have been provided with a charge tag and shortened by photocleavage can be measured from the reaction batch without further cleaning because the sensitivity has been increased by a factor of 100 first of all the selection primer pair or primary primer pair for amplifying the dna product by pcr is again selected so that the corresponding product from pcr amplification contains the mutation site the extension primers or secondary primers are then determined it must be possible for them to be attached next to the possible mutation site they contain a chain of 10 to 20 standard nucleotides at the 5 u2032 position after that a photocleavable linker according to the invention and approximately 3 to 7 phosphorothioate nucleotides up to the 3 u2032 position after the dna target sequence has been amplified by pcr the remaining dntps are removed by enzymatic digestion and the digestion enzyme is thermally deactivated extension primers ddntp terminators a suitable dna polymerase such as thermosequenase and a buffer which is adjusted to the enzyme are added specific primer extension is carried out in a temperature cycle which is repeated several times u03b1 thiodideoxynucleoside triphosphates u03b1 s ddntps are preferred for the extension next the phosphorothioate compounds are neutralized by alkylation after the solution has been applied to the support plate coated with the matrix this is radiated with uv light whereupon the photocleavable linker breaks due to the linker breaking a.