HYDROGEN AS A CARRIER GAS. Gas Chromatography new frontiers: can Hydrogen substitute Helium?

Transcription

1 HYDROGEN AS A CARRIER GAS Gas Chromatography new frontiers: can Hydrogen substitute Helium? Manufacturing UHP gas generators for lab analysis since 1979, CLAIND is seating in Lenno, on Como Lake, where it carries out the main activities of new solutions development and manufacturing. Recently Claind has commissioned to the well known laboratory DtoLABS, a study on the utilization of Hydrogen as an alternative to Helium as a carrier gas in gas chromatography. DtoLABS is the sole Partner Laboratory of Agilent Technologies in Italy. Here research projects and new methodologies are developed. Moreover, DtoLABS organizes training courses for users and for applied chemical analysis specialists. DtoLABS is also an Agilent Technologies European Demo Centre, so that customers can regularly visit the laboratory to be informed on the ultimate technical-analytical solutions available on the market. In the following pages we will present the results of the study. Scope and methodology of the study The scope of the project was to demonstrate the effectiveness of the use of Hydrogen as a carrier, not only in gas chromatographic gases (GC) with standard detector (FID, NPD, FPP e µecd), but also in the GC coupled with mass spectrometers (MSD). All results speaking about advantages and disadvantaged need to be mentioned and well considered because the aim of this job is to be a true guide for CLAIND s organization and Customer support. Historically Helium has always been employed as a carrier gas, and in some cases even Nitrogen. The peculiar characteristic of Nitrogen is the low cost of supply; its main limit is the poor gas chromatographic efficiency. On the other hand Helium has been always considered the best analytic choice. But by now everyone knows about his scarce availability, that doesn t enable to satisfy the whole analytic market. As a matter of facts many laboratories have verified that more and more often gas suppliers haven t the possibility to supply Helium at reasonable cost with timely delivery. For such reasons Claind decided to verify the feasibility of the conversion of the GC instrumentation from Helium to Hydrogen, particularly on GC equipments coupled with a MSD. Many GC analysis have been performed for this feasibility study using either Helium or Hydrogen as a carrier, and then comparing the results. The study has been carried out employing an Agilent Technologies GC 7890A MAS 5975 Triple Axis Detector and a Agilent Technologies GC Sampler 80. The Hydrogen generator employed was a Brezza Hygen 200 model. Brezza HyGen200 Flow rates up to 200 ml/min Touch screen display Safety : In case of any error or H2 Leakage the generator will stop production CLAIND Gas Generators Manufacturer since Feb-14 Pagina 1 di 11

2 GC 7890 with MMI injector Autosampler GC Sampler 80 MSD 5975C TDA The instrument selected is designed to use Hydrogen as a carrier. Agilent Technologies supplies the instrument along with specific safety manuals. WARNING Qualitative analysis As for qualitative analisys the scope was demonstrating that the acquired data with Hydrogen carrier does present spectrums comparable with the ones acquired in standard condition. This hypothesis has been verified with Library Reseach, i.e. a software that by means of algorithms compares the spectrum of an unknown substance with a spectrum database of known substances. These databases are produced by authorities that acquired the spectrums of thousand of compounds in standard conditions and particularly using Helium as a carrier. The spectrum of an unknown substance is compared with the spectrum database and the software Library Research will propose possible results. The research will return a list of possible identified substances and a percentage value that gives the indication of the similarity between the spectrum of the unknown substance and the substance hypothesized by the software. The more the percentage is close to 100%, the more reliable and sure will be the detection. There are many library on the market: in this study we used the NIST and the WILEY. In the light of the obtained results, we can state that the spectrums obtained with the Hydrogen carrier are analyzable with Library Research with excellent detection. The impact of the different carrier doesn t affect the fragmentation of the substances in the source of the mass spectrometer and therefore the correct detection through spectrum analysis. CLAIND Gas Generators Manufacturer since Feb-14 Page 2 of 11

