Frequently asked Questions
Here we have answered some of the most common questions
Welcome to the FAQ interaction
Are the CLAM Disks the same Disks laboratories use?
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.
Can the CLAM Disk be reused?
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.
Why is the CLAM field extraction better than conventional methods?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.
How much sediment does it take to clog the CLAM Disk?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
Is the volume of water extracted accurate in sediment filled water?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.
Should I use a CLAM Pre-Filter if I am sampling sediment filled water?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.
Which type of media should I use?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.
How long does the charge last on the battery?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.
How deep can I submerge the CLAM?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.
What happens if the unit stops pumping due to sediment build up or the battery expires?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.
What flow rate does the CLAM pump?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.
What can I expect for recoveries on certain compounds after extracted by the CLAM Disk?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.
Are there any special laboratory procedures needed to analyze a CLAM Disk?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.
Can CLAM Disks go right out to the field when I receive them?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.
Can the CLAM Disk test for metals?No… At this time, only organics commonly eluted through Solid Phase Extraction are targets for CLAM use. Metals capabilities are in development.
Can I use other media besides C-18 and HLB with the CLAM Disk?Other media can be customized with a minimum order.
Why is the CLAM field extraction better than conventional methods ?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.
Is CLAM able to collect very hydrophilic pesticides (e.g., dicamba, 2,4-D) or very hydrophobic pesticides (pyrethroids) ?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.