Malaysian Journal of Analytical Sciences Vol 26 No 2 (2022): 283 - 294

 

 

 

 

CHROMIUM (VI) ANALYSIS IN EFFLUENTS USING LIQUID-LIQUID EXTRACTION COUPLED WITH FLAME ATOMIC ABSORPTION SPECTROMETRY

 

(Analisis Kromium (VI) dalam Efluen Menggunakan Pengekstrakan Cecair-Cecair Bersama Spektrometri Serapan Nyalaan Atom)

 

Nguyen Cong-Hau¹, Le-Thi Anh-Dao¹, Nguyen Thanh-Nho¹*, Le-Thi Huynh-Mai², Le Nhon-Duc³, Do Minh-Huy¹

 

¹Faculty of Environmental and Food Engineering,

Nguyen Tat Thanh University, Ho Chi Minh City, Vietnam

²Faculty of Chemistry,

University of Science, Vietnam National University Ho Chi Minh City, Vietnam

³Warrantek Joint Stock Company, Testing Center, Can Tho City, Vietnam

 

*Corresponding author:  ntnho@ntt.edu.vn

 

Received: 1 September 2021; Accepted:  10 January 2022; Published:  28 April 2022

 

 

Abstract

Simple sample preparation was investigated and developed to selectively determine Cr(VI) in wastewater samples or effluents based on the liquid-liquid extraction principle using tetrabutylammonium hydrogensulfate (TBAHS) as the ion-pair reagent in an acidic medium. TBAHS was prepared in an organic solvent to improve the extraction efficiency. The extracted Cr(VI) in the organic phase endured the acid digestion, and its atomic absorption was measured at 357.9 nm. The influences of several working parameters, namely, organic solvents (methyl isobutyl ketone-MIBK, dichloromethane-DCM, and chloroform), pH values (lower than 1.0, 1.0, 2.0, and 3.0) in the aqueous phase, TBAHS concentrations in the organic solvent (0.02, 0.04, 0.05, and 0.06 mol L^–1), extraction duration (from 3 to 30 minutes), number of extraction cycles (single or repeated extraction), sample preservation duration at ambient temperature, and co-existence of Cr(III) in the sample matrices, were investigated to discover the optimized working parameters. The results showed that dichloromethane (DCM) was the most effective extraction solvent. The most favorable conditions for complex formation were determined as follows: a pH of around 1.0 to 3.0; 0.05 mol L^–1 TBAHS prepared in DCM, triple extraction, and a shaking duration of 15 minutes for each extraction cycle. The calibration curve was linear in the range of 0.05, 0.10, 0.20, 0.40, 0.60, 0.90, 1.2, 1.5 and 2.0 mg L^–1, and the regression equation was y = 0.1068x + 0.0012 with R² = 0.9994, exhibiting goodness of linearity. The method detection and quantification limit values were estimated to be 0.012 mg L^–1 and 0.04 mg L^–1, respectively. The repeatability (RSD_r = 0.71%) and reproducibility (RSD_R = 1.1%) were favorable according to the requirements presented in Appendix F of AOAC (2016) for analytical method validation. The proposed method was applied to real wastewater samples and spiked samples, showing very low Cr(VI) concentrations for most samples and proper recoveries (91.1-109%).

 

Keywords:  Cr(VI), Cr(III), liquid-liquid extraction, TBAHS, dichloromethane, DCM, ion-pair reagent 

 

 

Abstrak

Penyediaan sampel yang mudah telah dikaji dan dibangunkan bagi penentuan terpilih Cr(VI)  di dalam air sisa atau efluen berdasarkan prinsip pengekstrakan cecair-cecair menggunakan tetrabutylammonium hidrogensulfat (TBAHS) sebagai reagen pasangan ion di dalam medium berasid. TBAHS telah disediakan dalam pelarut organik bagi tujuan meningkatkan keberkesanan pengekstrakan. Cr(VI) yang telah diekstrak di dalam fasa organik melalui penghadaman asid, dan serapan atom telah diukur pada 357.9 nm. Pengaruh parameter seperti  pelarut organik (metil isobutil keton-MIBK, diklorometana-DCM, dan klorofom), nilai pH (dibawah 1.0, 1.0, 2.0 dan 3.0) di dalam fasa akues, kepekatan TBAHS di dalam pelarut organik (0.02, 0.04, 0.05, dan 0.06 mol L^–1), tempoh pengekstrakan (dari 3 hingga 30 minutes), bilangan kitaran pengekstrakan (pengekstrakan tunggal atau ulangan), tempoh pengawetan sampel pada suhu sekitar, dan kehadiran bersama Cr(III) dalam matrik sampel turut dikaji untuk penentuan parameter kerja yang optimum. Hasil kajian menunjukkan diklorometana (DCM) paling efektif sebagai pelarut pengekstrakan. Keadaan paling baik untuk penghasilan kompleks ditentukan seperti berikut: pH antara 1.0 hingga 3.0; 0.05 mol L^–1 TBAHS disediakan dalam DCM, tiga kali pengekstrakan, dan masa goncangan ialah 15 minit bagi setiap kitaran pengekstrakan. Lengkung kalibrasi adalah linear pada julat 0.05 hingga 2.0 mg L^–1, dan persamaan regresi ialah y = 0.1068x + 0.0012 dan R² = 0.9994. Had pengesanan dan kuantifikasi telah dihitung masing-masing pada  0.012 mg L^–1 and 0.04 mg L^–1. Kebolehulangan (RSD_r = 0.71%) dan kebolehhasilan semula (RSD_R = 1.1%) adalah baik berdasarkan keperluan yang dinyatakan dalam Appendix F of AOAC (2016) bagi validasi kaedah analisis. Kaedah yang dicadang ini telah digunapakai bagi analisis sampel air sisa sebenar dan sampel yang dipaku, ia menunjukkan kepekatan Cr(VI) yang rendah dan perolehan semula yang baik (91.1-109%).

 

Kata kunci:  Cr(VI), Cr(III), pengekstrakan cecair-cecair, diklorometana, reagen pasangan ion

 

 

 

Graphical Abstract

 

 

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