I want to know which is better for decomposition of matrix before Spectrophotometry analysis between dry ashing and wet ashing of samples.
It depends on what are you looking for. Ashing and filtering is a good general alternative
@teodoro, can wet ashing digestion be used to decompose plant materials for micro elements determination.
I guess by micro elements, you mean trace elements. Both wet digestion and dry ashing can be used for the determination of trace elements in plant materials and other biological/environmental materials. I have described a range of wet digestion and dry ashing methods that can be used for this purpose in the attached paper. Most of these methods will work more easily with spectrophotometric methods. Also see our paper on "Rapid Determination of Ultra-Trace Concentrations of Mercury in Plants and Soils by Cold Vapour Inductively Coupled Plasma Optical Emission Spectrometry".
Article Comparison of Some Wet Digestion and Dry Ashing Methods for ...
@Adeloju. Thank you sir for the response. I shall pretty go through it. But could the wet ashing be applied in determining plant nutrients like Ca, Mg, Fe, P etc?
Definitely, you can use the wet digestion method to determine nutrients as we did recently for P in the attached paper. This method will also be suitable for determination of Ca, Mg, Fe, etc but I recommend that you validate with a good reference material or by recovery study to make sure your results are reliable.
Article Evaluation of Some Wet Digestions Methods for Reliable Deter...
@sam adeloju-how do i carry out recovery study you mentioned. Am familiar with the use of reference materials and blank method. Do you mean calculating percentage recovery from CRM?
The determination will depend on the concentrations of elements present in the matrix.
if amounts less than 0.1 ppm is expected then I recommend ICP-OES with microwave digestion.
If not then the best method would be as follows.
Weigh the plant material to the nearest 0.1 mg. Freeze-dry the materiai, weigh again and then pulverize and press into a pellet. Coat the pellet with a thin layer of carbon. (We call this non-destructive preparation). Now you can perform scanning electron microscopy analysis (SEM) and X-ray analysis (XRA such PIXE, XRF etc.)
Use the SEM data to obtain the matrix composition elements (C,H,O,N,P,S) as the minimum detection limit is normally greater than 0.05 %wt and XRA data to obtain the trace element concentrations Here you might obtained concentrations in the 0.1 ppm ranges. As usual, keep the coated specimen(s) in a dust-free place.
Sorry, but I have assumed that SEM facilities are available as it should be at any university. XRA facilities are relatively costly. However these are normally national facilities that can be accessed freely when you are registered with a university.
We have ICP facilities available, but I use these for the concentration ranges of 0.1 ppm (that is 100ppb) and lower.
Most importantly, you can use these prepared specimens for any further analysis.
I am familiar with all international XRA facilities, so let me know where you and I will give you any recommendations.
If you do expect ppb concentrations than keep part to the pulverised specimen for these.
Hope this has been acceptable.
@ Johan Mars- Thank you for the contribution. I am in Nigeria but it seems such facility is unavailable here. Nevertheless, let me know if you know any in Nigeria and perhaps you can link me up. Regards
Clement, recovery study is done by spiking (adding) known concentration of your analyte to your plant sample prior to the digestion and determining how much you recover after digestion. For example, if you want to analyse for P in a plant sample: You will take a portion of the plant (usually in triplicate), digest and analyse. To another portion (again in triplicate), you will add known P concentration and then digest and analyse. Suppose your plant sample only (without spiking) gave a concentration of 0.50 mg P/kg and the portion you spiked with say 0.25 mg P/kg gave a concentration of 0.74 mg P/kg, then your % recovery = (0.74 - 0.50 / 0.25) x 100 = 96% recovery. My only other advice is that you should do the spiking at three different concentration levels within the expected concentration range to ensure that the spiking test work linearly within the whole range of P in your sample. In other words, with the example given here, I would repeat the spiking at 0.50 and 1.0 mg P/kg if my expected concentration range in the plant material is within 0.1 and 1.2 mg P/kg. If it works, I should get a recovery close to 100 + or - 5% or less.
@Sam Adeloju- Thank you so much for this tutorial. I think to be on a safer side, reference material would be better for me. Its easier to analyze and compute the recovery.. Please let me have your email contact.
Ok, yes you can do the recovery with certified reference materials (CRMs) by comparing the results you obtain with the certified values. My e-mail address is given on those papers I referred you to yesterday. You can also send me a message through RG.
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