiation

Capillary electrophoresis is based on what principle?

separation and resolution

Consider the use of photomultiplier tube measuring the intensity of a light source. In which type of domain is the transduced information?

analog

Consider this schematic of a ultraviolet-visible spectrometer, which measures light intensity at a particular wavelength. What purpose does the monochromator play?

information sorter

Which piece of the instrument serves as the input transducer?

photodetector

Which of the following represents an electrical data domain?

the readout of a pH meter

Which has a longer wavelength blue light or red light?

red

Again compare blue light and red light. Which has a higher frequency?

blue

Which of the following describes the trend you see in the number of ejected electrons vs. frequency?

there is a certain frequency, above which electrons are ejected

What is the effect of the light intensity if the light frequency is fairly low?

increasing intensity has no effect

Now repeat the same experiment, but with the high frequency of light. What happens?

increasing intensity leads to more ejected electrons

The energy of a photon is proportional to its frequency. The energy needed to remove an electron form the metal surface is equal to the energy of photons of a frequency equal to the cutoff frequency. When radiation of higher energy is used, what happens to the excess energy?

it increases the kinetic energy of the ejected electron

What electronic transition is responsible for the first peak (medium intensity, shortest wavelength)?

lambda 2

What electronic transition is responsible for the second peak (largest intensity, medium wavelength)?

lambda 1

What electronic transition is responsible for the third peak (lowest intensity, longest wavelength)?

lambda 21

if a sample has an absorbance of 1.0, what percent of incoming radiation (P0) is the transmitted through the sample (P)?

10%

If a sample has an absorbance of 2.0, what percent of incoming radiation (P0) is transmitted through the sample (P)?

1%

If a sample has a transmittance (P/P0) of 0.25, what is the absorbance of the sample?

0.602

which of the following is a unique property of laser?

coherence

Which of the following is an example of optical pumping?

Ruby laser

Calculate the wavelength of radiation emitted by an LED made up of semiconducting material with a band gap energy of 2.8 eV.

4430.8 Å

what is the need to achieve population inversion?

to excite most of the atoms

Lasing species loses all or part of its excess energy in the form of fluorescence or phosphorescence radiation in the process called:

spontaneous emission

Voltage dividers are used to ___________.

produce a fixed fraction of the input

In a voltage divider, resistors are connected _____.

in series

In a voltage divider, all resistors _____.

Share the same current

In most modern monochromator (also known as wavelength selectors), reflection gratings are preferred over prisms. The disadvantage(s) of prisms compared to gratings include:

grating have a linear dispersion of light along a focal plane, while prisms do not disperse light lineraly along a focal plane

In general for qualitative analysis one uses _____ slit settings on a monochromator an for quantitative analysis one uses _______ split settings on a monochromator

narrower, wider

In what device an icident beam of photons causes production of electron-hole pairs which when separated produce a voltage related to the photon flux

photovoltaic cells

In what device photoelectrons are emitted as a result of photon bombardment and attracted to the positively charged anode to produce a small photocurrent proportional to the photon flux

phototube

What is the most sensitve photon transducer?

photomultiplier tube

What device does not require external power supplies?

photovoltaic cell

Basic, single-beam spectrophotometers like the Spectronic 20 use simple phototubes for detecting electromagnetic radiation in the visible range. These are useful as transducers because at saturation potential the current is ________ to the radiation power of light striking the cathode. At the same time, one must consider that such detectors have a measurable __________ that must be accounted for.

proportional, dark currrent

Charge transfer devices and photodiodes are often used in instruments where there is simultaneous detection of a range of wavelengths of light. For this type of detection, individual transducers are arranged in two-dimensional __________ which detect light after it has been separated by a polychromator.

arrary

Referring to the diagram, identify the relevant components of a photomultiplier tube. Photomultiplier tubes (PMTs) are among the most sensitive radiation transducers for ultraviolet and visible light. Light (G) entering a PMT first passes through a ________(F) before striking a photoemissive _________(E). The resulting photoelectrons (b) strike a series of ________ (H) before being collected at the _________(D). The entire PMT assembly is encased in a __________ (C) which is sealed and evacuated to allow the photoelectrons (B) and secondary electrons (A) to travel without interference.

(F) grill (E) cathode (H) dynodes (D) anodes (C) quartz envelope

What type of charge-storing device is used to record the radiant intensity of light that impinges upon photodiode array detectors?

capacitor