Handheld XRF Analyzers are very capable and can indeed analyze on-site about 30 elements in some minutes, but this instrument is mainly used with samples under field conditions. Interferences, absorption and enhancement, surface effects, grain size and mineralogy as well as the presence of water change the measured signal intensities of the elements. Therefore accuracy problems may occur. You need a lot of experience to assess the validity of this data, but it is possible to handle this problem.  In desktop XRFs you can perform a sophisticated sample preparation (grinding, use of pellets) to reach more reliable results (higher accuracy) .

The detection limits of this XRF methods reach the lower ppm-range. Soil samples for AAS or ICP-MS need an acid digestion step before measurement which has to be validated too. AAS or ICP-MS are more sensitive (3 orders of magnitude and more) but are not applicable under field conditions.

We use both XRF and ICP-MS according to the conditions to be met.

Hi khalid,

The simples answer is: it depends...

To obtain the reliable results you really need to have a good quality sample and a reliable calibration. Technically even a simple hand-held device can give you a good result, especially for major elements present in the sample. Depending on the instrument model you can get better or worse sensitivity and resolution. For 120 second analysis I'd say you can only get the results for the elements with really high concentrations within the sample matrix.

I would also not rely completely on the results obtained for the unprepared sample.

Real life conditions and sample types may differ signifficantly from the nice and well homogenised standards used to calibrate the detectors. I personally would not use the result for the unprocessed sample for quantitaive analysis. I'd only ue it as an indicative measurement or screening, which shoul be followed by the measurement of the properly homogenised sample.

Kind regards,

Pawel

From an agronomic point of view, the most interesting soil analisys is extractable elements analisys. Then you need to extract them with several solution: different for macro or micronutrients. So you have solutions to measure and the best option is ICP, OES or MS. Of course agree with Gruber and Gaca.

Thank you for your relevant contributions, I would say that sample preparation is quiet regular in those cases. The company often advise users to prepare their sample (selling more materials), so the device will be calibrated (also given with tha package)  and results will be good for interpretation. The last point raised by Dr Baigorri is also important, and again we have AAS and UV-Vis devices. I'm concerned with the price difference between ICP/OES/MS and XRF, why we still working with heavy devices while we can use XRF with good and simple preparation of sample? I have just received this afternoon a quote for XRF ThermoScientific XRF NITON XL3t GOLDD with about 55 000 euros for the whole package (handheld XRF and sample preparation kit grinder excluded).

What is your point of view? should I go for it of look for ICP for soil elemental analysis?

Dear Khalid,

The choice of the analytical technique depends on what your element/compound of interest is, potential interferences (e.g. ovrlaping peaks), desired limit of detection, precision and accuracy, the type of sample and the number of samples you need to analyse in a given amount of time.

XRF is usually good enough to give you the concentration of elements from % to ppm, sometimes ppb level, although the later would rather be achievable using . ICP-MS can take it down  to ppt and sometimes lower levels, depending on the instument and your ablity to prepare a suitable sample solution using a variety of sample dissolution and purification procedures. Of course the price of the good ICP-MS and the runing and maintnance costs are at completely different level when compared to the 55000 EUR for the NITON XL3t device.

Regards,

Pawel

Dear Khalid,

we use the device that you cite above (NITON XLT3t GOLDD) and we made good experiences when using it for sediment samples, archaeological artefacts etc. However, we did not use it in the field for sediments as for the above mentioned problems (e.g. grain size effects, water content, sample inhomogenity etc.). We use dried and grinded samples for portable energy-dispersive XRF measurements and made good experience when using adequate certified reference material. You can find some hints in the following publication in the supplementary data for exactly this instrument (Schwanghart et al 2016, 08.January, Volume 351, Issue 6269, pages 147-150. DOI 10.1126/science.aac9865).

Please feel free to contact me if you need more information!

Cheers, Philipp

Dr.Khalid,what analysis you want to do using XRF?Do you want quick results without lab work or reliable analysis based on lab work for R&D purpose?Learned colleagues may highlight for what element the XRF can give reliable and reproducible results with in the normal level of their occurrence in soil or they should be present in high concentrations. AAS and ICP are very sensitive and can give  elemental concentrations especially micronutrients and heavy metals in ppm or ppb levels.

Khalid , your question  is very relevant . XRF could be effective for quick results  in field , simply as indicative values . But , I have my own reservation , whether   it can compete with the conventional analytical techniques involving ICP /AAS, when you talk of precision analysis.

The depth wise variation in clay soil plays an important role in water stress during flowering and its duration of stress too. The clay content (%), porosity, available depth of soil moisture and its holding all these factors affect flowering in different ways. This variation in soil moisture stress is heterogeneous due to soil types and flowering due to low temperature stress is uniform being air borne and so the regularity and uniformity in the flower induction. This is my opinion.

Thank you Dr Srivastava and all colleagues for your contributions. It's clear now that the XRF is also reliable than ICP/AAS and can go for ppm and also for ppb in precision. On the other, sample preparation is a crucial point to be raised. Samples should be dried and calcined prior to XRF analysis. Organic matter as humus like soil and compost should be transformed in mineral form by calcination for analysis. The limit in my opinion is the XRF do not support liquid sample (waster, wastewater, oils...).

Thank you all

To the best of my knowledge,I may not endorse your second sentence.Learned colleagues who have first hand knowledge of the XRF analysis may comment.

Thanks Dr Rao. Can give more details about your raised point? 

Dr.AzimI have only reservation about  your second sentence in the last reply.The limitations of XRF were already pointed out by Drs .Gruber,Gaca (in their second paragraphs) and also by Dr. Hoelzmann. You have also summarized the problems and solutions in using XRF based on colleagues' comments in your last reply. So based on samples'condition,nature of materials and elements of your interest and level accuracy needed,you can choose XRF or AAS and ICP.

I appreciate your feedback, I'm highly sensitive to your comments because I'm asked to make a decision between XRF and ICP (AAS is already in the lab but deuterium lamps are very expensive in addition to the digestion step).

Thank you all for your valuables hints.

Best regards

Dr.Azim,I understand your  sentiments.I think your best adviser is Dr.Hoelzmann who has first hand knowledge of the XRF analysis with different materials with and without processing.Also he has suggested a published paper which you may see(already seen?).Please take a decision based on your need , required accuracy  and reproducibility.

Dear Khalid 

By sure that you may the price to using pXRF instead a more powerful lab XRF or other techniques (ICP, AA) to estimate total elements. pXRF is quite accurate for qualitative and  semi-quantitative estimations (without calibration). If you are interested in an specific element  (as Fe, U) a target calibration can be also used. We are just testing the price of no preparation the sample (digest, press or fusion) and using the pXRF in the field, our preliminar result shows that it can be very useful to  delimit archaeological areas and also to separate management areas in precision agriculture. You should be aware about large difference in humidity and density of your samples.