**1. Introduction**

262 Polyurethane

2423

Sato, H.; Takebayashi, K. & Tanaka, Y. (1987). Analysis of 13C NMR of Polybutadiene by Means of Low Molecular Weight Model Compounds. *Macromolecules*, Vol.20, pp. 2418-

Zheyen, Z.; Zinan, Z. & Huimin, M. (1983). 13C-NMR Study on the equibinary (cis-1,4;1,2) Polybutadiene Polymerized with Iron Catalyst. *Polm. Comm.*, No. 1, pp. 92-100

> The ability to determine trace elements in various types of samples is important in many areas of science including environmental, food, geochemical, forensic, and pharmaceutical. The amount of certain elements can indicate the level of contamination in a region, the nutritional value of a food and the quality of a manufactured product, among other things. However, the matrix of the samples can be chemically complex due to the large number of substances that are present. Some of these substances can hinder the determination of trace elements due to incompatibility with some detectors, especially those based on spectrometry. For example, substances can influence the viscosity of a solution that is introduced into the flame atomic absorption spectrometer (FAAS), interfering with the nebulization process (Teixeira et al., 2005). Additionally, some substances may interfere with the pyrolysis of a sample that is introduced into the graphite tube of an electrothermal atomization atomic absorption spectrometer (ETAAS) (Zambrzycka et al., 2011; Serafimovska, et al., 2011). Another common problem occurs when the content of the element is measured at a very low level in some matrices. In this case, the technique does not provide a detection limit sufficient to determine the element in the sample. These difficulties can be resolved or reduced by improving the selectivity and sensitivity of the analytical method or by including separation and preconcentration steps in the procedure. Separation is the removal of measurable constituents or interfering substances from the sample matrix. Preconcentration is a procedure based on the separation of a measured quantity of constituents for a medium volume that is smaller than the sample matrix.

> Many procedures used for separation and preconcentration that involve different techniques are found in the literature, such as liquid-liquid extraction, coprecipitation, cloud-point extraction and solid phase extraction (Zeeb & Sadeghi, 2011; Tuzen et al.,2008; Lemos et al.,

2008; Oral et al., 2011). Among these techniques, solid phase extraction deserves special attention because of several advantages this technique offers. Among these advantages is the reduction or elimination of the use of toxic organic solvents, the achievement of high enrichment factors, a high versatility due to various types of sorbents that are low in cost, decreased operating time and ease of automation. Many substances are used as sorbents for solid phase extraction of trace elements, such as naphthalene, activated carbon, alumina, silica, biosorbents, such as hair, bagasse and peat, and polymeric sorbents, including polyurethane foam (PUF) and polystyrene-divinylbenzene (Beketov et al., 1996; Zhang et al., 2011; Jamshidi et al, 2011; Costa et al., 2011; Matos & Arruda, 2006; Gonzales et al., 2009).

Synthesis of a New Sorbent Based on Grafted PUF

for the Application in the Solid Phase Extraction of Cadmium and Lead 265

The polyurethane-based polymers are widely used for solid phase extraction, with or without treatment, due to their very low cost and simplicity of preparation (Moawed & El-Shahat, 2006; Saeed & Ahmed, 2005). Moreover, the sorbent is resistant to changes in pH and has a reasonable resistance to swelling in the presence of organic solvents. This material can also be used as a support for many reagents in separation and preconcentration. For example, the combination of PUF with chelating reagents has resulted in powerful sorbents for the extraction of metal ions. This association can be effected via impregnation, functionalization or grafting of chelating reagents in PUF. The use of this material to associate with organic reagents in the separation and preconcentration of trace species has many possible applications. However, the potential for grafted or functionalized foam in solid phase

Loading of chelating reagents in PUF is a fairly simple process. In this procedure, the chelating reagent is usually dissolved in an alcoholic solution and passed through a column that is packed with PUF. In batch procedures, the reagent solution is maintained in contact with the foam for a short period, while stirring. After sorption, the sorbent is washed with an alkaline solution to remove excess chelating reagents (El-Shahawi et al., 2011a; El-

Chelating reagents may be directly introduced into PUF by chemical bonding. This procedure, sometimes called functionalization, produces a very stable sorbent. The binding is based on the participation of amino groups, which are constituents of terminal toluidine groups of PUF, in typical reactions of aromatic amines, such as diazotization or azo coupling reactions (Lemos et al., 2010)]. These reactions result in the incorporation of a ligand by an

