In situ determination of organic reaction products by combining thin layer chromatography with surface-assisted laser desorption/ionization time-of-flight mass spectrometry

Abstract

This study presents an in situ determination of organic reaction products on a thin layer chromatography (TLC) plate using surface-assisted laser desorption/ionization (SALDI) time-of-flight mass spectrometry. This technique can rapidly identify products and byproducts on an intact TLC plate. The characteristics of low matrix interference and low suppression effects in SALDI make this technique particularly appropriate for small organic compounds. In addition, the SALDI liquid used in the SALDI matrix system helps to reduce the interaction between analyte and silica gel on the TLC plate, thus avoiding an extra extraction procedure when preparing the sample. Furthermore, preparing the sample by combining TLC with SALDI mass spectrometry on the TLC plate is a relatively easy task. A TLC/SALDI analysis takes less than ten minutes to complete. Copyright # 1999 John Wiley & Sons, Ltd. Received 1 February 1999; Revised 5 March 1999; Accepted 5 March 1999 Thin layer chromatography (TLC) provides a fast and inexpensive separation method for purification. TLC is frequently used in the separation of reaction products in organic synthesis. Different visualization methods are conventionally used to identify reaction products in TLC. However, the reaction products are normally purified by column chromatography for further confirmation. The collected fraction is then analyzed by nuclear magnetic resonance (NMR). This procedure is quite tedious and timeconsuming. Mass spectrometry has been used as an alternative detection method to confirm organic reaction products after TLC separation. Ideally, the TLC plate should be directly inserted into the mass spectrometer for analysis when the separation is achieved. The plate is heated in the source, and highly volatile compounds are released and detected by electron ionization (EI) or chemical ionization (CI).1-3 However, for nonvolatile or thermally labile compounds, this alternative method does not work. Instead, the analyte must be extracted from the TLC stationary phase by an appropriate organic solvent. Previous investigations have successfully detected analytes from the TLC plate by fast-atom bombardment (FAB) and matrix-assisted laser desorption ionization (MALDI) after solvent extraction. 4-8The major concern in FAB/TLC and MALDI/TLC is how to effectively extract the analytes from the TLC stationary phase. Preparing TLC/MALDI samples is complicated because not only must the analytes be extracted from the silica gel, but they must also co-crystallize with the MALDI matrix. 7,8 Recently, Meldal et al. presented a TLC/MALDI method for analyzing organic reaction products. 9 In this method, the analytes are scraped off and extracted from the TLC plate after the components of the reaction mixture have been separated on the TLC plate. The extracted fraction from the TLC plate is then mixed with the MALDI matrix for MALDI analysis. This is an indirect analytical method combining TLC with MALDI. However, this method poses the problem of matrix interference in the low mass range: mos...

Laser desorption-ion mobility spectrometry as a useful tool for imaging of thin layer chromatography surface

“…Mass spectrometry (MS) with different ionization sources is a powerful technique for detection and characterization of vast spectrum of chemical compounds. In TLC, the analyte is deposited on the plate, therefore, the analyte should be sampled from the TLC surface and gasified in order to be detected by MS. Coupling of TLC with MS has been carried out using different techniques and ionization sources such as laser desorption ionization (LDI) [6][7][8][9] secondary ion mass spectrometry (SIMS) [10] matrix-assisted laser desorption ionization (MALDI) [11][12][13][14][15] surface-assisted laser desorption ionization (SALDI) [16,17] electrospray ionization (EI) [18][19][20][21] electrospray laser desorption ionization (ELDI) [22,23] laser-induced acoustic desorption electrospray ionization (LIAD/ESI) [24] laser desorption/inductively coupled plasma (LD/ICP) [25,26] and so on. Also, different mass spectrometers including time of flight (TOF) ion trap and quadruple are used to detect and analyze the analytes sampled from the TLC surface.…”

Analysis of small molecules by ultra thin-layer chromatography-atmospheric pressure matrix-assisted laser desorption/ionization mass spectrometry

“…However, it has been shown that the matrix background can be suppressed by using appropriate analyte-to-matrix molar ratio in MALDI measurements [23,26,[32][33][34][35]. New potential matrices, producing low matrix background, have also been introduced [16,20,21,27,30,31]. A disadvantage of the MALDI method has been the relatively poor repeatability in quantitative analysis.…”

Sensitivity enhancement for nitrophenols using cationic surfactant‐modified activated carbon for solid‐phase extraction surface‐assisted laser desorption/ionization mass spectrometry

“…The activated carbon, used as SPE adsorbent and SALDI solid, was modified by passing 6 mL of a DTAB (10 mM) solution through an SPE cartridge. The peak at m/z 341 is the deprotonated molecule of sucrose, which is one of the essential components in the SALDI liquid,7,, 9–11 and is added in order to minimize ion source contamination by the carbon particles. This [M − H] − ion can be used as an internal standard ion for mass calibration of the SALDI mass spectra.…”

“…However, the chromatographic procedure may, in suitable cases, be omitted by performing the analysis with an appropriate method such as the hyphenated technique, SPE‐SALDI, in which surface‐assisted laser desorption/ionization (SALDI) mass spectrometry is carried out directly on the SPE adsorbent 7. SALDI involves mixing a sample solution with a matrix that is composed of a suspension of µm‐sized carbon powder in a mixture of glycerol, sucrose and methanol 8–11. The samples are irradiated with a pulsed UV laser in a time‐of‐flight mass spectrometer.…”