METALS DETERMINATION BY ATOMIC SPECTROMETRY TECHNIQUES IN COAL AND ASH SAMPLES USING RESPONSE SURFACE METHODOLOGY

Oliz, Camila M.; Lopes, Emanoelli R.; Medina, Aline L.; Ribeiro, Anderson S.; Nunes, Adriane M.

doi:10.21577/0100-4042.20160120

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Artigo • Quím. Nova 39 (8) • Sept 2016 • https://doi.org/10.21577/0100-4042.20160120 copy

METALS DETERMINATION BY ATOMIC SPECTROMETRY TECHNIQUES IN COAL AND ASH SAMPLES USING RESPONSE SURFACE METHODOLOGY

Authorship SCIMAGO INSTITUTIONS RANKINGS

This paper describes the method optimization using response surface methodology for Cu, Fe, Zn and Na determinations in coal and ash samples by spectrometry techniques. The sample preparation was performed using a recirculation system adapted in the digestion tubes. This system allowed increase of temperature in the digester block above the boiling point of the reaction medium, avoiding acid evaporation during the heating. The digestions were realized with HNO₃ and H₂O₂ for 1 h in a digester block at 145 °C. The limits of detection for determination of Cu, Fe, Zn and Na in both samples were satisfactory. The RSD for the analytes were lower than 6.0%. Statistical tests showed that results for all analytes do not vary significantly with official method (ASTM), considering a confidence limit of 95%. Besides, the accuracy was verified by recovery tests, whose values ranged from 92.7 to 104.7% in coal, and 98.7 to 115.3% in ash.

Keywords:
coal; ash; metals; atomic spectrometry; validation

Variáveis independentes	Nível
Variáveis independentes	-2	-1	0	+1	+2
Volume de HNO₃ (mL)	5	6	7	8	9
Volume de H₂O₂ (mL)	0,5	1	1,5	2	2,5
Tempo de digestão (min)	30	60	90	120	150
Temperatura (ºC)	120	145	170	195	220

Ensaios	Variáveis Independentes				Variáveis Dependentes
Ensaios	Vac	Vp	Tempo	Temperatura	Cu^* * Valores referentes aos sinais de absorvância;	Na^ Valores referentes aos sinais de emissão.	Zn^* * Valores referentes aos sinais de absorvância;	Fe^* * Valores referentes aos sinais de absorvância;
1	-1,0	-1,0	-1,0	-1,0	0,2030	1806,7	0,3084	1,0349
2	1,0	-1,0	-1,0	-1,0	0,1787	1969,3	0,2471	1,0167
3	-1,0	1,0	-1,0	-1,0	0,1783	2576,4	0,2927	1,0402
4	1,0	1,0	-1,0	-1,0	0,1713	2591,8	0,2481	1,0300
5	-1,0	-1,0	1,0	-1,0	0,1979	2018,4	0,2789	1,0452
6	1,0	-1,0	1,0	-1,0	0,1726	2077,4	0,2374	1,0293
7	-1,0	1,0	1,0	-1,0	0,2017	2527,8	0,2829	1,0496
8	1,0	1,0	1,0	-1,0	0,1817	2640,6	0,2432	1,0418
9	-1,0	-1,0	-1,0	1,0	0,2043	2093,3	0,2840	1,0461
10	1,0	-1,0	-1,0	1,0	0,1778	2065,8	0,2460	1,0403
11	-1,0	1,0	-1,0	1,0	0,1840	2539,4	0,2517	1,0528
12	1,0	1,0	-1,0	1,0	0,1927	2541,1	0,2600	1,0257
13	-1,0	-1,0	1,0	1,0	0,1897	2068,8	0,2653	1,0660
14	1,0	-1,0	1,0	1,0	0,1879	2043,0	0,3452	1,0221
15	-1,0	1,0	1,0	1,0	0,2075	2569,3	0,3135	1,0412
16	1,0	1,0	1,0	1,0	0,1902	2549,7	0,3467	1,0273
17	-2,0	0,0	0,0	0,0	0,2178	2370,0	0,2958	1,0741
18	2,0	0,0	0,0	0,0	0,1821	2204,0	0,2554	1,0259
19	0,0	-2,0	0,0	0,0	0,2150	1673,7	0,2834	1,0606
20	0,0	2,0	0,0	0,0	0,2071	2851,9	0,2916	1,0239
21	0,0	0,0	-2,0	0,0	0,2040	2277,2	0,2864	1,0223
22	0,0	0,0	2,0	0,0	0,2110	2332,0	0,2774	1,0400
23	0,0	0,0	0,0	-2,0	0,2018	2210,2	0,2362	1,0481
24	0,0	0,0	0,0	2,0	0,2038	2202,9	0,2440	1,0366
25	0,0	0,0	0,0	0,0	0,2290	2230,2	0,2730	1,0599
26	0,0	0,0	0,0	0,0	0,2100	1936,9	0,2657	1,0562
27	0,0	0,0	0,0	0,0	0,2294	1941,7	0,2804	1,0591

