NMR Probes _MOAYAD KHASHOQJI_ by stariya

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									                                 NMR Probes


Overview:

Nuclear magnetic resonance (NMR) has been used for more than 50 years,
and is one of the best techniques to determine the structure of organic
compounds. Although there are other types of methods, NMR is the only one
for a complete analysis and description of the whole spectrum (Davis, 2007)




With its recent developments, NMR has become appropriate for physical and
chemical applications in most laboratories. Bruker BioSpin (2010) mentioned
that NMR spectrometers are used in many ways, including in the fields of
‘Chemistry, biochemistry, medicine, pharmaceutical, and material science’.

Atomic nuclei have characteristic magnetic materials used to produce
chemicals. In quantum mechanics, the neutrons, protons and electrons of
atomic particles have a spin. In some atoms (e.g., 12C, 16O, 32S), the
magnetic spin is cancelled. Furthermore, the nuclei of some atoms (1H, 13C,
31P, 15N, 19F, etc.) do not have a magnetic spin.



The magnetic spin of the nucleus of an atom should be determined using one
of the following rules:
1 - If the numbers of protons and neutrons are equal, the nucleus does not
have a magnetic spin.
2 - If the number of protons plus neutrons is odd, the nucleus has a half
integer in the magnetic spin (i.e., ½, 3/2, and 5/2).




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3 - If the numbers of protons and neutrons are both odd, the nucleus has a
magnetic spin property (i.e., 1, 2, and 3). (Edwards, 1997).

A large number of samples are needed for mass spectroscopy analysis. This
is the case with NMR; however, with modern instruments we can obtain a real
result with samples which weigh less than a milligram (Reusch, 2007).

In this report, we will focus on the difference between probes and indicate
their mode of operation. Then, we will briefly describe the operation of
different types of probes that are routinely used and the trend towards using
cryo-probes, flow probes and low-volume probes.




Main body:

We will discuss some types of probes used in magnetic resonance
applications, and then focus our discussion on cryo-probes, flow probes and
low-volume probes, which are used increasingly in this area.

The interface of probes occurs between the sample and the spectrometer. It
has advanced performance and flexibility, which is an indispensable quality in
NMR spectrometers.




The inside of coil of the probe can be tuneable to more than one frequency
range, enabling observation of the nuclei 'between 19F resp. 31P and 15N',
according to Bruker BioSpin's research and development (R&D) group. This is
dependent on configuration, but the outside coil is perfect for 1H observation
and uncoupling (Bruker BioSpin, 2010).




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We will begin with the BBFO plus Broadband Probe, which has a high degree
of sensitivity.




This has features that facilitate the observation and radiation of the nuclei of
all NMR from 31P to 15N and to 1H and 19F. Any of these nuclei can be
chosen to be tuned and matched automatically.
These probes can provide high-quality observations of ‘19F with 1H
decoupling and to perform two dimensional 1H/19F spectroscopy’. There are
two uses of the nucleus due to the two separate coils, and ‘artefacts common
with double tuning of one coil are eliminated’.
Bruker asserted that the probe was designed for the highest linearity and
shortest time to recover the gradient. Finally, these probes can be used with
single or multiple solvents, ‘using supersaturation or pulsed field gradients’
required for samples from controlling the reaction that has happened, body
fluids, and biological samples (Bruker BioSpin, 2010).


Dual probes allow the exchange of observations for two nuclei. Internal coils
are best suited to a nuclei, for example 13C. On the other hand, for B nuclei,
for example 1H, the outer coils are good.
This probe is usually used with different spectroscopy samples.
Using this probe, we can easily obtain 13C and 1H NMR that with a large
number of samples.




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This probe is used to study the single and double resonance of chemical
samples that are set with the internal coil at 13C and external coil at 1H for
perfect sensitivity in both nuclei. Probe optimisation in laboratory 1 and 2D
only involved 13C and 1H (IET,2008; Bruker BioSpin ,2010; Macnaughtan et
al , 2002; Agilent Technologies, 2010).

DUL Plus Probes are very sensitive to 13C and 1H. The unique design allows
a shorter time to recover the gradient. For a single or multiple solvent any
methods of ‘suppression using super saturation or pulsed field gradients are
applicable’. This is what distinguishes X-observation probes, along with the
ability to study samples in solvents proteins and control the reaction, body
fluids and biological samples (Bruker BioSpin, 2010).

Now we will move on to discuss cryo-probes, flow probes and low-volume
probes.

Cryo-probes have a lot of applications that do not end with spectrometry.
These probes were developed a few decades ago, and resulted in a
substantial increase in the sensitivity of NMR. This gave more opportunity to
monitor the quantity of very small samples. This resulted in a significant
increase in productivity. According to Bruker, (2010) ‘every CryoProb
interfaced with a fully automated universal’, and the probe runs at a very low
temperature, reducing the amount of noise (Bruker BioSpin, 2010).




