Versatile sampling system
for gas chromatography
IMT is specialized in sample preparation of Volatile Organic Compounds (VOC) and offer a well proven and reliable solution for ultra low trace GC-MS analysis. The "purge-and-trap" system VSP4000 is characterized by carry-over free long therm results based on the unique "in-vial" purging without a purge vessel. The system has certain advantages in the analysis of water.
- Features and advantages
- Principle and flow chart
- Conventional techniques vs. "in vial purging"
- Peltier cryo focussing of the micro-packed trap at - 35°C
- Available water traps
- Analytical performance in the mode purge-and-trap
- Option: thermal desorption up to 280°C
- Analytical performance in the mode thermal desorption
- Option: Tedlar-Bag sampling
- Technical data
- ultra trace analysis of volatile organic compounds (VOCs) with detection limits in the lower ppt-range (ng/kg)
- best performance for the European water standard EN ISO 15680
- unique "in vial purging" - no glass sparkler - no blank runs - no hot water rinse
- 80 vials, 20ml; multi matrix system for liquid, solid and mixed samples (drinking water, surface water, ground water, wastewater, foil, paper, soil, flavor, cosmetics, food, spices, ...)
- one type of micro packed trap for all polar and non polar substances - no multiple beds of various sorbent materials
- integrated Peltier cryo-trap at - 35°C, holds even dichlorodifluoromethane
- automatic dosing of gaseous or liquid Internal Standard via sample loop
- temperature of all components in the purge-and-trap mode up to 200°C
- split-flow up to 50 ml/min by a massflow controller
- for all capillary columns with an inside diameter of 0.15 to 0.53 mm
- control of the system parameters by: optical foam sensor, EPC, MFC
- high sample throughput with low personal costs guarantees a fast amortization of investments
- compact and reliable purge and trap system - 100% "Made in Germany"
Principle and flow chart
The sophisticated concept allows for the first time - without any
purge vessel - a direct purging of volatile substances from 20 ml
vials, which can be filled with solid or liquid samples and optional
from thermal desorption tubes. In the purge-and-trap mode, each vial is
moved into a heated sample unit, where a long and a short needle
penetrates the sealing septum. All volatile substances are purged and
enriched in the micro-packed trap. The purged water is seperated
from the sample in a Peltier or membrane water trap. The purged
substances are froozen out
by a Peltier cooler at -35°C and finally transferred by fast thermal
desorption to the gas chromatograph. The cooling temperature at
-35°C is necessary to hold all analyts on the trap during purging
process. By use of a sample loop, additionally internal standards or
regents can be added to the sample vial. After processing a sample, the
needles and the watertrap are backrinsed with carrier gas, impurities
and water are removed securely from the system.
The inert sample pathway and the absence of a glass sparkler guarantees very low detection limits and nearly no carryover.
Conventional techniques vs. "in vial purging"
The following figure shows the gas flow of the conventional technique and the "in vial purging" of the VSP4000. The analytical advantages during the purging process are evident.
Due to the "in vial purging" of the VSP4000 system combined with inert analytical tubing material and without using a glass sparkler, the system archives an excellent performance in the lower ppt range with very low carryover and typical standard deviations less than 5% - even years later.
The system performance and low detection limits attainable with the VSP4000 are particularly based also on the very small adsorbent volume in the micro-packed trap. In the stable trap with an outside diameter of 1/16" different adsorbents (Tenax TA, Chromosorb G HP...) can be micro-packed. All substances from US EPA 524.2 can be measured with one trap material. With one trap material more than 100 different analyts can be measured and about 2000-3000 runs can be done. The minimum thermal mass of the trap allows a fast desorption with approx. 900°C/min, whereby excellent peak forms are obtained.
Available water traps
With the analysis of water samples it is important to separte the
purged water. According to the substances the separation can be done
with differnet water trap techniques:
- PWT Peltier water trap: polar and non polar substances, working at -15°C....-20°C
membrane water trap: non-polar substances, working at -45°C
- none: for all substances, only for absolute dry samples, working up to 280°C
The performance of the system is mainly based on the mikro packed
trap, the cryo focussing and the
"in vial purging".
- Substances from US EPA 524.2, 2ppb in
- Validation of vinyl chlorid, 1ppt in water, MS, SIM
- Validation of acetaldehyde in mineral water, 10 ml, FID
- Validation of epichlorohydrin, 10ml, FID
- List of measured substances (P&T)
- Reproducibility, 10 samples, 1 ppb
- List of measured substances in edible oil / olive oil
- Analysis with internal sample loop
- Trace Level VOC Analysis in Different Sample Matrices (International Labmate 4/2015)
The system can be converted from purge and trap mode to thermal desorption mode by a simple modification. This will allow the analysis of stainless steel sample tubes filled e.g. with Tenax TA, paper or by the use of 20 ml standard glass vials filled with the sample material.
The stainless steel sample tube is placed in the axis of a special stainless steel vial with the shape of a 20 ml headspace vial. During the purge process of the sample tube the carrier gas passes the sample tube upwards which is filled with Tenax at a volume of 1ml at maximum. All adsorbed substances of the Tenax are transported to the micropacked cryo-trap. The sample, all tubes and fittings are heated at a temperature of 280°C. Also substances with a higher boiling point of 280°C can be analysed with a high recovery.
Possible adsorbent material for filling the TD sample tubes:
|NAME||ADSORBENT MATERIAL||Size / Mesh||Desorb.- Temp.||Surface m2 / g|
|Carboxen 1000||Carbon molecular sieve||60/80||330°C||1200|
|Carbopack C||Graphitisized carbon||60/80||330°C||10|
Analytical performance in the mode thermal desorption
- Alkane series C5-C16; Tenax sample tube
- Alkane series C10-C40; empty sample tube
- Megamix US EPA 524.2 on
sample tube - Tenax
- Comparison polyethylene terephthalate, PET; new / recycled, 100mg
For the sensitive measurement of VOC's in gases or air samples up to 14 pcs
Tedlar bags are automatically analyzed. For this purpose, a 1.2 m high
aluminum panel is mounted on the left side of the VSP4000.
The bags with a
volume of 5 liter are connected on both sides of
the panel. No additional laboratory space is necessary for the
Tedlar bags. Needles and FEP tubes are connected to a multi-port
valve of the VSP4000,
to select the appropriate method in the software.
Option: Tedlar Bag sampling
The following picture shows the adaption of Tedlar bags to the VSP4000:
|Vials (P&T):||number: 80; volume: 20ml; dimensions: D=23mm; H=79mm; screw-caps; septa: silikone-PTFE|
|Desorption tubes (TD):||number: 80; material: stainless steel; inner diameter: 5 mm; outer diameter: 6 mm; length: 70 mm; max. volume: 1 ml|
|Trap:||diameter: 1/16" GLT-tube; different adsorbents availabel ( e.g. Tenax for more than 100 analyts, Chromosorb, ,...)|
|Signals and interfaces:||USB; GC-Ready; GC-Start; VSP-Ready|
|Electrical control:||16bit processor; graphics display
|Installation conditions :||power supply: 230V; 50 Hz; power consumption: 1100VA; weight: 35 kg; dimensions: 67x 70x 57cm (wxhxd); ambient temperature: 15-25°C|
|GC connection:||transfer line, length: 1.5m|
|Gases:||carrier gas: He 5.0, dry N2|