PUFs grafted with chelating reagents have shown excellent characteristics for use in systems of solid phase extraction, such as selectivity, high enrichment factors and stability. Grafted PUF is a material with two or more monomers polymerized through an addition reaction to provide a simple polymer containing different subunits. Grafted PUFs are considered excellent adsorbent materials that have good stability, high extraction capacity of inorganic and organic species, and good flexibility. Grafted PUF has been prepared by mixing PUF with an appropriate reagent prior to the addition of diisocyanate to form the foam material. Several substances, such as Nile blue A (Moawed & El-Shahat, 2006), methylene blue (Moawed et al., 2003; El-Shahat et al., 2007), rosaniline (Moawed, 2004), rhodamine B (El-Shahat et al., 2003) and brilliant green (El-Shahat et al., 2003), have been incorporated into PUF to obtain grafted sorbents. Table 1 summarizes the characteristics of various procedures

In this work, we have synthesized a new sorbent material based on PUF grafted with the chelating reagent 2-[2'-(6-methyl-benzotiazolilazo)]-4-aminophenol (Me-BTAP). The material was characterized by IR spectroscopy and thermogravimetry. The sorbent was used in a solid phase extraction system for preconcentration and determination of cadmium

extraction has not been fully explored (El-Shahat et al., 2003; Lemos et al., 2006b).

–N=N or –N=C spacer arm (Burhan, 2008; Azeem et al., 2010).

that use grafted PUF for solid phase extraction of trace species.

Shahawi et al., 2011b).

and lead in water samples.

Naphthalene is used in preconcentration procedures because of its ability to extract or form a complex with organic species (Fathi et al., 2011). This sorbent makes it possible to achieve high enrichment factors and is soluble in many solvents, which can facilitate the detection process. However, naphthalene is toxic and possibly carcinogenic, and its use is restricted to batch procedures.

Activated carbon is an excellent material for use in extraction procedures due to its large surface area and its strong interaction with organic species and trace elements (Zhang et al., 2011). The disadvantage of using activated carbon in extraction procedures is that the interaction with some species is so strong it can cause an irreversible sorption. In addition, activated carbon has a heterogeneous surface with active functional groups that often lead to low reproducibility. These sorbents are also very reactive and can act as catalysts of undesirable chemical reactions.

Silica gel is also widely used in solid phase preconcentration procedures due to its mechanical strength, resistance to swelling caused by solvent change and a high adsorption capacity of several species (Tzvetkova et al., 2010). The disadvantages of using this sorbent include a very low selectivity and hydrolysis at basic pH.

Biosorbents are materials of great interest for use in an extraction system because of their availability and versatility (Gonzales et al., 2009). However, some of these sorbents are difficult to recover and the mechanisms of sorption of trace species are not yet fully understood.

Macroporous hydrophobic resins are good supports for developing chelating sorbents. These materials are resins based on polystyrene-divinylbenzene with a high hydrophobic character and no ion-exchange capacity. Several reagents have been incorporated into polystyrene-divinylbenzene to form chelating resins for use in preconcentration procedures (Lemos et al., 2006a).

Among the sorbents used for the extraction of organic and inorganic species for separation and preconcentration, PUF is noteworthy due to the benefits achieved. This material was used for the extraction of aqueous species for the first time in the early 1970s (Braun and Farag, 1978). Since then, PUF has been used in several procedures for separation and preconcentration, and its use has been the subject of several books and reviews (Braun, 1983; Navratil et al., 1985; Lemos et al., 2007). PUF is low in cost, easy to purchase, and provides high enrichment factors. However, this sorbent may swell when treated with solvents (Braun, 1983; Navratil et al., 1985).

The polyurethane-based polymers are widely used for solid phase extraction, with or without treatment, due to their very low cost and simplicity of preparation (Moawed & El-Shahat, 2006; Saeed & Ahmed, 2005). Moreover, the sorbent is resistant to changes in pH and has a reasonable resistance to swelling in the presence of organic solvents. This material can also be used as a support for many reagents in separation and preconcentration. For example, the combination of PUF with chelating reagents has resulted in powerful sorbents for the extraction of metal ions. This association can be effected via impregnation, functionalization or grafting of chelating reagents in PUF. The use of this material to associate with organic reagents in the separation and preconcentration of trace species has many possible applications. However, the potential for grafted or functionalized foam in solid phase extraction has not been fully explored (El-Shahat et al., 2003; Lemos et al., 2006b).

