The lipid method, being a RPC method that initiates in a mixture of aqueous and organic solvents, is well served by organic extracts of biological samples which again generally precludes issues with protein precipitation on-column. Furthermore, our experience shows that the presence of small molecules in the sample does not pose a risk to the analysis of lipids by RPC LC-MS, as the former are handily eluted from the column prior to lipid elution and do not contribute a matrix effect (note that this would not be true for other methods e.g. DIMS that are outside our platform and beyond the scope of this manuscript). It is therefore unnecessary to perform complex and laborious biphasic separations, although lipid extracts prepared as such can certainly be analysed by the method. Rather, protein precipitation with 2-propanol as a strong organic solvent capable of solubilising complex and neutral lipids, e.g. from their native structures in blood products, has proven a simple and effective method for preparing blood products and is generally extendable to other lipid-containing biofluids. Finally, depending on the sensitivity achieved by the ionisation and MS system used, samples may require greater or lesser dilution to ensure that the majority of analytes are well situated within the linear dynamic range of the instrument for a given method. Range and response assessment involving pilot sample sets and dilution series data from pooled representative samples can be a useful tool to guide the most appropriate sample dilution for a given LC-MS system (see more details of the quality control system below). 5