Fig 1.
NIR spectra of purified water (gray lines) at various path lengths (1, 2, 5, 10 mm) and powdered KHP (black line).
Fig 2.
NIR second derivative spectra (gap-segment, 23 segments) KHP aqueous solutions at the wavenumber range of (A) 7500–5500 cm-1 and (B) 6300–5800 cm-1. Black line is the spectra of 0, 1000 and 2000 ppm solution, blue line is that of 3000, 4000 and 5000 ppm, green line is that of 6000, 7000, 8000 ppm and red line is that of 9000 and 10000 ppm.
Fig 3.
Relationships between measured and predicted KHP concentration (spectral pre-treatment: gap-segment second derivative, 23 segments, optical path length: 5 mm, aperture: BRM2065, co-added time: 32 scans) at incorporating the data for (A) 0–10 ppm (1 ppm steps), (B) 0–100 ppm (10 ppm steps), (C) 0–1000 ppm (100 ppm steps), (D) 0–10000 ppm (1000 ppm steps).
Table 1.
Statistical results of PLS regression analysis and LODmax.
Fig 4.
Variations in (A) SEN, (B) var(x), (C) LODmax and (D) the regression line for SEN divided by the var(x) regression line as a function of optical path length (spectral pre-treatment: gap-segment second derivative, 23 segments, aperture: BRM2065, co-added time: 32 scans).
Fig 5.
(A) Wavenumber dependent reference light intensity when aperture BRM2065 (black solid line), NG9 (gray solid line) and NG 11 (black dash line) were used. Variations in (B) var(x) and (C) LODmin as a function of sum of reference sum of light intensity among 6300–5800 cm-1 (spectral pre-treatment: gap-segment second derivative, 23 segments, optical path length: 5 mm, co-added time: 32 scans).
Fig 6.
Variations in (A) var(x) and (B) LODmax as a function of the number of co-added scan times (spectral pre-treatment: gap-segment second derivative, 23 segments, optical path length: 5 mm, aperture: BRM2065).