METHOD DEVELOPMENT FOR THE ANALYSIS OF C1-C5 HYDROCARBONS IN FUEL CELL HYDROGEN WITH CALIBRATION GAS GENERATED FROM STANDARD GAS AND LIQUIDS
The controlled introduction of liquid compound in gas mixtures is not a trivial analytical task and it was earlier only achievable by a permeation tube and old style static dilution techniques. Recently developed by AlyTech, the automated LiqMix Cascade system however introduces liquid into a gas stream at different concentrations in a simple and reliable way to perform multi-point calibrations, linearity and detection limit checks. This article describes an example of its use for LOQ / LOD validation of an analytical method GC-Precon-PDHID.
Introduction
To perform multi-point calibration, linearity checks, LOQ/LOD validation laboratories have to keep significant stock of the standard gas cylinders with various concentrations. Gas calibration standards are expensive to order, delivery times are long and validity of the certificate is relatively short. To save money and gain flexibility, many laboratories use dynamic gas mixers. With precise gas mixers/ diluters the calibration gas is easy to generate on site at the desired concentrations, even to very low levels. This practical solution is easy to put in place for gas standards available in the cylinders.
An issue may arise when some chemicals are not found in commercially available cylinders, like unstable, reactive compounds, or when it is a liquid. The introduction of the high boiling point compounds in gas mixtures was once only achievable with a permeation tube and old style static dilution techniques. Recently developed by AlyTech, the LiqMix Cascade system introduces liquid into a gas stream in a simple and reliable way.
Generate gas standard from a liquid
The LiqMix Cascade is an accurate calibration tool designed for automated generation of customised standard gas from neat liquids or liquid cocktail mixtures for the purpose of calibrating gas analysers, GC or GC/MS, and to validate the precision and reliability of GC sample introduction systems. Due to its unique intelligent multi-stage cascade dilution, AlyTech LiqMix Cascade can provide a very wide range of concentrations from % down to ppb levels with good accuracy, high repeatability and full traceability. Gas standards such as BTEX in air, other hydrocarbons, siloxanes, ethanol and phenol, humidity standards can be delivered.
All interconnections and outlet line of LiqMix are heated in order to maintain the vapours in gas phase and thus avoiding re-condensation up to the delivery point.
Easy to handle, dedicated AlyTech software controls the operation, manages mass flow controllers, its calibration tables, performs automatic calculation of liquid and span gas flows, to achieve desired concentration of analytes even for very complex multicomponent mixtures. Following highest metrology requirements the instrument not only accurately prepares the gas mixtures, but it also automatically calculates and reports maximum relative uncertainty for every delivered concentration.
Rich remote control
functionalities of the software and automated programmed sequences enable full automation by synchronising the mixer/diluter with a gas chromatograph, pre- concentrator, spectrometer, gas analyser or other system.
LiqMix Cascade
Investigation of common hydrocarbon contaminants in hydrogen fuel
Recently the AlyTech LiqMix Cascade was successfully used for validation of analytical methods to assess the purity of automotive fuel cell grade hydrogen. Impurities commonly found in hydrogen gas for fuel cell vehicles may have some disastrous long-term consequences on the fuel cells if their levels exceed 2 ppm. Appropriate analytical methods must be able to function in a hydrogen matrix, and detect and quantify regulated by ISO 14687-2 contaminants present at ppmv–ppbv concentrations. In the framework project called Metrology for Hydrogen Vehicles (MetroHyVe) funded by European Metrology Programme for Innovation and Research (EMPIR) AlyTech instrumentation was employed at Institute for Energy Technology (IFE) - one of the most experienced petroleum gas and research laboratories in Norway. The specific focus of IFE was on common hydrocarbon contaminants in hydrogen fuel that ranged from polar components - methanol, ethanol and acetone, to non-polar components - methane, ethane, propane, butanes, pentanes. The large span in boiling points and polarity of the analytes make the target matrix challenging to create in laboratory conditions and introducing it into pure hydrogen and analyse. This challenge was overcome by using the LiqMix Cascade to generate homogeneous mixture of hydrocarbons (see Table 1) and introduce sub-ppm impurities in pure hydrogen 5.0 gas. Working range of concentrations for hydrocarbons mixture was 0.2 – 20 ppm.
Table 1 Mix of hydrocarbons used in the study
C2 C3
Compound Analytical Method Span / ppb GC-Precon-PHID
C4’s C5’s C6
MeOH
Acetone EtOH
GC-Precon-PHID GC-Precon-PHID GC-Precon-PHID GC-Precon-PHID GC-Precon-PHID GC-Precon-PHID GC-Precon-PHID
200 3500 6800 10100 13400 16700 20000
The analytical setup
Linearity and detection limit were determined using the standard mix at different concentrations generated by LiqMix Cascade from liquids and gas, with 2 stages of dynamic dilution.
Liquid
Gas
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
