I agree with the remarks of Dr.Kenneth. You have not clearly mentioned.

You can read the following article. It is useful.

Heavy Metal and Trace Metal Analysis in Soil by Sequential Extraction: A Review of Procedures

https://www.hindawi.com/journals/ijac/2010/387803/

Best wishes

The assessment of binding forms by sequential elution must be considered as an approach and should not be regarded to be specific for single mineralization forms (operational binding forms). However, it gives much more information on your sample than just doing total analyses (e.g. anthropogenic vs. geogenic loads in environmental questions). Since the procedure proposed by Tessier at al. (1979) there appeared lots of modifications, some of which are very specific designs to identify binding forms of single elements (e.g. As, P, U). The reagents used for identification of a specific binding form will co-extract to some extent other components. As an example, in procedures developed on the Tessier approach besides the release of exchangeable ions ammonium acetate will also etch carbonates on particle surfaces.

A crucial prerequisite of thorough identification of binding forms is to take in account the redox condition of the sediments. Many authors have demonstrated that some of the characteristics of these sediments change rapidly in contact with O2 and, therefore, also binding form proportions will change. Handling of sediments (e.g. lake sediments) from reducing conditions without preservation of the original conditions is waste of time and will result in fake numbers. However, starting with sampling in the field the handling under reducing conditions remains cumbersome. Cores should be regularly sliced already in the field into subsamples in an Ar-flushed box and immediately stored under Ar in airtight sample containers (glass). The tightened containers should be transferred immediately in a cooled box filled with Ar until finally stored in a fridge at the laboratory in the dark at 4 ºC. All samples should be processed and analyzed immediately after the sampling campaign. The slices are split in the laboratory into subsamples under Ar atmosphere in a glove box (one part remains under anoxic conditions (sequential elution), the other part is used for total element analysis, grain size, X-ray etc.).

In case of oxic conditions sampling is much easier; specific precautions must not be applied.

The method I applied is described in detail in Zachmann et al. (2009 and 2013; publication can be found in RG); it is a 6-step procedure and is based on Tessier et al. (1979) but it contains some modifications concerning the anoxic processing. In summary the procedure is as follows (Step - Phase – (Extractant) – Duration):

1 - Adsorbed cations – (Ammonium acetate (1 M, pH 7, 20 mL)) - 2 h;

2 - Carbonatic - (Na acetate (1 M, pH 5, 20 mL)) - 5 h:

3 - Easily reducible – (Hydroxyle ammonium chloride (0.1 M, pH 2, 100 mL)) - 12 h

4 - Less easily reducible – (Ammonium oxalate/oxalic acid (0.2 M, pH 3, 100 mL)) - 24 h

5 - Organic + sulphidic – ((a) Hydrogen peroxide (30 %), 30 mL, time depends on reactivity; followed by repetition of step 4: Ammonium oxalate/oxalic acid (0.2 M, pH 3, 100 mL) - 24 h);

6 - Residual - Hydroflouric acid digestion (standard procedure)

Additional remarks:

In case of anoxic conditions also the procedure the steps 1 – 4 of sequential elution must be performed under anoxic conditions with fresh sample material in the glove box in an Ar atmosphere. All solutions used in steps 1–4 were washed O2-free by purging with Ar for about 24 h. The solutions were controlled by an O2 sensor.

In case of oxic conditions these precautions must not be applied. However and in any case, due to the high concentrations of extraction solutions the detection of potentially harmful trace elements in the different elution steps (e.g. Cd, Pb) is heavily hampered by the high matrix load. The very high sensitivity of ICP-MS allows high dilutions by this suppressing the matrix effects and still allowing reliable element signals.

In the case of Pb the procedure may cause an artifact by shifting an elevated portion from step 5 to step 6, which yields an apparently non-reasonable stable binding form (step 6: ‘‘silicate’’); most likely this portion belongs to the sulfidic binding form. Therefore, in the case of Pb the ‘‘residual’’ binding form is included to the sulfidic (C-org.) binding form.

Informative - scholarly explanation (Dr.Dieter). Thanks and regards

Dr. Dieter's answer is very comprehensive and his effort in providing insights to the question are commendable.

Dear colleagues,

Thank you for your answers!

Especially I am grateful to Dr. Zachmann for detailed analysis of the methodology of sequential extractions of heavy metals from. I sure it will be very useful for me and other specialists who work in geochemistry field.

1. Thanks due to your interesting question regarding suitable methods to determine the heavy metals in several geo-chemical fractions of sediments.

2. Common methods for the determination of heavy metals in the several geo-chemical fractions include Tessier 1979; Sposito 1982; BCR 1999 and Silveira 2006 .

3. Generally care should be taken when comparing the results obtained by different methods. Please consult the following helpful literature related to the application of several methods on the same sample in order to fully understand the variation of results due to application of different methods.

He et al. (2013). Assessment of Trace and Heavy Metal Distribution by Four Sequential Extraction Procedures in a Contaminated Soil. Soil & Water Research, 8(2).

http://www.agriculturejournals.cz/publicFiles/91845.pdf