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ACD/Labs Blog

Arvin Moser
A previous blog described how a sodiated ion peak can be used to locate or calculate the molecular ion for an unknown compound. In a similar fashion, the dimer ion peak can be used to identify the mass of the unknown even if the molecular ion is no visible. The ESI+ MS data below shows...

Arvin Moser
In addition to using chemical shift information to ascertain a carbon’s proton count (i.e. C, CH, CH2 or CH3), 13C NMR experiments can be set up in a variety of ways to assist with this process. The following simulated spectra compare a variety of 13C NMR experiments for aspartame. Please note that there are variations...

Arvin Moser
When presented with an NMR dataset, a highly-experienced elucidator can interpret the dataset without any direct need to do peak picking, integration and multiplet analysis through software. (This may not be the case every time as severe peak overlap can complicate matters.) In essence, this NMR interpretation skill equates to speed reading and can be...

Arvin Moser
A previous blog described the Internet as a valuable tool in searching for previous work based on a molecular formula. In addition to searching the Internet “directly”, certain online sites can assist and facilitate the search process. Some of these sites are free while others have a fee. Be aware that the Internet is full...

Arvin Moser
Searching for unknowns across an internal library or database can serve as a major time saver. A more accessible database is the Internet. Many chemists and elucidators search the World Wide Web using a mass, a molecular formula or a fragment. Be aware that proprietary data sent over the Internet runs the risk of being...

Arvin Moser
In a previous blog, the atoms C, H, O, and N were limited to a specific range, 0-50, 0-100, 0-10 and 0-10, respectively. Starting from a wide atom count range ensures molecular formulae are not overlooked. The ranges for the atom count can be restricted further using additional information such as NMR, IR, etc. A...

Arvin Moser
With a monoisotopic mass identified from a mass spectrum, the next step is to fit a molecular formula (or elemental composition) to the unknown. For organic compounds, the starting elements of choice are Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulfur. Information from starting material and known derivatives can also help when deciding what elements and...

Arvin Moser
Depending on sample preparation, adduct ions can be present on a mass spectrum. The goal of the elucidator is to identify whether an adduct ion(s) is present and its contribution to the mass (or elemental composition) of the unknown compound. The example ESI+ mass spectrum below exhibits 2 ion clusters at m/z 951.305 and 973.287,...

Arvin Moser
With a well-tuned and calibrated, high resolution MS instrument, a molecular formula(e) can be devised from the m/z for an ion peak. In cases where more than one molecular formula fits, knowing the accuracy of the MS instrument can help in narrowing down the choices. The first step is to identify the molecular ion peak...

Arvin Moser
When interpreting data from a 1H-13C HMBC without a high-resolution 1D 13C NMR, there is the possibility to miss coincidental overlapping carbons. As such, always consider a missing carbon or two as part of the structure elucidation for an unknown. The 1H-13C HMBC below—note the lack of a high-resolution 1D 13C NMR spectrum—exhibits a 2-3J...