Sampling is the process of obtaining representative samples of materials like solids, liquids, and gases. It is a critical step in analysis. For heterogeneous solids, several individual samples are taken and combined into a gross sample. For liquids, grab samples or devices like thieves or impingers are used. Gases can be sampled directly or with enrichment using adsorption tubes, impingers, or chemical reactions. The key steps are sampling, transport, analysis, and assessment. Careful sampling ensures accurate results.

1. Sampling

2. Sampling
• Sampling is the process of obtaining a representative sample
(We can not analyze the whole thing!)
• A sample is the representative of the whole bulk. It composition should
closely reflect the composition of the bulk.
• Critical step in analysis as the significance and accuracy depends on
sampling
• Sample can be solid, liquid, gas and heterogeneous or homogenous
• Homogenous Sample: A grab sample is often OK. For instance, in
clinical lab, gross sample (blood, urine) can be analyzed directly as it is
homogenous.
• Heterogeneous Sample: Several individual samples are taken. E.g.,
analyzing average protein content of shipment of grains, one has to
collect little grain from each bag during loading/unloading using a
sampling spear (sack sampler) and combine to obtain a gross sample.

3. Gross Sample consists of several portion of
the material to be tested
Laboratory Sample consists of a small portion
of gross sample made homogenous
Analysis Sample is that which is actually
analyzed
Gross Sample
Laboratory Sample
Analysis Sample
(Few g to Kg)
Bulk of Material
(Few g)
(a drop, few mg, few mL)

4. Sample Preservation
Sample Preparation
Analysis
Sampling
Collect sample
Reduce Gross sample to Lab sample
Analysis Sample
(Gross Sample)
Identify Population
(Laboratory Sample)
(a drop, few mg, few mL)
Steps involved in a
measurement process
(Bulk of Material)
Steps involved in
Sampling process

5. Examples
 Large particulates such as ores
 Smaller particulates
 Sheet material
 Tissue samples
Sampling of solids
o Solid samples are often the most difficult to sample
(Inhomogeneous, variation of particle size, variation within particles)
o Solids are usually heterogeneous and samples must be
collected carefully.
o Solids come in variety of forms, each of which is sampled
differently.

6. Grab Sample
o A grab sample is a sample taken at random and
assumed to representative.
o 1/50th of the total bulk
o Easiest but less reliable
o Satisfactory only for homogenous samples
o Best and easy time for sampling: during
transportation

7. Collection of sediments
 Bottom grab sampler is used.
 It has jaws that close when they are in contact with
sediments, scooping up sediments in the process.
 Ease of use and ability to collect large samples.
 Disadvantages include tendency to lose fine grained
sediments as water flows out of samples.
 Loss of spatial information both laterally and with
depth due to mixing of samples.

8. Collection of surface soil
 Soil samples collected at depths of upto 30 cm are
easily collected with scoops or shovels.
 Even small containers of solid materials may be
samples usig spatula or scoops.

9. Collection of soil at greater depth
 Soil samples collected at greater depth are obtained by
digging a trench and collecting samples.
 Drill a hole till the required depth. Remove soil from the drill
and analyze.
Soil Sampler
100 cm Length
25 mm diameter
1. Push the sampler
into the product
2. Rotate handle
3. Remove sampler
4. Use discharge rod to
push sample out
Operation

10. Sampling from bags
 Simple bag sampling spears (sack
samplers) are most commonly used for
taking samples from bags because they are
relatively cheap and sample quickly.
 To obtain a good cross section of sample,
the spear should be 40 to 45 cm in length.
 Tapered type of sampling spears penetrates
bags easily.

11. Sampling of powder
 Small particulate materials such as
powder are best collected with a sample
thief.
 Sample thief allow material to be
collected simultaneously from several
locations.

12. Powder Thief
Operation:
1. Insert the sampler into the product,
ensure that the tip is inside the sampler
body.
2. At the required depth pull up the
body to expose the tip. Powder will
flow in around the
tip.
3. Push down body of the sampler to
trap the sample.
4. Withdraw sampler.
5. Pull up body to release the sample.
The Powder Thief is suitable for sampling free flowing powders and
granules.

13. Sampling of metals and alloys
 Samples of these materials are obtained by sawing ,
milling or drilling.
 When sampling a metal, it is usually necessary to
obtain materials from both the surface and the
interior.
 Wire……cutting off pieces of appropriate length.
 Drilling can also be done.

14. Sampling of biological tissues
 It is done by removing the entire organ which is then
homogenized before smaller portions are taken for
the analysis.
 Alternately small portions may be combined to form
a composite sample.
 The composite sample is then homogenized and
analyzed.

