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   Home » Consumables & Supplies » Articles » Innovative Injection Port Septum Put to the Test
 
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Innovative Injection Port Septum Put to the Test
Innovative Injection Port Septum Put to the Test
10/23/2010

 by Douglas Tanner, Pawling Scientific Products, LLC

 

The o-ring design of the Cepure Zero molded injection port septum allows the needle to displace the septum but never pierce it.The Cepure Zero's molded injection port septum design allows the needle to displace the septum but never pierce it.

Because it never pierces the septum, the Cepure Zero outlasts conventional pierced septa by a wide margin and eliminates contamination from coring.
Figure 1. With patent-pending O-ring design of Cepure Zero molded injection port septum, needle displaces the septum but never pierces it. As a result, the new septum outlasts conventional pierced septa by a wide margin and eliminates contamination from coring.

The durability and bleed characteristics of injection port septa in gas chromatographs (GCs) can materially affect throughput and accuracy of results as well as the service life of the septum itself. The O-ring-designed Cepure Zero from Pawling Scientific Products is a new type of injection port septum. Both independent tests and user experience indicate longer life, elimination of septum coring, fewer needle problems and greatly reduced bleed than septa available today. The reduced bleed not only eliminates a major contamination source but can also shorten conditioning times upon startup.

 

Unique O-ring design eliminates piercing, coring

Unlike other septa, which are solid elastomers designed for repeated piercing, the Cepure Zero is built like a very fat O-ring (see Fig. 1) so the needle displaces but never pierces the septum material. Pressure from the mounting nut on the O-ring and the inherent elasticity of the septum elastomer combine to keep the aperture closed tight. The no-pierce O-ring design extends septum life and reduces or eliminates needle problems. Not having to puncture the septum means less wear and tear and elimination of a key system error source. Septum cores have been shown to adsorb analytes in the instrument’s inlet, leading to poor peak formation and ghost peaks.

Additionally, the aperture, when closed while under pressure, creates a self-guiding mechanism for the needle. Slight misalignments will get redirected and pass through the aperture.

The septum’s low-bleed characteristic arises from the combination of the basic material of construction along with proprietary processing. The elastomer is a low-bleed silicone containing minimal siloxane. The proprietary process, from blending and molding to inspection and packaging, includes several conditioning steps. This multiple-step process recognizes that the injection port septum can directly affect GC sample integrity.

Life-cycle tests predict five-fold gain

 

Despite the higher than normal 60-psi pressure differential across the septum, the seal remained as intact after the 1000th cycle as after the first.
Figure 2. Over all 1000 GC cycles with Cepure Zero septum in place, retention time remained constant at 0.406 min. This indicates that, despite the higher than normal 60-psi pressure differential across the septum, the seal remained as intact after the 1000th cycle as after the first. 
Source: EuTech Scientific Services, Morganville, NJ
Click here to enlarge.

Independent life cycle tests conducted by EuTech Scientific Services, Morganville, NJ, showed no failures, nor signs of deterioration, after more than 1000 injections at 400 C on an Agilent 6890 GC running ethanol scans. By contrast, typical service life for the top three septa average 200 to 300 piercings.

EuTech used three criteria to determine service life:

 

  • Deviation in retention time in the column. An increase in retention time indicates septum failure. 
    Finding: Over the 1000 cycles, retention time remained flat at 0.406 min, within a standard deviation of 0.005 min (see Fig. 2).
  • Pressure loss in the GC. A decrease in pressure would suggest leakage through the septum. Anticipating analysts’ natural concern about pressure loss through a septum with a hole already in it, EuTech used a 60-psi pressure differential across the septum for the entire test run. 
    Finding: EuTech observed no pressure loss in their system throughout the entire test (see Fig. 3). The aperture remained closed after every injection and during the analysis cycle.
  • Peak area decrease in the chromatogram due to sample loss. A decrease in peak area means loss of sample, which would indicate septum failure.
    Finding: Mean peak area showed no significant negative trend over the 1000 cycles (see Fig. 4).


20% lower bleed creates fresh options for volume GC work

Low-bleed components are necessary in today’s chromatography due to their ever-increasing sensitivity. The injection port septum is no exception. The lower the bleed, the fewer the error sources and ghost peaks, and the less downtime lost to septum conditioning. Principle sources of bleed are the volatile organics in the elastomer from which the septum is made.

