naked-eye detection of co(ii) ni(ii) and fe(iii) using ... for...

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© 38th Congress on Science and Technology of Thailand (Full paper)

NAKED-EYE DETECTION OF Co(II) Ni(II) AND Fe(III) USING SILICA GEL COATED WITH XYLENOL ORANGE BY COLUMN METHOD Panida Mongkhonwuttikun,1 Thawatchai Tuntulani,2 Wanlapa Aeungmaitrepirom, 1,* 1Environmental Analysis Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand 2Supramolecular Chemistry Research Unit, Department of Chemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand *e-mail: [email protected]. Abstract: Naked-eye detections of some heavy metal ions were investigated. The complexation between heavy metal ions (Cu(II), Cd(II), Co(II), Ni(II), Pb(II), Zn(II), Cr(III) and Fe(III)) and xylenol orange (XO) coated on silica gel in mini-column was studied. It was easy to observe the color change from orange to red-orange, pink and dark-blue for Co(II), Ni(II) and Fe(III), respectively. Moreover, no color change was found in the presence of Cu(II), Cd(II), Pb(II), Zn(II) and Cr(II). The optimum concentration of xylenol orange for naked-eye detection was 0.01 mM at pH 5. The optimum of flow rate was 1 mL/min. The naked-eye detection limits of Co(II), Ni(II) and Fe(III) were 0.2, 0.2 and 0.06 mg/L, respectively. Introduction: Heavy metals are highly toxic and dangerous. It can contaminate the environment. In addition, it can adsorb to the human body causing cancer and malfunction of the nervous system.1 Trace heavy metals in environments are determined by spectroscopic techniques such as UV-Vis spectrophotometry (UV-Vis), flame atomic absorption spectrometry (FAAS) and inductively coupled plasma-atomic emission spectrometry (ICP-AES).2,3 However, these techniques have many disadvantages such as complicated instruments, skilled technician and expensive equipments. Naked-eye detection is a simple technique for detection of heavy metal ions in environmental water. Naked-eye detection is a colorimetric method resulting from the interaction between the ligand and the target analyte. Although the color change can be observed without any special instrument but it is not sensitive enough to meet a standard water quality.4 So, the solid phase is used for enrichment of the trace analyte.

In this work, the naked-eye detection of heavy metal ions using xylenol orange coated on silica gel has been studied by column method to improve the detection limit. Xylenol orange was used as a ligand because it can form complexes with various metal ions by oxygen and nitrogen donor atoms as coordinating sites given mononuclear or binuclear complexes as shown in Figure 1.

Figure 1. Structure of the complex between xylenol orange and metal ions

Methodology: A. Apparatus pH values were measured on a Metrohm pH meter model 744. A peristaltic pump (REGLO Analog MS-4/8 model ISM 827 ISMATECR) was used to control the solution

CH3

O

CH3

O

N

SO3-

O

O

O

ONO

O

O

O

M M

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pH 3

pH 4

pH 5

flow rate in the column system. B. Reagents All reagents were analytical grade. Silica gel was purchased from Merck and xylenol orange was purchased from Fluka. Nitrate salts of metals were purchased from Carlo erba, Merck and UNIVAR. The metal nitrate solutions were prepared from 10−1 to 10−7 M in Milli-Q water. Acetate buffer was used in this experiment. C. Column procedure 25 mg of silica gel was packed in a mini-column (4 mm o.d., 2 cm length). Then, 10 mL of a test solution containing 0.01 mM of xylenol orange and 10−2-10−7 M of the metal salt at pH 5 was passed through the mini-column controlling by a peristaltic pump. Color of the silica gel was observed. Results, Discussion and Conclusion: Column method A. Effect of pH The pH of the solution is an important parameter that affects the complexation. In acidic medium, the hydrogen ion can protonate to some nitrogen or oxygen donor sites and in basic medium, the precipitation of metal ion can occur. The pH effect on the complexation was studied at pH ranging from 3 to 5. Figure 2 illustrates the colors of complexes in comparison with xylenol orange onto silica gel in mini-columns. The color change of all of complexes was clearly observed at pH 5. Thus, the pH 5 was selected in further studies.

