SMASH Poster Abstract Review

Polymeric NMR Sample Tubes Evaluated in a 1 mm Microprobe

Michael J. Cavaluzzi1, David J. Kiemle2, Deborah J. Kerwood3, and Philip N. Borer1,3
1. Advanced Resonance Technologies, Inc., 111 College Pl, 2-212 CST, Syracuse, NY 13244-4100 2. Chemistry Department, SUNY College of Environmental Science & Forestry, 121 Jahn Lab, 1 Forestry Dr, Syracuse, NY 13210-2726 3. Chemistry Department, Syracuse University, Syracuse, NY 13244

Polymeric NMR Tubes have advantages over glass in most applications: • Polymeric tubes are shatterproof • Ultra-thin walls afford sensitivity increases of 20-40% • Polymer tubes are easy to fill and to recover sample • Standard probeheads and sample changers can be used. Here we describe the performance of polymer tubes compared to glass capillaries, both having 1 mm outside diameter. The mass sensitivity of 1 mm probes about four times that of 5 mm probes, yet the former have not found wide acceptance due to the difficulty of using glass capillaries. Samples were tested on a Brüker DRX-600 with a 1 mm TXI room temperature probehead. Primary comparisons are between polymeric tubes with inside diameters of 0.826 (ART-1A), 0.851 (ART-1B), and 0.889 mm (ART-1C), and a glass capillary with ID estimated at 0.814 mm. The resolution for 1% CHCl3 in d6-acetone was comparable at half-height (1 Hz) while the lineshape for polymer tubes was typically 20% broader at the base. The signal-to-noise ratio in the polymer tubes scales almost exactly with volume increase in the active region of the receiver coil (tested with 0.1%, 1% and 10% ethylbenzene in CDCl3). 30-40% less time will be required to achieve the same S/N in the larger ID polymer tubes compared to glass capillaries. Spectra acquired in ART-1C tubes will be shown, including: (1) a 1D 1H-spectrum of 1 microgram of stigmasterol where the chemical shifts are easily resolved in 512 scans, (2) a 2D 1H-15N-HSQC of 70 micrograms of 15Nu-ubiquitin shows that a 21 min acquisition distinguishes the expected peaks and has an increase in S/N ~ 30% over a glass capillary, and (3) a 2D 1H-15N-HSQC of 15Nu-labeled NCp7 protein from HIV-1. The mass of the protein is about 2% of that often used in a 5 mm room temperature probe (1 mM, 500 microliters). MJC and PNB hereby disclose their financial interest in ARTech, represented at the SMASH conference by Norell, Inc. NMR tubes with other dimensions will be available soon. Supported in part by NIH grant RR18442 to MJC and PNB.

Pressure limits of NMR tubes

A customer recently asked if a glass NMR tube could hold 5 bar of pressure, and that he wanted to do a catalytic reaction under pressure during data acquisition. A standard NMR tube with a 0.38 mm wall and 5mm OD has a limit of about 10.3 bar, from P_max = tube wall thickness ÷ tube wall O.D. X 135 bar.

It is suggested that when using an NMR tube for higher pressure experiments within the recommended pressure rating, that you check for any damage to the surface of the glass tube before pressurizing, since this could lead to tube failure.

Can a NMR tube de-resolve a portion of a sample's spectrum?

Recently we received spectra from a customer who was questioning a loss in resolution between two different NMR tube brands using an identical sample for the test.

spectrum1

spectrum2

The data was acquired on a Bruker DRX 500 taken at a temperature of 303 K and spin rate of 20Hz. The compound was from a stock solution containing a chiral, aliphatic, small molecular weight organic compound. The customer also mentioned that a shim file derived from gradient shimming was used and then further hand shimmed on Z-Z5, 8 scans with no line broadening.

Looking at the aliphatic region between 1 and 2.2 ppm, the two spectra seemed identical. However, between 7.35 and 7.4 ppm there was a noticeable difference between the two tubes in resolving the long range H-H coupling of a imine CH peak. It was assumed by the customer that these differences were caused by quality differences between the tube brands.

The customer's concerns were very convincing until they realized that when a NMR spectrum is acquired, the raw data is in the form of a free-induction decay which is carried over the entire length of the spectrum, and converted into a frequency domain function by Fourier transform. Therefore, the entire spectrum is subjected to one resolution constant, not many at various points of the spectrum. Since NMR sample tube quality plays only a partial role in resolution, other effects such as slight changes in the sample's water content, pH effects from the glass, or others, can lead to chemical exchange broadening, which could have caused this customer's problem.

It is important to note that strict quality control standards are used in NMR tube manufacturing. Since variation in concentricity and camber is at its worst ± 0.025 mm and ± 0.075mm in a disposable tube, it is critical not to rule out chemical influences that will effect spectrum resolution.

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