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All 15 posts   Subject: The Tabletop NMR - An Object of Desire   Please login to post   Down

(Chief Bee)
11-16-03 01:56
No 471135
User Picture 
      The Tabletop NMR - An Object of Desire     

A Personal NMR Spectrometer: The Persimmon (

Nuclear magnetic resonance (NMR) is a valuable tool for determining the composition and structure of materials. It is used in fields such as biochemistry, chemistry, food testing, material science, petroleum, pharmaceuticals, physics, and polymers.

What are NMR Spectrometers used for? Biochemistry uses NMR to determine the structure and exact shape of proteins in their natural environment of an aqueous solution. Chemistry uses NMR to identify how each element is connected as part of a molecule. In food testing, the oil and moisture content of foods can be determined. In material science the chemical makeup and homogeneity of a material can be determined by NMR. In oil exploration NMR is used during drilling to check that the rock being drilled is consistent with the prescence of oil. The pharmaceutical industry uses NMR to verify the purity of drugs. In physics, NMR is used in quantum computing research. Polymer manufacturers use NMR to test plastic density and coating distribution on fibers.

We have created a small desktop NMR spectrometer which we call the Persimmon. The Persimmon has been designed from the ground up using common off-the-shelf components. The system design is modular allowing different parts of the spectrometer to be easily upgraded. The magnetic field is produced by strong rare earth magnets. The initial and operating costs of this spectrometer are therefore very low. This will make the Persimmon affordable for schools and individuals.

A note to the many people that have inquired about the Persimmon and others who are interested in purchasing one. First of all, thank you for you patience. The process of developing a cheap yet powerful and fully functional spectrometer has taken longer than we originally anticipated. We have developed numerous prototypes for the spectrometer. Many of these prototypes either did not perform as well as expected or their operation turned out to be too cumbersome. We have finally settled on a design that meets all our performance and usability requirements.

We call our final design: Software Defined NMR. The RF for the spectrometer is generated using a Direct Digital Synthesizer (DDS). This is a very versatile technique that allows for mHz resolution tunning, and fast frequency and phase shifting. The operation of the DDS and pulse generation is handled by a microcontroller and is fully programmable. The programming is done transparantly by a graphical user interface program running on a PC. The NMR signal is amplified and then directly digitized with a high speed ADC. Frequency down conversion and filtering is done in software. The overall system design is simple yet versatile and powerful.

We are now in the process of designing the final preproduction prototype. Once this is done it must be fully tested and characterized before it is released. This is all a very time consuming process and we appreciate your patience. At the moment it is not possible for us to give a firm date on when the Persimmon will be ready to ship.

NMR Without the Magnet or RF Coils (

To image an object's interior with nuclear magnetic resonance (NMR) a magnetic field of several tesla (1 T =10,000 gauss) is usually required to polarize protons in the sample and then radio waves are used to tip the protons and to detect a weak signal as they upright themselves again. The strength of the signal depends on the size of the magnetic field and the degree of polarization, which is often only one part in 105, and somewhat limits the use of NMR (including its medical application, MRI) because of the need for a bulky, expensive magnet. One way of improving things is to use laser light to produce a polarization as high as 10% in a gas of xenon atoms. The Xe atoms can then be injected into an empty space, such as lungs, and used to image their interior, which couldn't be done using conventional NMR. Another NMR advance has been the use of ultrasensitive SQUID detectors for picking up the magnetic fields produced by protons, greatly reducing the need for large magnets but at the expense of weak signals, with a proton polarization of only one part in 108.

Now, Princeton physicist Michael Romalis and co-workers, while studying whether the Xe nucleus is slightly nonspherical (equivalent to saying that the nucleus possesses a nonzero electric dipole moment, which would imply the existence of "new physics" beyond the Standard Model), have worked out a way to combine different techniques to obtain a strong NMR signal in a very weak 1 micro-tesla magnetic field. They transfer polarization from laser-polarized Xe to protons in an organic liquid and then use SQUID detectors to measure the magnetic field produced by the polarized protons. Romalis expects that this low-field NMR technique would work for any sample -- whether liquid, surface, or biological tissue -- with good solubility for xenon.

The Magnum (
NMR Instrument Using the Earth as its Magnetic Field Source
(Hive Bee)
11-20-03 18:57
No 472026
      Should be rated as excellent!!!!     

