Proposed Method Comparison
December 9, 2022
Originally, we had planned to analyze 60 dripwater samples and 60 calcite samples. After beginning the scraping process, it became evident that 60 calcite samples in such a short amount of time was unrealistic. Instead, we adapted our final sample selection to 55 dripwater samples and 15 calcite samples from 7 different plates (a center and an edge or middle-edge). Only moderate or high growth plates had enough calcite to be scraped. With that in mind, dripwaters cover five years and all seasons, and plates cover three years and moderate to high growth seasons to show as much variability as possible while still maintaining as much of the original plate as possible. This sample selection provides a wide range of moisture conditions to hopefully elucidate differences in fractionation of the dripwaters and farmed calcite.
Our goal was to scrape 100 micrograms of calcite off of the plates. This proved not enough sample, so we scraped between 240 and 3600 micrograms of calcite from each scrape location, with higher growth plates providing more calcite. This was diluted in 2% nitric (as opposed to dissolving the entire plate’s calcite in 7 N nitric and 18.3 megohm deionized water proposed in Tremaine and Froelich, 2013). Our method preserved the vast majority of calcite on the plate for future analysis.
We originally proposed to measure all analytes in pulse mode only in order to eliminate the normalization factor between pulse and analog mode. However, after deciding to complete one dripwater dilution instead of two, we continued to use both modes to analyze both dripwaters and plate calcite. This also allowed us to avoid performing semi-quant analysis on our already volume-limited samples.
We also planned to measure ratios directly for dripwaters, but we had not accounted for the fact that we could not assume stoichiometric calcium concentration for dripwaters. Because of this, we decided to develop a single-dilution method for measuring trace elements and calcium in dripwaters.