Related Experiment Video
Updated: Jun 3, 2026
05:59
New Framework for Understanding Cross-Brain Coherence in Functional Near-Infrared Spectroscopy (fNIRS) Hyperscanning Studies
Published on: October 6, 2023
Two-dimensional correlation analysis and waterfall plots for detecting positional fluctuations of spectral changes
Soo Ryeon Ryu1, Isao Noda, Chang-Hee Lee
1Department of Chemistry, and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chunchon 200-701, Korea.
Applied Spectroscopy
|March 15, 2011
Summary
Waterfall plots can be unreliable for detecting spectral band shifts. Two-dimensional (2D) correlation spectra, specifically the asynchronous butterfly pattern, offer a more effective method for distinguishing band shifts from overlapped bands.
Area of Science:
- Spectroscopy
- Chemometrics
- Data Analysis
Background:
- Waterfall plots are commonly used for spectral analysis.
- Distinguishing real band shifts from overlapping bands is crucial in spectroscopy.
- Various advanced waterfall plot techniques exist, including MW2D, PCMW2D, and MWPCA2D.
Purpose of the Study:
- To evaluate the effectiveness of different waterfall plot techniques in identifying spectral band position shifts.
- To compare the performance of waterfall plots with conventional two-dimensional (2D) correlation spectra.
- To determine the most reliable method for differentiating between actual band shifts and the presence of two overlapped bands.
Main Methods:
- Simulated spectral datasets were analyzed using conventional waterfall plots, 2D gradient maps, MW2D, PCMW2D, and MWPCA2D.
- Results from waterfall plots were compared with conventional 2D correlation spectra.
- Experimental data, including temperature-dependent IR spectra of ethylene glycol and FT-IR spectra of acetone in a mixed solvent, were analyzed.
Main Results:
- Different waterfall plots exhibited varying capabilities in differentiating frequency shifts from overlapped bands.
- Conventional 2D correlation spectra clearly distinguished between band position shifts and overlapped bands through characteristic cluster patterns.
- Experimental analysis showed that waterfall plots could not unambiguously differentiate between real band shifts and overlapped bands.
Conclusions:
- Waterfall plots have limitations and can be ambiguous in detecting band shifts.
- Two-dimensional correlation spectra provide clearer differentiation between band shifts and overlapped bands.
- The presence or absence of the asynchronous 2D butterfly pattern is the most effective diagnostic tool for band shift detection.
Related Concept Videos
01:08IR 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...
01:192D NMR: Heteronuclear Single-Quantum Correlation Spectroscopy (HSQC)
Heteronuclear single-quantum correlation spectroscopy (HSQC) is a 2D NMR technique that reveals one-bond correlations between hydrogen and a heteronucleus. The HSQC experiment is similar to the heteronuclear correlation experiment (HETCOR) but is more sensitive. In the HSQC spectrum, the proton chemical shift is plotted on the horizontal F2 axis, while the 13C chemical shift is plotted on the vertical F1 axis. The corresponding proton and 13C spectra are also shown. The HSQC contour plot does...
01:182D NMR: Overview of Heteronuclear Correlation Techniques
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 axis.
01:02¹H NMR: Interpreting Distorted and Overlapping Signals
Spin systems where the difference in chemical shifts of the coupled nuclei is greater than ten times J are called first-order spin systems. These nuclei are weakly coupled, and their chemical shifts and coupling constant can generally be estimated from the well-separated signals in the spectrum.
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
01:162D NMR: Overview of Homonuclear Correlation Techniques
Homonuclear correlation spectroscopy (COSY) is a powerful technique used in Nuclear Magnetic Resonance (NMR) spectroscopy to study the correlations between nuclei of the same type within a molecule. It provides information about scalar couplings between adjacent nuclei, which helps determine connectivity and structural information. There are several COSY variants, each with its unique strengths and experimental parameters.
COSY90 is the standard two-dimensional (2D) COSY experiment that...
COSY90 is the standard two-dimensional (2D) COSY experiment that...
01:062D NMR: Homonuclear Correlation Spectroscopy (COSY)
Homonuclear correlation spectroscopy, or COSY, is a 2-dimensional NMR technique that provides information about coupled protons. Typically, the geminal and vicinal coupling are observed. For example, consider the COSY spectrum of ethyl acetate, where its 1D proton NMR spectrum is plotted along the vertical and horizontal axes with their corresponding chemical shift scale. Three spots on the diagonal corresponding to the three peaks in the 1D proton spectrum are called diagonal peaks. The COSY...