Respostas	Fonte de variação	Soma dos quadrados	Graus de liberdade	Quadrado médio	Fcal
Cu	Regressão	0,00305	4	0,00076	4,75
	Resíduos	0,00372	22	0,00016	4,75
	Total	0,00677	26
Fe	Regressão	0,00357	4	0,00089	8,55
	Resíduos	0,00230	22	0,00010	8,55
	Total	0,00588	26
Na	Regressão	207211	5	414423	58,4
	Resíduos	148911	21	7091	58,4
	Total	222102	26
Zn	Regressão	0,0143	5	0,00286	7,24
	Resíduos	0,0083	21	0,00039	7,24
	Total	0,0226	26

Analito	Faixa Linear (mg L^-1)	a (L^-1 mg)	LD (mg L^-1)	LQ (mg L^-1)	R
Cu	0,5 – 3,0	0,056	0,023	0,079	0,999
Fe	1,0 – 5,0	0,032	0,038	0,128	0,999
Zn	0,25 – 1,0	0,218	0,003	0,010	0,998
Na	1,0 – 5,0	389,0	0,029	0,097	0,998

	média ± desvio (RSD)	Recuperação (%)	média ± desvio (RSD)	Recuperação (%)
	Amostras de carvão		Amostras de cinzas
Cu
Sem adição	0,092 ± 0,001 (1,1)	104,7	0,148 ± 0,004 (2,7)	115,3
Adição de 1,5 ppm	1,663 ± 0,026 (1,6)		1,877 ± 0,022 (1,2)
Fe
Sem adição	37,11 ± 0,76 (2,1)	93,6	23,79 ± 0,86 (3,6)	113,7
Adição de 3,0 ppm	39,92 ± 0,39 (0,9)		27,20 ± 0,39 (1,4)
Zn
Sem adição	0,288 ± 0,002 (0,7)	96,0	0,128 ± 0,004 (3,1)	114,8
Adição de 0,5 ppm	0,768 ± 0,026 (3,4)		0,702 ± 0,012 (1,7)
Na
Sem adição	0,696 ± 0,013 (1,9)	92,7	5,930 ± 0,085 (1,4)	98,7
Adição de 3,0 ppm	3,477 ± 0,182 (5,2)		8,890 ± 0,028 (0,3)

	Método Proposto (Dedo Frio)		Método Oficial (ASTM)
	Concentração (mg kg^-1)	RSD (%)	Concentração (mg kg^-1)	RSD (%)
Cu	25,9 ± 0,4	1,5	24,1 ± 1,9	7,9
Fe	10487,4 ± 184,0	1,8	11770,5 ± 66,0	0,6
Na	203,3 ± 8,3	4,1	229,0 ± 14,8	6,5
Zn	80,7 ± 0,4	0,5	78,9 ± 9,6	12,2

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