Table 3.

Representative applications of time-resolved ESI-MS for monitoring fast reactions and intermediate species.

(Bio)chemical reaction	Intermediate species	Instrumentation (reaction-sampling-ionization-detection)	Temporal resolution	Reference
Synthase catalyzed reaction	Tetrahedral intermediate	Pulsed flow (rapid-mixing) device—ESI-QMS	30 ms	[64]
Pre-steady state enzymatic kinetic	Transient enzyme intermediate	Two syringes in a reaction mixing tee—ESI-QMS	tens of ms	[65]
Chlorophyll demetalation	Specific reactive species (time profile)	Capillary mixer with adjustable reaction chamber volume—ESI-QQQ	ms	[111]
Pd(PPh3)4 decomposition	Pd-containing reactive species	Continuous pressurized sample infusion—ESI-QTOF	N/A	[145]
Sandmeyer’s cyclization	Three new cationic intermediate	Microreactor—ESI-QTOF	subs	[146]
Electro-oxidation	Perylene radical cation	Electrochemical cell—DESI-QTrap	N/A	[123]
Pyrolytic reactions	Reactive ketenes	Flow pyrolyzer-multichannel ESI-QQQ	~0.2 s	[147]
Electron-transfer cata-lyzed dimerization	Distonic tetramethylene radical cation	Gas/liquid setup—EESI-QTOF; Liquid/liquid setup—EESI-QTOF	ms	[69]
Catalytic transfer hydrogenation	Ru-complex intermediates	Microdroplet reaction vessel for reactive DESI-IT	ms	[66]
Catalytic transfer hydrogenation	Transient Ru-methyl formate species	Microdroplet reaction vessel for reactive DESI-Orbitrap	subms-ms	[50]
Morita-Baylis-Hillman reaction	Two key MBH intermediates	Venturi easy ambient sonic-spray ionization (V-EASI)-QMS	N/A	[135]
KDO8P synthase reaction	Noncovalent acyclic hemiketal intermediate	Rapid mixing device—ESI-QTOF	50−630 ms	[148]
Eschweiler-Clarke reaction	Reactive iminium ion; Sodiated amino alcohol	Reactive DESI-IT	ms	[137]
Fast oxidations of I− and S2O32− by O3	Short-lived ISO3− and IS2O3−	Reactive DESI-QMS	~1 ms	[149]
Catalytic acetylation of benzyl alcohol	Positively charged intermediates	Online ND setup—EESI-QTOF	<1 s	[126]
Borsche-Drechsel cyclization	Ionic intermediate (protonated hydrazone)	Electrosonic spray ionization (ESSI)-IT	N/A	[150]
Zemplén deprotection	Mono-deprotection intermediate	Capillary action supported sampling tool—contactless API emitter-IT	1 min	[15]
Electrochemical red/oxidization	N-hydroxyl and amine labile intermediates	Electrochemical flow cell—nanoDESI-LTQ/Orbitrap	N/A	[151]
Schiff base formation	Hemiacetals	PESI-QTOF	0.1−0.33 s	[61]
Monitoring of 3-D cell culture system	(Bio)chemical transients	Inline microdialysis—ambient nanoESI-QTOF	100 μm (spatial)	[152]