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The cryo-probe in a cold case can be used as a traditional probe. The
sample must be a few millimetres away from the coil RF cold. It must
be      made        stable        in      temperature       by    the    user.
The cooling system must be closed well to control all the functions;
the    probe      can        be    used       for   short    or   long   tests.
This system is simple to use.

Below, we discuss cryo probe mechanics, probe changes, sample
handing and optimisation for X-nuclei detection.

At low temperature, a high signal and less noise are generated by the
electrons’ radio frequency. This process is the real advantage of cryo-
probe technology.

Improvements can be achieved by reducing the temperature of the
coil for the NMR signal amplifier.

Cold helium gas is used in the cooling system in a closed annular
assembly process that cools the coil and amplifier. The helium gas is
compressed in one chamber; then it is allowed to expand to the other
chamber.

Coil assembly can access low temperatures through the isolated part
of the vacuum in the cooling system CSS. Thermal insulation in the
probe is very important, allowing samples to be measured at room
temperature.

The advantages of the cryo-panel created by Bruker are as follows:
automatically cool-down/warm-up and a timer system which provides
the user with a complete interface for the cooling system closed loop.

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Using one button, we can run cool-down and warm-up; these are
completed in 2.5 and 1.5 hours, respectively.

For sample handing, the cryo-probe is similar to the traditional high-
resolution probe. It is possible to change samples with the cryo-probe.
The cryo-probe is compatible with LC-NMR. Cryo FIT is available to
convert the cryo-probe from the tube to the flow method.

In these probes, the internal coil is optimised for one nucleus, such as
13C ‘that is without digital switch, DUL’ or three nuclei like 31C, 31P
and 15N ‘that is with digital switch, QNP’. 1H decoupling in the outer
coil is also optimised. For example, we can decouple 1H and then
acquire the 13C spectrum; it will then switch to 31P observation with
1H    decoupling     (Bruker    BioSpin,   2010;    Saitoh   et   al,   2008;    Doty
Scientific, 2010).

Flow-Probes

Bruker     has   provided   a   variety    of   high-resolution   flow-probes.   LC-
probes with optimised cell size in order to generate a flow-probe,
Chromatographic peaks in terms of reducing the bond broadening
through the transfer of the sample (Bruker BioSpin, 2010).

The advantages of flow-probes are as follows:

     1- The RF coil in the spatial geometry with the fixed flow cell, due
         to an improved filling factor, has high sensitivity in NMR in
         comparison to the standard probe tube.
     2- Optimisation in the preparation of samples such as shim or it is
         not even necessary, only the exchange of the sample solution.
     3- It is not necessary to prepare the sample in an NMR tube, as
         NMR tubes are expensive.

The chromatographic system provides a seamless link for the flow-
probe; the processor allows for the transfer of the liquid sample



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directly into the NMR tube and directly converts the displays. The
advantages of this are as follows:

      It reduces the risk of pollution and involves minimised sample
       handing.
      Measurement of the samples prepared for NMR at a very high
       speed and level.
      The        only   modification     necessary     to   convert       the   NMR
       spectroscopy index to flow application and back is the probe.


       The properties of the flow-probe are as follows:
      Field strength of 300–900 MHz.
      The flow cell is available in three sizes: 30, 60 and 120 µl.
      The NMR configuration is available as an SEI-probe, TXI or DXI
       (1H/19F).
      Z- or XYZ gradients, ATMA and BTO are available.
      It is compatible with all types of HR-NMR spectroscopy.
       (Bruker BioSpin, 2010; Haner et al, 2000).


Low-volume probes


In the past few years, there has been significant growth in the demand
for thumbnail sizes in R&D. There is also a need for analytical
methods      that   require     small   amounts   of   samples;     many of      these
applications      necessitate     technology   that    provide    better   productivity
and open the doors to research in NMR applications.

For this challenge, design of a new magnetic resonance probe has attracted
great interest.
The 1 mm micro-probe works with pipe samples; the sample size is 5
microlitres, and in fact a smaller sample can be used to be run every NMR
test for allergens. Furthermore, this method is up to 16 times faster than
traditional methods. This probe can be used for various NMR applications due
to the design types of the TXI-probe and Z-gradient coil, as well as the

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automatic matching and tuning accessories.


The most important advantages of this probe are as follows:
   1- The mass sensitivity is up to four times that of traditional probes
      (more than 5 mm).
   2- It has excellent solvent suppression properties.
   3- Salt does not have a practical impact.
   4- The sample       can be stored and sealed           because there     are
      discrete sample in the tubes.
   5- The preparation and handling of samples is automated.


The discrete and disposable 1 mm sample tubes may be sealed after
filling with the 1 mm micro-probe.


Now I will look at the application of microprobe, and specifically the
structure of the proton. From the determination of the proton, an 8 KD
structure is given as an example of the spectrum. Five microlitres
have been used out of the 1.4 mM solution, corresponding to Ca 72
micrograms of the proton.
Burker Biospin achieved a technological breakthrough of a new coil
called coil-on-a-chip technology, and this requires the investigation of
sub-millimetre samples at a very high isotropic level, and 10 µm from
the resolution and less than that number. This is for the application of
modern magnetic resonance micro-imaging.