264 Polyurethane

batch procedures.

undesirable chemical reactions.

(Lemos et al., 2006a).

(Braun, 1983; Navratil et al., 1985).

include a very low selectivity and hydrolysis at basic pH.

2008; Oral et al., 2011). Among these techniques, solid phase extraction deserves special attention because of several advantages this technique offers. Among these advantages is the reduction or elimination of the use of toxic organic solvents, the achievement of high enrichment factors, a high versatility due to various types of sorbents that are low in cost, decreased operating time and ease of automation. Many substances are used as sorbents for solid phase extraction of trace elements, such as naphthalene, activated carbon, alumina, silica, biosorbents, such as hair, bagasse and peat, and polymeric sorbents, including polyurethane foam (PUF) and polystyrene-divinylbenzene (Beketov et al., 1996; Zhang et al., 2011; Jamshidi

Naphthalene is used in preconcentration procedures because of its ability to extract or form a complex with organic species (Fathi et al., 2011). This sorbent makes it possible to achieve high enrichment factors and is soluble in many solvents, which can facilitate the detection process. However, naphthalene is toxic and possibly carcinogenic, and its use is restricted to

Activated carbon is an excellent material for use in extraction procedures due to its large surface area and its strong interaction with organic species and trace elements (Zhang et al., 2011). The disadvantage of using activated carbon in extraction procedures is that the interaction with some species is so strong it can cause an irreversible sorption. In addition, activated carbon has a heterogeneous surface with active functional groups that often lead to low reproducibility. These sorbents are also very reactive and can act as catalysts of

Silica gel is also widely used in solid phase preconcentration procedures due to its mechanical strength, resistance to swelling caused by solvent change and a high adsorption capacity of several species (Tzvetkova et al., 2010). The disadvantages of using this sorbent

Biosorbents are materials of great interest for use in an extraction system because of their availability and versatility (Gonzales et al., 2009). However, some of these sorbents are difficult

Macroporous hydrophobic resins are good supports for developing chelating sorbents. These materials are resins based on polystyrene-divinylbenzene with a high hydrophobic character and no ion-exchange capacity. Several reagents have been incorporated into polystyrene-divinylbenzene to form chelating resins for use in preconcentration procedures

Among the sorbents used for the extraction of organic and inorganic species for separation and preconcentration, PUF is noteworthy due to the benefits achieved. This material was used for the extraction of aqueous species for the first time in the early 1970s (Braun and Farag, 1978). Since then, PUF has been used in several procedures for separation and preconcentration, and its use has been the subject of several books and reviews (Braun, 1983; Navratil et al., 1985; Lemos et al., 2007). PUF is low in cost, easy to purchase, and provides high enrichment factors. However, this sorbent may swell when treated with solvents

to recover and the mechanisms of sorption of trace species are not yet fully understood.

et al, 2011; Costa et al., 2011; Matos & Arruda, 2006; Gonzales et al., 2009).

Loading of chelating reagents in PUF is a fairly simple process. In this procedure, the chelating reagent is usually dissolved in an alcoholic solution and passed through a column that is packed with PUF. In batch procedures, the reagent solution is maintained in contact with the foam for a short period, while stirring. After sorption, the sorbent is washed with an alkaline solution to remove excess chelating reagents (El-Shahawi et al., 2011a; El-Shahawi et al., 2011b).

Chelating reagents may be directly introduced into PUF by chemical bonding. This procedure, sometimes called functionalization, produces a very stable sorbent. The binding is based on the participation of amino groups, which are constituents of terminal toluidine groups of PUF, in typical reactions of aromatic amines, such as diazotization or azo coupling reactions (Lemos et al., 2010)]. These reactions result in the incorporation of a ligand by an –N=N or –N=C spacer arm (Burhan, 2008; Azeem et al., 2010).

