This report describes the manufacturing, the working and results of preliminary applications of a home-built electrospray ionisation source. The source was constructed for a quadrupole mass-spectrometer (MS) (Finnigan 4000). The elements of the source and interface are: a micro needle at high potential to the capillary, a capillary for transport of the ions and a sampling orifice (skimmer) to the mass analyser and detector. That interface enables the transport of ions from atmospheric pressure to the required high vacuum in the mass analyser as well as an appropriate focussing of ions corresponding. The design concerns the physical dimensions of the different parts and the electrical potentials. The results show that the electrospray process, the transport and the focussing operate satisfactorely. The highest sensitivity was measured for Gramicidin S (polypeptide, MW 1141 Dalton) of about 10 femtomol. For substances with a lower molecular weight the sensitivity was much lower and ranged from about 100 fmol for the polysaccharide streptomycin (MW 581 Da) to 50 pmol for polar low MW herbicides glyfosate and glufosinate. It seems useful to construct an extra focussing device between the skinner and the analyser to enhance the transmission efficiency for the low molecular weight species (<400 Da).