Nirsystems Incorporated

Perstorp Analytical, Inc.

David E Honigs

Donald C Lynch

Timothy G Kelly

In the system for analyzing aqueous samples, the aqueous sample is deposited upon a sheet of filter paper which is held in a filter holder by clamping the peripheral edges of the filter paper between male and female threaded members of the filter holder. The filter paper with the sample is dried by a heated air stream directed perpendicularly toward the paper so that it flows around and through the paper. After the sample has been dried, it is analyzed by near infrared spectral analysis to measure the constituents of the dried sample.

Drying method and apparatus for infrared analysis of aqueous samples

In a spectrophotometer having an oscillating grating, an automatic calibration system is provided to ensure that the instrument constants are recomputed before each measurement of an unknown sample. In the system, whenever a reference scan is carried out, a second scan through an absorbance standard is carried out automatically and the data obtained is used to correct the instrument coefficients relating the angular position of the grating to the wavelength. The corrected coefficients are then stored to be used in the measurement of the unknown sample immediately thereafter. For near infrared spectrum measurements, the absorbance standard is a polystyrene plate. For visual measurements, the absorbance standard is a didymium plate. The didymium plate is mounted on the polystyrene plates eclipse a portion of the polystyrene plate.

Automatic spectrophotometer calibration system

An improved near infrared spectrophotometer is disclosed which reduces wave shift errors arising from hot spots in a light source. A ground quartz plate uniformly diffuses radiation from the light source to evenly illuminate the entrance slit for a diffraction grating. Radiation emerges from the entrance slit with a uniform angular intensity distribution and is dispersed into a spectrum by a reflecting diffraction grating towards an exit slit. A narrow wavelength band of radiation passes through the exit slit to illuminate a sample. Because the entrance slit is uniformly illuminated, without regard to variations in radiation intensity due to hot spots in the source, wave shift errors in the reflectivity measurements for the sample are reduced.

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Laurel, MD, United States of America

David E Honigs