AIM : To Study The Various Methods of Collection and Storage of Water Samples
The objective of sampling is to collect a portion of material small enough in volume to be transported conveniently and handled in the laboratory while still accurately representing the material being sampled. This objective that relative proportions or concentration of all components will be the same in the samples as in the material being sampled, and that the sample will be handled in such a way that no significant changes in composition occur before the test are made. In some case the samples are presented to the laboratory for specific determination with the sample collector taking responsibility for the validity of the sample. Because of the increasing importance of the ability to verify the accuracy and representativeness of data, greater emphases are place on proper sample collection and preservation techniques. Often in water and water work, the laboratory conducts or prescribes the sampling program, which is determined in consultation with the user of the tests results. Such consultations are essential to insure selecting samples and analytical methods that provide a true basis for answering the question that promoted the sampling.
General Pre-Cautions :-
Obtain a sample that meets the requirements of the sampling program and handle it so that it does not deteriorate or become contaminated before it reaches the laboratory. In water sampling, before filling sample bottle, rinse it two or three times with the water being collected, unless the bottle contains a preservative or dechlorinating agent. Depending on determinations to be performed, fill container full (for most organic compound determination) or leave space for aeration, mixing etc, (for microbiological analysis). If bottle already contains preservative, take care not to overfill the bottle, as preservative may be lost or diluted. Except when sampling for analysis of volatile organic compounds, leave an air space equivalent to approx. 1 % of the container volume to allow for thermal expansion during shipment
Special precautions are necessary for samples containing organic compound and trace metals. Because many constituents may be present at concentration of mcg per liter, they may be totally or partially lost when proper sampling and preservation procedures are not followed; Representative sample of some sources can be obtained only by making composites (aggregates) of sample collected over a period of time or at many different sampling points. The detail of collection vary with local conditions, so specific recommendations, would not be universally applicable. Sometimes it is more informative to analyze numerous separate samples instead of one composite so as not obscure variability maxima and minima
Composite sampling is not recommended where quantitative values are desired. Such quantitative value includes acidity, alkalinity, BOD, carbon dioxide, chlorine residuals, iodine, hexavalnet chromium, nitrate nitrite, volatile organic compounds, dissolved oxygen, ozone and pH. The choice of the technique collecting a homogenous sample must be defined in the sampling plan. In the sample important factors affecting results are the presence of suspended matter or turbidity, the method chosen for its removal, and the physical and chemical changes brought about by storage and aeration.
Make a record of every sample collected and identify every bottle, preferably by attaching an appropriate inscribed tag or label. Record sufficient information to provide sample identification at a later date, including the name of the sample collector, the date, hour, exact location, the water temperature and any other data that may be needed correlation, such as weather conditions, water level stream flow, post-sampling handling etc
Sampling of Water :
- Sample of water should be regularly and frequently collected to find out seasonal variation regarding physical, chemical and microbial characters.
- Collection of water should be done in sterilized bottles, which bear important information like data, time, locality and source etc. these bottles containing sample are dispatched to laboratory as soon as possible.
- Volume of water collected should be 200 to 300 ml to be sufficient enough for laboratory test.
- Due care should be taken in the collection of water to avoid contamination during collection procedure
- Each 100 ml of water sample should contain 0.1 ml of fresh 1.8%(w/v) aqueous solution of sodium thiosulfate to neutralize the bactericidal effects of chlorine.
- The emphasis should be given to examine water bacteriological daily if the water supply is serving more than 100,000 populations.
Manual sampling: Manual sampling involves minimal equipment but may be unduly costly and time consuming for routine or large scales sampling programs.
Automatic sampling: Automatic samplers can eliminate human errors in manual sampling; it can reduce labor costs, may provide the means for more frequent sampling and are used increasingly. Be sure that automatic sampler does not contaminate the sample.
Types of Water To Be Sampled :
Water sample from tap :
- Remove the dirt from tap with clean cloth.
- Open the tap and let it flow for about 3 to 5 minutes.
- Close the tap and sterilize it with gas burner, spirit lamp for 1 to 2 minutes.
- Open the tap now and allow the water to run for about 1 minute.
- Sterilize the containers opened and allow the required quantity of water from tap to flow in. always leave airspace in the water container to facilitate shaking at the time prior to subjecting the water to bacteriology tests.
- The cap container is stopper and brown paper is fixed in the place and properly tightened with thread of string and related as required.
- Open the bottle and fill it by holding the lower part of bottle and submerging it to a depth of 20 cm, with its mouth facing sideward and then upward.
- All sterilized precautions are to be observed in this collection process.
