The performance of a portable near-infrared (NIR) spectrometer to determine organic carbon (OC) in marine sediments was evaluated. The NIR reflection spectra of 180 samples in the range 950 - 1650 nm were acquired using an ultra-compact spectrometer. NIR spectroscopy combined with the partial least squares (PLS) regression and Savitzky-Golay (SG) smoothing was successfully applied to rapid and reagent-free determination of OC. Using the PLS-SG model with 1 nd order derivative, 2 th polynomial and eleven smoothing points, the root-mean-square errors (RMSEP M) and correlation coefficients (R P,M) of prediction for modeling were 0.073% and 0.894, respectively, the root-mean-square errors (RMSEP V) and correlation coefficients (R P,V) of prediction for validation were 0.075% and 0.883, respectively. Results showed that the small portable NIR instrument achieved well prediction effect for the analysis of OC in marine sediments, which had advantages of rapid, easy to carry and operate suitable for large-scale applications to analyze marine sediments.
Marine sediments preserve an abundance of climatic and environmental information for reconstructing oceanic history [
Near-infrared (NIR) spectroscopy primarily reflects the absorption of overtones and the combination of the vibrations of X−H functional groups (e.g., C-H, O-H, and N-H). Given the weak NIR absorption strength, most sample types can be directly measured without chemical reagents. In the geological samples, the NIR spectroscopy as a rapid and reagent-free measurement has been effectively utilized in soil analysis [
Organic carbon (OC) is one of the major components in marine sediments and contains many hydrogen groups [
The marine sediment samples were collected from Daya Bay of China using a sediment corer and were cryopreservation at −30˚C for 5 h, then 48 h for freeze drying in a lyophilizer, sieved through 100 mesh screen and stored in hermetic bag finally. Then, a total of 180 samples were obtained. Every sample was 50 g. All samples were measured by the portable NIR spectrometer firstly, and then were determined through chemical method.
The OC values of these samples were measured with potassium dichromate redox titration [
A portable NIR spectrometer, the MicroNIRTM (JDSU Corporation, Milpitas, USA) Grating Spectrometer, which equips with a reflection accessory. This instrument, powered (5V) and controlled via USB port of a computer, originally employs two tungsten light bulbs as radiation source, a Linear Variable Filter (LVF) as dispersing element and an uncooled 128-element detector (InGaAs). An image of the MicroNIR spectrometer is provided in
A rigorous process of calibration, prediction and validation was performed to achieve parameter stability and objective evaluation for modeling.
In chronological order, the samples were divided into two groups. The first group (120 samples) was used for modeling, whereas the second group (60 samples) was used for validation. The second group excluded in modeling was used to validate and achieve an objective evaluation. The root-mean-square errors (RMSEPM) and correlation coefficients (RP,M) of prediction for modeling were calculated. The calculation formulas are as follows:
where n is the number of prediction samples;
against the validation set (60 samples). The corresponding root-mean-square errors (RMSEPV) and correlation coefficients (RP,V) of prediction for validation and were further calculated, respectively. The calculation formulas are as follows:
where mV is the number of the validation samples;
PLS method is widely used for spectroscopic analysis, and can screen spectroscopic data comprehensively and extract information variables [
The NIR spectroscopy of marine sediment samples contains more physical and chemical noises. To overcome the noises, the measured spectra require pretreatment. SG smoothing is a useful spectrum pretreatment method with a wide range of applications and a variety of smoothing modes [
The NIR spectra of the 180 marine sediments samples in the whole spectral collecting region (950 - 1650 nm) are illustrated in
The SG derivative spectra of all marine sediment samples on the whole spectral collecting region are illustrated in
The validation samples excluded from the modeling process were used to validate the PLS model. The PLS regression coefficients were calculated using the spectra and measured values of all modeling samples depending on the corresponding parameters. The predicted OC values of the validation samples were then calculated using the obtained regression coefficients and the spectra of the validation samples.
The relationship between the predicted and measured OC values of the validation samples are shown in
In this paper, the marine sediments samples were detected by the small portable NIR instrument and the NIR spectroscopy combined with PLS method and SG smoothing was successfully applied to reagent-free and rapid determination of OC in marine sediments and achieved well validation effect. Results showed that the small portable NIR instrument achieved well prediction effect for the analysis of OC in marine sediments, which had advantages of rapid, easy to carry and operate suitable for large-scale applications to analyze marine sediments.
This work was supported by National Key Technology Support Program (No. 2012BAD18B01, 2012BAD18B02), the Science and Technology Project of Shenzhen of China (No.JSGG20141015154342147, JCYJ20160331141759795), and the National Special Fund for Agroscientific Research in the Public Interest of China (No. 201003068).
Yu, J., Mao, J.M. Pan, T., Chen, P.M. and Yao, L.J. (2017) Application of Portable Near-Infrared Spectrometer for Analysis of Organic Carbon in Marine Sediments. Journal of Geoscience and Environment Protection, 5, 108-114. https://doi.org/10.4236/gep.2017.55008