Effective gas purification

The contamination of carrier support gases by water or oxygen drastically reduces detector sensitivity, leads to poorer peak separation and reduces the life of the apparatus. Up until now, the traditional solution for laboratories was to buy expensive, ultra-pure gases with a purity value of $ 5.0 and/or connect a filter system between the gas bottle and the measurement apparatus. Such equipment is expensive and in addition to strict monitoring of the saturation level of the filter cartridges, requires regular filter replacement. With the purified gases available with the Built-in Purifier, laboratories are offered a simpler and less costly alternative to the methods used previously. The BIP gases were tested and released by independent laboratories such as the Laboratory of Isotope Biogeochemistry of Paris University VI-INRA-CNRS and have already been used successfully by German customers such as Lobbe GmbH, a waste disposal company with state-approved testing laboratories.

Over the last ten years, legislators have issued increasingly strict environmental requirements and broadened the scope of informa-tion that must be disclosed. This relates in particular to special-category waste. Nowadays, prior to disposal, its composition must be rapidly and accurately determined together with any possible risks. Relatively costly analysis tests are therefore required at state-approved testing laboratories. One of these laboratories is run by Lobbe GmbH, the tenth largest waste disposal company for toxic substances in Germany.

The basic prerequisites of accurate laboratory analysis include the quality of the carrier and make-up gases used for gas chromatography. The more complicated the structure of the sample to be tested, i.e. the greater its contamination, the more important is it to prevent the presence of additional impurities such as moisture, oxygen or halogenated hydrocarbons in the gas from making the analysis unreliable. This is particularly important at the Lobbe laboratory in Letmathe: „As a state-approved testing laboratory we have to determine the composition of special-category waste and contaminated substances even down to a few parts per billion. We also have to undergo regular comparative tests with other state-approved testing laboratories in inter-laboratory trials. We cannot afford any unpurified carrier gases“, reports laboratory manager Dr. Barbara Ziegler. „If too many ghost peaks or an increase in baseline noise are determined, the whole procedure must be repeated until all impurities have been reliably identified and the composition of the sample determined. This costs the laboratory time and money because of the increased gas requirement with several analysis processes on the same sample.“ In addition, the contamination of carrier gases by oxygen, mois-ture and halogenated hydrocarbons impairs the detector sensitivity and the life of the columns. The laboratory at Letmathe has been one of Air Products‘ customers since 1992. Initially, helium 5.0 and nitrogen 5.0 with a 99.999% purity level were supplied as carrier and make-up gases for analyses. These gases have an oxygen content of less than 1 ppm helium or 3 ppm nitrogen and a water content of less than 2 ppm. In addition, in the laboratory at Lobbe, an external filter is connected between the gas cylinder and measurement apparatus to prevent unpurified gases. This type of filter equipment, like gases with a 5.0 quality level, is expensive and requires strict monitoring of the satura-tion level of the filter cartridges. In view of the need for high-purity gases, the state-approved testing laboratory in Letmathe was one of the first customers to be offered the new Air Products helium GC and nitrogen GC with the Built-in Purifier (BIP). These gases have a guaranteed oxygen content of less than 10 ppb and a guaranteed moisture content of less than 20 ppb. These extremely low values are made possible by a filter, the Built-in Purifier (BIP) which is integrated into the bottle and – using a patented process – reliably removes substances from helium 5.0 or nitrogen 5.0 which otherwise would have a negative influence on a GC-ECD or GC-MS analysis.

The laboratory at Letmathe currently receives an average of four cylinders of helium GC and five cylinders of nitrogen GC per month. Lobbe GmbH appears to be very satisfied with the quality of the BIP gases and the analysis results. They are now more reliable and more accurate with on average fewer repeat procedures being required.

This quality factor is also reflected in the figures. The quality of the gases can be seen especially clearly along with the resultant savings in the purification costs for ECD detectors. Before using BIP gases of GC quality, the ECD detectors had to be purified four times a year, whereas this is now only necessary once a year. The purification costs have decreased from DM 24 000 to DM 6000, a drop of 75%. The requirement for cleaning cartridges – which Lobbe GmbH does not wish to do without – has also been reduced: instead of the cartridges needing to be replaced six times per gas removal point and year as previously, entailing an outlay of DM 3240 for two removal points, replacement is now only necessary once a year. The cost saving here is DM 2500 or 77%.

Air Products

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Further information cpp-201

Lobbe GmbH is the tenth biggest waste disposal company in Germany with an annual turnover of DM 110 million and 450 employees. The company belongs to Lobbe Holding, which in 1997 made a profit of DM 365 million with 2475 employees in eleven countries worldwide in the area of special-category waste disposal and decontamination. Five qualified analysts and three trainees currently work in the testing laboratory of Lobbe GmbH at Letmathe, which has been state-approved since 1994. The laboratory is certified in accordance with § 25a of the Regional Refuse Disposal Act for solid wastes, liquid wastes, leach-ate and aqueous media biotests as well as in accordance with § 60a of the Regional Water Act. The following analyses are regularly carried out here:

• Chromatographic determinations, for example of polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), chlorinated hydrocarbons (CH) and general gas chromatographic analyses with GC-MS.

• Determination of combined parameters such as hydrocarbons, extractable halogen organic compounds (AOX) as well as total chlorine and total sulphur.

• Heavy-metal determinations in various matrices.

• Identification and quantification of individual substances such as pesticides, insecticides, benzene, toluene and xylene.

• Physical-chemical tests such as ignition point and calorific value, combustion and landfill analyses.