The Shell Seeker: What Is the Quantity of Shell in the Lido di Venezia Sand? A Calibration DRIFTS Experiment

Abstract

In this experiment, students are given a fanciful application of the standard addition method to evaluate the approximate quantity of the shell component in a sample of sand collected on the Lido di Venezia seashore. Several diffuse reflectance infrared Fourier transform (DRIFT) spectra are recorded from a sand sample before and after addition of known amounts of powdered shell. A peak, characteristic of shells, is selected and its normalized intensity is plotted against the percentage of added shell powder. By means of a linear regression, the initial concentration of the component from shells of the sand is estimated. The proposed approach, based on a method for mixtures and impurity determination, requires students to perform DRIFT spectroscopic measurements of a powdery material and, depending on the starting material, offers the chance to verify the influence of grain size on spectral features. Well-known distortion effects on peak intensities and line shapes due to sample inhomogeneities that usually make DRIFTS a poor technique for quantitative measurements are circumvented by asking students to follow a strict procedure for sample preparation. The proposed experiment can be carried out in one or two lab periods depending whether students are asked to prepare starting powders or determine the optical response curve and is designed for either undergraduate or graduate students.

Thermally Induced Aragonite–Calcite Transformation in Freshwater Pearl: A Mutual Relation with the Thermal Dehydration of Included Water

“…Figure S3 shows the XRD pattern and FT-IR spectrum of the FW-pearl. The XRD pattern (Figure S3a) is in agreement with that reported for aragonite (CaCO 3 , orthorhombic, S.G. = Pmcn(62), a = 4.9623, b = 7.9680, c = 5.7439, α = β = γ = 90.000, ICDD-PDF 00-041-1475). , The FT-IR spectrum (Figure S3b) shows all of the major IR absorption peaks attributed to aragonite. − The absorptions attributed to the ν 4 mode of CO 3 2– in the aragonite structure are observed at 700 cm –1 and 713 cm –1 . The IR absorption peaks at 864, 1082, and 1483 cm –1 are attributed to the ν 2 , ν 1 , and ν 3 modes of the CO 3 2– vibrations, respectively.…”

“…The details for the quantitative analysis of the IR absorption peaks are described in the Supporting Information (Section S4: Figures S10–S13 and Tables S2–S4). ,,− …”

Spectroscopic and Chemometric Comparison of Local River Sands with the Aggregate Component in Mortars from Ancient Roman Buildings Located in the X Regio Between the Livenza and Tagliamento Rivers, Northeast Italy

“…The powders were then diluted to 2.90-2.94 wt% in spectroscopic-grade potassium bromide (KBr; Fluka) and the mixture was homogenized using a 10 min vibrating mill cycle. This sample preparation procedure has been used previously in DRIFTS studies of sand 28 to give spectra in Kubelka-Munk units proportional to the absorptivity of the sample. 29 All the powders were dried in an oven at 120 C and stored in a desiccator to avoid unwanted interference from water absorption lines in the spectra.…”

An Exercise on Calibration: DRIFTS Study of Binary Mixtures of Calcite and Dolomite with Partially Overlapping Spectral Features

“…Two fragments of calcite and dolomite minerals of about half a gram, preliminarily reduced to a fine powder by hand in an agate mortar-and-pestle, were processed by means of a 20 min grinding cycle in a vibrating mill (Specac model Specamill; agate vial and three pestle-balls) to provide a material suitable for DRIFTS measurements. 7 The obtained powders were kept in oven (at about 170 °C) overnight to eliminate water that could both interfere with the weighing precision and give rise to unwanted spectral features. For the same reasons, the powders were kept in desiccator whenever possible.…”

“…The mixtures were prepared by directly weighing the two carbonates into a mixing vial to give a total of about 8.3 mg. Spectroscopic grade potassium bromide powder (Fluka), about 283.5 mg, was added to the vial to give an optimal sample percentage of about 3% in KBr. 7 The samples were homogenized by a 15 min vibrating-mill mixing cycle, then poured into a sample-holder cup (10 mm diameter, 2.3 mm depth) and placed into the Pike DiffusIR measurement unit together with a second sample-holder cup filled with pure KBr powder to be used as a reference. A Bruker Optik Vertex 70 spectrometer was employed to record the reflectance from the sample and the KBr powder whose ratio approximates the absolute reflectance R ∞ allowing the conversion of the sample spectra into Kubelka−Munk (K−M) units that result proportional to the molar absorption coefficient of the sample, provided that the latter is diluted in the nonabsorbing matrix to a certain extent.…”