Laboratory versus portable hydrogen measurements: an analytical strategy for natural hydrogen exploration

Natural hydrogen exploration requires analytical strategies combining rapid field detection of gas anomalies with reliable quantitative characterization. Portable analyzers provide near real-time field measurements, whereas laboratory chromatography offers greater analytical control and metrological traceability. This study compared H₂ measurements obtained with a portable GA 5000 analyzer and an Agilent Micro GC 490 within a metrological validation project developed by the Fluid Technologies Department at PETROBRAS Research Center (CENPES), in collaboration with the Brazilian National Institute of Metrology, Quality and Technology (INMETRO). Four primary H₂/N₂ gas mixtures prepared gravimetrically by INMETRO, containing 107.09, 269.83, 750.09 and 1279.31 µmol/mol H₂, were analyzed. GA 5000 measurements were performed directly from the cylinders on two days, with seven replicates per mixture per day. Performance was evaluated for linearity, trueness and precision according to INMETRO guidelines. Micro-GC closely reproduced the reference concentrations, yielding 106.30, 270.08, 749.30 and 1273.23 µmol/mol H₂. In contrast, the GA 5000 yielded 84.43, 207.71, 620.29 and 1000.00 µmol/mol, corresponding to underestimations of approximately 21.2%, 23.0%, 17.3% and 21.8%, respectively. Despite this negative bias, the portable analyzer showed good precision, with a relative standard deviation of 1.86%, while linearity and trueness criteria were not met. The highest-concentration mixture reached the upper calibration range, emphasizing the importance of calibration limits in field data interpretation. These results show that repeatable portable measurements do not necessarily imply quantitative accuracy. Laboratory and portable techniques should be considered complementary rather than interchangeable: portable measurements provide rapid information for identifying H₂ anomalies, whereas chromatographic analysis provides quantitative reliability for confirmation and characterization. Integrating field screening with laboratory confirmation therefore provides a robust analytical workflow for natural hydrogen exploration.