External/internal optical adapter for ftir spectrophotometer

A method of determining an optical spectrum for a sample substance relative to a reference substance, said method for use with a spectrophotometry system having a light source generating a source light beam of coherent light, said method comprising:

• 1) splitting by using a beamsplitter the source beam into a reference beam and a sample beam;
• 2) directing the reference beam into a reference cell having a substance therein, said substance in the reference cell interacting with the reference beam, said interacting yielding an output reference beam having a direction;
• 3) directing the sample beam into a sample cell having a substance therein, said substance in the sample cell interacting with the sample beam, said interacting yielding an output sample beam having a direction;
• 4) detecting at least a portion of the output reference beam and at least a portion of the output sample beam;
• 5) generating a reference signal representative of the detected portion of the output reference beam and a sample signal representative of the detected portion of the output sample beam;
• 6) generating a difference signal proportional to the difference between the reference signal and the sample signal;
• 7) placing the reference substance in the reference cell and in the sample cell;
• 8) determining a reference spectrum of the reference substance based on the difference signal;
• 9) moving the beamsplitter in a direction perpendicular to the propagation of the source beam to determine a minimized noise location of the beamsplitter at which a center burst of an interferogram is minimized;
• 10) determining a baseline difference spectrum;
• 11) placing the beamsplitter at the determined minimized noise location;
• 12) thereafter placing the reference substance in the reference cell and placing the sample substance in the sample cell;
• 13) determining a sample difference spectrum;
• and
• 14) determining the absorption spectrum of the sample based on the reference spectrum, the baseline difference spectrum and the sample difference spectrum.

A spectrophotometry system comprising:

• a light source generating a light beam;
• a lens in a path of the light beam and transmitting the light beam as a coherent source light beam;
• an optical system including a moveable beamsplitter for splitting the source light beam into a reference beam directed in a first path and a sample beam directed in a second path different from the first path wherein the beamsplitter is moveable between the first and second paths;
• a reference cell including a reference for interacting with the reference beam wherein said interacting yields an output reference beam having a direction;
• a reference light detector for detecting at least a portion of the output reference beam based on the direction of the output reference beam and generating a reference signal representative of the detected light;
• a sample cell including a sample for interacting with the sample beam wherein said interacting yields an output sample beam having a direction;
• a sample light detector for detecting at least a portion of the output sample beam based on the direction of the output sample beam and generating a sample signal representative of the detected light;
• a detector circuit for producing a difference signal proportional to the difference between the reference signal and the sample signal;
• a sealed housing for enclosing the above;
• and
• a processor configured to determine a spectrum of the sample based on the difference signal.