Dissolved Gas Sampling Instructions
In This Document
Serum Bottles
- Insert a needle into the rubber stopper until the tip slightly exits through the stopper. (See illustrations below).
- Fill a 1 or 2 liter beaker with well water.
- Place the water discharge tube at the bottom of the 150 mL sample bottle. After it is filled place the bottle in the water filled beaker. The water should be flowing into the bottle when it is put in the beaker. Do not filter the sample, use raw sample.
- Make sure that no bubbles are adhering to the sides of the bottle. Insert the stopper in the bottle while the bottle is submerged in the water. Make sure that you push the stopper all the way down. Take duplicates of all samples.
- Remove the needle from the stopper while the bottle is still submerged in the water. Properly dispose of all needles or return the used needles with the samples.
- Record the (a) sample name, (b) water temperature and (c) estimated recharge altitude on the label attached to the foam sleeve.
- Keep samples cool or about the temperature of the ground water. This will keep the stoppers from popping up as sample warms up. Store sample bottles upside down.
- Ship samples with ice in cooler overnight
express to:
Peggy Widman
U.S. Geological Survey
M.S. 432
12201 Sunrise Valley Dr.
Reston, VA 20192
Phone: 703-648-5347
Email: pkwidman@usgs.gov Do Not ship samples on a Friday. The samples will not be delivered here until Monday and may heat up in storage.
Illustrations
Collection and Analysis of Ground-Water Samples for Helium by Gas Chromatography
The water samples for He analysis are collected in 150-mL septum bottles that are filled without headspace in the field using procedures identical to those used to collect other dissolved gases (see above).� The samples are stored on ice in the field, and in a refrigerator at 4°C in the laboratory prior to analysis, to minimize expansion and possible sample loss, and to lower rate of biological activity in the sample prior to analysis.� In the laboratory, after allowing the samples to come to room temperature overnight, a 10-mL headspace is created by removing some of the water through the septum with a needle connected to a vacuum pump.� The water is allowed to equilibrate with this headspace overnight at room temperature before analysis.� The headspace gas is injected into a gas chromatograph.
The concentrations of He are measured with a thermal conductivity detector (TCD).� The procedure is similar to that described by Sugisaki and others (1982).� The instrument is calibrated with five standards by injections of 1, 2, and 3 cm3 of a gravimetric standard gas containing 35.0 ppm volume per volume of He.� The concentrations in this standard are known to within �1 percent.� The two other standards used were 2.0 and 3.0 cm3 of dry air.� The concentration of He is 5.24 ppm volume per volume of gas (Committee on Extension to the Standard Atmosphere, 1976).�� The precision of the helium gas-chromatographic analysis is approximately 5 percent.
