TITLE: Bubble strip aqueous gas sampling
AUTHORS: Daniel B Nothaft

[DESCRIPTION]
<div class = "text-blocks"><div class = "text-block">The "bubble strip" method has been shown to be an effective means for sampling a gas phase in equilibrium with water (Kampbell et al., 1998). Here, a method optimized for sampling large quantities of equilibrated gas (~60 mL) is demonstrated. This has applications for advanced isotopic analyses, which often require large sample sizes.</div><div class = "text-block">This version was used in Samail Ophiolite sampling in 2019.</div><div class = "text-block"><span>Kampbell D. H., Wilson J. T., Mcinnes D. M. (1998) Determining Dissolved Hydrogen, Methane, and Vinyl Chloride Concentrations in Aqueous Solution on a Nanomolar Scale With the Bubble Strip Method. In </span><span style = "font-style:italic;">Proceedings of the 1998 Conference on Hazardous Waste Research</span><span> pp. 176–190.</span></div></div>

[STEPS]
?. [Prepping sample vials]
Pre-treat blue chlorobutyl stoppers to reduce potential contaminants by boiling in 0.1 N NaOH for 45 min followed by immersion in distilled water for ~8 hours), according to procedure of Oremland et al. (1987).Oremland R. S., Miller L. G. and Whiticar M. J. (1987) Sources and flux of natural gasses from Mono Lake, California. Geochim. Cosmochim. Acta 51, 2915–2929.
?. [Prepping sample vials]
While still warm, insert stoppers into 37 mL borosilicate glass vials, and secure stoppers with aluminum crimp tops.
?. [Prepping sample vials]
Autoclave sterilize vials, stoppers, and NaCl solution (90 minutes at 125˚C).
[including cooldown time]
?. [Prepping sample vials]
Sampling vials will be filled with a near-saturation NaCl solution which will be displaced by the sample gas. Calculate the volume needed to fill all your vials. In a large beaker, prepare a near-saturation NaCl solution that is a bit larger than the volume of your vials.
Leave plenty of extra room in the beakers with NaCl because when you autoclave in the next step, the NaCl brine can expand and overflow the beakers.
?. [Field Sampling]
Attach a 100 mL borosilicate glass bottle (with appropriate fittings installed - see materials) to a ring stand, cap facing up. Connect inlet tubing of bubble strip to pumped water source (i.e. manifold).
?. [Field Sampling]
Slowly open water flow valve on manifold. Let bottle fill up with water.
?. [Field Sampling]
Flip bottle 180˚ such that the cap faces downwards.
?. [Field Sampling]
Attach a mininert stopcock to a 60 mL plastic syringe.  Fill syringe with 40 mL of air.
?. [Field Sampling]
Attach syringe to sampling port on bottle cap.
?. [Field Sampling]
Inject 40 mL air through the sampling port into the glass bottle. Close mininert valve. The setup should look like this picture. In this example (from 2018 Oman sampling), 2 bubble strip gas samples are equilibrating simultaneously. Other tubes connected to biomass filters and/or water sampling ports are unrelated to the bubble strip.
?. [Field Sampling]
Measure flow rate by timing the filling of a 500 mL graduated cylinder from outlet tube. Flow rate should be at least 300 mL/min.
?. [Field Sampling]
Periodically monitor flow rate and water temperature. If flow remains at least 300 mL/min, the headspace gas should equilibrate within 30 minutes of flow, and then can be sampled. The water temperature is good to note so that Henry's constants can be adjusted for temperature.
?. [Field Sampling]
After sufficient flow has been allowed for gas equilibration, re-attach syringe to bubble strip apparatus if it has been removed (although typically it is best to just leave syringe connected). Then, open mininert valve, and withdraw 35-40 mL of headspace gas. Close mininert valve.
?. [Field Sampling]
Remove syringe and mininert valve from sampling apparatus. Connect a sterile 0.2 µm syringe filter and sterile 18G needle (BD precisionglide) to the mininert valve.
?. [Field Sampling]
Open mininert valve on syringe. Inject gas through the filter and needle until the syringe reads 30 mL. Immediately stick the syringe and needle into the sampling vial through the rubber stopper. Using another sterile needle, puncture the sample vial stopper to provide and outflow for the NaCl solution. Displace 30 mL of NaCl solution with the gas in the syringe. Holding needle securely, remove syringe from vial. Store vials stopper-side down until analysis.
?. [Prepping sample vials]
Wait for vials, stoppers, and NaCl solution to cool down to near room temperature.
hot stoppers don't reseal well upon puncturing with needles
?. [Prepping sample vials]
Using  2 18G BD precisionglide needle per vial and a 60 mL syringe, fill the vial as completely as possible with NaCl solution.
It is not essential to use 100% sterile technique for the NaCl solution because it is so salty that microbial life is inhibited in it.