2. Water is the predominant chemical component of living
organisms.
Its unique physical properties, which include the ability to
solvate a wide range of organic and inorganic molecules,
derive from water’s dipolar structure and exceptional
capacity for forming hydrogen bonds.
The manner in which water interacts with a solvated
biomolecule influences the structure both of the
biomolecule and of water itself.
The water molecule has tetrahedral geometry.
3. A molecule with electrical charge distributed
asymmetrically about its structure is referred to as a
dipole.
Water’s strong dipole is responsible for its high dielectric
constant.
Its strong dipole and high dielectric constant enable water
to dissolve large quantities of charged compounds such as
salts.
4. A partially unshielded hydrogen nucleus covalently bound to an
electron-withdrawing oxygen or nitrogen atom can interact with an
unshared electron pair on another oxygen or nitrogen atom to form a
hydrogen bond.
Since water molecules contain both of these features, hydrogen bonding
favors the self association of water molecules into ordered arrays .
5. Hydrogen bonding profoundly influences the physical
properties of water and accounts for its exceptionally high
viscosity, surface tension, and boiling point.
6. hydrogen bonds are both relatively weak and
transient.with a half-life of a few nanoseconds or less.
Rupture of a hydrogen bond in liquid water requires only
about 4.5 kcal/mol, less than 5% of the energy required to
rupture a covalent O—H bond.
Hydrogen bonding enables water to dissolve many organic
biomolecules that contain functional groups which can
participate in hydrogen bonding.
7. Solute and solvents used in analytical work are reagent
grade chemicals among which water is a solvent of
primary importance.
National Committee for Clinical Laboratory
Standards(NCCLS) has established a standard for
REAGENT GRADE WATER.
The term reagent grade water better defines the specifications of
water and is independent of method of preparation.
8. REAGENT GRADE WATER:
1) Types
2) Method of filtration
3) Uses and storage
4) Testing
5) Preparation
9. Laboratory requirements generally call for reagent grade water that,
according to the Clinical and Laboratory Standards Institute, is classified into
one of six categories:
1)clinical laboratory reagent water (CLRW),
2)special reagent water (SRW),
3)instrument feed water,
4) water supplied by method manufacturer,
5) autoclave and
6) wash water
11. PREPARATION OF REAGENT GRADE WATER:
THREE TYPES OF FILTRATION
1)
PREFILTRATION
2) BED OF
ACTIVATED
CARBON
3) SUBMICRON
FILTER
12. 1) Prefiltration :
- prefilters are usually composed of microfiber glass
or cotton.
- they remove 98% or more of particulate matter and
thus protect the whole water flow and containment system.
- prefilters often enhance the economics of the
operation because these filters can usually be cleaned and
reused many times.
13. 2) Bed of activated carbon :
- the bed is effective in removing large amount of
organic materials and chlorine.
-a combination of prefiltration and carbon bed
filtration is extensively used to increase the life expectancy of an ion
exchange resin used later in the purification process.
14. 3)Submicron filter :
- this is typically a Millipore membrane filter
- which removes all particles or
microorganisms larger than the membrane`s pore size
(usually 0.2 micrometer) without releasing contaminants
that could alter the quality of the water.
-this filter used near the point of
delivery as the last stage of a system.
15. Distillation :
oldest method of water purification.
it involves phase changes from liquid to vapor to liquid, nonvolatile
materials are left behind in the boiling vessel where they may form a
crust on the inner surface of the vessel.
Volatile impurities may be partially carried over into the distillate.
16. During vigorous boiling a small number of water droplets
entrapped in vapor may be carried over and transport
sodium,potassium,manganese,carbonates and sulphates to
the distillate.
As a result water treated by distillation alone does not
meet the specific conductivity requirement of type I
water.
17. Deionized water :
o Water from which ionized salts have been removed by the process of ion
exchange.
o It is most conveniently prepared using commercial deionizing equipment
which ranges in size from small disposable cartridges to large resin-
containing tanks.
o The resin contained in large tanks is capable of being regenerated.
