Chapter 4 Flashcards

1
Q

Require a solid understanding of
analytical techniques available

Problem-solving skills

Experience

Intuition, logic and common
sense

A

DEFINE THE PROBLEM

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2
Q

CHOOSING YOUR TEST METHOD:
THE SAMPLE AND THE ANALYTE

A
  • What is the nature and background of
    the problem?
  • What is known about the history of the
    sample?
  • What analyte is important in the
    sample?
  • What is the concentration range of the
    analyte?
  • What degree of accuracy and
    precision is demanded?
  • What other components are present in
    the sample
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2
Q

CHOOSING YOUR TEST METHOD:
THE ANALYTE

A

Have prior, similar efforts been documented in the
literature?
* What instruments and equipment are available for
the determination?
* How much time is needed to perform the work?

  • How soon does the work need to
    be done?
  • How much money is available to
    accomplish the work?
  • How many samples must one
    measure?
  • Are there limitations to the amount
    of sample that can be used?
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2
Q

What Factors to Consider?
✓ What type of information does the method provide?
✓ What are the advantages or disadvantages of the technique
versus other methods?
✓ How reproducible and accurate is the technique?
✓ How much or how little sample is required?
✓ How much or how little analyte can be detected?
✓ What types of samples can the method be used with?
✓ Will other components of the sample cause interference?
✓ Other factors: speed, convenience, cost, availability, skill
required.

A
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3
Q

Green chemistry processes are
preferred for modern analytical procedures

The goal: minimize
waste and pollution

Use of less toxic
or biodegradable solvents

Use of chemicals that can be recycled

A

GREEN CHEMISTRY…A CONSIDERATION

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3
Q

CHOOSING YOUR TEST METHOD
(FOR WATER ANALYSIS)

  1. Is an approved/ regulatory method based on AWWA/ APHA available for use?
  2. What will the results be used for? (Regulatory compliance or Process Control)
  3. Is the LOQ achievable?
    (at least 1/10th of the regulatory value)
  4. Use a standard method/ test kit/ or developed
    “in-house” method?
A
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4
Q

QUALITATIVE INFORMATION ON THE
ANALYTE

Elemental Composition

Oxidation states

Structural
information

Isotopic
distribution of
elements in the
sample

Polyatomic ions,
Functional groups,
Specific molecules,
Molecular species

A
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5
Q

Major: >1%
Minor: 0.01 – 1%
Trace: 10-2 - 10-6 %
Ultra-trace: 10-6 – 10-9 %

A

QUANTITATIVE INFORMATIONROUGH CONCENTRATION

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6
Q

FACTORS IN SAMPLE
PREPARATION:

✓Phase of the sample- solid, liquid, gas

✓Properties of the analyte:
❑Organic or inorganic
❑Pure substance or mixture
❑Homogeneous or heterogeneous

✓Instrumentation- elemental or molecular

✓Decomposition or dissolution of a solid sample

✓Dilutions made prior to measurement

✓Approaches taken to prevent analyte losses or contamination

✓Separation of interferences from the matrix- element or
compound that respond directly to measurement; gives a false
signal; signal may be enhanced or suppressed

A
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6
Q

PROPERTIES OF THE SAMPLE/ ANALYTE:

Sample

Phase: solid,
liquid, gas,
dissolved,
suspended
* Amount
available for
analysis
*Homogeneity

A

Analyte
* Chemical and
physical
properties

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6
Q

Signal-to-noise Ratio (S/N):

random variation in signal or background

net response recorded by a method for a sample

A

Noise:
Signal:

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7
Q

▪ the smallest signal above the
background noise that can be
detected reliably
▪ Typically 3 X signal/noise ratio

A

❖ Instrument Detection Limit (IDL)

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7
Q

ANTICIPATED CONCENTRATION
OF THE ANALYTE

upper and lower
boundary of applicability and may not be
linear over all concentrations

calibration curve

most important part in
method selection

A

Linear dynamic range

Limit of linearity

Limit of detection

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8
Q

▪ minimum concentration reportable to 99%
confidence level that the analyte is > zero.

–Determined from the analysis of a low
sample concentration in a given matrix.
–MDL is the “criterion for detection”

A

Method Detection Limit (MDL)

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9
Q

It is a multiple of LOD at a concentration of the
analyte that can reasonably be determined with
an acceptable level of accuracy and precision
* Can be calculated using an appropriate
standard or sample, and may be obtained from
the lowest concentration on the calibration
curve (excluding the blank)
* LOQ is 10 SD.