The micro-coils on the surface have a small diameter, such as 20
micrometres. Their mass-sensitivity is up to 50 times that of the
traditional method, where 5 mm of the coil can be achieved. This
allows for 3-D MR imaging with a voxel volume of 1 picolitre in less
than an hour. It can use new micro-coils such as ‘exchangeable
inserts in vertical bore magnets’,        which are      fully compatible   with
standard micro-imaging probes (Bruker BioSpin, 2010).




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The standard bore micro 5 imaging probe has been developed for
applications of the bore magnets 52 mm ID, so as to achieve things in
small diameters, from smaller than 1 mm to a maximum of 10 mm.
This probe has ‘a modular construction with exchangeable rf-inserts of
various   designs   and   variable   temperature    operation   and   control’,
similar to those used by the standard, high-resolution spectroscopy
probes (Bruker BioSpin, 2010).
A removable gradient system is available in the micro 5, so that it
uses the same body as well as electrons, like the Diff 30 probe
(Bruker BioSpin, 2010; Doty, 2007; Varian, 1999).




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Conclusion:

There are several different types of probe; their advantages and
disadvantages and how to operate them in terms of efficiency and quality to
obtain satisfactory results have been described. Properties of the different
probes are summarised below.

The BBFO plus Broadband Probe can accurately identify allergens and
monitor the disengagement and the spectral analysis 19F with 1H. It also has
excellent gradients in the field of supersaturation through its springs and can
handle multiple samples of the solvent required, controlling the reaction that
occurs. The second type of probe is the Dual probe, which allows us to
monitor       exchange      when      there      are     for     two      cores.
And usually uses this investigation with different samples of spectral analysis
routinely. We also recognise the merits of DUL plus Probes, which have a
unique design.



In recent developments, several types of probe have been used in magnetic
resonance. This report has focused on three types of routinely used probes:


Cryo-probes, which have many applications in sensitivity spectroscopy; this
sensitivity allows scientists to monitor very small quantities of samples. The
advantage of this probe is that it maintains low temperatures to reduce the
rate of noise. In addition, this probe is optimised for a simple system and there
are no complications in its use.

Flow-probes are known to have the most appropriate cell size. The most
important feature is its improvement of the packing factor compared to
standard Ermspar tube. Om addition, the liquid sample can be transferred
directly into the MRI tube; this is compatible with all types of HR-NMR
spectroscopy.

Low-volume probes are used for mini sizes. This has opened the doors
towards applications in the field of MRI in terms of improved productivity and
working with very small samples.

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Each type of probe has its own advantage of independent, and the application
should be considered before the type of probe is selected.




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References:

   -   Agilent Technologies. (2010). Direct Detection Probes. Available at:
       http://www.varianinc.com/cgibin/nav?products/nmr/probes/liquids/direct
       &cid=LPKJOKHKFIH. Last accessed 2nd DEC 2010.

   -   Bruker BioSpin. (2010). NMR Probes. Available at: http://www.bruker-
       biospin.com/probes.html. Last accessed 20th Nov 2010.

   -   Davis, K (2007). New Techniques for Examining the Brian. New York:
       Chelsea House.

   -   Doty Scientific. (2010). The Cryo probe for Solids. Available at:
       http://www.dotynmr.com/solids/sol_cryocoilpg.htm. Last accessed 6 th
       DEC 2010.

   -   Doty, D. (2007). Probe Design and Construction. Encyclopedia of
       Magnetic Resonance.

   -   Edwards,     J.  (1997).  Principles of NMR.     Available         at:
       http://www.process-nmr.com/pdfs/NMR%20Overview.pdf.
       Last accessed 22nd Nov 2010.

   -   Haner, R. Llanos, W. Mueller, L. (2000). Small Volume Flow Probe for
       Automated Direct-Injection NMR Analysis: Journal of Magnetic
       Resonance. 143, 69–78.

   -   IET. (2008). NMR Probes. Available at: www.IetLtd.com. Last
       accessed 29th NOV 2010.

   -   Macnaughtan, M. Hou, T. MacNamara, E. Santini, R. Raftery, D.
       (2002). NMR Difference Probe: A Dual-Coil Probe. Journal of Magnetic
       Resonance. 156, 97–103.

   -   Reusch, W. (2007). Nuclear Magnetic Resonance Spectroscopy.
       Available:
       http://www2.chemistry.msu.edu/faculty/reusch/VirtTxtJml/Spectrpy/nmr/
       nmr1.htm#nmr1.

   -   Saitoh, K.Yamamoto,H.Kawasaki,K .Fukuda,Y.Tanaka,H.Okada, M.
       Kitaguchi,H. (2008). Development of Cryogenic Probe system for high-
       sensitive. Journal of Physics: Conference Series. 97, 12-41.




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-   Varian. (1999). Microimaging NMR Probes. Available at:
    http://cp.chem.agilent.com/Library/usermanuals/Public/0199912900a.p
    df. Last accessed 5th DEC 2010.




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