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Chemical Shift: Internal References and Solvent Effects01:17

Chemical Shift: Internal References and Solvent Effects

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In an NMR sample, precise measurement of the absolute absorption frequencies of nuclei is difficult. A standard internal reference compound is added, and the frequency difference between the reference signal and sample signals is measured.
The internal reference compound generally used in NMR spectroscopy is tetramethylsilane (TMS). TMS is preferred because it is chemically inert, soluble in NMR solvents, and easily removable. Also, the highly shielded methyl protons in TMS yield an intense...
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Applications Of NMR In Biology01:25

Applications Of NMR In Biology

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Nuclear magnetic resonance (NMR) spectroscopy is a very valuable analytical technique for researchers. It has been used for more than 50 years as an analytical tool. F. Bloch and E. Purcell formulated NMR in 1946 and won the 1952 Nobel Prize in Physics  for their work. Biological macromolecules such as proteins, nucleic acids, lipids, and organic molecules including pharmaceutical compounds, can be studied using this versatile tool that exploits the magnetic properties of certain nuclei.
4.4K
¹H NMR of Labile Protons: Deuterium (²H) Substitution00:48

¹H NMR of Labile Protons: Deuterium (²H) Substitution

1.3K
This lesson illustrates the role of deuterium substitution in simplifying the NMR spectrum of compounds comprising labile protons. One method employed is the use of deuterium. Amongst the three isotopes of hydrogen, deuterium (2H) has a nucleus composed of one proton and one neutron. When the D2O solvent is added to a pure dry ethanol solution, its labile proton is substituted with deuterium.
1.3K
NMR Spectroscopy Of Amines01:19

NMR Spectroscopy Of Amines

10.8K
In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is...
10.8K
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

1.4K
The 1D NMR spectrum of large and complex molecules like natural products has complicated splitting patterns and overlapping signals, which can be easily interpreted using 2-dimensional (2D) NMR. Unlike 1D NMR, 2D NMR has two frequency axes that provide the coupling information between the nucleus A and nucleus B in a molecule. The process from which 2D spectra are obtained has four steps.
The first step is the preparation period, during which nucleus A is excited with a radiofrequency pulse....
1.4K
2D NMR: Overview of Heteronuclear Correlation Techniques01:18

2D NMR: Overview of Heteronuclear Correlation Techniques

738
Heteronuclear correlation spectroscopy is an analytical technique that investigates the coupling between different types of nuclei, often a proton and an X-nucleus, such as carbon-13 or nitrogen-15. This method is commonly used in nuclear magnetic resonance (NMR) spectroscopy to gain insights into complex chemical compounds' structural and compositional aspects. A typical heteronuclear correlation spectrum displays X-nucleus chemical shifts on one axis and a proton spectrum on the other...
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Related Experiment Video

Updated: Jan 11, 2026

Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures
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Single-throughput Complementary High-resolution Analytical Techniques for Characterizing Complex Natural Organic Matter Mixtures

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Low-Cost NIR Spectroscopy Versus NMR Spectroscopy for Liquid Manure Characterization.

Mehdi Eslamifar1, Hamed Tavakoli2, Eiko Thiessen1

  • 1Institute of Agricultural Engineering, Max-Eyth-Straße 6, Kiel University, 24118 Kiel, Germany.

Sensors (Basel, Switzerland)
|November 13, 2025
PubMed
Summary

Near-infrared spectroscopy (NIRS) shows potential for on-site liquid manure analysis, accurately predicting dry matter (DM). Nuclear magnetic resonance (NMR) spectroscopy offers superior lab validation for chemical properties like total nitrogen (TN) and phosphorus (TP).

Keywords:
feature selection methodsliquid manuremachine learningnear-infrared spectroscopynuclear magnetic resonanceslurrytwo- and three-band indices

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Area of Science:

  • Agricultural Science
  • Analytical Chemistry
  • Spectroscopy

Background:

  • Accurate characterization of liquid manure properties (DM, TN, NH4-N, TP) is crucial for effective agricultural nutrient management.
  • Traditional laboratory methods can be time-consuming and costly for on-site analysis.

Purpose of the Study:

  • To investigate the potential of near-infrared spectroscopy (NIRS) for predicting liquid manure properties.
  • To compare the predictive accuracy of NIRS with nuclear magnetic resonance (NMR) spectroscopy.
  • To evaluate the impact of advanced spectral pre-processing and machine learning techniques on NIRS performance.

Main Methods:

  • 51 liquid manure samples were analyzed for reference properties using laboratory methods.
  • Samples were scanned using NIRS (941-1671 nm) and NMR spectroscopy.
  • NIRS data underwent pre-processing including two- and three-band index transformations and feature selection.
  • Partial least squares regression (PLSR) and LASSO regression were used to develop calibration models.

Main Results:

  • NIRS demonstrated fair predictive accuracy for dry matter (DM) (R² = 0.78, RPD = 2.15) using cohort-tuned models.
  • NMR spectroscopy provided superior accuracy for chemical properties: TN (R² = 0.89, RPD = 1.74), NH4-N (R² = 0.97, RPD = 5.70), and TP (R² = 0.95, RPD = 2.64).
  • Two- and three-band indices significantly improved NIRS performance, increasing R² by 34% for DM, 57% for TN, 25% for NH4-N, and 33% for TP.
  • Feature selection effectively reduced spectral dimensionality without compromising prediction accuracy.

Conclusions:

  • NIRS shows promise as a portable tool for on-site characterization of liquid manure, particularly for dry matter.
  • NMR spectroscopy remains the benchmark for accurate laboratory validation of chemical manure properties.
  • Combining NIRS with advanced pre-processing techniques enhances its utility for nutrient management applications.