Flavonoids are water-soluble plant pigments, which are proven to have antioxidant properties and therefore possible health benefits. In an average diet, containing vegetables and fruit, 1g of flavonoids are consumed every day. Whether this is enough, taken their poor absorption rate into account, to have a positive impact on our well-being is still in debate. Today there is no standardised method for analysing flavonoid concentration in human plasma and this study aims to contribute with a possible standardised analytical method using GC-MS/MS. The method was developed using reference compounds for optimising a temperature program and to identify specific mass transitions for detecting phenolic compounds. The method was finalised by analysing plasma from volunteers, to ensure qualitative and quantitative analysis were possible with the developed method. In conjunction with developing the method, a trial was conducted to see if consuming berry juice increased the plasma levels of flavonoids. The results from the trial did not show a significant increase in the overall flavonoids concentration in plasma, but due to the small amount of human test subjects, a larger and controlled study is proposed. However, the analysis did show that the developed method is reliable when it comes to detecting a large number of polyphenols in plasma. To confirm the reliability of the quantitative data further method validation is suggested.