To quantify HCl impurity in biomethane, a new matrix-specialized laser spec-trometer has been developed based on direct-tunable diode laser absorption spectroscopy (dTDLAS). The spec-trometer is equipped with a 3.6 µm in-terband cascade laser, a single pass gas cell, and can determine absolute HCl gas species concentration in CH₄ or biomethane with a relative standard un-certainty of 2.3 %. For HCl concentra-tion measurements at 161.7 mg/m³, the dTDLAS HCl concentration result agrees with the HCl in CH₄ reference gas mixture, demonstrating the capabil-ity of the sensor. The repeatability of the dTDLAS HCl concentration results was determined to be 0.05 mg/m³.