Home> Technical Library > Sampling Procedure for Benthic Chambers

Sampling Procedure for Benthic Chambers

Sampling in the Aquos™ BC-8 Benthic Chamber is accomplished by the use of a syringe with a non-coring needle.  The needle is inserted through the rubber septum of the Sampling Valve on the headplate of the benthic chamber, and the required volume of sample is aspirated.

The Sampling Syringe

The sampling syringe is made of polypropylene plastic or borosilicate glass.  Plastic syringes are disposable while glass syringes are reusable. 

Plastic Syringes

Plastic syringes feature Luer-lock tips for a positive lock with the non-coring needle.  They also feature positive plunger stops to prevent spillage during aspiration.  Plastic and glass syringes supplied by Aquanoss are designed for sampling with benthic chambers and are not fit for clinical or other uses.

Glass Syringes

Glass syringes are made of borosilicate glass and are reusable.  They are easy to clean, offer accurate sampling volumes, are resistant to most chemicals including acids and alkalies and are economical.  The plungers feature a tight fit with the glass barrel and prevent backflow.

Non-coring Needles

Needles used for sampling are designed to penetrate the rubber septum on the Sampling Valve.  The needles have deflected tips that are designed to prevent coring of the septum even after repeated sampling of the rubber septum.  These stainless steel 18ga. needles with regular wall thickness offer repeated sampling ability without bending, breaking, septum coring or jamming.  The 6-inch length of the needle allows sampling of the chamber water in the central region inside the chamber, where the water is well mixed.

Sampling Septum

The Sampling Port on the Aquos BC-8 Benthic Chamber is furnished with a rubber sampling septum.  The septum features a tapered grooved lower portion that fits securely inside the nickel-plated brass Sampling Port.  The cup-shaped upper portion of the septum is then folded down over the Sampling Port, thus gripping the port firmly on the inside and the outside surfaces.  This design provides for a firm, secure fit that will not slip or allow the septum to become unseated during sampling. 

Sample Aspiration

Before sampling can begin, the Volume Equalization Valve (VEV) is turned from the Closed to the Open position.  This will allow water from outside the benthic chamber to flow into the chamber to compensate for the removal of the aspirated sample.  The VEV is a two-way valve.  If it is necessary to inject a required volume of some liquid into the benthic chamber (e.g., a chemical tracer) then the VEV must be in the open position, to allow a volume of water equal to the injected volume to be expelled from the benthic chamber.

To sample water from the benthic chamber, the non-coring needle is used to puncture the septum and the user aspirates the required volume of water from the benthic chamber into the syringe.  The needle is then withdrawn from the septum.  The septum offers a large, flat puncture target for the non-coring needle, and we recommend that the septum be punctured at different points during multiple sampling, to prolong the life of the septum.

If multiple samplings are going to be made over short periods, we recommend 'Quadrant Sampling' to prolong the life of the septum underwater.  Quadrant Sampling simply means that you divide the puncture target circle into 8 quadrants using a ball-point pen or fine-tip indelible marker (see photo below).  Once the septum is marked off into quadrants, remember to puncture a different quadrant every time you sample the chamber.  This will minimize the chance of repetitive puncture of the septum in the same area leading to either jamming the needle or allowing leakage from or into the benthic chamber.

Upon completion of sample aspiration, the VEV is returned to the Closed position and sampling is now complete.

Sampling Port and Sampling Septum

Septum base inserted into sampling port
Septum top folded down over sampling port; septum ready for use

Volume Equalization Valve (VEV) in Closed position

Volume Equalization Valve (VEV) in Open position.

Quadrant Sampling.  The sampling septum has been marked off into 8 quadrants to enable needle punctures in different locations of the septum, thus prolonging the usable life of the septum.