Reference standard for chemical shift

The individuation of a suitable reference standard to determine chemical shift is an inconvenience for many nuclei, but in the case of 33S it is a serious difficulty. Indeed, there is an unfortunate lack of standardization in the choice of reference compounds, which often makes it difficult to compare different data in the literature. 

Many compounds have been used as reference standards, including CS2, some inorganic sulphates in aqueous solutions at different concentrations and 

In this work, all chemical shifts have been referred to SO4, if not otherwise specified. Chemical shifts reported in the literature and referred to CS2 or 

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