Analysis of mass-limited mixtures using supercritical-fluid chromatography and microcoil NMR

Abstract

A protocol is presented for offline microfluidic NMR analysis hyphenated with supercritical chromatographic separation. The method demonstrates quantitative detection with good sensitivity. Typical sample amounts of 10 nanomoles can be detected in a fast and cost-effective manner.

Hyphenation of Supercritical Fluid Chromatography and NMR with In-Line Sample Concentration

“…Separation of the four isomers of tocopherol, differing in the methylation pattern of the aromatic ring, has been achieved before by SFC. 22 The same tocopherol mixture as used by Tayler et al has been used in this research consisting approximately of 9.7% α-, 1.1% β-, 66.7% γ-, and 22.5% δ-tocopherol, determined by integration of their separate peaks in the UV chromatogram ( SI S1 ). A good separation can be achieved within 2.5 min using a gradient of methanol in CO 2 , but the β- and γ-isomers slightly coelute.…”

“…As mentioned in the introduction, the limit of detection (LOD) for the stripline chip used in these experiments is 0.1 nmole 1 H spins/ . 20 , 22 This detection limit is defined as the number of nuclear spins of a specific molecular site needed for a signal-to-noise ratio of 1 in the FID, for a single scan experiment. When more scans are acquired and averaged, a better signal-to-noise ratio is achieved, scaling with the square root of the number of scans.…”

“…In the off-line experiment described by Tayler et al, 22 the tocopherol isomers were collected 10 times after separation and redissolved in 0.5 μL methanol-d 4 . The concentration in the stripline of β-tocopherol, the lowest abundant isomer, was therefore 3.2 mM, which is close to the detection limit for this stripline probe in 500 scans.…”

“…In the work by Tayler et al this was done by evaporating the sample off-line before detecting it with NMR. 22 The authors first separated a mixture of four isomers of vitamin E (tocopherol) by SFC. Each isomer ( Figure S1b of the Supporting Information , SI ) was then collected separately in a vial 10 times, the excess solvent was removed and each isomer was redissolved in 0.5 μL methanol-d 4 .…”

Denoising applied to spectroscopies – Part II: Decreasing computation time

“…Non-hydrated non-protonated Sr(PO 3 F) was studied on a Bruker Avance III spectrometer operating at 699.98 MHz for 1 H and 30.34 MHz for 87 Sr in a 5 mm static probe. In order to enhance sensitivity, DFS (55), WURST (56) and CPMG were used with 58,000 transients and a relaxation delay of 6 300 ms, leading to a total acquisition time of 5.5 h. 260 echoes were acquired with a full echo delay of 0.12 ms.…”