Thanks for this.

In have a dream, that one day i ll build my own NMR.
Just a little one to use it in my kitchen.
I have several NMRs at office but they are busy for the next 5 jears so that i only can do some 1H-NMR between the other measurements.
(Hive Bee)
11-21-03 06:19
No 472157
      sounds good     

not too long ago, ning happened upon a thread mentioning this. After some internet research, it appears that making at least a 40 Mhz NMR machine is within personal range.
That requires a 1 T magnet. Ning has seen some papers regarding construction of 3 and 4 T permanent magnets that fit on desk-tops, done by (of course), the physics guys for their beam tubes.

Probably the hardest design problem on the physical side is to make the magnetic field uniform. That will require some cleverness.

Oh, and the electronics. If ning was going to do this sort of thing, the way ze would do it is pulse NMR--time domain signal capture.

In other words, at 40 Mhz, a pulse would be sent out, probably a couple microseconds long, with sharp edges. The reciever coil would go through a mixer to downconvert the recieved signal to the 1 Mhz range, and would be sampled by the baddest-ass ADC that ning could get zer clawz on, which would probably bee either the AD-6645-105 (14 bits, 105 Msps) for speed, or a very nice AD9260, 16 bits sigma delta at 2.5 msps. With the data time-domain sampled in such a rude and overbearing manner (might need a homebuilt firewire or USB 2 interface for the data rate generated, alternately a fake hard drive connector might do as well), all that remains is to perform heavy-duty signal processing on it. Thankfully, that sort of thing is what Moore's law is best for, so our new 20-Ghz Quad-processor massively parallel Quantum-coprocessor augmented wintel boxen should have no trouble with this little problem. Or, more in the real world, a clever programmer could probably take advantage of both their sound card and video card's hardware acceleration functions, as most of the tasks they perform are similar matrix multiply-add operations. That would surely bee worth a tech award: soft-nmr using your old voodoo cards as IIR filters and your SB live to do the FFT! Or maybe one of those hardware MPEG decoder cards....after all, the heart of MP3 is FFT, so hey! it could work.

Of course, we're talking a miserable, large, and involved homebuilt programming job here, but it's a hell of a lot easier than building it in hardware. Plus if you screw up, a lot easier to fix...the use of pulse/FFT would give you the ability to do just about anything your twisted little spectroscopic mind could dream of, as you would have direct access to the return signal from the atoms in the sample. Plus the FFT function would effectively allow averaging to be done for all frequencies at once, giving the famous FT-NMR speed advantage, or to put it another way, allowing you to use a smaller, shittier homemade magnet and still have it work at

So ning would say...anybee, look on ebay, or the web sites of those magnet suppliers. See how big of a magnet you would need to get the required flux. Then compute the cost. Doable?
I think not.
A great
11-22-03 02:02
No 472382
(Rated as: good read)

This article from the Amateur Science column from Scientific American should answer some of your questions wink

