Bazı eser elementlerin adsorpsiyonla zenginlestirilmesi ve alevli AAS ile tayini

Abstract

Bu çalışmada, amino ve tiol modifiye silikaların özellikleri ve hazırlanışları, zenginleştirme uygulamaları ve alevli atomik absorpsiyon spektrometresi (AAS) ile eser miktardaki Kadmiyum ve Bakır elementlerinin tayinleri anlatılmıştır. Modifiye silikalar hazırlanırken, ilk olarak silika derişik hidroklorik asitle 30 dakika muamele edildi, sonra, yıkama sularında klor iyonu kalmayıncaya kadar saf su ile yıkandı ve 150°C de bir gün kurutuldu. Kuru silika metanol içine kondu ve amino modifiye silika eldesi için (C2Hs0)3 Si(CH2)3NH2 ( 3-aminopropil trietoksisilan), tiol modifiye silika eldesi için de (CHaO) Si(CHa)3 SH( 3-merkaptopropil trimetoksislan) ilave edildi. Metanol vakum altında uzaklaştırıldıktan sonra kalan silika tekrar 150°C kurutuldu ve yıkama suları berraklaşıncaya kadar distile su ile yıkandı. Modifiye silikaların özellikleri, hazırlamada kullanılan silikaların özelliklerine bağlıdır. Bu çalışmada, 496 m2/gr yüzey alanlı silika kullanılmıştır. Bu yüzey alanı amino modifiye silikalarda 290 m2 / gr iken tiol modifiye silikalarda 410 gr/m2 dir. Bütün adsorbsiyon deneylerinde "Batch (çalkalama)" ve "Kolon" yöntemleri kullanılmıştır. Kadmiyum ve bakır elementlerinin adsorbsiyonunda, pH'ın çalkalama süresinin ve tampon çözeltisinin cinsinin etkileri incelenmiştir.

In this work, the preparation and characteristics of amino-and thiol-modif ied silicas and their applications to the preconcentration and determination of trace amounts of copper and cadmium by flame atomic absorption spectrometry are described. Normally metal ions can be deposited by ionexchange or adsorbtion on metaloxid surfaces. This procedure can be modified and sometime be more selective by changing the surface properties of the oxide. This has frequently been done by physical methods like treatment at higher temperatures. The last 20 years chemical reactions have been widely employed. Being covered with hydroxyl groups (silanol groups), the surface of silica can be modified in many ways and a large number of different groups can be attached to its surface. Silica gel can be considered to be an amorphous condensation polymer of silicic acid. Conventionally, it is made by mixing aqueous solution of sodium silicate and trisilicic acid are formed and condense with one another. Silicic acid first condenses with itself to form disilicic acid and water, the Vll disilicic acid condenses with silicic acid to form trisilicic acid and so on. Condensation between two molecules of disilicic acid is also possible. This stage leads to a collodial solution o f spheroidal particles of polysilicic acids which have a diameter of about 10 nm (10 nm = 100 A ) and contain roughly ten thousands silicon atoms each. The collodial solution eventually forms a hidrogel that is washed and dried to produce silica gel. Further condensation, inter and intraparticle, occurs during these stages. During drying, the surface tension forces of water collapse the original, very open, texture until the mechanical strength of the agglomeration of particles becomes sufficient to resist further collapse. The remaining water then evoparates leaving a material of large area and substantial pore volume whose texture must rather resemble that of a loosely packed gravel bed. Silica gels of differing textures can be prepared by variations in the techniques of preparation and by aging of the gel subsequent to its formation. Most commercial silica gels are either of the narrow pore type (average pore diameter about 2.5 nm, specific area about 700 m* per g, and pore volume about 0.4 cc per g) or of the wide pore type (average pore diameter about 14 nm, spesific area about 300 mz-per g, and pore volume about 1.1 cc per g). Our work has employed mostly the narrow pore silica gel. The following silylation reaction offers attractive posibilities for the attachment of a variety of organic residues to silica gel. viii a - OH CH O OCH 3 \ / 3 cr - OH CHoO X : Any amino group, eg.-NHz or -NHCH2CH2CHZNH2 If either the -NH or -NHCH CH CH NH gel 2 2 2 2 2 is treated with a solution of metals, substantial quantities of ions are taken up by the gel via coordination to the amino groups. In many respects, the chemistry of thiols is like that of alcohols. Thus thiols can be readily prepared by the reaction of sodiumhdyrosulf ide (NaSH) with those alcly holides, sulfates or sulfonate. C HcBr + NaSH C H SH + NaBr 2 -J 2 » Since thiols are acids of comparable strengdth to hydrogensulf ide (Ka = 6 x 10"^, more or less of the thioether may be produced by the following sequence of reactions unless the sodium hdyrosulfide is used in large excess. C2H5SH + NaSH C2H5SNa + H2S C2H5SNa + C2HBBr