Frequently Asked Questions
The CLAM Disk uses the same media wafer disks that labs use every day for automated SPE extractions. The CLAM wafer incorporates a larger custom loading of a C-18 or HLB media type, and a pre-filtration layer that allows high capacity loading in the field. The CLAM Disk is much more than just the media wafer. It is a field tested encasement that disperses flow and provides an extraction and elution holder. The CLAM Disks include luer plugs. The sealed disks provide secure containers for shipping and transport, vastly reducing shipping costs compared to the standard liter bottle shipments. The disks allow for a truly unique field sample which represents a time integrative extractive event for large volume screening or compliance.
No…. the CLAM Disk can be used for only one sample collection and elution. The sediment and colloidal buildup with in the filtration SPE media over time will decrease the efficacy of the disks as has been determined by surrogate studies. The resulting solvent extract can be split into multiple aliquots allowing multiple methods to be run on a single sample.
The disks allow for a truly unique field sample which represents a time integrative extractive event for large volume screening or compliance. The ability to extract large volumes of water provides elution extracts that can be aliquoted into many method subsets, all still representing many liters obtained from a single disk in-situ extraction. This provides a great cost saving not having to perform many extractions using numerous SPE disks, cartridges, and extractions one liter bottle at a time in the laboratory.
The loading capacity is particle size and type dependent. The CLAM disk loading capacity using a silica reference sediment Sil-Co-Sil 106 which contains particles in known ratios from micron to submicron is excellent as the unit could not be totally plugged off as the particles could not seal off like colloidal clay. With the use of colloidal clays such as Bentonite the disk capacity was found to be approximately 0.75 grams. If the TSS of the water and idea of the type of sediment is known the (0.75 gram factor) could be used to roughly estimate the number of liters one could expect to field extract. Example 100ppm TSS = 0.1 grams/liter. 0.75g/0.1 g/ l = 7.5 liters of could be extracted.
YES…..The Totalizer on board the new CLAM reads the volume of water after it has been filtered through the media disk. As a result the water remains constant and free of sediment. The volume collected may be reduced due to sediment clogging, but the oval gear mechanical flow sensor will not be quantitatively affected.
A CLAM Disk that includes HLB or C-18 media does also contain pre-filtration in the same configuration as a CLAM Pre-Filter, so it is not necessary to use a Pre-Filter. Some projects are designed to analyze a particle phase and dissolved phase separately, so a CLAM Pre-Filter can be put in series in front of a CLAM HLB or C-18 Disk to provide analyses of sediment in the first Disk and dissolved in the second media Disk.
Media use is dependent on which analytes are to be extracted. The SPE media manufacturers have selection guides and applications for many methods and analytes which can give guidance. The CLAM is designed to extract in situ trace organic semi volatiles with KOW values above 2.5. The extraction one obtains in the laboratory can be expected with the same media in the field.
The expected run time is greater than 48 hours fully charged, the USB takes 12 hours to completely recharge. There is no indicator other than time elapsed to determine the charge level of the unit when submerged, so it is imperative to know the start time of the deployment.
The unit can be submerged to 20 feet. Greater depths can be obtained by lowering a weighted CLAM Disk connected to tubing down to greater depths and drawing the water up using a surface pump. An external totalizer can be used to measure the volume of water extracted or the water could be collected.
With the onboard flow sensor and totalizer the true volume extracted will be recorded and displayed. The amount extracted might be lowered but the accuracy of that volume will not be compromised.
Optimum pumping rates are set within the pump capacity. The pumping rating is 130 ml/min free flow and with the CLAM Disk attached the rate averages about 80-90 ml/min. Flow rates above 150 ml/min will have decreased efficacy and retention due to loss of contact time for the reverse phase sorption to occur. The flow will lower with filter plugging over time but the efficacy of sequestration will only improve with decreased flow rates.