- Bottle is closed with lid or cap and packed. ideally it should be sealed and must have a label attached containing all vital information.
- After collection it should be dispatched to laboratory for processing as early as possible.
- When samples are collected from a river or stream , observed results may vary with depth, stream flow and distance from one shore to others.
- Attach a stone or lead of suitable size weight to the sampling bottle with a piece of thread or string.
- About 20-meter long clean thread or string is tied on the bottle.
- Bottle is opened by removing the cap and lowered into the well right to the bottom of the well.
- When bottle get filled up with water, it is pulled out
- A little water is thrown out to create air space in the bottle.
- The water bottle is closed with cap, properly packed and sealed.
- A label bearing important information is stickled on the bottle.
- Sample should be preferably tested in the laboratory within one hour of collection and in no case testing should be delayed beyond six hours of collection of sample (Better bottles should be kept in ice).
- Where delay is inevitable, water can be filtered using a membrane filter and then it can be transported on an absorbent transport medium.
- Using aseptic sampling technique(as above), remove cap from sample container using one hand. hold container at the base with other hand.
- Plunge container into water(Lip of bottle first) until container is approximately 1 foot below surface of water.
- Turn open end of bottle into the direction of current and allow container to fill. If there is no current, (As in the case of lake or reservoir) Create one by slowly moving bottle in the direction away from hand.
- Remove container from water. if bottle is overfilled , pour out a small amount leaving at least one inch of air space at top of bottle to allow for adequate mixing.
- It is acceptable to pour water from a sampling container in this instance as sodium thiosulphate neutralizing reagent is not required.
- Immediately replace lid tightly.
- Samples should be replaced on ice/ice packs transit to laboratory to maintain temperature below 10 degree Celsius.
- If there is any question as to whether or not a sample has become contaminated , discard and resample.
The most important factor when conducting a field monitoring program is personnel safety. If an adequate program cannot be carried out in a reasonably safe manner, then an alternative to the monitoring program should be used. Most of the hazards reflect site selection and sampling times. The use of automatic samplers and well trained crews (more than one person in the field!) will reduce many of the hazards. Sampling may expose field personnel to hazardous conditions. Obviously, water hazards (high flows, deep pools, soft sediments, etc.) are usually of initial concern. In some studies, sampling during rainy weather in streams that may undergo rapid velocity and depth changes is necessary. Great care must be taken when approaching a stream in wet weather, as steep and slippery banks may cause sliding into the water. Always sample in pairs and have adequate safety equipment available. At a minimum, this will include:
· wear gloves
· throw rope
· Inflatable life vests
· Nylon covered neoprene waders (that offer some floatation, even when swamped)
· 2-way radio or cellular phone
· Weather radio
If the conditions warrant (such as with steep and slippery stream banks), the sampler personnel should be tied together, with an attachment to a rigid shore object. In all cases, only go into the stream if absolutely necessary. Try to collect all samples from shore, especially if during heavy rains. Be extremely cautious of changing weather andstream conditions and cancel sampling when hazardous conditions warrant. Never enter a stream where footing is unstable or if the water is too deep (probably more than 2 feet deep) or fast (probably more than 2.5 ft/sec). Always enter the water cautiously and be prepared to make an efficient retreat if insecure.
To minimize the potential for volatilization or biodegradation between sampling and analysis, keep samples as cool as possible without freezing. Preferably pack sample in crushed or cubed ice or commercial ice substitutes before shipment. Avoid using dry ice because it will freeze samples and may cause glass containers to break. Dry ice may also effect a pH change in samples. Keep composite sample cool with ice or refrigeration system set at 4oC during composting. Analyze sample as quickly as possible on arrival at the laboratory. If immediate analyze is not possible, storage at 4oC is recommended for most samples.
Use chemical preservative only when they are shown not to interfere with the analysis being made. When they are used, add them to the sample bottle initially so that all sample portions are preserved as soon as collected. No single method of preservation is entirely satisfactory; choose the preservative with due regards to the determinations to be made. Because of preservations method for one determination may interfere with another one, sample for multiple determinations may need to be split and preserved separately. All methods of preservation may be inadequate when applied to suspended matter. Because formaldehyde affects so many chemical analyses, do not use as preservatives.
Method of preservation are relatively limited and are intended generally to retard biological action, retard hydrolysis of chemical compounds, the use of amber and opaque bottle, refrigeration, filtration and freezing.
The typical information provided on a chain-of-custody form includes:
· The sampling location.
· The sample identification number.
· The type of test or analytical procedure.
· The name of the person who relinquishes the samples.
· The date and time of sample collection.
· The date and time when samples are relinquished.
· The name of the person who should receive the sampling results.