I have not ever dealt with mineralizing manure, I did analysis of soils and sediments, but I think you can try this method and the analysis should be careful before you dilute samples well before analysis by AAS or ICP-MS

Perchloric acid digestion should only be carried out in a perchloric hood not with the Kjeldahl equipment.  What is your normal hot plate digestion method, it should not take weeks to complete

Hello, for this you should apply aqua regia. However, the acid mixture depends on the required elements to bei dissolved.  The aqua regia mixture also be used in Kjedahl apparatus.  For this procedure it is extremely important to clean all material as best as possible (acid cleaning) prior to digestion. Please ensure that you are informed about the risks of the acid mixture as best as possible. Prior to digestion the material should be dried (lyophilization or 105 degree celsius) and hhomognized. There are several guidelines for open digestion/extraction. 30 mL of aqua reagia is added to  3g of dried matetial. Please wait for potential reactions overnight, followed by heating up. Reflux should be maintained for two ours. Afterwards the mixture is filled up to an exact volume with ultrapure water (Please be careful). If insoluble residues remain filtration is needed.  To exclude metal adsorption on the filter, polyethersulfon membrane - 0.45 micrometer or less - has to be used. For quantification by ICP or AAS a matrix adjusted calibration is needed. 

You can also apply an microwave assisted digestion if you have such a possibility.  There are several guidelines, too. I can give you more details on request. 

Best Regals

Thorsten

Perchloric acid digestion should only be carried out in a perchloric hood not with the Kjeldahl equipment.

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Judy, you've pointed out a very, very important safety issue!

Sorry, for my bad spelling. I'm on a business trip and using my mobile. The german word recognition makes it rather hard to write in English

The sample size should be dependent on how statistically significant data you wish to obtain, sometimes it depends on how much sample you have been supplied, though.  The apparatus type/shape and how the digestion is performed; flame, hot plate, microwave or any heat source is irrelevant, all you want to do is to have a quantitative transfer of digested sample into an appropriate sized volumetric flask for the final dilution without contamination.  Acid mixture you mention will do the job but to get rid of H2SO4 and HClO4 after all of organic component of manure is oxidized or just before all of organics are eliminated; this is when HClO4 explosion occures, is difficult/dangerous.  It would be better to use H2SO4 as a catalyst and HNO3 as the major oxidizing acid(keep adding until you obtain straw color to colorless solution as the solution concentration increases and look for darkening of the solution which indicates presence of more organic component.).  When you get clear straw to clear colored solution, heat the solution intensely until you no longer get white fume evolving from the sample solution.  Dissolve the residue, if any, in matrix matched HNO3 or HCl  solution(acid concentration to be similar to the standard solutions).  If you are looking for precious metals, dissolve the residue in aqua regia then dilute to final volume.  Microwave digestion can be done without H2SO4 and  usually without contamination since it is a sealed system.  See website for CEM or Milestone, they have many application notes of many different matrices.  You could also use Parr bomb to digest the samples, too.

Good luck!

To answer this question correctly the metals of interest and analytical technique should be known. If using a hot plate or microwave HNO3/HCl 10ml and 5ml should do fine for flame AA or ICPOES. If ICPMS or graphite furnace is used you need to eliminate HCL as this could cause interferences for certain metals such as As.

Kjedahl digestion for AAS elemental analyses is a waste of time and resources. Use HNO3/H2SO4, ratio 2:1 in a nickel crucible. Digest in a fume cupboard and transfer to a muffle furnace to ash. Prepare your solution using conventional methods. Aspirate in your AAS using the appropriate AAS lamp.

Hi,

1. A loonnggnn answer  2. ..and an oops

1. I will be more comfortable with a 1:4:0.5 ratio. For ICP-AES (or -OES) use as little HCl possible as possible. I also prefer that you use the ICP-AES in stead of the AAS, for minimum detection limits (MDLs). If you now calculate the time for preparation for the analysis you will realize that it is very very long. As I am a forerunner of X-ray emission (XE) analysis and backscaterring (BS), I advise that you perform PIXE and SEM analysis. The C, (H), O and N analysis can be obtained with SEM (later on on H). The metal analysis including elements from K onwards can be obtained with PIXE. [Call an Physics Dept of a university near you [Gouvernments normally buy ($3 Million)  these instrumentation for the universities. See that you are affiliated to one. They will have the equipment available or refer you to a research centre nearby].

a. Weigh and dry the sample, w1 and w2 (for dilution calculations), then pulverize, press into a pellet (tablet) and coat with a thin layer of Carbon. Then bombard the sample with particles. [In SEM we use electrons and in PIXE we use protons.] The main difference between SEM and PIXE is the MDLs. For PIXE it is 0.5 ppm and for SEM 0.05% m/m. The major elements (determined with SEM) of your specimen are C, (H), O, N, K, P and S. Since these are always present in the percentage concentration range, MDLs is not of importance. Use the same tablet/pellet for PIXE. Here you will get the concentrations of the elements of K and greater Z till Uranium.

b. H is calculated by difference, I normally use a factor of 16.7% (average of about 150 compounds) of the value of carbon. Eg. From SEM C=42%, O=22%, N=11%, K=7%, P=3% and S=2%. Total % = 87. Concentration of H =7%. Total % now 94. Multiplication factor 87/94. New Concentrations  C%=38.87; H%=6.49; O%= 20.36 etc. You can do the same calculations for the H2O content (wet composition). The concentrations will change. [Note With N and S, protein composition can be approximated and to the types.ALSO no Na and Mg, but follow the same calcs]

2. If you encounter difficulties (from individuals allowing you to do it) for the analysis, just consider that your need for analysis is that you want to show the ease with which XE analysis can be done.

At first this seems a daunting exercise, but an all, you get more results than you bargained for. Remember O cannot be determined with ICP. C can but only as organic acid such as tartaric acid.

I agree with Dr. Andre Mars which is the ratio 1:4:0.5 (H2SO4, HNO3, HClO4). u can also add H2O2.  Perchloric acid digestion should only be carried out in a perchloric hood. u must know which media in icp-oes. if HNO3 acid means that end of residue in HNO3. First stage, Dryness all sample. and then add HNO3 and H2O2 until dry (melting). make sure the temperature of digester not too high cause it will eliminate some of the metals. After u get the residue (melting), add 1% HNO3. use ultra pure water to produce weak acids (1% HNO3). how many ml u want depends on your decision. i suggest (50-70ml) solution. u only need 10ml to run in icp-oes. make sure u weigh of sample and state it cause it will use in your calculation. this is one of  the simple digestion that i hv used before to run my sample (solids phase).

Thanks a lot colleagues. Very enlightening. Really appreciate it.

welcome

For the digestion step, you can also use, a microwave digestion system in order to obtain the samples compatible with ICP-OES analysis technique.

yes camelia... you are right. microwave digestion is more effective and simple. i've done before.

Is there any specific protocol for Microwave digestion. Kindly provide us some info. 

Dear all, 

I think we are loosing the main question. As I understood he is looking for a straight forward

yeah... at least we give some ideas for him... if he can compare method or else..