Sample preparation techniques including Dilution Filtration /Centrifugation,Solid phase extraction, Digestion and Distillation.

Sample preparation techniques including Dilution, Filtration/Centripetal,

Solid phase extraction, Digestion and Distillation

Sample Collection

Various physical, chemical and biological processes can affect a sample from the time of collection to that of analysis. The use of appropriate sampling equipment, containers and preservation methods to maintain sample integrity will prevent/minimize these effects. Samples must also be analyzed within stipulated holding time limits. Care is required to avoid contamination of the sample during sampling, handling and transport to the laboratory.

Sampling Devices

Sampling devices should be made from materials that have minimum interaction with, and do not contaminate or disturb the sample.

Sample Containers

Containers must be clean and may need to be retained and submitted to the laboratory for analysis as a blank. Where reagents are added during the preservation step, a sample of the added reagents must also be submitted to the laboratory for analysis as a reagent blank.

Sampling Surface Water

For well mixed water, a sample taken 100 mm below the surface, away from the edge, may be adequate. Deep and stratified water may require careful handling techniques for unstable chemical species. When sampling shallow water, contamination from disturbed sediment should be avoided by using an extended inlet of thin tube on the sample bottle and drawing water in by suction. To collect a sample of the surface layer, the container should be held horizontally in the water, half submerged. To collect n sample of water beneath a surface layer, a syringe or other device with an extended inlet tube that is capable of piercing the surface layer, may be appropriate, depending on the thickness of the surface layer.

Sampling Groundwater

Groundwater sampling should be undertaken in accordance with Groundwater sampling guidelines (EPA publication 669, 2000). Regular testing of groundwater quality is usually done from monitoring bores. These bores should be constructed according to the guidelines of the Agriculture and Resource Management Council.

Sampling a Waste Discharge

The most representative waste discharge sample is from a point where the effluent is thoroughly mixed and close to the discharging premises outlet. For a licensed discharge, a sampling point will normally be described in the license where samples must always be taken.

SAMPLE PREPARATION TECHNIQUES

Sample preparation strategies for water analysis is the simplification of sample matrix

and enrichment of target analysis. Sample preparation includes Dilution,

Filtration/Centrifugation, Solid phase extraction and Digestion

FILTRATION AND CENTRIFUGATION

Filtration is the process of removing suspended solids from liquid solution by passing the liquid through a permeable fabric or porous bed of materials. And the Centrifugation is a process which involves the application of the centripetal force for the sedimentation of heterogeneous mixtures with a centrifuge. This purification technique is used to separate two liquids or a liquid and a solid, speeding up sedimentation.

CENTRIFUGE

FILTRATION ASEEMBLY (1) FIG (2)

DILUTION:

Dilution is the process of reducing the concentration of a solute in solution, usually simply by mixing with more solvent. For Example you can add water to concentrated orange juice to dilute it until it reaches a concentration that is pleasant to drink.

(FIG)

Dilution factor = =

Digestion

Digestion is the breakdown of large insoluble molecules into small molecules in the presence of Acid (HCL, Nitric Acid and S) and so that they can be absolved into the water
Digestion of a dry sample requires less than ten minutes, while liquid samples require about minute/ml. The digestion is done in a special flat-bottomed, 100-ml. volumetric flask.
Aliquots (sample portions) are taken for analysis using colorimetric methods

Digestion

Digestion of Metals:

To reduce interference by organic matter and to convert metal associated with particulate to
form (usually the free metal) that can be determined. Use the least rigorous digestion method
required providing complete and consist recovery compatible with analytical method and the metal being analyzed. Nitric acid will digest most samples adequately. Some samples may require addition of perchloric, hydrochloric, or sulfuric acid for complete digestion. Following table shows the suggested sample volume for analysis of metal concentration.

Metal concentration, = A X B / C
Where: A = Conc. of metal in digested solution

B = Final volume of digested solution

C = Sample size, mL