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food toxicants and analysis > Inorganic Contaminants: Trace Metals > Flashcards

Inorganic Contaminants: Trace Metals Flashcards

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1
Q

True/False: organic produce is not permitted to use any synthetic pesticides or chemicals

A

False; list of approved synthetic substances for crop production

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2
Q

Meat from a seal and an arctic char (fish) are harvested from the same waters. How would the trace metal levels compare in each?

A

Seal would have higher levels (higher trophic level on food chain)

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3
Q

What are some sources of possible trace metal contamination? (3)

A
  1. pesticides
  2. Food processing equipment (contact materials)
  3. Environment
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4
Q

What trace metal is of particular concern in environmental contamination, especially in seafood? What causes the high levels?

A

Methylmercury

Bioaccumulation + biomagnification (concentration increases up the food chain)

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5
Q

What trace metal is of concern in organic produce? Why?

A

copper

approved use of copper sulfate as pesticide/algicide

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6
Q

How might food processing equipment cause trace metal contamination?

A

acidic or salty foods + high velocity -> erosion and corrosion of equipment (leech metals into food)

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7
Q

What properties of metals are important to consider and why? (4)

A
  1. Effect of WATER + pH on speciation -> affects chem behaviour, toxicity
  2. Volatility -> behaviour, possible losses
  3. Binding to Ligands -> speciation in food (bind with components), behaviour in body, bioavailability
  4. Atomic absorption/emission spectra -> affect analytical methods
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8
Q

Metals can be present in a variety of forms, known as ____ _____.

A

metal speciation

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9
Q

In Canada, the safe limits of metals in foods is outlined in the:

A

Food and Drug regulations

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10
Q

the toxicity of ____ depends on its charged form. Which is more toxic?

A

Chromium

Cr (VI) is much more toxic than Cr (III)

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11
Q

Is speciation relevant in terms of trace metal analysis? Does it have any implications on health?

A

analysis: No, do not differentiate between species
health: Some species may be less toxic than others

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12
Q

What differences in exposure lead to different adverse health effects? (2)

A

Dose (higher dose -> greater risk/severity)

Frequency (acute vs chronic will have different effects)

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13
Q

____ arsenic is extremely toxic, while ____ arsenic is less toxic.

A

inorganic; organic

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14
Q

The speciation of the metal will affect: (3)

A

environmental fate
food chemistry
toxicity

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15
Q

The 2 general types of ashing:

A

Dry

Wet

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16
Q

After initial preparatory steps (drying, homogenize, etc), what is the general first step in trace metal analysis

A

Ashing (removal of organic matrix)

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17
Q

What trace metal is known to be volatile?

A

Mercury

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18
Q

The organic matrix must be completely destroyed to prevent: (3)

A
  1. interference (signals/noise)
  2. deposition inside instrument
  3. complexation with metals
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19
Q

3 general steps for trace metal analysis:

A
  1. sample prep
  2. Destroy organic matter
  3. instrumental analysis
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20
Q

Dry ashing is also known as:

A

thermal decomposition

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21
Q

Should conventional wet ashing be done in an open or closed system?

A

Open

Closed system will cause explosion!

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22
Q

Wet ashing is also known as:

A

acid digestion/oxidation

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23
Q

What is the procedure for dry ashing? What agents may be added and why?

A

complete combustion in furnace at 450-550 over several hours

Can add oxidizing agents (Mg nitrate, Mg oxide) to speed up process

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24
Q

What acid is a common reagent for wet ashing, either alone or with others?
Why is it good to use? (2)

A

HNO3

Good oxidizer; does not impact analytical tools

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25
Q

Which wet ashing reagent is highly poisonous? In what case must it be used?

A 
HF
Silica digestion (sand)
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26
Q

When doing conventional wet ashing, what is used to provide heat? Where should the experiment take place?

A

Hot plate or block heater

Under fume hood (noxious fumes)

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27
Q

In wet ashing, the organic matrix is ____ through use of ____. In dry ashing, the organic matrix is ____ through use of ____.

A

wet: oxidized; strong acid
dry: combusted; heat

28
Q

Why might peroxide be included with nitric acid for digestion?

A

H2O2 reconvert reduced nitrate species back to NO3 (re-oxidize)
No impact on analytical instrument

29
Q

Why are sulfuric acid or HCl not used alone as reagents for wet ashing?

A

Non-oxidizing; cause interferences

30
Q

What reagent can be combined with HNO3 for wet ashing but rarely used alone due to its explosive nature?

A

perchloric acid (HClO4) (strong oxidizing agent)

31
Q

What are the advantages of microwave assisted digestion? (3)

A
  • much faster
  • contained system
  • less manual labour
32
Q

After the process of wet ashing, what is the appearance of the sample? what does it contain?

A 
Clear solution
solubilized cations (metals) in acid
33
Q

Is the vessel for microwave ashing an open or closed system?

A

Can be either.
Open: open focused systems (under atmospheric pressure)
Closed: pressurized closed vessel (digestion bomb)

34
Q

What is “aqua regia”

A

1:3 mix of HNO3 and HCl (use for wet ashing)

35
Q

What is the process of microwave assisted digestion?

