Protocols for environmental geochemical sampling
MAD EGG LAB
(Dr. Jeff R. Havig)
Current as of: 06-06-2015
Protocol for geochemical water sampling
For sampling a complete geochemical suite, the following samples should be collected. They are listed in the order of sample collection, all are filtered through a sterile 0.2 µm polyethersulfone syringe filter, using a syringe and any other filtering apparati that have been cleaned (soaked in 10% trace element grade HNO3 and then triple-rinsed with 18.2 MΩ/cm DI water). The order is important for flushing the filter to remove trace element and organic carbon contamination. Prior to starting filtration, flush the filter with ~ 10 mL of sample water.
Cations (Na, K, Ca, Mg, NH4)
10 mL of filtered sample water in a 15 mL centrifuge tube that has been soaked with 18.2 MΩ/cm DI water for three days. Acidify with 0.400 mL of trace element grade HNO3 for preservation of NH4. Refrigerate until analysis. Analysis conducted via Ion Chromatography.
Anions (Cl, SO4, Br, F, NO3, PO4)
10 mL of filtered sample water in 15 mL centrifuge tube that has been soaked with 18.2 MΩ/cm DI water for three days. Refrigerate until analysis. Analysis conducted via Ion Chromatography.
Nitrite (NO2)
5 to 10 mL of filtered sample water in a 15 mL centrifuge tube that has been soaked with 18.2 MΩ/cm DI water for three days. Freeze immediately on dry ice. Keep frozen until analysis. Analysis conducted via Ion Chromatography.
DIC (dissolved inorganic carbon)
10 mL of filtered sample water in an exitainer, close cap. Analysis for DIC concentration and δ13C values conducted at UC Davis Stable Isotope Facility.
DOC (dissolved organic carbon)
30 mL of filtered sample water in a 50 mL centrifuge tube that has been soaked with 18.2 MΩ/cm DI water for three days. Freeze immediately on dry ice. Keep frozen (and in the dark) until analysis. Analysis for DOC concentration and δ13C values conducted at UC Davis Stable Isotope Facility.
Trace elements
10 mL of filtered sample water in a 15 mL centrifuge tube that has been soaked in 10% trace element grade HNO3 and then triple-rinsed with 18.2 MΩ/cm DI water and doped with 0.4 mL of ultra-pure trace element grade HNO3. Refrigerate until analysis.
Blanks
Field blank – fill a trace element clean (soaked in 10% trace element grade HNO3 and then triple-rinsed with 18.2 MΩ/cm DI water) 500 mL Nalgene bottle with 18.2 MΩ/cm DI water, take into the field. During sampling, treat the 18.2 MΩ/cm DI water as a regular sample, collecting a complete geochemical suite. This will provide the baseline for contamination that occurs during sampling. Any environmental sample parameter that falls near or below the values of the field blank should be considered ‘BDL’ (below detection limits). This should be done at least once during a sampling trip, and preferably for each day/new sampling location.
Lab blank – While processing any samples for dilution (which may be needed for major ion or trace element analysis, depending on the concentrations in your samples and the limits of your instrument), make a sample of any DI water used for diluting samples. This will tell you if there is any contribution of contamination from dilution.
METERS AND OTHER FIELD MEASUREMENTS:
Always collect pH, mV, temperature, and conductivity with meters for any geochemical sample that you collect. Oxidation-Reduction Potential (ORP) can be useful, and is another parameter that can be measured with a meter and probe. Dissolved oxygen can also be measured with a meter for lower-temperature samples (not for hydrothermal samples until someone develops a high temperature D.O. probe). Redox-sensitive chemical species (e.g. sulfide, Fe+2) can be measured via field spectrophotometry, but note that sulfide and Fe+2 can cause significant interference with Hach tests, and the tests are also temperature sensitive (especially for hydrothermal samples), so I try to steer clear of spectrophotometers if I have access to lab instrument options. If you will be using a spectrophotometer, make stock solutions of what you are measuring and build yourself a calibration curve, especially if you will be sampling at anything other than ~20°C.
Sampling Apparatus:
The sampling device that I helped develop while part of GEOPIG at Arizona State University is pictured. The syringe is a 140 mL syringe, and the caulking gun is one you can find online. The opening of the caulking gun has to be ground out by about 1 to 2 mm in order for the syringe to fit (I did this with a Dremel tool and grinding bits…be ready for sparks). The three-way stopcock at the end allows you to draw from the 500 mL bottle that acts as a sample reservoir. A 1 mL syringe end is cut off and put into tygon tubing to allow for easy attachment. The syringe filter then goes on the end of the stopcock (not pictured). This setup allows one to collect water from a site, and then filter it at a different location, making it easier to minimize impact at a site. Everything (except the caulking gun, of course!) can be acid washed. SPECIAL NOTE: The black butyl-rubber stoppers carry trace elements that will leach out, and they come with oily lubricant on the rubber part. To acid clean the rubber stoppers, you have to remove them from the stem, wash them with warm soapy water until the lubricant is removed, and then they should be acid washed separately from the rest of the plastic-ware (they will contaminate your 10% acid solution).
I have found that making a sample container holder makes life much easier in the field. I like to use the plastic foam that usually comes as packing material for larger instruments, and then cut holes ¾ of the way into the foam so that the containers fit snug and are not loose. To make things easier, I also put them in order of filtration. For the example here, there are sample containers for (from left to right) anions, nitrite, DIC, trace elements, and DOC.
To make things even easier in the field, we assemble sample container kits, consisting of a quart-size plastic freezer bag filled with all the containers you would need for one sample. This makes things super easy and reduces chances of messing up sampling/forgetting something. The freezer bag helps in that you can write the sample site and ID on the bag and put all of the non-freezing samples back in and toss the bag into your cooler with ice.
Protocols for geochemical biofilm/sediment sampling
Sampling of biofilms/biological samples and/or sediments, soils, and rocks for geochemical analysis should be done with care to minimize the potential for contamination.
C and N (content and isotopic values), major elements, trace elements
I have found that a single sample can be collected for carbon, nitrogen, major elements, and trace elements. I collect a sample into a container that has been trace element cleaned (soaked in 10% trace element grade HNO3 and then triple-rinsed with 18.2 MΩ/cm DI water). Depending on the sampling location and potential sample size limitations, a 5 mL cryovial, 15 mL centrifuge tube, or 50 mL centrifuge tube can be used. I prefer to use Teflon tweezers or plastic scoopulas that have been trace element cleaned if the sample must be handled in any way. I also recommend clean nitrile gloves if there is any chance that you may touch the sample with your hands. For larger samples (esp. rocks), a canvas bag or large plastic bag can be used.
For samples that may degrade, breakdown, or potentially alter (especially for C and N), I prefer to freeze the samples in the field on dry ice (along with nitrite and DOC samples) and keep them frozen until analysis.