I assume you are referring to the new Picarro, Los Gatos, etc. instruments? Or are you talking about buying a stand-alone laser and building your own instrument? And which stable isotopes are you interesting in analyzing? And in what kinds of samples?

From what I understand, TDL is best used for stable C and O isotopes in CO2.

Our group has a Picarro for measuring C isotopes in CO2 and CH4, and we have a Picarro on order for measuring N isotopes in N2O. We have used it in a large number of applications and we are very happy with the instrument. I think the price was ~ $100K (Aus) the N2O instrument is ~ $150k. Pros = Field portable (with modifications), robust, simple sample preperation/conditioning cheap (ompared to an IRMS). Cons = not quite as precise as IRMS (this is dependant upon measurement time, which is dependant upon sample size), there can be influences in the measurement from high concentrations of other gases (eg sulfides, VOC etc), data analysis (the instrument logs takes measurements at ~ 1 sec intervals, so for long term use there is a whole heap of data which needs to be processed) and you are restricted to measuring only one isotope in one or two compounds. All up I would say it all depends upon the application you want it for as to whether TDL (or cavity ring down spectrometers) are better than IRMS

Hi Miquel,

It all depend what you want to do with it and if you want something you versatile or rather something plug and play.

First of all is about what Isotopes of what molecule (to my knowlege the most common on are 13C and 18O (some also 17O) in CO2, D and 18O(17O) in H2O, 13C and D in CH4, 15N (site spec, this is a major advantage compared to IRMS ) and 18O in N2O other options are also possible.

To measure these some companies (Aerodyn (15N15N18O, 13C218O, 13CH3D) and campbell (13C218O)) use Mid infrared technology, which are the preferred (most sensitive) wavelength zone to measure these rotational-vibrational adsorptions, however these lasers (and /or detector) have to be could (sometimes with LN2) and are verry expensive and not robust. The other companies work in the near IR (cheap, robust lasers) where the adsorption (by overtones of these rotvib interactions) is much lower reducing the sensitivity, which they remedy by using extremely long pathlength using cavity ringdown technology (for mor info see http://www.picarro.com/technology/what_is_crds). Two companies use this technology picarro and los gatos (both D en 18O (LG also 17O) in H2O (liquid,vapor (picarro also leafwatter) etc....), 13C, 18O (LG also 17O) in CO2 , 13C in CH4, 15N15N18O (to be able to measure ate ambient concentrations they also use mid IR, increasing price and lesser the robustness). Recently Thermo develeoped a system working with the interference of two NIR lasers to obtain the adv of a midIR (but not jet on the market.)

Manny more factors have to be taken into account in order to take a decision about what to chose.

Shortly my impression of the companies and their instruments (but this is only an impression as we only have an instrument of picarro)

Campbell; quite large instrument, when asking for info not very helpful (instrument 80 till 120k$) couldn't telore about them.

Airodyne: from a theoretical point of view these are probably the most sensitive and versatile instruments, but cost is high 160 - 180k$ plus high cost (20k$ per laser, with limited lifetime ). But I think that you have to be a well trained in spectroscopy and optics to be able to get the most out of it

Picarro and Losgattos are similar, quite easy, robust instruments (from 50 till 150k$(N20)) with multiple possibility of coupling with prep units etc....

Thermo not clear jet, probably a nice alternative (they will be competitive price wise they told me).

Hope this help and if you decide what you are interested in I could give you more detailed info.

To answer your question it is needed to know which are the isotopes you wish to study and or separate because the wavelength of the laser to be utilized is function of the izotope.

Picarro Tunable Diode Laser (TDL). Cost: ~$102,000.... www.picarro.com.

I installed a Los Gatos CO2 instrument in the lab in Mitra, Portugal for Birgit Arnholodt-Schmidt. Since we wanted to do isotopes in O2, I also built a device on the front end that measures O2 consumption rate and converts the O2 into CO2 for isotope measurements.

Lee Hansen

In what compounds do you want to measure stable isotopes and in what kind of samples? Also, what is the application area? For example, are you doing stable isotope labeling experiments, or are you looking at natural isotopic abundances? Do you need high accuracy of the isotopic abundances (for example, looking at isotopic fractionation in different metabolic processes, such as C3 vs. C4 metabolism), or can you use something with a bit less accuracy? Do you need to distinguish different kinds of isotopes (e.g. 13C from 15N) or not? Are you looking at organic compounds or doing elemental analysis of metals? What kind of sample preparation do you have in mind? For example, will you be preparing the samples by combustion or looking at the intact molecules? All of these questions, and more, may influence your technology choices.

If you have enough money the best way to measure stable isotopes is often by mass spectrometry. Then, depending on exactly what you want to do, you may want to use an accurate mass instrument such as a magnetic sector instrument, a time-of-flight instrument, an Orbitrap instrument, or an FT-ICR instrument.

By the way, hello Lee Hansen, from your friend Alan.