After the digestion part, the heavy metals tend to form non-uniform clusters. Try homogenizing the samples after the acid digestion.

Hope it works

Thankyou for your response sir.

But I filtered the digested sample uniformly covering the content of whole beaker.

Can there any other reason sir?

What kind of dust was it? Is its phase composition known? Are you sure about the accuracy of previous and current results? Did you then and now use any solution reference material to validate your solution concentration measurements? Which elements are affected by this multiple increase in concentrations? What were the concentrations of these elements then and what are they now? What acid did you treat the dust sample with and was it in accordance with any official procedure? Was this resulting solution then filtered or not? Was there any suspension present in the solution then, and is it still present? What is the concentration of acid in this solution? Do you have a sample of this or similar dust for possible testing of the effectiveness of the method of dissolving the sample you used at that time?

If the case of this dust sample is important to you, the first thing you need to rule out is error in concentration measurements.

ZJ

Zbigniew Jońca thankyou so much. will surely look into all these comments.

Dear colleague,

In our questions is not shown the collected sample methods, the correct decomposition procedure, as well as and the methodology of measurement by ICP-OES..

In accordance with our experience I will note the following:

The possibility of ICP-AES was shown in the quantitative estimation of pollutants around the “Kremicovtzi” metallurgical works “in Sofia, Bulgaria (Ba, Cd, Cr, Mn, Pb and Zn), and in the region of the meteorological stations Milesovka and Kopisty, located in one of the highly polluted industrial region of the Czech Republic (As, Ba, Cu, Mn, Zn, Pb, Fe, Mg, Ca, Al and Ti) [1].

I. Samplling

1. Particles with aerodynamic diameter larger than approx. 10 were collected by Bergerhoff’s method around metallurgical works. The samples were air-dried and ground in a rotating plastic drum.

2. Samples of atmospheric particles smaller than approx. 10 µm were collected by filter technique (nitrocellulose membrane filters with pore size of 0.45 µm ) from the meteorological stations Milesovka and Kopisty, located in a highly polluted industrial region of the Czech Republic.

II. Dissolution of samples of atmospheric particles

1. The samples of atmospheric particles, collected by the

Bergerhoff’ s method, were dissolved in accordance with ISO 11466 [2].

0.5 g sub - sample was weighed accurately in a reaction vessel. 0.5 mL of tri-distilled water was added to obtain a slurry, followed by 4.5 mL of hydrochloric acid (12 mol L-1) and 1.5 mL nitric acid (15.8 mol L-1). Then 10 mL of 0.5 mol L-1 nitric acid were added to the absorption vessel which was connected to the reflux condenser. The apparatus was placed on the top of the reaction vessel. The samples were allowed to stay for 16 h at room temperature for slow oxidation of the organic matter and reduction of the gases produced during the subsequent heating cycle. They were boiled under reflux for 2 h and allowed to cool slowly at room temperature. The content of the reaction vessel was transferred quantitatively to a 25 mL graduated flask and filled up to the mark with nitric acid (0.5 mol L-1). After the undissolved material has settled, the supernatant solution was subjected to analysis by ICP-AES. A blank sample, containing the acids used for digestion, was prepared in the same way.

2. Dissolution of nitrocellulose filters with a pore size of 0.45 µm

The apparatus described in Ref. [3] was used. The nitrocellulose filter was weighed and placed in a reaction vessel. 1.0 mL of tri-distilled water was added, followed by 7.0 mL of hydrochloric acid (12 mol L-1) and 2.0 mL of nitric acid (15.8 mol L-1). The nitric acid was added dropwise. The samples were allowed to stay for 1 h at room temperature. They were heated on the water bath under reflux for 8 h and allowed to cool slowly at room temperature. After that the solution was heated over plate (the distance between the plate and the reaction vessel was 5 mm). The solution was evaporated to a volume of 2 mL. The content of the reaction vessel was transferred quantitatively to a 10 mL graduated flask and filled up to the mark with tridistilled water. A blank sample was prepared in the same way. It contained the acids used for digestion and an unused nitrocellulose filter.

I will note, that the accuracy of analytical results can be ensured by an appropriate ICP–AES methodology: quantification of spectral interferences in the presence of Al, Ca, Mg, Fe and Ti as a complex environmental matrix around the prominent lines of the analytes and line selection for trace analysis[1].

With kind regards, N.Daskalova

Nonka Nedjalkova Daskalova thank you for your reply.

I would like to tell as i collected the floor and the dust near the exhaust fan with the help of a brush (you can say like scrapping). Then for acid digestion, I used aqua regia i.e. 9ml HCL and 3ml HNO3 and digested the 1 gm of sample for 2-3 hours and then filtered it with wattmann filter paper and made up the solution to 100 ml with distilled water.

