Tunable laser spectroscopy measurement of c13 ethane

A method for making isotopic ethane measurements of a gas sample, the method comprising:

• introducing the gas sample into a gas cell, the gas cell deployed in a path between a tunable infrared laser and an infrared sensor, the tunable infrared laser configured to emit an infrared laser beam that passes through the gas cell and is received at an infrared sensor;
• scanning the emitted infrared laser beam between first and second wavenumbers;
• measuring a spectrum corresponding to the scanned infrared laser beam;
• identifying a first C13 ethane absorption peak and a second C12 ethane absorption peak in the measured spectrum;
• computing first and second amplitudes of the first and second absorption peaks by removing a spectral background;
• and
• computing a ratio of the first and second amplitudes to estimate a ratio of C13 ethane to C12 ethane in the gas sample.

An apparatus for making isotopic ethane measurements of a gas sample, the apparatus comprising:

• a tunable infrared laser configured to emit an infrared laser beam;
• an infrared sensor configured to receive the infrared laser beam;
• a gas chromatography column configured to isolate an ethane gas sample from the gas sample;
• a hollow wave guide deployed in a path between the tunable infrared laser and the infrared sensor such that the infrared laser beam passes through the hollow wave guide, the hollow wave guide configured to receive the ethane gas sample via a gas inlet and expel the ethane gas sample via a gas outlet, the hollow wave guide having an inner diameter in a range from 0.2 mm to 1 mm and a length in a range from 0.2 m to 10 m;
• and
• a controller configured to process a ratio of a first absorption peak to a second absorption peak in the received infrared laser beam to estimate a ratio of C13 ethane to C12 ethane in the gas sample.