Internal Reference
Internal Reference - Related Videos
01:17
Chemical Shift: Internal References and Solvent Effects
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2024
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...
01:23
Reference & Citation Tools in Practice
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2026
Citations play a key role in academic writing by documenting the evidence that supports scholarly claims. Beyond giving credit to original authors, they show engagement with existing research and strengthen the credibility of an argument. Effective citation practices are central to research literacy because they reflect a writer’s ability to locate, evaluate, and integrate reliable sources into their work. Digital Tools for Citation Management Advances in digital technology have simplified the...
16:11
Implementation of a Reference Interferometer for Nanodetection
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2014
A reference interferometer technique, which is designed to remove undesirable laser jitter noise for nanodetection, is utilized for probing an ultra-high quality factor microcavity. Instructions for assembly, setup, and data acquisition are provided, alongside the measurement process for specifying the cavity quality factor.
09:18
Internal Standards
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2023
Source: Laboratory of Dr. B. Jill Venton - University of Virginia The goal of many chemical analyses is a quantitative analysis, where the amount of a substance in a sample is determined. In order to accurately calculate the concentration of an unknown from a sample, careful sample preparation is key. Every time a sample is handled or transferred, some of the sample can be lost. There are strategies however, for minimizing sample loss. There are also strategies for coping with sample loss and...
02:00
Internal Energy
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2020
The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with initial internal energy, Uinitial, undergoes a change in energy (transfer of work or heat), and the final internal energy of the system is Ufinal. Change in internal energy equals the difference between Ufinal and Uinitial. Although the values for Ufinal and Uinitial cannot be determined for a system, the first law of thermodynamics only...
FAQs
The reference provides a stable basis for comparing signals or measurements within the same sample. Because it is introduced directly into that sample, its response reflects the measurement conditions experienced by the analyte. This helps account for variations in sample volume, instrument response, and other conditions that could otherwise make comparisons less reliable.
A characteristic chemical shift gives the reference signal a known position on the NMR scale. Other resonances can then be reported relative to that signal rather than relying only on instrument settings. This creates a consistent framework for interpreting spectral positions and supports structural identification by making chemical-shift comparisons more meaningful.
When the reference has a known amount, its signal can be compared with analyte signals through integration, which measures the area under each resonance. Comparable measurement conditions allow the relative signal areas to support quantitative assessment. This approach is useful when determining amounts or evaluating composition, provided the relevant signals are integrated under comparable conditions.
Direct introduction into the sample allows the reference to experience the same sample volume and instrument response as the material being analyzed. Its signal therefore supplies an internal comparison point rather than an external benchmark. This can improve accuracy when measurement conditions vary and helps distinguish chemical differences from changes caused by the analytical setup.
The reference is added directly to the sample before measurement. Its signal is then located at the characteristic chemical shift, and other resonances are reported relative to it. If quantitative information is needed, the reference and analyte signals are integrated under comparable conditions, allowing their measured areas to be compared with the reference amount.
They are useful when analysts need a consistent basis for structural identification, purity assessment, reaction monitoring, or quantitative analysis. In NMR, the reference supports chemical-shift reporting and signal comparison. More broadly, its known amount and direct presence in the sample can help make measurements more consistent across changing sample volumes or instrument responses.