**3.7. Analytical characteristics**

The analytical characteristics of the method were calculated under the optimized conditions for preconcentration. Table 2 summarizes the analytical characteristics of the method. The analytical curves were constructed using solutions of cadmium and lead ranging from 1.0 to 10.0 and from 10.0 to 100.0 mg L-1, respectively.

Regression curves without preconcentration resulted in the following equations: A = 3.97 x 10-4 C + 6.40 x 10-3 for Cd and A = 1.98 x 10-5 C + 2.38 x 10-4 for Pb, where A is the absorbance and C is the metal concentration in solution, in µg L-1. These equations were obtained under optimum conditions of the spectrometer. Enrichment factors (EF) were calculated as the ratio of the slopes of the linear section in the calibration graphs for preconcentration and direct aspiration (Fang et al., 1992). The term concentration efficiency (CE) is defined as the product of EF and the number of samples analyzed per minute (Fang et al., 1992). Therefore, if f is the sampling frequency expressed in samples analyzed per hour, CE = EF x (f/60).


**Table 2.** Features of the preconcentration system for the determination of cadmium and lead (A, absorbance and C, metal concentration, g L-1).

The transfer phase factor is defined as the ratio between the analyte mass in the original sample and that in the concentrate. Consumptive index (CI) quantifies the efficiency of an FI on-line column preconcentration system in terms of the sample volume consumed to achieve a defined EF. The term CI is defined as the sample volume (V), in mL, consumed to achieve a unit EF, expressed by the equation CI = V/EF (Fang et al., 1992).

The limits of quantification and detection of the method were also calculated. The detection limit was calculated using the following equation: 3sb/b, where sb is the standard deviation for eleven measurements of the blank, and b is the slope of the analytical curve for each metal. The limit of quantification was calculated as 10sb/b.

The accuracy of the proposed procedure was evaluated by determining the amounts of Cd and Pb in a certified reference material. The following material was analyzed: BCR-713, Wastewater (effluent) from the Institute for Reference Materials and Measurements (IRMM, Geel, Belgium). The results were 4.8 ± 0.5 µg L-1 for cadmium and 45 ± 4 µg L-1 for lead. According to the results, no significant difference was found between the results that were obtained and the certified values of the reference material (5.1 ± 0.6 µg L-1 and 47 ± 4 µg L-1 for cadmium and lead, respectively).

#### **3.8. Application of the proposed procedure**

274 Polyurethane

**3.6. Lifetime of minicolumn** 

**3.7. Analytical characteristics** 

10.0 and from 10.0 to 100.0 mg L-1, respectively.

The life of the sorbent was investigated by monitoring the analytical signal corresponding to solutions of Pb (100.0 mg L-1) or Cd (10.0 mg L-1) at the end of a work day and by counting the number of runs. It was observed that the packed minicolumn did not provide a

The analytical characteristics of the method were calculated under the optimized conditions for preconcentration. Table 2 summarizes the analytical characteristics of the method. The analytical curves were constructed using solutions of cadmium and lead ranging from 1.0 to

Regression curves without preconcentration resulted in the following equations: A = 3.97 x 10-4 C + 6.40 x 10-3 for Cd and A = 1.98 x 10-5 C + 2.38 x 10-4 for Pb, where A is the absorbance and C is the metal concentration in solution, in µg L-1. These equations were obtained under optimum conditions of the spectrometer. Enrichment factors (EF) were calculated as the ratio of the slopes of the linear section in the calibration graphs for preconcentration and direct aspiration (Fang et al., 1992). The term concentration efficiency (CE) is defined as the product of EF and the number of samples analyzed per minute (Fang et al., 1992). Therefore, if f is the sampling frequency expressed in samples analyzed per hour, CE = EF x (f/60).

significant change in the extraction, even when used 350 times.

**Element Cadmium Lead** 

Preconcentration time, s 120 120

Enrichment factor 30 35

Concentration efficiency, min-1 13 15

Transfer phase factor 0.91 0.86

Sample volume, mL 9.00 14.0

Consumptive index, mL 0.30 0.40

Sample frequency, h-1 26 26

Limit of detection, µg L-1 0.8 1.0

Limit of quantification, µg L-1 2.7 3.3

Precision, % 4.1 4.8

absorbance and C, metal concentration, g L-1).

Calibration function A= 3.20 x 10-3 + 1.19 x 10-2 C A= 7,78 x 10-4 + 6.93 x 10-4 C

**Table 2.** Features of the preconcentration system for the determination of cadmium and lead (A,

The preconcentration procedure was applied to determine the metal content in water samples. These real samples were collected at Jequié, Bahia, Brazil. Known concentrations of Cd and Pb were added to the samples to minimize the change in the matrix of the original sample. Recoveries of the spiked samples (2.0 and 30.0 g L-1 for cadmium and lead, respectively) were determined. The results shown in Table 3 demonstrate the applicability of the method. Recoveries (R) were calculated as follows: R (%) = {(Cm-Co)/m} x100, where Cm is the concentration of metal in a spiked sample, Co is the concentration of metal in a sample and m is the amount of metal spiked. The described procedure can be successfully applied to these matrices for the preconcentration and determination of cadmium and lead.


