The document outlines various sampling types and procedures crucial for accurately analyzing chemical parameters, highlighting that the sample must represent the parent material effectively. It discusses different sampling strategies such as judgemental, systematic, random, grab, and composite sampling, along with techniques for preparing and homogenizing samples. Additionally, it details methods of analysis and decomposition, including microwave digestion and the use of acids, outlining procedures to ensure reliable and valid chemical analysis outcomes.

1. Sampling
Types and procedures

2. The composition of the sample should be identical to that from which it is collected and the sample represent the
same chemical parameters as that of the parent one at the time and site of sampling.
The relevant factors that affect sampling programme are; (1) frequency of sample collection, (2) total number of
samples, (3) size of each sample, (4) site of sample collection, (5) method of sample collection, (6) data to be
collected, (7) transportation and care of the samples prior to analysis and (8) method of analysis of parameters.

3. The principal types of sampling procedures are;
(1) Judgemental sampling is the result of a bias of the analyst and usually occurs when one collects the sample from a
place where the concentration of the pollutants is thought to be high or low. This type of sampling is not usually
representative of the entire site, but is useful in locating ‘Best case’ or ‘Worst case’ scenario of a pollutant source.
(2) Systematic sampling usually involves dividing the site into equal sized areas and sampling each area. Creating a
measured grid or regular pattern of sample sites is an easy way to set up a systematic sampling scheme.
(3) Random sampling involves selecting sample sites with no particular pattern or reason. The choice of the sites is
truly a random process.
(4) Spot or grab samples are discrete portions of water samples taken at a given time. A series of grab samples,
collected from different depths at a given site, reflect variation in constituents over a period of time.

4. (5) Composite samples are essentially weighted series of grab samples, the volume of each being proportional to the rate
of flow of water stream at the time and site of sample collection. Sample may be composite over a period of time e.g., 24
h. Such composite samples are useful in computing the material balance of a stream of water body over a period of time.
Composite sampling makes it possible to sample a large area with fewer samples.
(6) Real Time or In-situ analysis: With the advent of portable field analytical kit, several water quality parameters can
now be quantified on location and in real time. Parameters such as pH, salinity, dissolved oxygen and temperature can be
measured directly by inserting the probe into water.
Samples of different water bodies should be taken in different ways.

5. Sample Preparation
The given sample must represent as possible the average composition of the bulk of the material.
Step 1
• Identify the population
Step 2
• Collecting gross sample
Step 3
• Homogenisation

6. Gross Sample- Miniature replica of the population and should represent the entire
population
Preparation for inhomogeneous solids
Crushing, grinding, sieving, mixing etc.
Common errors in Homogenizing
Oxidation of certain metals
Change in water content of the sample
Loss of volatile components
As the SA increases, unwanted reactions with external environment can happen.

7. Machinery involved for homogenisation
Ball Mill
Disk Pulverizer

8. Moisture in samples
Moisture in the sample depends on the relative humidity of the atmosphere and the
ambient temperature.
Keeping the moisture content before analysis in a constant value to a reproducible limit
that can be duplicated.
Drying was used using a conventional oven or by storing in a desiccator.
Desiccators
Desiccators are sealable enclosures containing desiccants used for preserving moisture-
sensitive items such as cobalt chloride paper or Calcium chloride.
A common use for desiccators is to protect chemicals which are hygroscopic or which react
with water from humidity.

9. Forms of Water in Solids
Water can be essential or nonessential water in solids.
Essential Water
Essential water forms an integral part of the molecular or crystalline structure of a compound in its solid state.
Therefore, the water of crystallization in a stable solid hydrate (for example, CaC2O4.2H20 and BaCI2. 2H20
qualifies as a type of essential water.
Water of constitution is a second type of essential water and is found in compounds that yield stoichiometric
amounts of water when heated or decomposed.
2KHSO4(s) K2S2 O7(s) + H2O(g)
Ca(OH)2(s) CaO(s) + H2O(g)

10. Nonessential water is retained by the solid as a consequence of physical forces. It does not occur in any sort of
stoichiometric proportion.
Adsorbed water is a type of nonessential water but is retained on the surface of solids. The amount adsorbed
is dependent on humidity, temperature and the specific area of the solid.
Another type of water is sorbed water and is found in protein, starch, charcoal, zeolite, silica etc. It is held as a
condensed phase in the interstices or capillaries of the colloidal state.
A third type of nonessential water is occluded water. It is the water trapped in microscopic pockets in solid
crystals. Such cavities occur in minerals and rocks.

