Table 2 PLS model parameters and statistics for the calibration of PG, VG, water and nicotine concentrations in e-liquid.

From: Rapid determination of levels of the main constituents in e-liquids by near infrared spectroscopy

Analyte

Conc. (% w/w)

No. of samples

Region (cm−1)

No. of factors

Standard error

R2

Calibration

Validation

Calibration

Expanded

PG

30–70

125

11

8038–8856

2

0.92

1.84

0.995

VG

18–65

123

14

7996–9041

2

0.94

1.88

0.995

Water

0–18

124

12

6441–8212

4

0.31

0.62

0.997

Nicotine

0–6

221

47

5701–6067; 8274–9192

9

0.11

0.22

0.995

  1. PG propylene glycol, VG vegetable glycerol, PLS partial least squares.
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