People have used ATR with FTIR for airborne particle analysis, however, in my experience precise quantitation is often difficult via IR. Depositing particles on the ATR crystal is very convenient however!

Thanks for the answer.

You hit the nail. I wonder if anybody replicated the benefit of the ATR (mutliple passage on the sample) to increase the sensitivity of the transmission FTIR technique. ATR is not an option for an accurate quantification. But transmission IR has been used with good success in several techniques for the quantification of a mineral component in the dust.

Mr. Cauda, If I understood properly, you would like to quantify using transmission (or absorbace) from depoosited sample surface (I assume a large surface, than usually employed for standard FTIIR spectrometers) , avoiding the attenuated total reflection techniques. The set of IR mirrors most probably would result to a successful quantitation.

It has however other instrumental scheme, which would be applied for IR (most probably). Nevertheless that for Raman spectrometers I am almost sure that it would be run successfully. It involves 'moving source' or 'moving sample holder'. Than the whole area of sample would scan and thus quantify iin transmiission or absorbance.

In such principe functionalize UV-MALDI mass spectrometers. Where actually the ionization/desorption mechanism involves surface scanning by laser beam (UV or IR), quantifying the compound of interest within the frame of a large surfface area. Really the method has completely different physical background. But the ionization is achieved by surface laser ablation and the analysiis is quantitative.

The construction of FTIR (or Raman) instrument scheme with 'moving sample holders' is technically more easy than multi-mirrors scheme. For each scan can be measured different surface area encompassing whole sample. And then the process would perform repeatedly achieving increasing of the intensing of the S/N ratio via a multi-scan mode and cumulation of the spectra, which is usually perform by each FTIR spectrometers operating in transmission mode. Neverthelless that I am not sure even with such scheme is it possible to achieve the method performance parameters typical for mass spectrometers of UV (IR)-MALDI type?! Most probably not?! They operate at concentration limits of detection of fmol-attomol range. But IR-(Raman) methods, have their irreplaceable advantages for the chemical analysis.

Dear Bojidarka,

Thanks for your reply.

I'm using 37 mm filters for the collection and deposition of the sample. The deposition is known but with a single passage the sensitivity of the method (with our instrument) might not be enough if you consider that I'm trying to quantify a component in the dust with a low percentage.

A moving sample holder is interesting and I agree that it can more "easy" than a multi-mirrors scheme. Raman is not an option for our application (we tried) because the matrix is too noisy. I never worked with any UV (IR) MALDI but I'm interested in knowing more. The analytical/monitoring solution that I'm seeking must be cheap, user friendly, and portable.

Regards

Emanuele

Mr. Caude, Really the portable instrumentation of mass spectrometers are among the perspectives for the instrumental design of the method, because of for case analysis it is very difficult to applied them currently. In this respect really the IR-method has its advantages. Why you do not try in your current instrumentation to cumulate large number of scans (I hope that your instrument is with Fouriier transformation!). Than perform the same experiments only of your filters without the deposited compounds. Afterwards subtract both the spectra. Under this procedure you eliminate the matrix IR-bands, and remain only the substances of interest. By the way by this methodology we achieved concentration limiits of detection for pharmaceutics below than 0.43 %. Taking into account that we are not used strongly intensive IR-bands, such for example classical nC=O band. For codeinone in mixture with codein for example, using the latter IR-mode, however, even we have achieved LOODs of 0.11 %. Please account that it was only 'prima vista' analysis at sample sets of 10 scans. The data are even not published. Therefore if you found that such method would be applicable for your sample sets and indiviidual compound/s of interest, than it would be most cheap and easy variation for you. If the analyte has strong characteristic IR-bands, than it would be most probably applicable approach. Because of it consiists actually only of processing of the spectra by the available IR-softwares.

If you want to analyze thin films attached to IR transparent substrates like silicon, CaF2, etc

you can of course prepare stacks of those coated substrates and measure the sample intensity spectrum.

However you have to use the intensity spectrum of the stacks of the uncoated bare substrates as the reference.

Maybe you could not increase the stacks above a certain value,

since you have to compensate also background signals from the substrate material. Just try out.