11. Temperature and humidity effects on the water content of solids
Concentration of water in a solid tends to decrease with increasing temperature and decreasing
humidity.
On essential water
The unhydrous componds will take up the moisture and convert to hydrous compounds.
On nonessential water
On occluded water

12. Decomposition or dissolution methods
 Using inorganic acids
 Using microwave heating
 Ignition in air or oxygen
 Heating with a molten salt
Possible common errors
 Incomplete dissolution
 Loss by volatilization
 Introduction of analyte as solvent contamination
 Unwanted reactions of reagents/solvents with the reaction vessel

13. I. Decomposition using inorganic acids in open vessel
Sl.
No
Inorganic acids Applications Properties
1 HCl For inorganic samples, Metals that are
easily oxidizable, some metal oxides
Non-oxidising acid
Highest concentration is 12M
Forms 6M constant boiling liquid
BP is 110oC.
2 HNO3 All common metals except Al, Cr (forms
oxide). Can oxidise non active metals
like Cu and Ag.
BP is 120oC.
Fuming nitric acid is 86% acid.
3 HNO3 + HCl
(1:3) (aqua
regia)
Precious metals such as Au and Pt Used in metal refining and
purification processes
4 H2SO4 Used for wet ashing
-Organic samples are dehydrated and
oxidised.
Many metals and alloys
High BP (340oC)

14. 5 HClO4 No. of iron alloys, stainless steel Good oxidizing agent
Explosive reaction
Carried out only in hoods which are lined with glass
or inert materials.
Constant boiling mixture forms at 72.5% acid with
203OC
6 Acids with
Oxidising
agents
Nitric acid with H2O2 or Br2 is used for
decomposing organic samples- Wet
ashing. It converts organic samples to
CO2 and water.
Aqua regia
Nitric acid with perchloric acids
Usually done in closed vessels to prevent volatile
gas loosing.
7 HF For silicate rocks and minerals. After the decomposition fluoride must be
eliminated as it interferes with cation analysis.
Done in well ventilated hood.

15. II. Microwave decomposition
Advantages
• Oxidative decomposition, wet ashing and dry ashing
• Decomposition of refractory materials
• High speed (usually within 5 to 10 minutes)
• Heat transfer is by convection
• Can be automated
• Real time analysis is possible
• Smaller amounts of reagents used
• Loss of volatile components can be eliminated

16. Microwave decomposition can be of open or closed.
The microwave acid digestion method was applied to the decomposition of rock samples and optimum conditions
were investigated. Samples of 10–100 mg were decomposed by this method.
100 mg of sample were also decomposed successfully by heating for 45–110 s with 0.3–1.0 ml of concentrated
HNO3 and 0.4–0.7 ml of concentrated HF.
Types
1. Moderate pressure digestion
Made up of low loss materials, have thermal and chemical resistance like Teflon.
Acids like nitric acids and hydrochloric acids can be frequently used. Sulphuric acid and
phosphoric acid can be used with care. In this case borosilicate or quartz glass is used.
Max temp is 300oC
Dis-HF cannot be used and so samples such as silicates and alloys cannot be used.

17. 2. High pressure microwave vessels
It is a closed microwave bomb which operate at a pressure up to 80atm or 10
times the pressure of the first one.
The max temp is 250oC.
The wall of the vessel is a polymeric material transparent to MW.
Decomposition is done in a Teflon cup.
It has a Teflon made O-ring which can retract with excess pressure using the help
of a screw and can free the evolved gases.
Useful for digesting high refractory materials and even for organic materials.
Dis-Risk of explosion due to the evolution of hydrogen gas.
Less than 1g of sample only can be used.
Also cooling and depressurization is needed.

