Hi, we are using method with 1M dm-3 ammonium acetate solution without any La or Sr chloride during exchange cations determination.

Our lab uses LaCl3 in AAS analysis to avoid a range of phosphate precipitations in the flame. However, we add the LaCl3 (as the diluent) into the filtered/centrifuged extract prior to AAS analysis not in the original exchange experiment so that we don't alter the quantity of ions actually exchanged from the soil.

Yes, we do add special AAS grade LaCl3 in the samples prior any AAS analysis. We perform a lot of analysis about Ca and Mg and we never detect any kind of problems. The Ca and Mg trace contained in LaCl3 solution are very low compare to the level of Ca and Mg you can measure in soil or plant. In addition, if you add the same amount of LaCl3 to all your samples and your blank, the error will disappear when you subtract the blank measurement to the sample measurement.

The use of 1000 to 2000 ppm (final concn) of SrCl2 is effective in enhancing the Mg and Ca signal in the flame AAS. The SrCl2 is only added to the final filtrate of the NH4Cl extract. Be careful with the use of Sr is too much sulfate is present, especially in acidic solutions. They form a precipitate. The use of LiCl is useful in this case, but not as effective as CrCl2.

Hi,

Our lab use strontium chloride for estimating of K and Mg. For estimating of Ca we are using potassium chloride.

Hi

We do not use Sr o Li to extranct Ca and Mg from soils, We employ Ammonium Acetate 1 N because Ammonium occupy the exchangeable sites, releasing the other ions.

I think few of my peers got confused on the question. The strontium or lanthanum chloride is usually added as a releasing agent just before it is introduced to the flame AAS. The step is basically for dissociating the strong recalcitrant phosphates which is not usually atomised in the Air-acetylene flame. These are not used for the extraction purpose. Usually ammonium acetate is the extractant used.

I posed the question because, in recent times the step of adding SrCl2 or LaCl is avoided in some of the labs. This may have a bearing in the result of Ca estimation.

I feel a serious delibration is required on this especially when acid soils that receive high amount of rain is continuously getting depleted on Ca and Mg contents (in fact all soluble cations). In such cases Ca estimations need to be extremely precise and accurate.

Thanks to all my peers responded. Still welcome your views on the matter.

Joshua

Ok, if your soil is rich in phosphates it is neccesary to employ the Sr or La to avoid the precipitation or association of Ca with P for the atomization, manily when the Ca concentration is too low. I think that you have to add the Sr or La to be sure that you will get accurate results.

Because of the higher affinity of strontium with calcium, generally, better results are got with strontium chloride than with lanthanum chloride (though lanthanum chloride has the advantage of a higher solubility in water). So, you can get more precise results for low calcium in acidic soils. If you do not want to use either SrCl2 or LaCl3, it is possible to use in some cases barium chloride (not if you have sulphates in your extracts). By the way, barium chloride is less soluble and more toxic.

If you're using a Air / Acetylene combination as Oxidant, the oxygen rich environment can cause Mg and Ca to form insoluble oxides and hydroxides. This can lower the detection signal resulting in erroneously low readings for the cations. We always add SrCl2 to our filtrate before reading on the AAS allowing the preferential formation of Strontium oxides and hydroxides.

Thanks to all my peers who had given very very valuable answers

We have ever used LaCl3 with good results