15. REDUCTION OF SAMPLE SIZE
 Reducing particle size
 Sub-sampling of gross sample
Coning and quartering
Riffling

16. Coning and quartering
 Gross sample is piled as cone
 Flattened
 Divided into quarters
 Separation of quarters
 Discarding opposite quaters
 Process is repeated

17. Riffling
Riffle tank is used

18. Sampling of Liquids
Examples
 Those drawn from containers of commercial
solvents
 Beverages
 Natural waters
 Biological fluids
 Suspensions in the form of oral medication

19. Sampling of liquids
 Tend to be homogeneous and much easier to sample.
 A Grab sample is often sufficient.
 If natural diffusion of water is slow (pond), shake/stir it
before sampling
 Large bodies of water are bests sampled after a transfer,
or if in a pipe, after passing through a pump.
 Large stationary liquids can be sampled using thief
sampler.

20. Biological Fluids
 Timing for biological samples is important. E.g., blood
composition changes before and after meal. Sampling after
12h fasting is often recommended. 24h urine collection is
better than a single specimen.
 In case of blood, a grab sample is OK. Syringes are used to
collect blood samples.
 Glass or plastic with stainless steel needle are available.

21. Vacutainers (evacuated tubes with rubber
cap) are Used to collect blood samples.
Blood can be analyzed as whole blood or separated into serum and
palsma
Serum: Fluid separated from clotted blood. Serum does not clot
Plasma: Fluid separated from unclotted blood. It contains fibrinogens
Preservatives (such as NaF for glucose) or anticoagulant (Heparin) are
often added to blood samples.
vacutainers
Storage of Biological Fluids:

22. Thief sampler
 It is used for the sampling of large
stationary liquids.
 The separate portions of liquids can be
analyzed individually and results combined.
 Portions can be combined into one gross
sample and replicate analysis is performed.

23. pipets
 Used for sampling of homogeneous
samples.

24. Grab sampler
 Liquid samples are often obtained
with a device known as grab
sampler.
 It consists of metal container into
which a small bottle is placed.
 The top of bottle is closed with a
stopper connected to a link held
by the person doing the sampling.

25.  It is lowered to the desired depth in the
liquid ,the wire attached to it is jerked to
open the sample bottle .
 It is filled.
 It is automatically sealed.
 Cable connected to it is used to lift the
sampler.

26. Sampling bags

27. Sampling of gases

28.  Assessment of air quality
 Workers during their work at many workplaces are
exposed to gases and vapours (inorganic gases
and organic (solvent)-vapours). These exposures
need be categorized and measured analytically,
Examples of workplaces and activities, as well as gases and vapours,
which can occur at workplaces occupational settings
Chapter: Sampling and
Analysis of Gases and
Vapours,
DOI:13140/2.1.1036.1925

29.  Sometimes, a grab sample is OK
 Usual method is displacement of liquids (not reacting with or
solubilizing the samples)
 Breath sample: The person blows into an evacuated bag.
 Auto-exhaust is collected in a large evacuated plastic bag.
 O2, CO2 dissolved in liquid (e.g., blood) is considered as liquid
sample.
 Sampling with enrichment: Substance (gas) is adsorbed onto
a solid collection phase or absorbed into a solution.
 In active sampling procedures, workplace air is drawn onto a
collection medium using especially designed sampling pumps.

30.  T and P is important in determining volume
and hence concentration.
 For direct sampling, gas storage vessels or gas
sample bags (TedlerTM bags) are used.
 Bag is connected to pump and air is drawn at
1 to 3 L/min
 V= r x t V= volume, r= flow rate (L/min), t= timing of
sampling
TedlerTM bags

31. Measurement Principles
To estimate the exposure of hazardous substances,
in principal the workplace air is drawn through an
adequate collection medium using a pump. The
complete measurement
 procedure comprises the following steps:
 1. Sampling
 2. Transport and storage
 3. Analytical determination
 4. Assessment

32. Chapter: Sampling and Analysis of Gases and Vapours, DOI: .13140/2.1.1036.1925

33. Sampling
 Workplace air can also be analyzed directly in its original state
or enriched first.
 The gases and vapours that occur in workplace air can be
separated and enriched in the collection medium
 Substance (gas) is adsorbed onto a solid collection phase or
absorbed into a solution. During enrichment by adsorption or
absorption the analyte is collected in its original state
 Chemical Reactions: Respective reactions of the analysed
substances can be used also for derivatization and
enrichment.

