  This paper presents a spectra normalization method for laser-induced
breakdown spectroscopy (LIBS) measurements by converting the recorded
characteristic line intensity at varying conditions to the intensity under a
standard condition with standard plasma temperature, degree of ionization, and
total number density of the interested species to reduce the measurement
uncertainty. The characteristic line intensities of the interested species are
first converted to the intensity at a fixed temperature and standard degree of
ionization but varying total number density for each laser pulse analysis.
Under this state, if the influence of the variation of plasma morphology is
neglected, the sum of multiple spectral line intensities for the measured
element can be regarded proportional to the total number density of the
specific element, and the fluctuation of the total number density, or the
variation of ablation mass, was compensated for by the application of this
relationship. In the experiments with 29 brass alloy samples, the application
of this method to determine Cu concentration shows a significant improvement
over generally applied normalization method for measurement precision and
accuracy. The average RSD value, average value of the error bar, R2, RMSEP, and
average value of the maximum relative error were: 5.29%, 0.68%, 0.98, 2.72%,
16.97%, respectively, while the above parameter values for normalization with
the whole spectrum area were: 8.61%, 1.37%, 0.95, 3.28%, 29.19%, respectively.
