In situ Raman spectroscopic measurement of the 13C/12C ratio in CO2: Experimental calibrations on the effects of fluid pressure, temperature and composition

Unlocking ultimate precision of intensity and area ratio measurements in Raman spectroscopy: Insights from simulation, experimentation, and theory and implications for isotope ratio analysis

“…Data plots present the uncertainties obtained from simulations under various f (=30, 40, 50, 80, 120, 160, and 200 cm), w CCD (=5, 10, 15, and 20 μm), and G (=1200, 2400, and 3200 grooves/mm) conditions for four 13 I þ F:D: conditions. Bands and horizontal dotted lines were calculated, respectively, by Equations ( 22) and (23) and Equation (14). Vertical lines are Γ w / Δx w in the experiment conditions used for the present and earlier studies.…”

“…60,62 In δ 13 C measurements of CO 2 , 13 I þ F:D: =I þL F:D: is influenced not only by δ 13 C but also by temperature and pressure. 23,26 These dependencies can cause apparent 13 I þ F:D: =I þL F:D: shifts because of laser heating. CO 2 inclusions in quartz, olivine, pyroxene, and spinel show different temperature increases per unit laser power at 532 nm: about 0.01 C/mW, 0.5 C/mW, 1.0 C/ mW, and 6.0 C/mW, respectively.…”

“…62 Consequently, at P ill = 100 mW, the temperature increase will be only 1 C for quartz but about 600 C for spinel. Because a temperature increase of around 1 C does not significantly affect 13 I þ F:D: =I þL F:D: , 23 increasing P ill might be a useful way to improve the σ α I of fluid inclusions in minerals with low optical absorption coefficients, such as colorless quartz. However, at several hundred degrees, 13 I þ F:D: =I þL F:D: will also change because of changes in the Raman quantification factor.…”

“…Isotope ratio analysis is a challenging analysis that demands the highest degree of precision. In recent years, nondestructive local isotope analysis methods have been developed for various substances, such as H 2 O, 20,21 CO 2 , [22][23][24][25][26][27][28][29][30][31][32] H 2 , 33,34 N 2 , 35 humic acids, 36 and calcite. 37 Local nondestructive δ 13 C measurement of CO 2 by Raman spectroscopy has long been the subject of research; it has recently been investigated actively for application to various PVTX conditions.…”

“…37 Local nondestructive δ 13 C measurement of CO 2 by Raman spectroscopy has long been the subject of research; it has recently been investigated actively for application to various PVTX conditions. 22,23,[26][27][28]32 However, because of the large variation of more than two orders of magnitude in the reported precision (σ δ 13 C ) of δ 13 C measurements (Table 1), some researchers 24 assert that this method is applicable to natural samples, whereas other researchers 23,26 consider that it is limited to samples with highly variable or greater δ 13 C. Although the magnitude of the weakest peak intensity is commonly regarded as a factor indicating the precisions of α I and α A (σ α I and σ α A ), 25,27 this factor alone does not account for the reported variation in σ δ 13 C (Table 1). Identifying parameters that strongly affect σ α I and σ α A would help improve σ δ 13 C , but no comprehensive or quantitative studies particularly addressing the precision of α I and α A have been conducted to date.…”