A

Sample + acid added to Teflon vessel, placed in microwave

Microwaves used to generate heat directly in solution

36
Q

what parameters would give the least time for ashing?

A

Microwave assisted wet ashing, in a digestion bomb (closed vessel)

37
Q

metals are (soluble/insoluble) in acid

A

highly soluble

38
Q

What are the two instrumental analyses used to quantify trace metals?

A 
atomic spectroscopy (emission, absorption, fluorescence)
mass spectrometry
39
Q

Describe the heating curve in microwave assisted digestion, and when the sample is safe to remove.

A 
Heating ramp (linear) -> plateau -> cooling (logarithmic)
Must wait until after cooling curve
40
Q

Compare emission vs absorption

A

Absorption: measure amount of energy ABSORBED by particle to become “excited” - go from ground state to higher energy level

Emission: energy RELEASED by particle returning to ground state from excited state

41
Q

Advantages of the “digestion bomb” method:

A

faster

closed system -> no volatile loss

42
Q

What are the current methods of atomic spectroscopy for trace metal analysis? (4)

A

flame AAS
graphite furnace AAS
ICP-OES (Inductively coupled plasma - optical emission spectroscopy)
MP-AES (Microwave plasma - atomic emission spectroscopy)

43
Q

What energy can be used to cause excitation of particles?

A

thermal or electrical

44
Q

How is the sample flamed?

A

drawn up from sample via capillary action into chamber, with injected OXIDANT and FUEL

45
Q

Name the basic parts of an atomic spectroscopy instrument, and their purposes.

A

Flame/Plasma -> atomize (also excitate)

Monochromator (or polychromator, for emission) -> filter out other wavelengths (tuned for that specific wavelengh to be measured)

Detector -> detect signal (connected to computer)

*lamp (for absorption/fluorescence): shine through sample, measure DECREASE IN SIGNAL (absorption) or EMISSION from absorbed light (fluorescence)

46
Q

What is the method of MS used for trace metal analysis?

A

ICP-MS

47
Q

What other method can be used to atomize the sample in AAS? How does it work?

A

Graphite furnace
sample contained in small graphite tube
high voltage -> high heat (1000s degrees)
sample atomized, light passed through

48
Q

Describe ICP steps:

What analyses is it applicable for?

A 
sample nebulized (fine spray) into plasma
In plasma: molecules broken down into atoms
- recombine in plasma, emit certain wavelengths -> emission spectroscopy
- or become CHARGED IONS (lose electrons), can analyze mass -> mass spectrometry
49
Q

How do you create high temperature plasma?

A

Microwaves

MIP

50
Q

A benefit of the graphite furnace method is it has higher ___ ___ than flame atomization

A

atomization efficiency

51
Q

List the analytical methods for trace metals in decreasing order of LOD:

A

Flame AA, ICP emission, GFAA, ICP-MS

52
Q

The purpose of plasma in trace metal analyses is to: (3)

A
  1. atomize
  2. radiation source (for AES or OES)
  3. ionization source (MS)
53
Q

What element is usually used as a plasma source and why?

A

Argon; inert gas

54
Q

How do flame and graphite furnace AA differ in LOD?

A

Flame has higher LOD (Less sensitive)

55
Q

True/False: ICP-MS can confidently detect levels as low as parts per trillion for some analytes

A

True

56
Q

The two types of plasma atomizations are:

A

ICP, MIP

57
Q

The LOD depends on: (2)

A

analyte

analytical method/instrument

58
Q

What method can be used to make analysis of metals like As, Pb, Se, or Sn easier?

A

HYDRIDE GENERATION

convert to hydrides -> more volatile

59
Q

What are the 3 main problems with trace metal analysis?

A

contamination
matrix effect
volatile metals (losses) vs non-volatile oxides (can’t atomize)

60
Q

what reagents are used for hydride generation?

A

H, NaBH4

61
Q

Where can contamination come from? (4) How can we help prevent it?

A
  • residue on equipment/tools: wash with acid prior to use
  • environment: avoid exposure to open air
  • reagents: use high purity (analytical grade)
  • Water: ultra pure (milli Q) water
62
Q

Describe the process of cold vapor atomic absorption spectroscopy: (5)

A
  1. REACTION: mercury sample oxidized by nitric/sulfuric acid, reduced by tin chloride
  2. Air pump -> stream of inert gas carries sample through system
  3. water vapor + mercury travel into drying tube (agent removes water)
  4. mercury vapor travel to QUARTZ chamber
  5. measure absorbance of gas
63
Q

How is ultra pure water different from distilled water? (3)

A

Deionized
No trace of metals
known resistivity/other properties

64
Q

What property related to matrix effect should be adjusted when preparing a calibration curve? why?

A

pH: should have similar pH as matrix of sample (adjust % acid)

pH affect speciation and signal -> affect calibration curve (need adjustment so that curve is valid for your sample)

65
Q

____ is problematic because of its high vapor pressure, making it incompatible with flame methods - so what is used instead?

A

mercury

cold vapor AAS

food toxicants and analysis (11 decks)

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