Construction and Design

The main part of a NANOES source is the conductively coated spraying capillary, which is placed inside the spraying field. The capillary position had to be chosen as far away as possible from the standard spraying tip to reduce the field disruption caused by the existing source equipment. Furthermore, the new source itself had not to interfere with the spraying field of the standard ES. To assure a fast change between both sources, the NANOES source was placed inside the source housing. The design of the ES source and the source housing allows a rapid change between both sources by adjusting the position of the spray arm using the $xyz$-manipulator.

Figure 3.7: Construction of the NANOES capillary holder. The holder is made from a conducting material (brass) and fits on top of the spray arm of the standard ionspray source. The capillary holder which places the capillary in the correct postion is coloured yellow, the capillary purple. The lower image shows the NANOES source mounted to the spray arm of the IonSpray source. (CAD drawing realised by THOMAS ZINK)

A schematic drawing of the capillary holder is displayed in figure 3.7. The complete source modification is made from a conducting material (brass) to ensure power supply from the spray arm to the capillary. The modification consists of two parts; a holder mounted to the spray arm (brown and green) and a rod with a hollow end (yellow) which receives the capillary (purple). To adjust the capillary position, the rod may be rotated and the position can be fixed with a nut. The capillary is fixed inside the rod with a screw, which also ensures a conducting connection between the capillary and the source construction.

Using the $xyz$-manipulator of the source housing, it is possible to position both the NANOES capillary and the standard ES spraying tip in the correct position for spraying. Moreover, the source can be changed quickly, even during a sample run [44,48]. The capabilities of this source regarding the special properties of a NANOES source (low sample flow rate, spraying from aqueous solutions) were investigated using different samples. On-line reaction monitoring (see 3.2) was performed using buffered substrate solutions. The low flow rates obtainable provide a virtually unlimited time for MS/MS experiments, even with very low sample amounts. This characteristic was applied to elucidate metabolite structures of several antioxidant compounds[46,47,77] and to identify phenolic compounds[68]. Furthermore, it was possible to monitor on-line the decay of certain anthocyanidins under almost physiological conditions[45].

In contrast to existing NANOES sources, no gas supporting the spraying process is needed and the spraying tip is placed at a distance of approximately 10 to 20 mm (compared with only a few millimetres in other sources). However, the applied spraying voltage is significantly higher and resembles the voltage used in standard ES, by what the applied spraying field is comparable with other NANOES sources.