Raman spectroscopy (785 nm excitation) was used to determine the overall carotenoid (astaxanthin and cantaxanthin) and fat content in 49 samples of ground muscle tissue from farmed Atlantic salmon (Salmo salar L.). Chemically determined contents ranged from 1.0 to 6.8 mg/kg carotenoids and 36 to 205 g/kg fat. In addition to the raw Raman spectra, three types of spectral preprocessing were evaluated: the first derivative, subtraction of the fitted fourth-order polynomial (POLY), and the intensity normalized versions of POLY (POLY-SNV). Further, variable selection based on significance testing by use of jack-knifing was performed on each spectral data set. Partial least-squares regression resulted in a root mean square error of prediction of 0.33 mg/kg (R = 0.97) for carotenoids for the variable selected versions of all the preprocessed spectral data sets. The fat content was best estimated by the variable selected POLYSNV, resulting in a root mean square error of prediction of 15.5 g/kg (R = 0.95). Both preprocessing and variable selection improved the regression models significantly. The results demonstrate that Raman spectroscopy is a suitable method for simultaneous, rapid, and nondestructive quantification of both pigments and fat in ground salmon muscle tissue.

The development of a field portable fiber optic Raman system modified from commercially available components that can operate remotely on battery power and withstand the corrosive environment of the hydrothermal vents is discussed. The Raman system is designed for continuous monitoring in the deep-sea environment. A 785 nm diode laser was used in conjunction with a sapphire ball fiber optic Raman probe, single board computer, and a CCD detector. Using the system at ambient conditions the detection limits of SO(4)(2-), CO(3)(2-) and NO(3)(-) were determined to be approximately 0.11, 0.36 and 0.12 g l(-1) respectively. Mimicking the cold conditions of the sea floor by placing the equipment in a refrigerator yielded slightly worse detection limits of approximately 0.16 g l(-1) for SO(4)(-2) and 0.20 g l(-1) for NO(3)(-). Addition of minerals commonly found in vent fluid plumes also decreased the detection limits to approximately 0.33 and 0.34 g l(-1) respectively for SO(4)(-2) and NO(3)(-).

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This article will demonstrate that Raman spectroscopy can be a useful tool for monitoring the chemical composition of hydrothermal vent fluids in the deep ocean. Hydrothermal vent systems are difficult to study because they are commonly found at depths greater than 1000 m under high pressure (200-300 bar) and venting fluid temperatures are up to 400 degrees C. Our goal in this study was to investigate the use of Raman spectroscopy to characterize and quantitate three Raman-active salts that are among the many chemical building blocks of deep ocean vent chemistry. This paper presents initial sampling and calibration studies as part of a multiphase project to design, develop, and deploy a submersible deep sea Raman instrument for in situ analysis of hydrothermal vent systems. Raman spectra were collected from designed sets of seawater solutions of carbonate, sulfate, and nitrate under different physical conditions of temperature and pressure. The role of multivariate analysis techniques to preprocess the spectral signals and to develop optimal calibration models to accurately estimate the concentrations of a set of mixtures of simulated seawater are discussed. The effects that the high-pressure and high-temperature environment have upon the Raman spectra of the analytes were also systematically studied. Information gained from these lab experiments is being used to determine design criteria and performance attributes for a deployable deep sea Raman instrument to study hydrothermal vent systems in situ.

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