PUFs grafted with chelating reagents have shown excellent characteristics for use in systems of solid phase extraction, such as selectivity, high enrichment factors and stability. Grafted PUF is a material with two or more monomers polymerized through an addition reaction to provide a simple polymer containing different subunits. Grafted PUFs are considered excellent adsorbent materials that have good stability, high extraction capacity of inorganic and organic species, and good flexibility. Grafted PUF has been prepared by mixing PUF with an appropriate reagent prior to the addition of diisocyanate to form the foam material. Several substances, such as Nile blue A (Moawed & El-Shahat, 2006), methylene blue (Moawed et al., 2003; El-Shahat et al., 2007), rosaniline (Moawed, 2004), rhodamine B (El-Shahat et al., 2003) and brilliant green (El-Shahat et al., 2003), have been incorporated into PUF to obtain grafted sorbents. Table 1 summarizes the characteristics of various procedures that use grafted PUF for solid phase extraction of trace species.

In this work, we have synthesized a new sorbent material based on PUF grafted with the chelating reagent 2-[2'-(6-methyl-benzotiazolilazo)]-4-aminophenol (Me-BTAP). The material was characterized by IR spectroscopy and thermogravimetry. The sorbent was used in a solid phase extraction system for preconcentration and determination of cadmium and lead in water samples.


Synthesis of a New Sorbent Based on Grafted PUF

for the Application in the Solid Phase Extraction of Cadmium and Lead 267

Ultrapure water from an Elga Purelab Classic was used to prepare all solutions. Working solutions of cadmium and lead at the µg L-1 level were prepared daily by diluting a 1000 µg mL-1 solution of each element (Merck). Hydrochloric acid solutions were prepared by direct dilution of the concentrated solution (Merck) with ultrapure water. Acetate buffer solutions (pH 4.0-6.0), borate (pH 7.0-8.5) and ammonia (pH 9.0-9.5) were used to adjust the pH. The reagents 2,4- toluene diisocyanate (Aldrich), tin(II) 2-ethylhexanoate (Aldrich), dimethylamino-1-propanol (Aldrich), polyethylene glycol (Aldrich) and silicone oil AP 100

The synthesis of the reagent 2-[2´-(6-methyl-benzothiazolylazo)]-4-aminophenol (Me-BTAP) was performed as described previously (Lemos et al., 2006a). The production of the reagent has been completed in two steps: diazotization of 6-methyl-2-aminobenzothiazole followed by the coupling of the diazotized product with 4-aminophenol. The diazotization reaction was performed by dissolving 6-methyl-2-aminobenzothiazole (3.0 g) in 50 mL of a 6.0 M hydrochloric acid solution. Then, a solution of 2.0 g of sodium nitrite in 20 mL of water at 0- 5 C was added dropwise, and the mixture was stirred at a constant temperature of 0–5 C for 1 h. The diazotate mixture was added dropwise to a solution of 3.0 g of 4-aminophenol in 20 mL of an 1.0 M sodium carbonate solution at 0–5 C under vigorous stirring. The system was allowed to stand overnight in a refrigerator at 0–5 C. The resulting dark-green precipitate was filtered and purified by recrystallization in ethanol. The proposed structure

Preparation of the grafted sorbent was performed according to the following procedure (El-Shahat et al., 2003; Moawed, 2004): 20.00 g of polyethylene glycol and 0.04 g of dimethylamino-1-propanol were added to 1.0 g of distilled water under vigorous stirring. Next, silicone oil (0.05 g) and tin(II) 2-ethylhexanoate (0.04 g) were added to the mixture. The system was shaken to obtain a homogeneous mixture. The reagent Me-BTAP (0.02 g) was then added, and the mixture was stirred for ten minutes. Afterward, approximately 13.0 g of toluene diisocyanate was added gradually. The resulting polymer was cut into small pieces and washed with 1.0 M HCl, ethanol and water. After washing, the polymer was

N

S

N = N

OH

NH2

**2.2. Reagents** 

(Aldrich) were used in the synthesis of the sorbent.

**2.3. Synthesis of the reagent Me-BTAP** 

of Me-BTAP is shown in Figure 1.

**Figure 1.** Proposed structure of Me-BTAP.

H3C

**2.4. Synthesis of the sorbent** 

dried at room temperature.

**Table 1.** Procedures involving grafted PUF applied in the preconcentration of chemical species by spectrophotometry.