Figure 2. Effect of pH on the complexation (silica gel = 25 mg, xylenol orange (XO) = 0.5 mM, metal ions = 10−2 M

and flow rate = 0.5 mL/min)

B. Effect of concentration of xylenol orange The objective of this work is to detect some metal ions at very low concentration by the naked-eye method. Therefore, the concentrations of xylenol orange of 0.001, 0.005, 0.01, 0.05 and 0.1 mM in the presence of 10−5 M metal ion at pH 5 were examined. Figure 3 shows the colors of Ni(II), Co(II) and Fe(III) complexes as pink, red-orange and dark-blue when 0.01 and 0.005 mM of xylenol orange were used.

XO Zn(II) Ni(II) Pb(II) Co(II) Cu(II) Cd(II) Fe(III) Cr(III)

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0.01 mM

0.005 mM

Co (II) Ni (II) Fe (III)

Figure 3. Effect of concentration of xylenol orange (XO)

(silica gel = 25 mg, pH = 5, metal ions = 10−5 M and flow rate = 0.5 mL/min) C. Effect of the flow rate

The complex adsorption onto silica gel depends on the time. Therefore, the flow rate of the solution is an important parameter. At high flow rate, the solution passes through the mini-column too quickly. So the contact time between silica gel and the solution may not be enough for complete adsorption. In this work, the solution flow rate were studied from 0.5 to 5 mL/min for Co(II), Ni(II) and Fe(III). The color of the metal adsorbed silica gel was clearly different from silica gel adsorbed only xylenol orange at the flow rate of 0.5-1 mL/min. No color change was observed at the flow rate of 2-5 mL/min. D. The detection limit of the naked-eye detection The naked-eye detection limit was tested by using xylenol orange at the concentration of 0.01 mM and the concentration of metal ions was varied in a range of 10−4 - 10−7 M at pH 5. The lowest concentration of metal ions that can be detected by naked-eye are 3X10−6 M,

3X10−6 M and 1X10−6 M for Co(II), Ni(II) and Fe(III), respectively as shown in Figure 4.

Figure 4. Detection limit by naked-eye method for Co(II), Ni(II) and Fe(III) (silica gel = 25 mg, pH = 5, xylenol orange (XO) = 0.01 mM and flow rate = 1 mL/min)

The naked-eye detection limit for Ni(II) and Fe(III) was found in a same level of the

standard water quality provided by the U.S. Environmental Protection Agency (EPA) and World Health Organization (WHO) as shown in Table 1.5 This method can thus be applied to on-site determination of Ni(II) and Fe(III) in environmental water samples.

XO Zn(II) Ni(II) Pb(II) Co(II) Cu(II) Cd(II) Fe(III) Cr(III)

XO 100 10 9 8 7 6 5 4 3 2 1 0.1 ( X 10−−−−6 M)

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Table 1. Limit of naked-eye detection for Ni(II) and Fe(III) Metal ions LOD of this work

(mg/L) Guideline value of drinking water

(mg/L)

Ni(II)

0.2

0.07A

Fe(III)

0.06

0.3B

A = World Health Organization (WHO) B = the U.S. Environmental Protection Agency (EPA)

References:

1. Duruibe JO, Ogwuegbu MOC, Egwurugwu JN. Int J Phys Sci 2007;2:112-118. 2. Koh J, Kwon Y, Pak YN. Microchem J 2005;80:195-199. 3. Detcheva A, Grobecker HK. Acta Part B 2006;61:454-459. 4. Gil CD, Caballero A, Ratere I, Tarraga A, Molina P, Veciana J. Sensors 2007;7:3481-

3488. 5. WHO’s guideline for drinking-water quality, 2011. [Online]. (n.d) Avalible from:

http://www.who.int/water_sanitation_health/publications/2011/dwq_guidelines/en/ [2012, July 20]. Keywords: Xylenol orange, Naked-eye detection

naked-eye detection of co(ii) ni(ii) and fe(iii) using ... for...

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