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Chemistry > Chem Exam 1 > Flashcards

Chem Exam 1 Flashcards

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1
Q

What are the approximate wavelengths of visible light?

A

400-700 nm

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2
Q

How does wavelength relate to energy?

A

Shorter wavelength = higher energy

Longer wavelength = lower energy

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3
Q

What is the formula that relates absorbance and transmittance?

A

A = -log T = -log (T1/T0) = 2- log %T

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4
Q

Examples of light sources for spectrophotometer

A

tungsten lamp, quartz-halogen lamp, deuterium discharge lamp, mercury arc lamp, or laser

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5
Q

Types of monochromators

A

Colored glass filters, prism, interference filters (mirrors), diffraction grating

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6
Q

What are these types of: colored glass filters, prisms, diffraction grating

A

Monochromators

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7
Q

What is the measure of the monochromator’s spectral purity?

A

Bandwidth - specifically a narrow bandwidth

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8
Q

What characteristics must a cuvette have in spectrophotometry?

A

Standard in size, clean, unscratched

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9
Q

Types of photodetectors

A

Photocell, phototube, photomultiplier tube, diode array

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10
Q

Advantages and disadvantages of a photocell as a photodetector

A

Adv: cheap, easy, does not need a current/voltage
Disadv: needs a LOT of light, quick to fatigue

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11
Q

Advantages and disadvantages of a phototube as a photodetector

A

Adv: simple to use
Disadv: requires a current, requires a lot of light, cannot multiply a light signal, quick to fatigue, requires time between measurements

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12
Q

Advantages and disadvantages of a photomultiplier tube

A

Adv: most sensitive of the detectors, can multiply a low light signal, slow to fatigue
Disadv: expensive and very complex

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13
Q

Advantages and disadvantages of a diode array

A

Adv: can measure more than one wavelength simultaneously, specific
Disadv: not quite as sensitive as photomultiplier tube

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14
Q

What are some measurements used to assure quality results from a spectrophotomer?

A

Linearity, stray light check, wavelength check

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15
Q

How can we limit background interference in spectrophotometry?

A

Sample blanking - contains everything except patient sample to detect any baseline absorption

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16
Q

What are the light scattering measurements?

A

Nephelometry, turbidimetry, laser light scatter (flow cytometry)

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17
Q

Nephelometry

A

Nephelometry measures the scatter of light from particles in a reaction solution with a detector for scattered light at an angle to the source light (forward scatter position)

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18
Q

Turbidimetry

A

Measures the reduction in amount of light by particles in a reaction solution, can be measured with most traditional spectrophotometers

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19
Q

What is unique about the light source for A.A.S.?

A

Lamp contains the material that will be measured (heavy metals)

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20
Q

What does a chopper do?

A

Chops the light signal coming from the lamp to allow for detector to distinguish between light coming from lamp and light coming from excited atoms in the flame

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21
Q

What does the monochromator do in A.A.S.?

A

Selects wavelength that reaches the detector after light enters sample
Protects the detector from large amounts of light

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22
Q

What does the detector do?

A

Distinguishes between light from the light source and light emitted by excited atoms in the flame

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23
Q

Name a few elements A.A.S. measures

A

Calcium, lead, copper, chromium, aluminum

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24
Q

Advantages of A.A.S.

A

sensitive and precise, can be used for analytes that are difficult to measure in other ways (measures heavy metals)

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25
Q

Disadvantages of A.A.S.

A

possibility for chemical interference and possibility of excitation of atoms by flame if flame temp is too high
need a separate lamp for each analyte

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26
Q

What does lanthanum do?

A

acts as a competitor for phosphate leaving calcium free for measurement during A.A.S.

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27
Q

Limitations in calcium measurement? What is used to help with this?

A

calcium will frequently bind to phosphate and calcium levels will not be accurately measured. Lanthanum is added to act as a competitor for phosphate.

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28
Q

What is a fluorophore?

A

A substance that can fluoresce –> it absorbs energy at higher energy wavelengths and emits light at lower energy wavelength

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29
Q

What type of solution is best suited for fluorometry?

A

DILUTE solutions

30
Q

What is a unique feature of a fluorometer?

A

It has two monochromators

Detector is at a right angle to the light source

31
Q

Advantages of fluorometry?

A

Very sensitive and specific

32
Q

Disadvantages of fluorometry?

A

Only useful in dilute solutions
Extremely sensitive to environmental changes such as temperature, pH, light scattering, concentration quenching, and contaminating chemicals

33
Q

What is fluorescence polarization?

A

A fluorometer that has the source light passed through a polarizer so all the light that reaches the sample is moving in a single plane

34
Q

What is fluorescence polarization commonly used for?

A

Therapeutic drugs and drugs of abuse (compounds in low concentrations)

35
Q

What is unique about luminometry?

A

There is no lamp and there is no monochromator

36
Q

What are some advantages of luminometry?

