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Introduction: Imaging using X-ray absorption contrast by synchrotron nano-computed tomography of a Ryugu pyrrhotite crystal (C0002-FC012 - from the second Hayabusa2 spacecraft touch-down site) revealed probable fluid inclusions in the center of a crystal of pyrrhotite, suggesting the parent fluids were trapped in the early stages of crystal growth on Ryugu's parent asteroid. We previously described the performance of Time-of Flight-Secondary Ion Mass Spectrometry (TOF-SIMS) depth profiling and high-resolution mapping at -120°C to expose and measure the composition of the trapped fluids in a frozen state in two Ryugu inclusions [1,2]. Here we report results from follow-on measurements of additional inclusions in the same pyrrhotite crystal, and the initial results of measurement of standards. The ultimate goal is to reveal the quantitative composition of the fluids that caused aqueous alteration, in particular the H2O:CO2 ratio, which will also facilitate cosmochemical modeling of the alteration process. Measurements of Ryugu Fluids: TOF-SIMS measurements of four Ryugu fluid inclusions revealed that the ancient, trapped fluids on Ryugu's parent asteroid were saline aqueous solutions containing H2O, CO2, sulfur species, and nitrogen- and chlorine-bearing organic compounds identified by representative secondary ion species including O-, OH-, CO-, S-, Cl-, C2-, C2H-, and CN-. The inferred presence of CO2 indicates formation of the sulfides, and by implication the Ryugu parent body, beyond the H2O and CO2 snow lines of the early solar system, i.e. > 3-4 au from the Sun [3]. In this work we made measurements of only a few planes exposed by sputtering. We later discovered that we should have measured the inclusions from top to bottom, as shown by our subsequent measureents of standards. Standards: The next step in these analyses was the measurement of appropriate fluid standards, reported here. Artificial aqueous fluid inclusions in quartz were made at Virginia Tech (see [4] for technical details), with a known ratio of H2O to CO2 of 1:1. The surface of a quartz grain was carefully polished to bring promising artificial fluid inclusions to within 2 µm of the surface. Before freezing, the boundaries between water and CO2 ice were apparent, as was a separate H2O-CO2 clathrate phase at that boundary. Thus, even before freezing the inclusions were compositionally heteorgeneous, although the bulk compositions should all have been equal and constant. H2O:CO2 Measurements: For the previous smeasurements in the pyrrhotite crystal we used CO-as the molecular fragment to indicate the presence and apparent concentration of CO2 [1]. However, host quartz in the standards contained major oxygen, which precluded reliance on the CO- molecule. Therefore, we used the molecular fragment Cto measure CO2. Measurement of five standard fluid inclusions (entire inclusions rather than measurements of a few "slices") produced the following results. In four of the five standard inclusions the ratio H2O:CO2 varied by less than 10% relative, which was considered a success. The fifth inclusion produced a ratio 2x greater than the others, possibly due to leakage of CO2. The next step is to measure stardards inclusions with at least one additional, different H2O:CO2 ratio, which will permit construction of a calibration curve for determining actual H2O:CO2 ratios in fluid inclusions. In the course of this work we also verified that different species in the fluid inclusions freeze at different temperatures, resulting in frozen inclusions whose composition varies unpredictably as they are sequentially sputtered and measured by TOF-SIMS. This behavior necessitates that fluid inclusion contents must be measured in-toto in order to produce accurate bulk compositions. [ABSTRACT FROM AUTHOR]