Shortly after World War II a group of physicists wrapped a coil of wire around a glass tube in which water had been sealed, put the assembly be­tween the poles of a magnet and sent a high-frequency current through the coil. When the frequency was raised or low­ered through a critical range, the current flowing in the coil varied sharply. This occurred precisely at the point where the frequency of the oscillating magnetic field set up by the coil resonated with the magnetized nuclei of hydrogen
atoms in the water. Further experiment showed that other atoms as well as mole­cules of many kinds react in the same way. Of more interest, however, was the observation that the current varies uniquely for each kind of substance sen­sitivc to the test. In the dozen years since these relatively simple experiments were made the technique has given rise to an instrument called the magnetic-reso­nance spectrometer which rivals the power of the optical spectroscope for investigating the structure of matter
In the course of applying the new technique to the analysis of biological substances, a group working under Miles
 A. McLennan in the Bioelectronics Sec­tion of the Aero Medical Laboratory at the Wright Air Development Center has designed a simple version of the Tuagnetic-resonance spectrometer that amateurs can make at home.It should­serve not only as an introduction to an interesting new field of experimental physics but should also make an attractive classroom demonstration or science ­fair project.
According to the "classical" theory of Physics, all elementary particles of mat­ter spin on their axes like tops, and those that have an electric charge (e.g., elec­trons and protons) generate magnetic fields. (The classical picture has now been superseded by the quantum-me­chanical view, but it will suffice for the purposes of this discussion.) Particles bound in atoms and in molecules not only spin but also move on orbits. This motion adds to the field generated by the spin. The fields of neighboring par­ticles merge; depending on the structure of the atoms or molecules and on the di­rection in which the -magnetic forces point, the fields tend to cancel in some cases and to reinforce in others. In con­sequence all atoms and molecules are characterized by unique patterns of in­teracting magnetic forces.
What will happen to these tiny mag­nets if they are subjected to the influence of an external magnetic field? It was this question that led to the development of the new technique. In the case of the single-proton.nuclei of the atoms of water, the magnetic axes nor­mally point in random directions. It might therefore be supposed that an ex­ternal field would cause the proton axes to line up in the direction of the field. This, however, does not happen. Instead the field causes the protons to precess, or wobble like a spinning top that has been tipped from the vertical. We might say that each particle now has two axes, one about which it spins and the other about which it precesses. The axes on which the particles precess line up with the external field, but attempts to align the axes on which they spin get nowhere. Increasing the strength of the external field merely causes the particles to pre­cess faster. In fact, the rate of precession varies in proportion to the field strength and is equal to the intensity of the field (expressed in gauss) multiplied by 4,228.5. Thus when a sample of water is placed between the poles of a typical magnetron magnet with a field strength of 1,450 gauss, the hydrogen nuclei pre­cess at the rate of 6,131,325 revolutions per second.
It is possible to disturb the particles, however. They can even be flipped over so their "north" and "south" poles are reversed. This is accomplished by setting up a second external field at right angles to the first and causing it to oscillate or reverse direction  precisely in step with the rate at which the particles are pre­cessing. In the case of water in a biasing field of 1,450 gauss the critical frequen­cy is 6.1 megacycles. Energy is absorbed by the particles from the oscillating field during each alternation, just as a tuning fork is set into vibration by the sound waves to which it is resonant. Resonance between the particles and the oscillating field can be established by adjusting either the frequency of the current through the coil or the strength of the biasing field (which determines the rate at which the particles precess). As the oscillating field frequency approaches resonance the particles absorb energy. As they recede from resonance the bor­rowed energy is emitted, part being re­turned to the coil and the remainder be­  shared with neighboring particles. In most substances the exchange of energy between the particles and the coil is surprisingly sluggish with respect to the speed of most atomic processes. Some particles respond immediately at resonance, but others require intervals ranging from a few seconds to several minutes. This complicates the design of magnetic resonance spectrometers be­cause their electrical circuits must be made extremely stable and their output must be observed with the aid of pen recorders.
It turns out, however, that the addi­tion of ferric nitrate to water increases the susceptibility of the particles to the outside field and radically decreases the time required for energy exchange with­out affecting the rate at which the par­ticles precess. According to the Aero Medical Laboratory group, no complete­ly satisfactory explanation for the action of ferric nitrate has been advanced. It may be that ferric ions in solution de­crease the magnetic interaction of the particles and thus render them more sus­ceptible to the influence of external fields. Whatever the explanation, ferric nitrate dissolved in water makes it pos­sible to demonstrate the phenomenon of magnetic resonance with relatively simple apparatus.
The experiment consists of placing containing the solution of ferric nitrate in the pulsating field of a magnetron magnet and, by means of an oscilloscope, observing the exchange of resonance between the sample and a coil around the test tube which is energized by a vacuum-tube oscillator. The energy absorbed during a single flip of the particles is too small for detection  by conventional electronic devices. ­Hence in this experiment the frequencies are brought in and out of resonance 60 times per second. The frequency of the vacuum-tube oscillator is held constant while the rate of precession is varied by modulating the biasing field of the magnetron magnet. This is accomin­plished by placing a second coil energized by 60-cycle alternating current between the poles of the magnetron magnet; the flux of this modulating coil. alternately reinforces and opposes that ­of the magnet. The rate of precession varies in proportion. The vacuum-tube oscillator is equipped with two controls, for adjusting the frequency to the average rate at which the proton axes precess and the other for adjusting the amount of energy fed back from the plate circuit of the vacuum tube to the grid circuit. The latter control regulates the intensity at which the tube oscillates. With this control the oscillator can be a put into or out of operation or, when desired, set at the marginal oscillating  condition.. The modulating coil is wound  with a space in the center to admit the  test tube, and placed so that its axis is concentric with the biasing field, as illustrated.
With the sample in position the oscillator is turned on-and adjusted as closely  as possible to 6.1 megacycles, the aver­age frequency at which the protons precess. The feedback control is adjusted  for the marginal condition at which oscillations are barely sustained. At this critical point current flowing in the plate circuit of the oscillator tube highly responsive to changes of energy. in the coil around the test tube. The intensity of the plate current is observed by connecting the plate circuit to the  vertical terminals of the oscilloscope as shown in the illustration.
A spot of light will appear on the screen. indicating that a fixed value of plate current is flowing. The modulating coil of the biasing magnet is now energized If the frequency of the oscillator has been adjusted to the average rate precession, the spot of light will expand into a vertical line, indicating that the plate circuit is responding to energy exchanged between the coil and the particles. The display can be made more in­teresting by connecting the horizontal plates of the oscilloscope to the 60-cycle power supply which energizes the modu­lating coil. Typical patterns are shown in the diagram.