I will show the quoted references:

References

[1]. Nikolaya Velitchkova, Olga Veleva, Serafim Velichkov, and Nonka Daskalova, Possibilities of High Resolution Inductively Coupled Plasma Optical Emission Spectrometry in the Determination of Trace Elements in Environmental Materials, Hindawi Publishing Corporation, Journal of Spectroscopy Volume 2013, Article ID 505871, 12 pages http://dx.doi.org/10.1155/2013/505871

[2]. ISO 10381-2:2002, “Soil quality—sampling—part 2: guidance on sampling techniques,” International Organization for Standardization,

2002.

[3] ISO 11466:1995, “Soil quality—“Extraction of trace elements

soluble in aqua regia”,”International Organization for Standardization,

1995

Dear colleague

The methodology for determination of impurities in road dust, include the followings steps:

1. Sampling and sample preparation

Samples of road dust can be collected by using a vacuum cleaner. The samples must air-dried, ground in a rotating plastic drum and then sieved through a nylon sieve with an appropriate diameter. In other to obtain real-time and forecast air Pollution Map see Ref. [1]. The samples have to store in a desiccator until further treatment for analysis. There I will note that the concentrations of heavy metals in roadside dust varied significantly due to sampling seasons and the land-use category. The homogeneity of samples is of prim importantly. The samples have to store in a desiccator until further treatment for analysis.

2. Dissolution of the samples

Extraction of trace elements soluble in aqua regia in close system must be used in accordance with ISO 11466: 1995 E [2]. In our second post this is not clear. In addition, the authors do not list the impurities, which they must determine, as well as and the ICP-OES equipment.

There I note that in open system, the loss of volatile elements can be occurred and the reproducibility of analytical results cannot be expected. In addition, the final sample solution must be filled up to the mark with nitric acid (0.5 mol L-1), but not with high purity water. The stability of the sample solution is of prime importance for accuracy of analytical results.

3. ICP–AES measurement technique

3.1 Line selection

The road dust samples normally contain high concentrations of Al, Ca, Mg, Fe and, to a lesser extent Ti, which cause significant background enhancement in many regions of the spectrum or give rise to serious line overlap interferences in the determination of trace of elements. Our research group use the methodology of Boumans and Vrakking for quantification of the interferences in terms of Q-value [3]. In the case of a multicomponent environmental matrix, it is possible to choose analysis lines free of line interferences, which ensure the lowest possible detection limits in the determination of impurities in environmental samples. The selected analysis lines are shown in our publications [4,5].

3.2. Calibration procedure

The analytical evaluation function is assumed to be a straight line through the origin. A correct calibration from the point of view of spectral interferences requires a background subtraction by using of the background signal below the analysis line. The correct calibration from the point of view of multiplicative interferences means a precise matching of the acid and matrix contents in both the reference and the sample solutions. The matrix blank contained both the acid blank and complex matrix [4,5].

3.3. Accuracy of analytical results

The accuracy of analytical results in the determination of impurities in environmental materials can be experimentally demonstrated by using Certified Reference Materials (International Atomic Energy Agency Austria) IAEA/Soil 7—soil reference material prepared from the fraction which passed through a 70 𝜇m sieve or IAEA Certified Reference Material, marine sediment SD-N-1/2 [4,5].

Conclusion

Systematic errors in ICP-AES in the determination of traces of elements in environmental materials may arise from both the different steps in the analytical procedure (sampling, collection, storage, preparation) and measurement technique. In practice, it is of paramount importance to distinguish the errors due to the measurement technique from those ascribed to the sample preparation procedure.

References

[1]. National Air Quality and Emissions Trends Report, 1999 (US-EPA, 1999)

[2]. International Organization for Standardization (1995) - Soil Quality, Extraction of Trace Elements Soluble in Aqua Regia, ISO 11466 E.

[3]. P.W.J.M. Boumans, J.J.A.M. Vrakking, Line selection in atomic emission spectrometry using physically resolved spectra, Spectrochim

Acta Part B 43 (1988) 69– 74.

[4]. N. Daskalova and Iv. Boevski, Spectral interferences in the determination of trace elements in environmental materials by inductively coupled plasma atomic emission spectrometry, Spectrochim.Acta, Part B 54, (1999) 1099 – 1122

[5]. N. Velitchkova, E. N. Pentcheva, N. Daskalova, Determination of arsenic, mercury, selenium, thallium, tin and bismuth in environmental materials by inductively coupled plasma emission spectrometry, Spectrochim Acta Part B 59 (2004) 871- 882.