Table 5 Concentration levels of trace metal distribution in three South African coal samples obtained by using the proposed MW-ASE followed by ICP-MS (n = 4) and comparison of the sequential sum values with other literature reports.

From: An improved microwave assisted sequential extraction method followed by spectrometric analysis for metal distribution determination in South African coal samples

Coal sample

Extraction step

Be

Sc

V

Cr

Co

Ga

Sr

Y

Ba

Ce

Pb

Th

Concentration (µg g−1)

CSA

H2O

a < LOD

 < LOD

 < LOD

 < LOD

 < LOD

1.21

20.0

 < LOD

17.3

 < LOD

 < LOD

 < LOD

HCl (5 M)

1.48

2.97

29.8

9.97

3.98

5.18

350

9.56

220

35.0

4.22

4.37

HNO3 (2 M)

 < LOD

1.00

4.99

3.23

1.28

9.84

50.3

3.63

12.7

4.47

1.12

1.17

H2O2-HNO3 (3&7 M)

 < LOD

 < LOD

4.89

7.34

 < LOD

1.28

11.2

 < LOD

3.29

 < LOD

 < LOD

 < LOD

bCurrent study

1.52

3.96

40.0

20.5

5.27

17.5

412

13.2

236

39.5

5.26

5.58

Ref. 26

cND

ND

39.4

ND

5.13

15.5

400

ND

239

ND

5.21

6.54

Ref. 27

1.91

4.48

38.5

20.7

5.19

16.0

400

13.5

236

40.0

5.56

5.88

CSB

H2O

 < LOD

 < LOD

 < LOD

 < LOD

 < LOD

1.47

11.6

 < LOD

20.7

 < LOD

 < LOD

 < LOD

HCl (5 M)

1.77

3.68

15.9

11.4

8.18

2.97

60.5

9.29

158

37.2

17.4

8.27

HNO3 (2 M)

 < LOD

1.46

2.95

5.66

1.98

7.17

7.34

2.28

14.6

6.34

1.97

2.28

H2O2-HNO3 (3&7 M)

 < LOD

 < LOD

1.18

12.0

 < LOD

 < LOD

3.12

 < LOD

10.8

 < LOD

 < LOD

1.35

Current study

1.78

5.17

19.9

29.1

10.2

11.7

82.5

11.6

204

43.5

19.4

12.0

Ref.26

ND

ND

19.4

ND

8.95

10.6

80.1

ND

189

ND

17.7

ND

Ref.27

2.22

5.27

19.0

27.0

10.0

11.0

81.0

11.5

199

42.0

19.0

12.7

CSC

H2O

 < LOD

 < LOD

 < LOD

 < LOD

 < LOD

3.38

30.0

 < LOD

73.0

 < LOD

 < LOD

 < LOD

HCl (5 M)

1.55

3.87

19.3

12.7

5.34

5.65

470

8.68

255

20.7

7.46

6.18

HNO3 (2 M)

 < LOD

1.00

7.03

6.25

2.17

12.4

25.7

1.98

21.1

11.3

2.45

1.03

H2O2-HNO3 (3&7 M)

 < LOD

 < LOD

0.997

10.7

 < LOD

1.96

15.0

 < LOD

10.7

 < LOD

 < LOD

1.17

Current study

1.56

4.88

27.3

20.7

7.47

23.5

541

10.7

360

320

10.0

8.38

Ref.26

ND

ND

27.3

ND

7.19

22.2

537

ND

354

 < LOD

9.55

ND

Ref.27

1.78

4.26

27.6

26.6

7.04

21.5

540

10.0

361

320

10.5

8.47

  1. a< LOD (below detection limits).
  2. bCurrent study (sum of the four sequential steps).
  3. cND (not determined).
  4. Values in bold are reported values from published literature reports.
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