Table 1.

Summary of common techniques for detection of H${}_2$, with lowest detected concentration, LOD, and measurement time, when reported.

Method	Lowest Detected Conc. (ppm)	Estimated LOD (ppm)	Measurement Time (s)	Reference
Chemiresistors	50	0.01	∼20	[17]
Schottky diode	10,000	0.1	∼10	[44]
MEMS	6	0.1	∼2	[45]
IR absorption	5000 at 0.1 MPa	1000	1	[23]
Raman:
• PARS	10 at 0.3 MPa	3.4	∼10	[28]
• FERS	5	4.7	1–100	[31]
• CERS	100 at 0.1 MPa 0.5 at 0.1 MPa	0.069 -	500 2500	[36]
• Multipass cavity	0.075 at 0.2 MPa	0.06	600	This work