Preparation of Modified Nanocellulose with 5-Br-PADAP for Preconcentration and Determination of Trace Amounts of Cobalt Ions in Natural Water Samples

Separation and determination of trace amounts of cobalt ions in real samples due to their toxicity to humans is very important. In the present study, a nanocellulose was synthesized by the acid hydrolysis and then modified with 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP). The size of cellulose nanofibers was determined using transmission electron microscope (TEM). After modification of the nano-sorbent with the 5-Br-PADAP, the thermogravimetric analysis (TGA) of the modified nanocomposite was carried out, and the BET technique was used to determine the surface area of the nano-sorbent before and after modification. In the present work, the aim is to modify the surface of nanocellulose with ligand of 5-Br-PADAP to use them to extraction and pre-concentration of trace amounts of cobalt ions before determination it by flame atomic absorption spectroscopy in real samples.

Certain volume of cobalt ion into the test tube containing the modified nanosorbent was Poured and buffer solution with pH = 9 was added and place it in a shaker and finally centrifuged for 15 minutes and then discard the top solution and 1 mL HCl was added to recover cobalt ions and placed in a shaker for 10 minutes and then centrifuged, and the absorption of the supernatant was determined by FAAS. The results showed that the modified nanocellulose is very sensitive and selective towards the determination of cobalt ions which could be affected by several parameters such as pH, adsorbent amount, sample volume, extraction time, and type of eluetion.

The calibration curve is linear in the range of 10-500 ng/mL, and the detection limit and the relative standard deviation (RSD) are calculated to be 4.3 ng/mL and 1.8 %, respectively, that result in a high preconcentration and enrichment factor.

By using the flame atomic absorption spectrometry and applying the standard addition method, the proposed method was used to determination of the trace amounts of cobalt ions in the natural water samples such as seawater, river water, well water, lake water and tap water, with satisfactory results.