Performance Comparison of TDS3 Storage Containers to Swagelok Fittings and Glass Storage Containers

By: Kristen Schultz,Jamie Brown, Reporter US Volume 28

Kristen Schultz and Jamie Brown

Kristen.schultz@sial.com

Introduction

The typical analytical process for air sampling using thermal desorption tubes almost always involves shipping and storing the sampling tube before and after sampling prior to analysis. The most common approach to preventing contamination of the tube during shipment and storage has been to attach Swagelok end-cap fittings, using PTFE ferrules to both ends of the tubes before and after sampling. Another common technique is to place the sampling tube in a glass vial-like container, constructed to seal at one end with a Teflon®-faced screw cap.


Figure 1. TDS3 Container with Carbotrap 300 Glass-Fritted TD Tube

The clear body of the TDS3 is shorter than the actual tube (as shown), so the septa seals on the end of the thermal desorption tube, creating an air-tight seal.


The TDS3 (Thermal Desorption Storage & Sampling System) offers advantages over both the Swagelok end-cap fittings and glass storage containers because it is designed to eliminate internal dead volume, minimize the area of migration of the sample from the adsorbent during the storage period, and eliminate breakage risks when shipping and handling in contrast to glass storage containers bearing this same risk. The TDS3 storage container holds the tube in its hard polycarbonate shell and seals with inert end-caps fitted with Teflon-faced silicone septa that are easily replaced. This eliminates the need for extensive cleaning or thermal conditioning of the device before it can be used for storing another tube.

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Experimental

The performance of the TDS3 storage container was measured by its effectiveness for storing a collected sample relative to Swagelok end-cap fittings and glass storage containers.

A mix of twelve analytes were spiked onto twelve Carbotrap 300 thermal desorption tubes (6 mm O.D x 4 mm ID x 11.5 cm L), containing three carbonaceous adsorbents: Carbotrap C, Carbotrap B, and Carbosieve S-III. The sampling tubes were spiked with 40 ng of each analyte in 0.2 μL of methanol, using flash vaporization and 0.5 liters of inert nitrogen (50 mL/min for 10 min) to transfer the vaporized analytes onto the sampling tube.

The twelve tubes were assigned to three sets, each stored in a different storage device. Tubes in Set One were stored in TDS3 storage containers, Set Two were fitted with brass Swagelok nut and end-cap fittings, using PTFE ferrules; and Set Three were stored in a threaded glass vial-type container which seals with a Teflon screw cap at one end.

After spiking, the tubes were quickly sealed and placed in a paint can (all tubes in the same can) containing a small amount of activated charcoal and placed in a laboratory freezer for 14 days at -24 °C. After 14 days, the samples were removed from the paint can and thermally desorbed to a gas chromatograph.

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Results

Percent recoveries in Table 1 were calculated by comparing peak areas for the desorbed analytes to those for calibration standards spiked onto the Carbotrap 300 tubes in the same manner on the day of analysis. Values shown are means for the three samples. Area counts for the first six listed compounds were normalized to an internal standard, bromodichloromethane; the last six compounds were normalized to 1,3-dichlorobenzene.


Table 1. Recovery of Analytes Stored for 14 Days

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Conclusion

The results in Table 1 demonstrate that the TDS3 storage containers are equivalent to both Swagelok end-cap fittings and glass storage containers in terms of sample stability during storage.

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