A

quick assay time, easy to use and relatively simple, sensitive (low detection limits)

37
Q

What are some disadvantages of luminometry?

A

Impurities can cause background noise or false signal

38
Q

Name a unique characteristic of reflectance photometry

A

No water is required for testing - all components are contained in a dry slide or a dipstick

39
Q

What is the principle behind refractometry?

A

As light enters liquid it will be bent from its original path - the angle at which it is bent can be related to the concentration of the liquid

40
Q

What does an electrochemical cell consist of?

A

Two electrodes (reference electrode and indicator electrode) and a salt bridge

41
Q

What is a liquid junction?

A

The area where two differing solutions are allowed to interact with one another. This is where a potential develops

42
Q

What is measured in potentiometry?

A

The potential generated between a reference electrode and an indicator electrode. No current is applied.

43
Q

What does ISE mean?

A

Ion Selective Electrode

44
Q

What are the two types of electrodes in an ISE?

A

Reference and Indicator electrodes

45
Q

What makes an ISE an ISE?

A

The selectivity the ISE has for a particular ion over others found in solution.
The electron used is very selective for particular ions.

46
Q

Name three common types of reference electrodes

A

Hydrogen
Calomel (mercury/mercurous chloride)
Silver/silver chloride

47
Q

Name types of ISEs

A

Inert metal
Metal
Membrane - solid, liquid, special (gas-sensing and enzyme)

48
Q

What does the Nernst equation describe?

A

The membrane potential at the surface of an ISE

49
Q

What is the most difficult characteristic to achieve in an ISE?

A

Selectivity for one ion over others

50
Q

What is the difference between direct and indirect ISE?

A

direct - no dilution of patient sample

indirect - dilution is made of patient sample

51
Q

What is the assumption about “normal” plasma?

A

It is approximately 7% solids and 93% liquids

52
Q

What is the electrolyte exclusion effect?

A

In indirect ISE, samples with higher solid content (lipemic or high protein samples) have a decreased liquid portion, but a standard amount of diluent is added. The sample is then overdiluted and can cause an inaccurate falsely decreased sodium content.

53
Q

What is unique about an electrochemical cell that uses voltammetry?

A

Has 3 electrodes - reference, indicator, and auxiliary

54
Q

What electrochemical reaction occurs in voltammetry?

A

Electrolysis

55
Q

What are the two steps to anodic stripping voltammetry measurement of lead?

A
  1. free lead is concentrated onto electrode

2. lead is stripped off the electrode and current is measured

56
Q

What is the difference between the potential in voltammetry vs. amperometry?

A

they both involve a current applied to the cell and the generated current is measured, but amperometry is always fixed potential.
Amperometry is a specific type of voltammetry

57
Q

What is an example of a coulometric measurement?

A

Old chloride meters

58
Q

How does conductometry work?

A

Measures the changes in electrical conductivity to count the number of cells as well as gather information about size of cells

59
Q

Is whole blood a good conductor of electricity? Plasma?

A

Whole blood is not a good conductor

Plasma is a good conductor and essentially an electrolyte solution

60
Q

Where is conductometry used in the lab?

A

Hematology analyzers (Coulter principle)

61
Q

What is a colligative property?

A

Property based solely on the number of particles in a solution (not the size/shape/chemical characteristics)

62
Q

Identify the four colligative properties

A

Freezing point depression
Osmotic pressure
Boiling point elevation
Vapor pressure depression

63
Q

What is the colligative property most commonly used for osmolality measurement?

A

Freezing point depression

64
Q

What is the difference between osmolarity and osmolality?

A 
Osmolarity = number of moles solute per liter of water 
Osmolality = number of moles solute per kilogram of water
65
Q

What substances in the plasma typically contribute to osmolality?

A

sodium, chloride, glucose, and urea nitrogen (BUN)

66
Q

How do we represent chloride in the osmolality calculation?

A

multiply sodium by 2

67
Q

What is osmolal gap? What does a difference greater than 10 indicate?

A

difference between calculated osmolality and measured osmolality
A difference greater than 10 may indicate that another substance is present in the plasma that the calculation does not account for, such as alcohol or mannitol

68
Q

What are the common uses for osmolality measurements?

A

Quick screen for toxic ingestion (not specific)
Evaluate mannitol therapy
Evaluate kidney’s ability to properly concentrate urine

69
Q

How does freezing point osmometry work?

A
  1. solution supercooled to several degrees below freezing point by gently stirring
  2. Once supercooled, stirring stops rapidly and solution freezes
  3. As solution freezes, heat is released and it warms slightly to its actual freezing point
  4. slush reaches a plateau, and the concentration is measured at that plateau (freezing point)
70
Q

T/F: The more particles there are in solution, the more the freezing point is elevated.

A

FALSE; the freezing point is more depressed when there are more particles in a solution

Chemistry (12 decks)

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