A

LIMIT OF QUANTITATION (LOQ) /
PRACTICAL REPORTING LIMIT (PRL)

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10
Q

(within batch, internal)

(between batches, variability)

  • Influenced by changes in analyst, instrument
    conditions, reagents, etc
  • Can be assessed by analysis of at least 10X,
    calculate SD within batch and between
    batches
  • Long term assessment can be derived from QC
    chart
A
  • Repeatability
  • Reproducibility
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11
Q

Is the closeness of
agreement between
a test result and the
accepted reference
or true value of the
property being
measured

A

Trueness

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12
Q

The way in which the result or signal of a method
varies with the amount of compound or property being
measured.

A

Response

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13
Q

A plot of the result or signal vs. the known amount
of a known compound or property (standard) being measured.

A

Calibration Curve:

14
Q

Dictates:
* instrument to be selected for
measurement
* Sample preparation
* Separation

A

INTERFERENCES

15
Q

The analytical method should not be sensitive to small
changes in procedures e.g., flow rates, reagents, etc
Robust methods (using standard methods) will generally
produce similar results for the same sample when used in
independent laboratories

A

ROBUSTNESS/ SYSTEM
SUITABILITY

16
Q
A

EXISTING METHODS

17
Q

SAMPLING

A
18
Q

Type of sample preparation
depends on:
➢Nature of sample
➢Technique/ method
chosen
➢Analyte to be measured
➢The problem to be
solved

A
  • Samples may be:
    ➢Dissolved in water or
    other solvents
    ➢Pressed into pellets
    ➢Cast into thin filmssurface analysis
19
Q

➢Homogeneously distributing the analyte in a solvent
* Aqueous
* Non-aqueous: for organic compounds and
polymers
* Acid-water mixture: HCl, HNO3, H2SO4 (HF, HClO4
with special care & supervision)
* Complexing agents-water : ligands aid solubilit

A

DISSOLUTION

20
Q

Chemically converting the sample into a form
that can be dissolved in a solvent

A

DECOMPOSITION

21
Q

inorganic analyte into soluble
form with concentrated mineral acids (HCl, HNO3,
H2SO4 (HF, HClO4 with special care & supervision)

A

Acid decomposition-

21
Q

fused with acidic or basic salt (K2CO3 or
K2S2O7) at high T, cooled melt is dissolved

A

Fusion

22
Q

sealed oxidation with O2, followed by
absorption of product in a solvent

A

Combustion

23
Q

organic sample in hot oxidizing reagent,
then elemental analysis

A

Wet ashing-

24
Q
  • heating an organic sample in flame or
    furnace, followed by dissolution of the ash
A

Dry ashing

25
Q
  • high pressure in sealed vessel
    (automated
A

Microwave assisted

26
Q

➢Selective removal of an analyte from a mixture by
partitioning between two immiscible phases

A

EXTRACTION

27
Q

=➢Removal of a solid substance from solution by
exclusion proces

A

FILTRATION

27
Q

distribution into two
immiscible liquid phases

A

Liquid-Liquid Extraction (LLE)

28
Q

analyte retention on
solid sorbent; followed by elution

A

Solid Phase Extraction (SPE)

29
Q
  • analyte sorbed
    on a thin layer of sorbent (solid, liquid) coated on the outer
    surface of a fiber exposed to a liquid mixture, followed by
    redissolution or volatilization of analyt
A

Solid Phase Microextraction (SPME

30
Q

a supercritical
fluid is created using a gas (like CO2) above the critical
temperature; the resulting supercritical fluid is typically
used to extract organic analytes from a solid sample
followed by its collection by depressurization, on a
sorbent or in a solvent

A

Supercritical Fluid Extraction (SFE)- a

31
Q

microwave-accelerated extraction of organic
analytes from a solid sample with a liquid

A

Microwave Assisted Extraction (MAE)

32
Q

a sample is placed in
contact with a membrane that allows the sample to
selectively permeate into a new gas or liquid

A

Membrane Extraction-

33
Q

volatile organic compounds
are allowed to diffuse from a liquid into a headspace
above the liquid; analyte-containing gas in the
headspace is sampled

A

Headspace Extraction-

34
Q

➢Removal or enrichment of a volatile substance
based on differences in boiling point

A

DISTILLATION

35
Q
A
36
Q

Gravimetric Methods determine the mass of the analyte or some
compound chemically related to it

  • Volumetric Methods measure the volume of a solution containing
    sufficient reagent to react completely with the analyte
  • Electroanalytical Methods involve the measurement of such
    electrical properties as voltage, current, resistance, and quantity of
    electrical charge
  • Spectroscopic Methods are based on the measurement of the
    interaction between electromagnetic radiation and analyte atoms or
    molecules, or the production of such radiation by analytes
  • Miscellaneous Methods include the measurement of such
    quantities as mass-to-charge ratio, rate of radioactive decay, heat
    of reaction, rate of reaction, sample thermal conductivity, optical
    activity, and refractive index
A
37
Q
A