3 Instrumental conditions: Injection Volume: 1 ul Front MM Inlet Mode: Split Split Ratio: 25 : 1 Column: mod. Agilent J&W DB m x 250 µm x 0.25 µm In: Front MM Inlet H2 Out: Vacuum Flow 2 ml/min carrier H2 (Pressure 6.4 psi - Velocity 76.1 cm/sec ) Tune File: stune.u Acquistion Mode: Scan Scan range: amu MS Source: 230 C MS Quad: 150 C Analyzed substances: Name CAS number Bromoform Chlorobenzene ,2-Dichlorobenzene Trans 1,2 Dichlorobenzene Naphtalene Toluene ,2,3-Trichlorobenzene Trichloroethylene Bromoflurobenzene Dibromofluoromethane ,2 Dichloroethane-d Toluene-d CLAIND Gas Generators Manufacturer since Feb-14 Page 3 of 11

4 Quantitative analysis Considering the quantitative aspect, the analysis of the polyciclic aromatic compounds (IPA) has been valued. First, some chromatograms of the above-mentioned compound have been acquired in standard condition and in different concentration, building calibration lines, first using Helium and in a second time Hydrogen. Instrumental conditions: Injection Volume: 1 ul Front MM Inlet Mode: Splitless Column: mod. Agilent CP8982: VF-17ms 30 m x 250 µm x 0.25 µm In: Front MM Inlet H2 Out: Vacuum Tune File : dftpp.u Acquistion Mode: SIM MS Source: 300 C MS Quad: 150 C CLAIND Gas Generators Manufacturer since Feb-14 Page 4 of 11

5 Compounds present in the mixture: DtoLABS realized calibration lines with following concentration: μg/l of IPA in Hexane solution Chromatogram: Solution of IPA 5 μg/l in Hexane - 1 ul injected SIM diagram obtained with an Hydrogen Carrier CLAIND Gas Generators Manufacturer since Feb-14 Page 5 of 11

6 The chromatography obtained with Hydrogen resulted excellent: you can see that from some IPA separation generally considered as critic. The calibration line obtained with Hydrogen carrier and the one with Helium resulted substantially comparable. In both cases, the linearity of the reply of the system enables to build lines with an excellent linear regression in the same concentration interval. Examples of significant IPA: Hydrogen Naftalene Helium Hydrogen Acenaphthylene Helium CLAIND Gas Generators Manufacturer since Feb-14 Page 6 of 11

7 Hydrogen Fluorene Helium Hydrogen Benz[a]pyrene Helium Technical consideration The transition from Helium to Hydrogen for the instrument has to be evaluated and analyzed with following considerations: Substitution of the Drow out plate of the source Vacuum pumps limits Column choice Safety consideration In order to change to Hydrogen as a Carrier, it is recommended the substitution of this internatle part of the source. CLAIND Gas Generators Manufacturer since Feb-14 Page 7 of 11

8 G Drawout Plate 6 mm Standard Drawout Plate 3 mm The gas extraction limit of the vacuum cell is lower for the Hydrogen compared with Helium. For this reason the flow limit of the instruments have to be reconsiderated when using Hydrogen. Performance turbo: Standard turbo: Diffusion pump: Pressure pulsing: 2 ml/min 1 ml/min 0.75 ml/min turbo <= 3 ml/min, diffusion <= 2.5 ml/min Please monitor the high vacuum level in order to avoid exceeding the limit of 5 x 10-5 torr (measurable using an Ion Gauge). Should this limit be exceeded, the performance of the system will be influenced. On the other hand, we can notice a reduction of the reply in absolute terms of the areas and the evaluation of the signal/noise ratio seems to confirm the reduction of the same of about 2-3 times. This is due to the reduced efficiency of the turbo molecular pumps compared to Helium to evacuate Hydrogen from the area of the detector. Column choice Another consideration is that the change of gas leads necessarily to different parameters of pressure in the head of the column, because the same flow value applied to the column requires different pressures using different gases. Particularly, shifting from Helium to Hydrogen in the same instrumental condition, the pressure applied to the column is inferior and it is necessary to verify if it is manageable from the injector. Considering the Van Deemter equation, the best linear velocity for Hydrogen is superior to the one of Helium. CLAIND Gas Generators Manufacturer since Feb-14 Page 8 of 11