18. 3. Atmospheric Pressure MW digestion
Open vessel method
Do not have an open but have a cavity.
No safety concerns.
Can be purged with gases and reagents can be added.
Can be coupled with ICPMS or GCMS
4. Microwave Oven
Used for the decomposition of many samples simultaneously.
The vessels are rotated in 360 degrees.
5. MW furnace
-Used for digestion of large amounts of organic samples before acid dissolutions.
- Dry ashing or fusion method.
- Constructed with Silicon carbide material.
- Temperatures upto 1KoC can be attained.
- High speed with large amounts of sample.
- Samples after digestion are cooled immediately
MW oven

19. III. Decomposition using combustion
1. Over open flame (dry ashing)
Dry ashing- Oxidizing a sample with air at high temp leaving inorganic samples for analysis.
-For determining cations.
Done in open dish or crucible.
Red heat is required.
Completeness of decomposition is not sure.
Volatile materials will be lost.
2. Combustion tube method.
-Pyrolysis method with suitable apparatus.
Possible to trap the volatile components.
Heating is in a glass or quartz tube.
With the help of a carrier gas the volatile gases are separated and retained for measurement.
Coupled with MS or GC.

20. Requires only 15minutes time for decomposition.
Catalyst for oxidation are used.
Main component for CHNX analyser.
3. Combustion using O2 in a sealed container.
-Using oxygen.
Decomposed matter is absorbed in a suitable solvent.
Volatile components also can be easily trapped using the solvent.
Determination of halogens, sulfur, phosphorus, arsenic, B, C and other
metals in org compounds.

21. IV. Decomposition using fluxes (for inorganic materials)
In the case of silicates, some mineral oxides and a few iron alloys, digestion is slow due to its inert nature.
In such cases the sample is mixed with alkali metal salt (flux) and the combination is then fused to form a water soluble
product known as melt. Fluxes decompose by virtue of the high temperature (300- 1000oC) and the high amount of
reagent used in the process.
The sample is fine powdered and is mixed with tenfold excess of the flux in the crucible.
Time required from few mnts to hours.
The formation of a clear melt indicates completion of the process. It is cooled and contents are analysed.
Disadvantages
• High amount of contamination by the impurities in the flux.
• The high salt content that remains in the solution can interfere in the further analysis.
• Volatilization loses due to high temperature.
• Unwanted reactions with the sample or reagents

22. Types of fluxes
• Fluxes are of three types, viz, acidic flux, basic flux and oxidizing flux.
• (a) Acidic flux: They can be pyrosulfates, acid fluorides or acidic oxides (oxide of a non-metal) like SiO2, P2O5,
B2O3 (from borax). It can attack basic materials like like CaO, FeO, MgO etc in the sample. The acidic flux
combines with the basic component of the sample to form a slag.
• (b) Basic flux: They can be alkali metal carbonates, hydroxides, peroxides etc. It will attack acidic materials like
SiO2, P2O5 etc. The basic flux combines with an acidic impurity to form a slag.
• Thus, slag can be defined as a fusible mass, which is obtained when a flux reacts with an infusible, acidic or
basic impurity present in the oxide ore.
• (c) Oxidizing flux: If in addition of the above types if we use additionally an oxidizing agent like sodium
peroxide.

24. Sodium Carbonates
• -Silicates and other refractory materials can be decomposed by
heating to 1000-1200oC with Na2CO3.
• It converts cationic constituents of the sample to acid-soluble
carbonates or oxides.
• The non-metallic constituents are converted to soluble sodium salts.
• Fusion is carried out in Pt crucibles.

25. Potassium Pyrosulfate
• It is a highly potent acidic flux that can attack intractable metal
oxides.
• Fusion is performed at 400oC in Pt or porcelain crucibles.
• On heating it decomposes; K2S2O7 → K2SO4 + SO3

26. Lithium metaborate (LiBO2)
• It is a powerful basic flux that attack refractory silicates and alumina
minerals.
• Carried in 900oC in Pt or graphite crucibles.
• The glass that results after melt formation can be directly used for X-
ray florescence measurements. It is readily soluble in mineral acids.