The recoveries will be similar to what one finds on the bench using unmodified water. They are analyte, instrument and method dependent. The SPE wafers used are the same used in automatic SPE extraction devices in the lab. The CLAM Disk uses the same media as used in EPA method 3535, but the automatic extraction device extracts the environment in situ under water, leaving the water behind.
There are Laboratory Application Notes for use of the CLAM Disks that show step by step instructions on conditioning, cleaning, adding surrogates, and finally elution of the CLAM Disks in the lab. These are not unusual steps for a laboratory, but guidance from lessons learned on the most effective steps to take.
No…. CLAM Disks need to be conditioned and cleaned with a solvent scheme before deployment. See the Laboratory Application Notes. The laboratory that performs the final analysis should be the lab that cleans, conditions, spike and ships the units back into the field just like is done with bottles now.
No… At this time, only organics commonly eluted through Solid Phase Extraction are targets for CLAM use. Metals capabilities are in development.
Other media can be customized with a minimum order.
The disks allow for a truly unique field sample which represents a time integrative extractive event for large volume screening or compliance. The ability to extract large volumes of water provides elution extracts that can be aliquoted into many method subsets , all still representing many liters obtained from a single disk in-situ extraction. This provides a great cost saving not having to perform many extractions using numerous SPE disks, cartridges, and extractions one liter bottle at a time in the laboratory.
The Pyrethroids are the compounds which our in situ SPE extraction was made for. Because Pyrethroids are very hydrophobic they tend to adhere to surfaces like bottles, sediments ect. Since the CLAM draws the water into the SPE media first, and elutes the encased disk with solvent entirely, it has no surface contact losses found in auto samplers, or composite samplers either manual or automatic. It can obtain a large sample volume of the water column to provide very low detection. There are many references of SPE extraction methods using either C-18 to HLB in the literature. The elution for a GC/MS/MS analysis should follow our application notes where the media is first dried with methanol, then extracted with DCM which is blown down with N2 and concentrated for analysis. If the SPE media is only eluted with polar solvents, the pyrethroids will remain bound to the media resulting in low recoveries. Labs running or developing methods using LC/MS methods using polar solvents will experience this. They simply have not fully eluted the pyrethroids from the disk because of solvent choice. The DCM extract can be exchanged to a more polar solvent for LC/MS analysis after elution. See a USGS method using HLB cartridge. The polar compounds such as phenoxy herbicides will exhibit low recoveries dependent on each KOW value. This is because the pH of the water cannot be modified in the field to 2.0. If it were recovery efficacy would be much higher. The methods described in this report were developed by the USGS’s Pesticide Fate Research Group (PFRG), Sacramento, California, to analyze 14 pyrethroids. Water samples were extracted using SPE. Using the HLB media in a cartridge. See full report USGS-Determination of Pyrethorid.
We recommend not exceeding 100ml/min on flow rate through the CLAM Disk. This flow rate has been tested for recoveries and to ensure there is no channeling around the media wafer. The Pre-Filter CLAM Disk (GF) is typically used in front of a media disk for total and dissolved studies.
The housing capsule is a two piece polypropylene unit which encapsulates the SPE media and pre-filter. This assemblage is welded together into a rugged capsule which acts as a field extraction tool, a shipping container a storage vessel and an elution funnel when in the laboratory. The unit cannot be opened without causing destruction.
This is routinely done when the disks are field-deployed using either peristaltic pumps or the CLAM field unit under vacuum or solvent eluted in the laboratory using positive pressure from a positive displacement pump or a syringe.
This is not possible in the SPE capsule. However, we do supply an eDNA Disk (environmental DNA) that contains a triple lofted glass fiber filter from 20 um to 1 um designed to allow collection of a large volume, time integrative filtration event for biodiversity studies. The unit has a security shrink wrap band that can be cut allowing the filter to be removed and inspected.
The eDNA disk would allow the filter removal from the capsule for oven drying allowing gravimetric analysis. The welded SPE glass filter disk could be dried to constant weight in an oven using vacuum convection air to evacuate moisture in the closed unit to constant weight but it would take time.