18. o Deionization is accomplished by passing feed water over insoluble resin
polymers that exchange H and OH ions for the impurities present in ionized
form in water.
o These insoluble resin polymers are prepared with acid or amine functional
groups.
o The tank may contain cation exchangers, anion exchangers, or a `mixed-
bed resin exchanger,` which is a mixture of cation and anion-exchange
resins in the same container.
19. A “two-bed deionizer” consists of two columns of separate
ion-exchange resins connected in a series that is, a cation
exchange column followed by an anion-exchange column
or vice versa.
A “single bed deionizer” generally is capable of producing
water that has a specific resistance in excess of 1
Mohm/cm
20. Reverse osmosis:
A process by which water is passed through a membrane
that acts as a molecular filter.
Membrane removes 95 to 99% of organics,bacteria and
other particulate matter and 90 to 97% of all ionized and
dissolved minerals.
This process inadequate for producing reagent grade
water for laboratory,it may be used as a preliminary
purification method.
21. Basic considerations affecting the selection of the type of
reverse osmosis equipment are:
1) Quality of raw water
2) Capacity in terms of flow
3) Performance in terms of salt passage compared with
water passage
4) Stability in terms of operating life.
22. Use and storage of Reagent Grade Water :
Type I water should be used in test methods requiring minimal
interference and maximum precision and accurancy.
-such procedures include trace metal determination,enzyme
measurements,electrolyte measurements and preparation of all
calibrators and solution of reference materials.
-this water should be used immediately after production.
-no specifications for storage systems for type I water are given,as it is
not possible to maintain the high resistivity while drawing off water and
storing it.
23. Type II water is used for general laboratory testing not requiring type I
water.
- Storage should be kept to a minimum and storage as well as delivery
systems should be constructed to ensure a minimum of chemical or
bacterial contamination.
Type III water may be used for glassware washing.
It may also be used for certain qualitative procedures such as those used
in general urinalysis.
24. Testing for water purity :
- At a minimum water should be tested for microbiological
content,pH,resistivity and soluble silica.
- The maximum interval in the testing cycle for purity of
reagent water should be one week.
- Specifications measured at the time of production may
differ from those at the time and place of use.
25. Specific systems for preparation of Reagent Grade
Water:
- Considerations in the selection of a system to produce type I reagent
grade water include quality of feed wate, amount of water needed,
availability of space,and electical energy.
- If the feed water contains more than 1000ppm of total dissolved solids
reverse osmosis should be considered as a pretreatment option.
26. - Type I reagent water, with a neutral ph and 170ppm of
TDS can be produced from municipal feed water by use of
primary dual filtration cartridge to remove particulate
matter and organics followed by two tanks containg a
mixed bed ion-exchange resin.
- The tanks are followed by a 0.2 micrometer membrane
filter.
- A conductivity light installed between two ion- exchange
tanks is automatically turned off when resistance of the
effluent from the first tank goes below 200000 ohm/cm.
27. - The second tank then `polishes` the waterto yield water
with a resistance of up to Mohm/cm.
- When the deionizers are exchanged the first tank is
removed for regeneration,the second tank is put in its
place and the new tank is put in the second position.
- The spigot for water delivery should be within a few feet
of the final filter.
water molecule is said to be dipolar because it has a positive and a negative pole as a result of the uneven distribution of electrons within it
The dipole nature within a water molecule creates attractive forces known as hydrogen bonding, allowing them to stick together
*microbiological content of viable organism as determined by total colony count after incubation at36+or-1 C for 14 hours followed by 48 hrs at 25+or- c and reported as colony forming units per ml
*specific resistance or resistivity- the electrical resistance in ohms measured between opposite faces of a 1.00 cm cube of an aqueous solution at a specified temperature.for these specifications the resistivitywill be corrected for 25 c and reported in ohm/cm.the higher the amount of ionizable materials the lower the resistivity and higher the conductivity.
*particulate matter- when wateris passed througha membrane filter with a mean pore size of 0.2 micrometer,it is considered to be free of particulate matter.
*organic material- when water is passed through a bed of activated carbon it is considered to contain minimum organic material.
