Sample preparation - how critical are which mistakes

There are those happy users who dissolve their sample in the mobile phase and inject right away. If you are one of these and you also have isocratic conditions with acetonitrile/water, you can forget about sample preparation for now. There are however those users who need to quantify minor unknown impurities of a metabolized metabolite from bile fluid and others who hunt after heterocyclic sulfur-containing compounds in crude oil residue from Iran and compare it with Iraqi oil. They all have my sympathy. In the following table, a few typical errors occurring in a normal sample preparation are listed. 

Difficult to dissolve samples are acidified and/or heated and directly injected you should anticipate a precipitation since the stationary pha.se is a good solid cataly.st. Sample ad.sorbs irreversibly on glass container, stainless steel capillaries, filter, etc. 

Is the sample solvent. stronger than the mobile phase (e.g. higher amount of acetonitrile) Fronting, double peaks and retention time shift are po.ssible. 

Sample is dissolved in ultrasonic bath. Here, new solutes might arise, sample components might change (fomiation of radicals, thermal decomposition). 

Use acidic mobile phase and/or run your separation at elevated temperature Cool down, filter and only then inject Never inject a saturated solution  

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