34.  For sampling with enrichment, the substances to be
determined are either adsorbed onto a solid
collection phase, or absorbed in a solution. The
samples afterwards need to be prepared so that
they can be subsequently analysed.
 Sampling pumps are often used
V= r x t V= volume (L), r= flow rate (L/min),
t = timing (min) of sampling
Sampling with enrichment
Source: Sampling and determining aerosols and their chemical components

35. Adsorption Tubes
For sampling with enrichment using adsorption tubes, the
substances to be determined are adsorbed onto a solid
collection phase (adsorbent) placed inside a tube
The adsorption tubes are heated in a compatible thermal
desorber, whereupon the collected substances are transferred
into a cold trap using a carrier gas. When desorption is
complete, the cold trap is heated abruptly and thereby
transferring the sample onto the GC column for subsequent
separation
Chapter: Sampling and Analysis of Gases and Vapours, DOI: .13140/2.1.1036.1925

36. [24] DFG (Deutsche Forschungsgemeinschaft) Analysis of hazardous substances in air,Volumes 1 – 8 (1991– 2003). From Vol. 9
(2005) the title changes to: The MAK-Collection for Occupational Health and Safety, Part III,Wiley-VCH Verlag,Weinheim.
Chapter: Sampling and Analysis of Gases and Vapours, DOI: .13140/2.1.1036.1925

37. Reaction samplers
 A sampling that utilizes chemical reactions
 The sampling occurs using either a bottle, in which the reagent is
dissolved in an appropriate liquid, or with sample media (filters or
adsorbents) that have been pretreated with a reagent.
 The reaction between the investigated substance and the reagent
takes place in situ during sampling
 Examples include the collection
(i) of aldehydes using enrichment systems impregnated with
dinitrophenylhydrazine,
(ii) of diisocyanates collected on filters impregnated with 2-
methoxyphenyl-piperazine
(iii) hydrogen peroxide in solutions containing titanium.

38.  The method can either deliver the result instantly on
location (e. g., via direct reading), or by analysis in the
laboratory after sample collection in a suitable vessel.
 For air sampling without enrichment, gas storage vessels
(e. g., gas mouse) or gas sample bags (e. g. Tedlarä-
bags) can be used.
 This type of sampling is also used for the determination of
organic gases that occur permanently in the air of
workplaces (e. g. propane, propene)
 For the analysis of gases and vapours collected without
enrichment, a gas-tight syringe is normally used for
sampling from the collection device
Sampling without enrichment
TedlerTM bags

39. Sampling of gases
 Different types of sampling devices are used for the
collection of gaseous samples.
 GAS SAMPLING BAG
 STAINLESS STEEL CONTAINER
 FILTERATION UNIT
 GAS ADSORPTION TUBES
 IMPINGERS
 CENTRIFUGAL COLLECTOR
 ELECTROSTATIC SAMPLERS
 THERMAL PRECIPITATOR

40. Impingers
Air drawn into the impinger is forced through a
nozzle, which is covered by a liquid such as high
purity water. The pollutant dissolves in the liquid and is
subsequently analysed, usually by colorimetric
techniques.
impinger
Impingers are special glass tubes designed to collect
airborne contaminants by bubbling the sampled air
at a high flow rate through a method specific
asbsorbing liquid inside. The liquid used can then be
analyzed to determine airborne contaminate levels.

41. Centrifugal collectors
Centrifugal collectors
The particles are removed by
the application of a centrifugal
force. The polluted gas stream is
forced into a vortex. The motion
of the gas exerts a centrifugal
forces on the particles, and
they get deposited on the inner
surface of the cyclone.

43. Resources
 http://www.sampling.com/manual_samplers.html
 Hebisch R., Fricke H.-H., Hahn J.-U., Lahaniatis M., Maschmeier C.-P.,
Mattenklott M. (2005) Sampling and determining aerosols and their chemical
components. In: Deutsche Forschungsgemeinschaft (Greim H., Parlar H. eds.),
The MAK-Collection for Occupational Health and Safety, Part III: Air Monitoring
Methods”,Vol. 9. Wiley-VCH,Weinheim.
 Giese U. (2000) Materialien zur Adsorption von organischen stoffen aus Luft In:
“Analytische Methoden zur Prüfung gesundheitsschädlicher Arbeitsstoffe”,
Band 1: Luftanalysen (Greim H., Hrsg.), 12. Lieferung. Teil II: Spezielle
Vorbemerkungen Kap. 8, Wiley-VCH, Weinheim.
 Chapter: Sampling and Analysis of Gases and Vapours, DOI:
.13140/2.1.1036.1925
 [24] DFG (Deutsche Forschungsgemeinschaft) Analysis of hazardous
substances in air,Volumes 1 – 8 (1991– 2003). From Vol. 9 (2005) the title
changes to: The MAK-Collection for Occupational Health and Safety, Part
III,Wiley-VCH Verlag,Weinheim.