PREDICTION OF PRECISION FROM SIGNAL AND NOISE MEASUREMENT IN LIQUID-CHROMATOGRAPHY - LIMIT OF DETECTION

A method to determine the limit of detection (LOD) in high performance liquid chromatography (HPLC) is described. The power spectral density of instrumental baseline variation is fitted by the simplex least squ ares methods with a mixed random process of white noise and Markov pro cess as a model. The white noise is characterized by standard deviatio n (SD), w; the Markov process by the SD, m, and auto-correlation degre e, rho. All required parameters for calculating the LOD signal are obt ained by experiment without repeat measurements. No arbitrary constant s are needed. The LOD signal is uniquely determined and is characteriz ed by 33.3 % relative standard deviation (RSD) of analyte measurements and 0.13 % of the error of the first type. This signal also specifies that the signal-to-noise ratio = 3, using the definition of noise ori ginating from the white noise and Markov process. The theoretical conc lusion is verified by the Monte Carlo simulation using real baseline a nd peaks. The LOD concentrations for naphthalene, acenaphthene, pyrene and perylene are given.