TY - JOUR
T1 - Environmentally friendly microwave-assisted sequential extraction method followed by ICP-OES and ion-chromatographic analysis for rapid determination of sulphur forms in coal samples
AU - Mketo, Nomvano
AU - Nomngongo, Philiswa N.
AU - Ngila, J. Catherine
N1 - Publisher Copyright:
© 2018 Elsevier B.V.
PY - 2018/5/15
Y1 - 2018/5/15
N2 - A rapid three-step sequential extraction method was developed under microwave radiation followed by inductively coupled plasma-optical emission spectroscopic (ICP-OES) and ion-chromatographic (IC) analysis for the determination of sulphur forms in coal samples. The experimental conditions of the proposed microwave-assisted sequential extraction (MW-ASE) procedure were optimized by using multivariate mathematical tools. Pareto charts generated from 23 full factorial design showed that, extraction time has insignificant effect on the extraction of sulphur species, therefore, all the sequential extraction steps were performed for 5 min. The optimum values according to the central composite designs and counter plots of the response surface methodology were 200 °C (microwave temperature) and 0.1 g (coal amount) for all the investigated extracting reagents (H2O, HCl and HNO3). When the optimum conditions of the proposed MW-ASE procedure were applied in coal CRMs, SARM 18 showed more organic sulphur (72%) and the other two coal CRMs (SARMs 19 and 20) were dominated by sulphide sulphur species (52–58%). The sum of the sulphur forms from the sequential extraction steps have shown consistent agreement (95–96%) with certified total sulphur values on the coal CRM certificates. This correlation, in addition to the good precision (1.7%) achieved by the proposed procedure, suggests that the sequential extraction method is reliable, accurate and reproducible. To safe-guard the destruction of pyritic and organic sulphur forms in extraction step 1, water was used instead of HCl. Additionally, the notorious acidic mixture (HCl/HNO3/HF) was replaced by greener reagent (H2O2) in the last extraction step. Therefore, the proposed MW-ASE method can be applied in routine laboratories for the determination of sulphur forms in coal and coal related matrices.
AB - A rapid three-step sequential extraction method was developed under microwave radiation followed by inductively coupled plasma-optical emission spectroscopic (ICP-OES) and ion-chromatographic (IC) analysis for the determination of sulphur forms in coal samples. The experimental conditions of the proposed microwave-assisted sequential extraction (MW-ASE) procedure were optimized by using multivariate mathematical tools. Pareto charts generated from 23 full factorial design showed that, extraction time has insignificant effect on the extraction of sulphur species, therefore, all the sequential extraction steps were performed for 5 min. The optimum values according to the central composite designs and counter plots of the response surface methodology were 200 °C (microwave temperature) and 0.1 g (coal amount) for all the investigated extracting reagents (H2O, HCl and HNO3). When the optimum conditions of the proposed MW-ASE procedure were applied in coal CRMs, SARM 18 showed more organic sulphur (72%) and the other two coal CRMs (SARMs 19 and 20) were dominated by sulphide sulphur species (52–58%). The sum of the sulphur forms from the sequential extraction steps have shown consistent agreement (95–96%) with certified total sulphur values on the coal CRM certificates. This correlation, in addition to the good precision (1.7%) achieved by the proposed procedure, suggests that the sequential extraction method is reliable, accurate and reproducible. To safe-guard the destruction of pyritic and organic sulphur forms in extraction step 1, water was used instead of HCl. Additionally, the notorious acidic mixture (HCl/HNO3/HF) was replaced by greener reagent (H2O2) in the last extraction step. Therefore, the proposed MW-ASE method can be applied in routine laboratories for the determination of sulphur forms in coal and coal related matrices.
KW - Coal
KW - Greener reagents
KW - Microwave sequential extraction
KW - Sulphur forms
UR - http://www.scopus.com/inward/record.url?scp=85042260055&partnerID=8YFLogxK
U2 - 10.1016/j.talanta.2018.02.041
DO - 10.1016/j.talanta.2018.02.041
M3 - Article
C2 - 29501194
AN - SCOPUS:85042260055
SN - 0039-9140
VL - 182
SP - 567
EP - 573
JO - Talanta
JF - Talanta
ER -