Geological Society of America

T89 Spectroscopy for the Geosciences in the 21st Century

Monday, 10 October 2011
8:00 AM - 12:00 PM
Room 102D-F

CALIBRATING RAMAN SPECTROSCOPIC SYSTEMS FOR QUANTITATIVE ANALYSIS OF GEOLOGICAL FLUIDS USING STANDARDS PREPARED IN FUSED SILICA CAPILLARIES

Paper number: T89-6
Program: Technical Sessions
Time: 9:15 AM – 9:30 AM

Authors

I-Ming Chou Presenting Author
U.S. Geological Survey, Reston, VA
Wanjun Lu
China University of Geosciences, Wuhan, N/A
Guoxiang Chi
University of Regia, Regina, SK
Shunda Yuan
Chinese Academy of Geological Sciences, Beijing, N/A
Yucai Song
Chinese Academy of Geological Sciences, Beijing, N/A
Junying Ding
Nanjing University, Nanjing, N/A
Pei Ni
Nanjing University, Nanjing, N/A
Robert C. Burruss
U. S. Geological Survey, Reston, VA

Abstract

Standards were prepared in fused silica capillaries for the calibration of Raman systems for quantitative analyses of geological fluids, such as those found in fluid inclusions in minerals. The standards include fluids in unary (CH₄, CO₂), binary (CH₄-CO₂, CH₄-H₂O, CO₂-H₂O, CH₃COOH-H₂O) and ternary systems (CH₄-CO₂-N₂). They were prepared in three different ways: (1) fluids were loaded in a fused silica capillary with one end sealed and the other end connected to a pressure valve, such that various gases and their mixtures were loaded with controlled total pressure; (2) similar to (1) except the outer wall of the open-end of the fused silica capillary was sealed to the inner wall of a stainless steel capillary tube with epoxy, while the other end of the steel tube was connected to a pressure valve, and after the fluid sample of known composition and pressure was loaded, the steel tube was cut with a cold-seal pliers; and (3) gases were loaded cryogenically in a fused silica capillary with one end sealed, and the open end of the tube was then sealed with a hydrogen flame to form a fused silica capsule (Chou et al. 2008, Geochim. Cosmochim. Acta (GCA), 72, p. 5217).

The first type of standard is the most reliable in terms of composition and total pressure, but it is bulky and not convenient for inter-laboratory calibration. The second type of standard is reliable and compact, but currently the total pressure must be less than 4 MPa due to the pressure limit of the cold seal. The third type of standard is small, normally less than 3 cm in length, but the compositions of mixed gases and their total pressures must be estimated after sealing the capsule.

After calibrating our Raman spectroscopic system with some of these standards, we were able to determine, for example, (1) the pressures of CH₄ in fluid samples (Lu et al., 2007, GCA, 71, p. 3969), (2) the diffusion coefficient of CH₄ in water at room temperature (Lu et al., 2006, Appl. Spectr., 60, p.122), and (3) the solubility of methane hydrate in water (Lu et al., 2008, GCA, 72, p. 412). It should be emphasized that every Raman spectroscopic system needs to be calibrated before it can be used for quantitative analyses of fluid mixtures. Fluid standards prepared in fused silica capillaries are reliable for calibration of Raman systems and small enough that they can be used for inter-laboratory comparisons.