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ACD/Labs Blog

Arvin Moser
The line shape of a peak on a chromatogram can offer some insight into the presence of a functional group. However, issues with the instrument are also known to affect the line shape for a peak. The GC/MS EI+ Total Ion Chromatogram/Current (TIC) below shows five peaks. All of the peaks with the exception of...

Arvin Moser
In the constant pursuit of new pharmaceutical drugs, process chemists (sometimes referred to as medicinal or synthetic chemists) must investigate all impurities detected in a new drug manufacturing process. The chemist’s procedure is simple: identify, elucidate and synthesize each and every single impurity. The chromatogram (UV detector set at 254 nm) below shows three peaks....

Arvin Moser
With any type of data, there is an inherent risk of misinterpretation. My advice to elucidators is to consider multiple solutions and examine each one thoroughly. In the end, the answer to any problem set lies in tying together the bits of information in hopes of understanding the bigger picture. Recap of the problem: The...

Arvin Moser
Pattern recognition is an integral part of the process of structure elucidation. The quicker the elucidator can pick up on the pattern, the faster the elucidation can be accomplished and the less time wasted in elucidating the unknown. Recap of the problem: The ESI+ MS shows a single [M+H]+ at m/z 102 allowing a maximum carbon...

Arvin Moser
Whenever data appear to contradict each other, an instinctive reaction to this problem is to collect more data. Collecting more data can help to understand the problem and/or complicate the matter. Remember the model for Elucidation Evolution? Maximize data extraction (MDE) while minimizing data collection (MDC). Recap of the problem: The ESI+ MS shows a...

Arvin Moser
Structure elucidators will routinely use data from multiple techniques such as MS and NMR to build a proposed structure(s). When dealing with data from multiple techniques, the issue may arise that the data seem to contradict each other. In these cases, it is best to step back and re-evaluate the data from a different angle....

Arvin Moser
Tandem mass spectrometry involves the process of selecting and separating a product ion(s) (or daughter ion(s)) and fragmenting it in a second mass analyzer. This is commonly referred to as MS/MS or MS2. Additional tandem processes can be applied to ions in the MS/MS data to create MS3 data, and so forth. The metabolites A...

Arvin Moser
Peak matching involves the process of comparing spectral data from a parent or starting material to an unknown compound. (The unknown compound can be referred more specifically as the product, impurity, degradant, metabolite, etc.). The similarities between the data indicate regions that have not changed while the differences indicate regions of change. The full scan...

Arvin Moser
When you work on enough NMR datasets, eventually you will run into cases where peaks are overlapping. One approach is to apply a peak deconvolution (or fitting) algorithm in an attempt to separate out the contribution of each overlapping peak. The 1H NMR spectrum below shows a multiplet (dd) nearly buried by a large water...

Arvin Moser
In the blog series entitled Distinguishing Impurities, several types of NMR experiments were outlined to offer some insight into what to be on the look out for. Although there is no set guideline in this process, the best advice I may offer is to keep track of all the solvents, be aware of the possibility...