(US4771176-A)      Total mass of gaseous and condensed hydrocarbons in a sample which also contains C particles is determined by measuring the intensity of electromagnetic radiation passed through a sample and a reference vol. The radiation has a frequency band of central wavelength 3465 +- 0.05 micron, half-band width 0.07-0.18 micron, 5% cuton at wavelength more than 3.35 microns and a 5% cutoff at wavelengths less than 3.58 microns. The difference (I) in the intensity values measured provides a preliminary value. Radiation of wavelengths 3.8-4.15 microns is then passed through the sample and reference vol. and the difference (II) in intensity values measured provides a value of the total mass of C particles. The value of (I) is then corrected using (II).    USE/ADVANTAGE -   Analysis of unfiltered exhaust gases. Result obtd. are accurate even if the relative compsns. of the hydrocarbon components varies considerably.    (EP226569-B)      A method for quantitative analysis of hydrocarbons in samples of unfiltered exhaust gases, in which the infrared transmission of the electromagnetic radiation penetrating the sample and a reference volume is measured and the difference in radiation intensities is used as a measured value, wherein the total mass of gaseous and condensed hydrocarbons present in the gaseous sample is determined with the use of electromagnetic radiation with a frequency band of a central wavelength of 3.445 +- 0.03 micro-m, and a half-band width of 0.07 to 0.14 micro-m, and a 5% cuton at a wavelength of more than 3.35 micro-m, and a 5% cutoff at a wavelength of less than 3.58 micro-m, and the integral infrared absorption of this band is measured, and wherein the total mass of carbon particles contained in the sample is determined by measuring the transmission of infrared radiation in the range of 3.8 to 4.15 micro-m, and wherein the value obtained in this context is employed for correction of the value obtained upon measuring the total mass of hydrocarbons. (8pp)    (JP93004627-B)      The total mass of gaseous and condensed hydrocarbons in gas mixtures, specially in the exhaust gases of motor vehicle engines, can be determined by passing infrared radiation alternatively through a reference gas and through a gas sample to a detector. The wavelength is chosen such that the infrared absorption of all hydrocarbons is at least approximately the same.    ADVANTAGE -   This gives accurate results even when the percentage fluctuation is great; it can also be extended to differentiate between gaseous and condensed hydrocarbons. (J62137540-A)