Ion Mobility Spectrometer - Expert Design

Do you have a working prototype?

Yes, we do have a model that is slightly different design.

Existing model has

1. Ni-59 radioactive source for ionization of the gas - to be replaced by highly reproducible corona discharge

2. Discrete drift field electric potential electrods - to be replaced by countinuous gradient electric field drift tube

3. 40 ms total scan time for the ion mobility - to be optimized for the size of the tube using air flow control, field gradient control

4. 200ns gate pulse - to be reduced to 100ns ot lower to get narrow peaks and greater resolution

Idea is to change the design and to make it environmental freiendly. radioactivity is thus not a good idea inside the system.

I have some work on controlled corona discharge but it never reproduced with very high accuracy. This part is to be either taken as an average effect for several hundreds of discharges or have to be some kind of new design.

I have also noticed that the electrodes used to become black after some use even though I have used Gold electrodes. This perhaps was happening due to ionized contamination sticking to the electrodes and making corona discharge less reproducible after say million sparks. Considering that only single spak may be enough to do the job, this numbers looks OK to be tried once again. Moisture may play a greater role in corona discharges and hence, that part is also to be solved. This problem does not exist with Ni-59 radioactivety based ionization.

Hi Shyam,

Why reject the radioactive ionisation principle?

Its an accurate, stable way of producing an ionising source, that's why millions of household smoke detectors use a spec of Americium isotope to provide the ionisation source for them, one to act as a reference the other to have the gas present to ionise...

Corona discharge and sprks are so unpredictable and liable to change over time and with pressure/ humidty/ contamination etc...

John.

Dear John,

In some of our designs we used Ni-63 long life beta energy sources up to 3mCi, and yes they work fine. However, there going to be an increasing restrictions on such sources and I can carry or transport such device by air.

Nuclear stuffs are highly mood based for the governments. Hence to be avoided in future designs. These sources also do not allow us to miniaturize. Hence looking for electric discharge, UV laser, and perhaps other similar sources. Even heat based ionization is not preffered.

I agree that Ni-63 is the best choice as it lasts for about 100+ years and has only 1cm range for the beta particles in air and can't really harm outside. But it is hard to convince people who think even small radioactivity is nuclear environmental disaster. In fact in USA Ni-63 3mCi is allowed to be disposed easily. It's beta can't come out of 1mm dust over it.

In India, I need to account for the source for my entire life and if missed then it is almost a serious crime. Hence, if I give to some one then it is my responsibily to account for it, else government may never allow me to use radiation source and may stop my research.

Let us see if anything else is a better solution. As energy is limited in portable systems, I need to economize everything. I am not going to give up that Ni-63 but have to keep those systems under strict regulation.

Ni-59 is dangerous as it has high gamma of 1MeV and lasts only few days. Only Ni-63 is used in IMS these days. I could have used Cs-137 of 660keV but again gamma sources are to be avoided.

Recently developed IMS has beta source. However, my friend who has designed it suspects that thin film of contamination can alter ionization capability considerably and it can affect the output of the ionization and current calibration. Cleaning beta source is also a problem as these are actually coating done by deposition and touching them means damaging them.

I have developed electronics for this IMS drift tube. Developed one has 12 field electrodes, operated on 4kV HV Supply and uses -500V gate pulse of 1us to 1000us.

We are working as a team to develop few models to see which one is most effective one.

Hi,

please send me more info:

my capabilities are 1 ppb, 1 minute resulets.

Rina

zrina@nana.co.il

Dear Rina

I will sure welcome your technology. Kindly respond on my private email.

Thanks.

Just a couple of comments:

This is a pretty long cell, particularly for a hand held device. You should be able to get sufficient resolution in a much shorter cell.

What are you using for the continous field? This can be difficult to implement, and may be more expensive than using rings.

Spark discharges are difficult to reproduce. Also, they tend to create NO3- (as opposed to O2- ions for NI63), which severly limits the ability to detect anything in the negative mode. I have been developing a non-radioactive source which is stable, and allows detection in the negative mode.

0-1000 ppm is a very high concentration for IMS. Typically, IMS saturates at mid to high ppb ranges. Also, IMS has a rather limited dynamic range. IMS saturates at 200-300X of the limit of detection.

I don't see any air drying equipment for the drift and carrier gas. Are you using dry air?

Dear Tad,

To your questions;

1. Ion drift tube right now is with discrete electrodes, set of 20. It is now being replaced by continuous coating similar to channel electron multiplier tube in a linear way.

2. Size of the tube is to be reduced and also drft flow is to be supplementing the ion flow and not going to be against the flow in future designs.

3. Diameter of the drift tube is to be reduced to 1mm

4. I agree that spark discharge is nasty to control and photo-ionization is better with controlled vacuum UV energy of about 10eV to 11eV range.

5. Idea is to use small dry gas cylinder with 1mm tybe which will hardly require any gas for drift zone. Small moisture filter membrane is there and perhaps a cartridge for drift gas recicuilation is used only in bidder systems.

6. Now I am planning FFT based double gated IMS to reach ppb level. Large tube was for ppm level.

7. I am also working on increasing sensitivity and methods to detect ion. Perhaps will think of a way to multiply the ions or separate them spacial point for mass. It is yet to be planned. It is now used only in vacuum based systems.

Thanks for writing in details.

Hello Friends

We do the same work in our Lab.Discharge ionization has a lot of work to do, theritical and practical.

In fact 63-Ni is classified as safe grade source,but radiation material alway a afraid thing for public.Discharge ion source is a good choice.