Chemistry is our Covalent Bond
11-22-03 02:05
No 472383
(Rated as: good read)

In the apparatus designed at the Aero Medical Laboratory the magnetic bias­ing field is supplied by a Type 220A 150 surplus magnetron magnet. The pole faces of the magnet were replaced by soft iron disks 3 1/2 inches in diameter and 7/8 inch thick to provide a field over a large area. For maximum response all protons must precess at the same rate, which means that all must be acted upon uniformly by the modulated biasing field. The intensity of the field will vary with the distance between the pole faces. Hence these must be made par­allel and free from surface irregularities. Surplus magnets from magnetrons of the radial-cathode type usually bear a small white dot on the base which gives an approximate figure in gauss for the field strength that may be expected in the air gap. The magnet used in the instrument constructed at the Aero :Medical Labora­tory is rated at 1,450 gauss. It was modulated by a coil consisting of 20 turns of No. 30 cotton-covered magnet wire wound on a Bakelite tube 1 5/8 inches in outside diameter and 7/8 inch long. Ten turns of the coil are wound at one end of the tube and 10 turns are wound in the same direction at the other end. A hole 5/8 inch in diameter is cut in the center of the coil form to admit the test tube. A second hole 3/8 inch in diameter is made at right angles to the first to admit a length of coaxial cable for linking the oscillator coil to the source of high-frequency current. The modulating coil is energized by the transformer which supplies the tube heaters, and it sweeps the strength of the biasing field 50 gauss above and below its mean value.
The test tube is 12 millimeters in di­ameter and 75 millimeters long. A two ­layer coil of No. 22 enameled magnet wire, consisting of 16 turns per layer, is wound on the straight portion of the tube as close as possible to the closed end. The tube and coil are mounted vertically in the Bakelite form on which the modulating coil is wound.
The circuit construction is conven­tional. The oscillator is designed around a 6AK5 pentode tube. When used with an oscilloscope of high sensitivity, out­put from the oscillator may be taken at the junction between the 22,000-ohm resistor and the 200,000-ohm resistor in the plate circuit. With 'scopes of lower sensitivity, such as the Heathkit Model 0-10, a single-stage amplifier using a 6AU6 pentode is added as shown in the circuit diagram. A variable capacitor, such as the Hammarlund Type MG 140-MI, is used for adjusting the fre­quency of the oscillator. These compo­nents are assembled on an aluminum chassis three inches high, five inches wide and six inches long. Input and out­put connections are made through RC 58/U coaxial cable equipped with UC 290/U and UG 88/U terminals. Power may be taken from any supply capable of delivering 100 milliamperes of direct current at 150 volts to the tube heaters and 60-cycle alternating current at 6.3 volts to the modulating coil.
The test solution is prepared by dis­solving .4 gram of ferric nitrate in 100 cubic centimeters of distilled water. Two cubic centimeters of this solution are added to the test tube and placed in the biasing field. Power is applied. After the horizontal-sweep circuit of the oscillo­scope has been made synchronous with the 60-cycle modulating voltage, a pat­tern should appear on the screen. The pattern may resemble a horizontal figure eight, as shown at left in the illustration. This indicates that the frequency of the oscillator coil lies outside the lim­its within which the particles are pre­cessing and that resonance is not estab­lished. To search for resonance, set the oscillator capacitor for minimum fre­quency (the plates of the capacitor meshed fully) and adjust the intensity (feedback) control to the point where the oscillator is on the verge of going out of operation. Then increase the fre­quency slowly while observing the scope. It may be necessary to trim the feedback control occasionally to maintain the marginal oscillating condition. The procedure can be simplified with the aid of a short-wave radio receiver. If the receiver is equipped for continuous­ wave-reception, the oscillator signal will be heard as a shrill whistle.  If not, it will make a rushing sound, perhaps accom­panied by a 60-cycle hum. The receiver is particularly useful in checking the point at which the oscillator goes out of operation when adjusting the feedback control. If the receiver is calibrated, it may be used to calibrate the oscillator. If not, the receiver can be calibrated easily by tuning in on the time signal of Station WWV.
