Kerogen origin, evolution and structure

FTIR absorption indices for thermal maturity in comparison with vitrinite reflectance R0 in type-II kerogens from Devonian black shales

Studying individual macerals using i.r. microspectrometry, and implications on oil versus gas/condensate proneness and “low-rank” generation

Micro-FTIR spectroscopy of liptinite macerals in coal

Fourier Transform Infrared (FT-IR) microspectroscopy provides an in situ, nondestructive chemical analysis of individual algal cells. Algae play key roles in nutrient cycling and energy flow through aquatic ecosystems and are pivotal in the sequestration of inorganic nutrients (e.g., carbon, nitrogen, and phosphorus) and transformation into organic forms. However, most methods used to measure algal nutritional and physiological changes are limited to detecting whole community responses because of the relatively large quantity of material needed for analysis (i.e., milligrams to grams). The spatial resolution achievable with infrared microspectroscopy allows for the analysis of macromolecular pools (e.g., proteins, lipids, carbohydrates) in individual cells that allows species specific measurements within heterogeneous microscopic communities. Initial applications characterized molecular pools within marine macroalgae and have since progressed toward ecologically based questions concerning algal p...

FT-IR Microspectroscopy Enhances Biological and Ecological Analysis of Algae

A microscope sampling accessory interfaced to a Fourier transform infrared (FT-IR) spectrometer has been employed to characterize the remains of individual microscopic fossil algae and algal colonies contained in organic-rich shales. The microspectrometer is able to measure reflectance IR spectra of samples with cross-sectional areas as small as 20 × 20 microns. The fossil algae studied include the colonial green alga Botryococcus braunii, the unicellular green alga Tasmanites, and n unidentified filamentous alga. It was found that IR spectra of the fossil algae, in common, contain intense aliphatic C-H stretching bands in the 2900-cm−1 region relative to the C=C stretching band at 1600 cm−1. The carboxylic acid C=O stretching band at 1710 cm−1 is moderately intense. The relative intensities of these bands vary among the three different fossil algae. Maximum-likelihood spectral restoration and subsequent curve fitting of the stretching vibrations of the aliphatic C-H bands provide greater insight into the aliphatic structures of fossil algae. The CH2/CH2 intensity ratio can be calculated and used to assess the relative average aliphatic chain length and the degree of branching.

Reflectance FT-IR microspectroscopy of fossil algae contained in organic-rich shales

Alternating current coupled inverse Raman spectrometry

ac-coupled inverse Raman spectroscopy is shown to yield detection limits comparable to those obtained by spontaneous Raman spectroscopy. For an aqueous nitrate ion, inverse Raman limits are about 2.5 times higher than those reported for conventional measurements with similar laser powers and measurement times. Proposed improvements in instrumentation may lower detection limits another 10 times with no change in laser powers or measurement times.

Detection Limits of ac-coupled Inverse Raman Spectroscopy

Pulsed laser systems produce spectroscopic signals with large shot-to-shot variations, short durations, and low duty cycles. The most satisfactory signal processing system is gated integration, with pulse averaging and ratioing to a reference signal. We describe a system based on commercially available modular integrators and a hobbyist microcomputer which performs the averaging and ratioing digitally. System performance is equal to or better than that of fully analog systems, while the cost is low and construction is straightforward.

G. Patrick Ritz

Papers

Reflectance FT-IR microspectroscopy of fossil algae contained in organic-rich shales

Alternating current coupled inverse Raman spectrometry

Detection Limits of ac-coupled Inverse Raman Spectroscopy

Microprocessor-controlled Data Acquisition System for Pulsed Laser Spectroscopy