9 As per the mass spectrometer, and particularly for the vacuum management, generally speaking the flow limits of the manageability of the pumps are halved by using Hydrogen. For these reasons, using Hydrogen it would be better to use capillary columns with smaller diameter and length. Thanks to this change of column and using Hydrogen as a carrier gas, the pressure in the head of the column will be more elevated, and there will be a smaller gas flow in the analyzer, ensuring a major degree of vacuum and a better sensitivity. In the test DtoLABS performed in order to demonstrate the immediate switch to Hydrogen, they always maintened standard dimension columns for GC MSD: 30 m 0,25 mm. But let s make some examples to understand what will the best column be. Example 1 lenght 30 m and internal diameter 0,25 mm Conditions: Oven 50 C Inlet 250 C Outlet Pressure : Vacuum Helium Flow 1 ml/min Inlet pressure 7.6 psi Velocity: 36 cm/sec Hydrogen Flow 1 ml/min Inlet pressure 0,35 psi Velocity: 54 cm/sec Pressure difficult to manage for the GC Example 2 lenght 30 m and internal diameter 0,25 mm Conditions: Oven 50 C Inlet 250 C Outlet pressure : Vacuum Helium Flow 2 ml/min Inlet pressure 17 psi Velocity: 51 cm/sec Hydrogen Flow 2 ml/min Inlet pressure 6,6 psi Velocity: 76 cm/sec Limit pressure in the vacuum cell ( ses pumps ) High linear velocity Example 3 lenght 20 m and internal diameter 0,18 mm Conditions: Oven 50 C Inlet 250 C Outlet pressure : Vacuum Helium Flow 1 ml/min Inlet pressure 20 psi Velocity: 44 cm/sec Hydrogen Flow 1 ml/min Inlet pressure 9,0 psi Velocity: 66 cm/sec Initial choice ideal for Hydrogen carrier Tip: try to have a minimum inlet pressure to the injector of 5 psi Safety The connection to a vent toward external environment of all the drain of the Gas chromatograph and of the Spectrometer (rotative pump) isn t necessary when the laboratory has the minimum air recycle requested by applicable laws on working environments. Leak detectors for Hydrogen aren t necessary only when using a Claind Brezza Hydrogen generator (equipped with built-in safety device) In any case it is mandatory to follow safety indication of the Manufacturer of the employed instrumentation. CLAIND Gas Generators Manufacturer since Feb-14 Page 9 of 11

10 Promising conclusions Summarising the results of the study we can affirm that: The effectiveness of Hydrogen as a carrier in GC MSD is demonstrated; This demonstration has been performed with serial instrumentation, normally are predisposed by the manufacturer for managing also Hydrogen as a carrier gas; The spectrums obtained with Hydrogen carrier are analyzable through library research with excellent identifications. The impact of the different carrier doesn t influence the fragmentation, and therefore the identification. Also particular substances, such as Deuterated compounds, that could react with Hydrogen, don t seem to be influenced. Even Aldehydes analysis, that are particularly sensitive, gave positive result. The data obtained with Hydrogen carrier and the ones of the Helium carrier are substantially comparable. In both cases, the linearity of the system reply allows the construction of lines with an excellent linear regression and a good RSD % of the response factor on different level. The migration of analysis methods already employed using Helium is possible when effecting the choice of the adequate capillary column. Safety of the laboratory and of the users must always be a priority: the Claind Hygen series anyway is equipped with alarms, implementation systems, innovative controller software and guarantees the safety of users and environments. HyGen: carrier gas generator The solution developed by Claind, taking into account the investments on the verify of the possibility of employing Hydrogen as a carrier gas and on the identification of the advantages compared to Helium solution, is the Hygen: an Hydrogen Carrier Gas generator for GC and GCMSD. HyGen satisfies all the necessities involved with the use of Hydrogen as a Carrie Gas: Safety, interruption of the carrier in case of leaks in the oven with possible switch on a inert gas; Ultra High Purity, to obtain a neat and reliable analysis; Iterfaceability of the generator with the data processing system The Hygen series is part of the Brezza series to which belong other generators for gas chromatography as Zero Air and Nigen. CLAIND Gas Generators Manufacturer since Feb-14 Page 10 of 11

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