Development and validation of a methodology for quantifying parts-per-billion levels of arsine and phosphine in nitrogen, hydrogen and liquefied petroleum gas using a variable pressure sampler coupled to gas chromatography-mass spectrometry.

ABSTRACT

The reliable determination of arsine (AsH3) and phosphine (PH3) in hydrogen (H2), nitrogen (N2) and liquefied petroleum gas (LPG) is of great importance because of its drastic effects on the efficiency of catalysts, as well as the strict regulations associated with health, safety and environmental issues. It is challenging for an analyst to determine the parts per billion of AsH3 and PH3 in H2, N2, and LPG at low and high pressures without collection procedures using adsorption, desorption, and dissolution techniques. To overcome this analytical need an analytical methodology was developed, employing a variable pressure sampler (VPS) coupled to a gas chromatograph (GC) with mass spectrometry (MS) for the identification and quantification of traces of AsH3 and PH3. The instrumentation, tubing and accessories of the VPS were made of passivated steel to avoid losses from absorption of AsH3 and PH3 in the steel which would generate significant analytical problems. The VPS had a homogeneous heating block that prevented analyte losses from condensation. With the VPS, 24 AsH3 and PH3 standards were prepared between 0.005 and 0.1 mg kg-1 in balance of H2, N2 and LPG. The separation and quantification of the analytes was achieved with an improved GC with 4 valves and 5 columns in series that guaranteed the elimination of impurities. The proposed method was optimized in VPS and GC-MS and then validated showing highly accaptable linearity (r2 > 0.9999), detection limits (<0.0009 mg kg-1), limits of quantification (<0.003 mg kg-1), intra-day and inter-day precision and accuracy (<1.14% and ≤3.0% respectively), recovery for the standard addition (86-109%), P values> 0.05 for the test Student's t paired who evaluated the effect of the matrix on pressure and concentration. The speed of analysis was high (<5.2 min). The method was applied to real samples, showing values between 0.005 and 0.1 mg kg-1 and an effect on the efficiency of the Ziegler Natta catalyst between 5 and 56%.