When resonance is established, the display will resemble the center figure. Usually two peaks appear which are joined at the bottom by loops. This indicates a displacement (phase differ­ence) in the time at which signal arrives, at the vertical and horizontal plate of the 'scope. The Heathkit Model 'scope is equipped with a line sweep switch and a phase control for manipulating the display. When these are properly adjusted, the peaks coicide, shown in the figure at right.
What does the display mean? The height of the figure is proportional to the number of protons resonating with the oscillator; the width of the figure, to the range through which the particles precess. Accordingly if all of the particles were precessing at precisely the same rate and all flipped over precisely in resonance with the oscillator, the pattern would resemble an inverted T. The spectrometer could then be said to have perfect resolution. Evidently in the instrument all the particles do not precess at the same frequency. Part of the explanation lies in the interaction of magnetic forces within the test sample, The fields of neighboring protons merge in such a way that some particles are partially shielded from the influence of the outside field. But in this instrument the breadth of the peaks is large, explained by cross-sectional variations in the strength of the biasing field. Particles  in regions of high-field intensity precess at higher rates than those in regions where the field is relatively weak. These differences are preserved when the field is modulated. Some particles are swept into resonance with the oscillator earlier or later than others, and the displayed peak is broadened accordingly. The width of the peak illustrated is 26 gauss, which means a difference of 85,000 revolutions per second in the of precession of the slowest and fastest particles.
With an instrument of high resolution many substances show fine multiple peaks. This is due to the complex magnetic interaction between systems of partitles and the consequent shielding of ­the biasing field. Many substances are not sensitive to an external magnetic field because the magnetism of the spinning particles cancels out. But those substances that do respond can be identified by the characteristic pattern that shows up on the 'scope. The resolutionof the apparatus described here is high enough for fine spectroscopic work As indicated earlier, it is intended to serve as a simple demonstration of the magnetic-resonance effect.
Modifications to adapt the apparttus for limited applications would include the provision of larger pole faces on the magnetron magnet to provide a more uniform biasing field. In contrast the 20-gauss peak-width displayed by the apparatus, the best instruments made. today resolve to a few ten thousands of a gauss; this means that irregularities in the biasing field must be kept below this figure. High resolution also requires precise and calibrated control of the intensity, frequency and amplitude of the biasing field. in this demonstration the. high sweep-rate of 60 cycles per second,: is made possible by limiting the experiment to a test solution of ferric nitrate. Few substances are so responsive.


Chemistry is our Covalent Bond
(Chief Bee)
11-23-03 18:12
No 472670
User Picture 
      I got a reply to my email to Exstrom     

I got a reply to my email to Exstrom:

[green]Hi Rhodium,

We haven't yet determined the price, but we expect it to set a new standard in terms of price/performance. We think the Persimmon will be ready for sale sometime early next year but we can't give you a firm date at this point. The Persimmon will operate in the neighborhood of 20 MHz, and the signal will be acquired using a 16 bit ADC.

Richard Hollos
Exstrom Laboratories LLC
Longmont, Colorado]
(I'm Yust a Typo)
11-23-03 18:34
No 472675
      *heh*. IIRC, 20 MHz NMR spectra are difficult...     

