A spectrometer system for speciation and quantitative determination of two or more hydrocarbon constituents of a hydrocarbon fluid comprising n-pentane and n-butane, wherein the hydrocarbon fluid contains no greater than 1.0% n-pentane and at least 5% n-butane, the system comprising: a broadband light source ; a gas flow cell through which the hydrocarbon fluid flows and through which or to which light from the light source passes; an optical detector for receiving the light after transmission through or reflection from the hydrocarbon fluid flowing through the gas flow cell and for generating a scan signal indicative of spectral information of the detected light over a continuous broadband region or over multiple discrete wavelength bands, where the scan covers a range that is equivalent to, is a subset of, or overlaps, the range from about 800 nm to about 12μm; a processor; and a non-transitory computer readable medium storing instructions thereon, wherein the instructions, when executed, cause the processor to: identify two or more bands of spectral data from the signal corresponding to the hydrocarbon fluid in the gas flow cell, wherein the two or more bands are non-contiguous and comprise a first band of spectral data that is a subset of 1300 nm to 1800 nm and a second band of spectral data that is a subset of 1850 nm to 2500 nm; combine the two or more identified non-contiguous bands of spectral data to form a combined spectrum of spectral data; and process data from the combined spectrum of spectral data to speciate and quantify in real-time two or more hydrocarbon constituents of the hydrocarbon fluid based on the combined spectrum of spectral data, wherein the processor is configured to speciate and quantify n-pentane and n-butane in the hydrocarbon fluid. a broadband light source ; a gas flow cell through which the hydrocarbon fluid flows and through which or to which light from the light source passes; an optical detector for receiving the light after transmission through or reflection from the hydrocarbon fluid flowing through the gas flow cell and for generating a scan signal indicative of spectral information of the detected light over a continuous broadband region or over multiple discrete wavelength bands, where the scan covers a range that is equivalent to, is a subset of, or overlaps, the range from about 800 nm to about 12μm; a processor; and a non-transitory computer readable medium storing instructions thereon, wherein the instructions, when executed, cause the processor to: identify two or more bands of spectral data from the signal corresponding to the hydrocarbon fluid in the gas flow cell, wherein the two or more bands are non-contiguous and comprise a first band of spectral data that is a subset of 1300 nm to 1800 nm and a second band of spectral data that is a subset of 1850 nm to 2500 nm; combine the two or more identified non-contiguous bands of spectral data to form a combined spectrum of spectral data; and process data from the combined spectrum of spectral data to speciate and quantify in real-time two or more hydrocarbon constituents of the hydrocarbon fluid based on the combined spectrum of spectral data, wherein the processor is configured to speciate and quantify n-pentane and n-butane in the hydrocarbon fluid. identify two or more bands of spectral data from the signal corresponding to the hydrocarbon fluid in the gas flow cell, wherein the two or more bands are non-contiguous and comprise a first band of spectral data that is a subset of 1300 nm to 1800 nm and a second band of spectral data that is a subset of 1850 nm to 2500 nm; combine the two or more identified non-contiguous bands of spectral data to form a combined spectrum of spectral data; and <EOS>