 

Inlet flow pressure remained within spec through a 1000 cycle test.
Figure 3. Inlet flow pressure remained within spec through 1000 cycle test on Cepure Zero septum running in GC at 60 psi, 400 C.
Source: EuTech Scientific Services, Morganville, NJ

EuTech compared the bleed levels of the Cepure Zero septum and one of the top three low-bleed solid septa currently used in the market. The test method used was a thermal outgassing technique on a piece of septum material left in the inlet for 1 hour at 250 C. Thereafter, two consecutive chromatograms were run to see if the septum would continue to bleed. This protocol emulates the standard conditioning cycle after replacing a septum in the field.

 

The Cepure Zero sample generated a peak area of 2563 versus 3152 for the other leading septum. This is a 20% improvement over what is popularly regarded as the cleanest septum presently available. In practice, this advantage could be used to reduce the 1 hour conditioning time by 20% with every septum change-out and still maintain the same low level of bleed. Additionally, a 20% reduction in total bleed provides a greater confidence that chromatograms will be free from interfering peaks due to the septum.

 Peak area remained essentially constant over 1000 runs with the Cepure Zero.
Figure 4. Peak area remained essentially constant over 1000 runs in a GC column equipped with new Cepure Zero injection port septum. 
Source: EuTech Scientific Services, Morganville, NJ
Click here to enlarge.

ILE reports “orders of magnitude” cleaner septum

One of the earliest users of the new Cepure Zero septa is Rob Wohleb, Ph.D., who founded Wohleb Scientific. These days, he is head of ILE, Inc., which specializes in improved sample preparation methods and tools for GC work, mainly in environmental bioanalytical testing. He recognizes that most errors in GC analyses originate in sample preparation, and focuses on eradicating them.

The company typically runs about 20 single-ion analyses a day, looking for particular organics. “It’s not high volume repetitive work; rather it’s high sensitivity work with very high stakes,” explains Dr. Wohleb. “Those GC results influence the design of our sample handling products, which in turn influence the results of thousands of GC practitioners.”

Earlier beta tests

Before standardizing on the Cepure Zero, ILE ran its own bleed tests, comparing the Cepure Zero septum with one of the other top three conventional flat septa. They placed each septum in a 10-ml conical-bottom reaction vial with 500 uL of redistilled acetone. They then sealed the samples in vials with PTFE-lined caps and agitated the sample for 1 hour with a wrist shaker. At that point, 1 uL of each extract was analyzed by GC-MS. Results are shown in Fig. 5. “The Cepure Zero septum is the cleanest I’ve seen – orders of magnitude cleaner than the previous one,” states Wohleb.

 

 Recent chromatograms show order-of-magnitude lower bleed in Cepure Zero septum versus another “top three” septum.
Blue trace represents the “top three” septum. Green line, barely visible along the axis, represents Cepure Zero.
Figure 5. Recent chromatograms from early user ILE, Inc. show order-of-magnitude lower bleed in Cepure Zero septum versus another “top three” septum specifically billed as “Low Bleed.” Blue trace represents the “top three” septum. Green line, barely visible along the axis, represents Cepure Zero.
Source: ILE, Inc., Ferndale, CA
Click on an image to enlarge.

He adds that a clean septum is especially important in low volume GC work because it eliminates the need for purging after the unit has stood idle for a period of time. “Most septa have a habit of loading up when the instrument stands idle,” he says. “Even when unpurged before daily startup or after an extended idle period, the Cepure Zero Septum contributes zero background noise.”

 

As to the life-cycle issue, after three months of operation, ILE analysts have seen a couple of positive signs. “We haven’t run long enough to reach an end point; however, so far we have seen absolutely no signs of deterioration and no needle hang-ups, syringe problems or coring. With the other septum, we averaged one or two such problems each month.”

During the earlier development stages of Cepure Zero, Wohleb’s company at the time, Wohleb Scientific, served as a beta-site host.

Other early users report similarly cleaner operation and complete elimination of needle coring. High-volume users also report higher throughputs due to less purging downtime and no stretch-outs of reaction time due to analyte adsorption onto septum cores. As to service life, it is too early to tell, but anecdotal feedback points to at least five times the “mileage” of other leading septa. There have been no negative reports.

Availability

Cepure Zero injection port septa are available from Pawling Scientific Products LLC in commercial quantities in 9-mm and 11-mm standard sizes. They come in 50 or 100 unit packets, preconditioned and ready to use as drop-in replacements on all popular GCs. Cepure Zero is packaged in EPA-precleaned jars with PTFE-lined closures and extraction packets to further reduce contamination. To order or for more information, go to www.cepure.com

For more information on the technology discussed in this article, visit www.pawling.com or www.cepure.com.

Pawling Scientific Products, LLC
157 Charles Colman Blvd.
Pawling NY 12564
Phone: 845-855-1000
Fax: 845-855-1139
http://www.cepure.com

 
 
 
 
 
 
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