27. Elimination of interferences
• The interference in a chemical analysis arises whenever a species in
the sample either produces a signal that is indistinguishable from that
of the analyte or attenuates the analyte signal.
• Methods to overcome interferents are;
- Masking
- Separation

28. Masking
• Masking agents mask certain species that can interfere in the analysis
of certain analytes.
• Cyanide ion is an effective masking agent, that can form stable
cyanide complexes with the cations of Cd, Zn, Hg(II), Cu, Co, Ni, Ag,
and the platinum metals, but not with the alkaline earths,
manganese, and lead.
• F- ions can mask Fe(III) in the iodometric determination of Cu(II)

29. Separation
Converting either the interferant or analyte into a separate phase that
can be separated from each other.
-By precipitation
-By changing pH
- Sulfide separations
- By using inorganic precipitants
- By using organic precipitants
- By electrolysis
- By extraction

30. 1. Separation by Precipitation
• Can be used if the solubilities of analyte and interferants differ largely.
2. Separation by changing pH
Many precipitations from solutions containing both are pH dependent.
They can be further divided into
a) Using concentrated acids
b) Using buffered solutions at intermediate pH.
c) Using Na or K hydroxides

31. Sl. No Reagents Species forming
precipitates
Species not ppted
1 Hot Con HNO3 Oxides of W(4), Sn(4) Si(4),
Ta(4)
Most other metal ions
2 NH3/NH4Cl buffer Fe(3), Cr(3), Al(3) Alkali and alkaline earth
metals, Mn(2), Cu(2),
Zn(2), Ni(2)
3 NaOH/Na2O2 Fe(3), most dipositive
metals, rare earths
Zn(2), Al(3), Cr(4) etc

32. Sulfide Separations
• Using the help of S2- and adjustments in pH.
• Most cations except from alkali and alkaline earth metals form
sparingly soluble sulphides.
• Example: Fe(2) can be precipitated as sulphides using NH3/(NH4)2Cl
buffer with pH 9.

33. Separations by inorganic precipitants
• Chloride and sulfate are useful because of their highly selective
behaviour. Former is used to separate silver from most other metals
(eg. Mohrs method for the determination of Cl- in water sample, and
the latter is frequently employed to isolate a group of metals that
includes lead, barium, and strontium.

34. Separations by organic precipitants
• Organic reagents like DMG(Dimethylglyoxime forms complexes with
metals including Nickel, Palladium, and Cobalt), 8-hydroxyquinoline
which have the capacity to form complexes. It can precipitate cations
selectively.

35. Separation by coprecipitation
• Used in trace analysis.
• In some cases if the analyte is only in trace amounts, the complete formation of a
precipitate is often delayed.
• In such cases some other ions that can precipitate simultaneously can be added in large
amounts (Collector).
• The collector can help to precipitate the entire analyte along with it without leaving any
analyte in the solution.
• Eg. Basic Fe(III) can be used as a collector in the determination of trace amounts of Mn

36. By electrolysis
• It is based on the selective electrolytic reduction of certain metals
with varying reduction potential.
• For example if mercury is used as the cathode, metals which are more
easily reduced than Zn are deposited in the cathode, leaving ions such
as Al, Be, alkali metals and alkaline earth metals in solution.

37. • The extent to which solutes, both inorganic and organic, distribute
themselves between two immiscible liquids differs enormously and is
used for the analytical separations for decades.
Separation by extraction

38. Simple extractions
• When the distribution ratio for one species in a mixture is reasonably
favourable (on the order of 5 to 10 or greater), simple extraction methods
like separating funnels (polar and nonpolar components) can be used.
Exhaustive extractions
• Separations of components when the distribution ratio is less than 1.
• Several hundred extractions with the solvent in one hour is required.
• Extractions using Soxhlet extractor

39. Soxhlet extractor

40. Countercurrent Fractionation
• When the distribution ratio of components are very close
to each other (differ by less than 0.1), countercurrent
extractions are used.
• It permits hundreds of automatic successive extractions
in one minute.
• Aminoacids, fatty acids can be separated from each other
by this technique.

41. Theory
• The distribution coefficient is an equilibrium that describes the distribution of a solute
species between two immiscible solvents.
When an aqueous solution of an organic solute A is shaken with an organic solvent, such as
hexane, an equilibrium is established.
A(aq) ⇌ A (org)
Where (aq) and (org) refer to aqueous and organic phases.
The ratio of the concentration of solute A dissolved in organic and aqueous solvent is defined
as distribution coefficient (Kd)
Kd =[A]org/ [A]aq …….(1)

42. • The terms in brackets are activities of species A in two solvents

46. Substituting in equation 34-4