*heh*. IIRC, 20 MHz NMR spectra are difficult to interpret. Not only because you've got relatively large linewidths (thus giving you nice overlapping triplets and doublets), but also because all you don't have nice AX or AMX-spectra, but instead you got AB2CDX-spectra. (in other words: you don't see nice first-order spectra, but something wildly dependent of the coupling constants of the protons in your sample.). See for instance

I'm not saying that a 20 MHz NMR is useless, but I do believe that it might costs you a lot of effort to interpret those spectra, and that you might learn a whole lot of theory to make some sense of them. And I'll bet that most bees won't have the dedication to go through all that.
(Active Asperger Archivist)
11-23-03 20:53
No 472704

Yeah, but the idea of owning an NMR (table-top, no less) is wonderful.  Plus, in a few more years, imagine how this will likely be turned into a much upgraded version capable of higher resolution.

Act quickly or not at all.
(I'm Yust a Typo)
11-24-03 07:57
No 472817
      Why? Sudden invention of new high Tc ...     

Why? Sudden invention of new high Tc materials?

(stated otherwise: if 'they' are going to bring out a better version in a few years, why don't 'they' bring out a good version right now?)
(Horrible Personality)
11-25-03 20:58
No 473148
      no - profit maximation     

thats a usual principle in economics NEVER to do the second step before the first or in other words:

- first bring the high priced 20MHz
- lower the price till the market is saturated, meanwhile
- lance the 40Mhz machine in the high-price segment
- and so on
- if any possible create a new standard you hold the patents for - 33,58MHz or else

thats the way it is done.

the company is either by now already bought up by the established manufacturers of NMR machines or will get bought up or liquidated through a superior product to a superior price by one of those manufacturers pushed onto the market just in time.

You will see it.
But nevertheless it will trigger a development which will lead to handhold NMR apparati to the usual insane prices - rather cheap to buy used and surplus. Five years from now.
(Stoni's sexual toy)
12-01-03 09:51
No 474036
User Picture 
      I've seen low-megahertz NMRs for tabletops...     

I've seen low-megahertz NMRs for tabletops years ago. Don't remember many details, but their biggest disadvantage was that you can only record fluorine or phosphorus spectra with them if I remember correctly.

I'm not fat just horizontally disproportionate.
04-07-04 06:16
No 499474
      I don't suppose anyone has seen this page?     

Speaking of tabletop nmrs, this guy built his own. 5 Mhz.

I did some research on the topic, and came up with a decent coil design. It seems that you can have a 1.6 Tesla field or so (about the best you can do with iron core), across a 1 cm gap, for about 70 watts. The coil would weigh about 8 pounds. That is a bit tight, but it can bee done.

As for tricky spectra due to overlapping of multiplets, since you control the input pulses, you can do spin-decoupling to clear up stuff. And part of my solution to the troublesome issue of field uniformity would bee to apply reference deconvolution. Not trivial, I know, but hardly insurmountable. So maybe a homemade electromagnet with lapped poles, some ham radio gear, and a laptop computer could make a portable NMR with decent resolution. Who knows?

Catching a buzz @ the Hive
(Stoni's sexual toy)
05-11-04 09:58
No 506395
User Picture 
      Repeat after me: A low frequency NMR is ...     

Repeat after me:
A low frequency NMR is useless for regular organic chemistry purposes. You won't be able to measure proton NMRs with one.

There is a reason why these things aren't built industrially. The company who could do this would corner the market immediately. The reason happens to be that it does not work.

BUSH/CHENEY 2004! After all, it ain't my country!
05-12-04 05:45
No 506604
User Picture 
      Low frequency?     

So 40 to 60 Mhz is low frequency for you? I bet I could do some real work on something like that. Iron saturates at around 1.8 - 2.2 teslas. NMR frequency 42.6 MHz per tesla. My magnet design should net around 1.2 tesla without much trouble.

Low frequency? Not really. Not the easiest to interpret, but scientists have made fine use of 50 Mhz units when they were all that was available.

Don't underestimate the powers of deconvolution, either.'s an AOL chatroom for dyslexic spider monkies...
(Hive Adickt)
05-12-04 08:32
No 506619
      NMR *lol*     

60Mhz is cuite low, not much more usefull than an HPLC if you ask mee. By the way, an 60MHz is quite cheap from time to time on e-bay.

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