**Table 3.** Results for the determination of Cd and Pb using the proposed procedure. LOQ: limit of quantification, R: recovery.

The results obtained from this procedure are comparable to those of other preconcentration methods for Cd and Pb determination. Table 4 summarizes some of these methods and their characteristics.


Synthesis of a New Sorbent Based on Grafted PUF

for the Application in the Solid Phase Extraction of Cadmium and Lead 277

Azeem, S. M. A., Arafa, W. A. A. & El-Shahat, M. F. (2010). Synthesis and application of alizarin complexone functionalized polyurethane foam: Preconcentration/separation of metal ions from tap water and human urine. *Journal of Hazardous Materials*, Vol.182,

Beketov, V. I., Parchinskii, V. Z. & Zorov, N. B. (1996). Effects of high-frequency electromagnetic treatment on the solid-phase extraction of aqueous benzene,

Braun, T. (1983) Trends in using resilient polyurethane foams as sorbents in analytical chemistry, *Fresenius' Journal of Analytical Chemistry,* Vol. 314, No. 7, p.p. 652-656. Burham, N. (2008). Uses of 5-Methylresorcin-Bonded Polyurethan Foam as a New Solid Phase Extractor for the Selective Separation of Mercury Ions from Natural Water

Costa, L. M., Ribeiro, E. S., Segatelli, M. G., Do Nascimento, D. R., De Oliveira, F. M. & Tarley, C. R. T. (2011). Adsorption studies of Cd(II) onto Al2O3/Nb2O5 mixed oxide dispersed on silica matrix and its on-line preconcentration and determination by flame atomic absorption spectrometry. *Spectrochimica Acta Part B-Atomic Spectroscopy*, Vol.66,

El-Shahat, M. E., Moawed, E. A. & Farag, A. B. (2007). Chemical enrichment and separation of uranyl ions in aqueous media using novel polyurethane foam chemically grafted

El-Shahat, M. F., Moawed, E. A. & Zaid, M. A. A. (2003). Preconcentration and separation of iron, zinc, cadmium and mercury, from waste water using Nile blue a grafted

El-Shahawi, M. S., Bashammakh, A. S. & Abdelmageed, M. (2011a). Chemical Speciation of Chromium(III) and (VI) Using Phosphonium Cation Impregnated Polyurethane Foams Prior to Their Spectrometric Determination. *Analytical Sciences*, Vol.27, No.7, p.p.757-

El-Shahawi, M. S., Hamza, A., Al-Sibaai, A. A. & Al-Saidi, H. M. (2011b). Fast and selective removal of trace concentrations of bismuth (III) from water onto procaine hydrochloride loaded polyurethane foams sorbent: Kinetics and thermodynamics of

Fang Z., Dong L. P. & Xu S. K., (1992). Critical Evaluation of the Efficiency and Synergistic Effects of Flow Injection Techniques for Sensitivity Enhancement in Flame Atomic

Fathi, M. R., Pourreza, N. & Ardan, Z. (2011). Determination of aluminum in food samples after preconcentration as aluminon complex on microcrystalline naphthalene by

bismuth (III) study. *Chemical Engineering Journal*, Vol.173, No.1, p.p.29-35.

Absorption SpectrometryJ. *Anal. Atom. Spectrom*. Vol.7 pp. 293-299.

spectrophotometry. *Quimica Nova*, Vol.34, No.3, p.p.404-407.

naphthalene and phenol. *Journal of Chromatography a*, Vol.731, No.1-2, p.p.65-73. Braun, T. & Farag, A. B. (1978). Polyurethane foams and microspheres in analyticalchemistry - improved liquid-solid, gas-solid and liquid-liquid contact via a new

geometry of solid-phase. *Analytica Chimica Acta*, Vol.99, No.1, p.p.1-36.

Samples. *Central European Journal of Chemistry*, Vol.6, No.4, p.p.641-650.

with different basic dyestuff sorbents. *Talanta*, Vol.71, No.1, p.p.236-241.

polyurethane foam. *Talanta*, Vol.59, No.5, p.p.851-866.

**5. References** 

No.1-3, p.p.286-294.

No.5, p.p.329-337.

763.

#### 276 Polyurethane

**Table 4.** Analytical characteristics of various procedures for the determination of Cd and Pb by FAAS, \* µg g-1.
