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

In this experiment students are proposed a fanciful application of the method of standard additions to evaluate the approximated amount 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 and after addition of known amounts of powdered shell. A peak characteristic of shells is selected and its normalized intensity plotted against the percentage of added shell powder. By means of a linear regression the initial concentration of the biogenic component of the sand is then estimated. The proposed approach, based on a method of general validity for mixtures and holding also for 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 lineshapes 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 experience can be carried out in one or two lab shifts depending whether students are asked to prepare starting powders and/ or determine the optical response curve and is designed for either undergraduate or graduate students.