Why do GC Capillary Connections Leak?
The 3 Leading Causes of Column Leaks
Among some chromatographers, capillary connections using press fit connectors have a reputation for leaking. Where there was a time when this was true, that time has past. InnovaQuartz collected and studied leaks from the field for a period of three years; 28 of the leaks were in our own products (of over 1,000,000 sold in that same period) and most of those were Y-splitters. We found that 98+% of leaks in press fit connections arise from three classes of problems, all of which may be addressed by a correctly designed connector:
Less than perfectly flat and square (normal to the axis) column ends (including chips on the column end face)
Damaged or missing polyimide coating (the brown plastic coating on capillary)
Cracked column ends
Prior versions of press fit connectors, even ours, were not thoughtfully constructed. They were made to work with best case scenario column cuts but failed in the real world where column cuts are rarely perfect.
The Press2Fit™ Solution
First we tried to fix the capillary. We built a draw tower and drew some fantastic materials, but it cost too much. (See chromatographyonline for an archive paper on the subject: "Fused Silica Capillary -- The Story Behind the Technology".)
That solution having gone bust, we realized that we could upgrade our manufacturing equipment to produce press fits that would not have leaked in the vast majority of the failures we’d studied -- designed for an imperfect world.
The reason all of the studied leaks occurred was that a defect was bigger than the seal was wide. Seals in standard press fits are only about 0.05 to 0.01mm wide, as shown in the photo. Any irregularity that extends beyond this very narrow region has a potential of leaking.
The obvious fix for all of these problems is to make the seal wider so that is just what we did….
It all in the angles
By lowering the angle of the restriction, we increased the contact area between the column and the union and increased the compression of the polyimide: the seal got much wider. (This also explains why Y-splitters leaked more often than unions: the Y restriction had to be several millimeters shorter than in unions to accommodate the bend and weld zone, so the angles were higher and the seals were narrower. Our new Y-splitters take this into consideration and compensate with slightly longer legs and a far smaller weld region than before, with lower dead volume as a bonus.