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Related Concept Videos

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations01:08

IR Spectrum Peak Splitting: Symmetric vs Asymmetric Vibrations

Identical bonds within a polyatomic group can stretch symmetrically (in-phase) or asymmetrically (out-of-phase). Similar to hydrogen bonding, these vibrations also influence the shape of the IR peak. Generally, asymmetric stretching frequencies are higher than symmetric stretching frequencies. For example, primary amines exhibit two distinct IR peaks between 3300–3500 cm−1 corresponding to the symmetric and asymmetric N-H stretching, while secondary amines exhibit a single stretching vibration...
¹³C NMR: ¹H–¹³C Decoupling01:04

¹³C NMR: ¹H–¹³C Decoupling

The probability of having two carbon-13 atoms next to each other is negligible because of the low natural abundance of carbon-13. Consequently, peak splitting due to carbon-carbon spin-spin coupling is not observed in spectra. However, protons up to three sigma bonds away split the carbon signal according to the n+1 rule, resulting in complicated spectra.
A broadband decoupling technique is used to simplify these complex, sometimes overlapping, signals. Broadband decoupling relies on a...
Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule01:10

Interpreting ¹H NMR Signal Splitting: The (n + 1) Rule

In the AX proton spin system, proton A can sense the two spin states of a coupled proton X, resulting in a doublet NMR signal with two peaks of equal (1:1) intensity. When proton A is coupled to two equivalent protons (AX2 spin system), the spin states of each X can be aligned with or against the external field, creating three possible scenarios. This results in a 1:2:1  triplet signal, where the central peak corresponds to the chemical shift of A and is twice as large or intense as the others.
IR Spectrometers01:25

IR Spectrometers

There are two main infrared (IR) spectrophotometers: dispersive IR spectrometers and Fourier transform infrared (FTIR) spectrometers. In a dispersive IR spectrometer, a beam of infrared radiation produced by a hot wire is divided into two parallel equal-intensity beams using mirrors. One beam passes through the sample, while another is a reference beam. The beams then move through the monochromator, which separates the radiations into a continuous spectrum of different frequencies. The...
Two-Dimensional (2D) NMR: Overview01:12

Two-Dimensional (2D) NMR: Overview

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.
NMR Spectrometers: Resolution and Error Correction01:14

NMR Spectrometers: Resolution and Error Correction

When magnetic nuclei in a sample achieve resonance and undergo relaxation, the signal detected in NMR is an approximately exponential free induction decay. Fourier transform of an exponential decay yields a Lorentzian peak in the frequency domain. Lorentzian peaks in an NMR spectrum are defined by their amplitude, full width at half maximum, and position, where the peak width is governed by the spin-spin relaxation time alone. In real experiments, however, the applied magnetic field is rendered...

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O-cresol Concentration Online Measurement Based On Near Infrared Spectroscopy Via Partial Least Square Regression
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O-cresol Concentration Online Measurement Based On Near Infrared Spectroscopy Via Partial Least Square Regression

Published on: November 8, 2019

[A simple and convenient standardization algorithm of NIR spectra].

Xin Bao1, Lian-Kui Dai

  • 1National Key Lab of Industrial Control Technology, Zhejiang University, Hangzhou 310027, China.

Guang Pu Xue Yu Guang Pu Fen Xi = Guang Pu
|July 16, 2008
PubMed
Summary
This summary is machine-generated.

This study introduces a new algorithm for standardizing near-infrared (NIR) spectra, improving model transfer across different instruments. The novel spectra standard error (SSE) metric effectively evaluates algorithm performance, simplifying spectral analysis.

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A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy
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A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy

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O-cresol Concentration Online Measurement Based On Near Infrared Spectroscopy Via Partial Least Square Regression
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Published on: November 8, 2019

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Area of Science:

  • Analytical Chemistry
  • Spectroscopy
  • Chemometrics

Context:

  • Near-infrared (NIR) spectral analysis model transfer is limited by current algorithms.
  • Developing robust and transferable spectral analysis models is crucial for various industries.
  • Instrument-to-instrument variability poses a significant challenge in spectral data analysis.

Purpose:

  • To propose a simple and convenient algorithm for standardizing NIR spectra.
  • To introduce a new performance index, spectra standard error (SSE), for evaluating model transfer algorithms.
  • To optimize spectral standardization parameters, including wavelength range and Savitzky-Golay smoothing window width.

Summary:

  • A novel algorithm combining Savitzky-Golay smoothing, standard normal variate (SNV) standardization, and polynomial filtering was developed.
  • The algorithm effectively corrects baselines, reduces noise, and standardizes spectra for improved model transfer.
  • The spectra standard error (SSE) metric, defined as the ratio of J2 to J1, quantifies the success of spectral standardization.

Impact:

  • The new algorithm significantly reduces SSE, from 1.418 to 0.167 for gasoline samples, demonstrating its effectiveness.
  • This method eliminates the need for extensive sample collection or measuring all training samples on multiple instruments.
  • Enables more reliable and efficient spectral analysis model transfer, reducing costs and complexity.