General Purpose, Low Pressure, and SPME Microseals
Wiper rib
Spring
Injection port
septum cup
Duckbill
Valve
O-rings make sliding seal around needle
O-rings
Needle forces duckbill valve open
Microseal nut
Merlin Microseal
Syringe needle
Microseal Injection Sequence
Microseal Cut-Away Views
General Purpose and SPME Microseals
Dust wiper rib
O-rings seal needle
during injection
Duckbill opens easily,
seals reliably
Spring
O-rings
Duckbill
Spring
Low Pressure Microseal
Introduction
The Merlin Microseal
TM
is a microvalve alternative to the
conventional silicone rubber septa used in gas chromatography
(GC). Its unique design gives it high pressure capability and
resistance to wear which results in long life and excellent
chromatographic performance. The Microseal is available in three
versions for all major GC manufacturers’ instruments.
How the Microseal Works
A GC injection port septum performs two discrete functions.
It seals the port while the syringe needle is inserted and also
while the needle is not inserted. The Microseal is distinct from
traditional septa in that the Microseal has two independent sealing
mechanisms to perform these functions. O-rings seal the syringe
needle during sample injection. Aduckbill valve seals the injection
port during analysis, but allows the needle to slide through without
damage. In contrast, a conventional septum is repeatedly pierced
by the syringe needle and eventually leaks or sheds septum
particles into the injection port liner.
Because the two seals perform separate, individual functions
and are only slightly distorted in operation rather than being
pierced, the Microseal can be made from a high-temperature,
wear-resistant fluorocarbon elastomer. In combination with the
cone-tipped needle, this means the Microseal will not shed pieces
into the injection port, even after thousands of injections.
The cut-away views show the location of the individual seals
and the diagram at the lower right illustrates the following
sequence of Microseal functions.
1. Pressure in the injection port, aided by a stainless steel
spring, squeezes the duckbill closed and maintains a tight
seal on the port. Higher pressures seal it more tightly.
2. As the syringe needle enters the Microseal, the wiper rib
removes any particles adhering to the needle.
3. The O-rings then make a sliding seal around the needle.
4. As the needle penetrates further, the tip pushes the duckbill
valve open and slides into the injection port. The O-rings
maintain the seal around the needle.
5. As the needle is withdrawn from the Microseal after sample
injection, the spring pushes the duckbill valve closed before
the needle leaves the O-rings. The port remains sealed
during the injection process.
Choosing a Microseal
Three versions of the Microseal are available.
General Purpose Microseal (P/N 410)
- Formerly known as the
“High Pressure Microseal,” this Microseal is recommended for
use in most GC applications with injection port pressures between
3 and 100 psi (20 - 690 Kpa). The General Purpose Microseal is
the best choice for most GC applications.
Special purpose Microseals are also available for for low inlet
system pressures and solid phase microextraction (SPME).
Low Pressure Microseal (P/N 310)
- Formerly known as the
“Original Microseal,” this is recommended for injection port
pressures between 1 and 45 psi (7 -310 Kpa). Particularly useful
for fast GC/MS applications with 530 micron columns. The Low
Pressure Microseal is made from a softer elastomer and does not
have the needle wiping rib.
SPME Microseal (P/N 21-01)
- This Microseal was developed
with a stiffer elastomer specifically for 23 gauge SPME probes,
which have a square end instead of the cone shaped tip
characteristic of syringe needles. These probes can cause additional
wear and this version provides extended lifetime for SPME.
Microseal User Manual