Study On Determination Of Trace Elements In Environmental Samples By Atomic Absorption Spectrometry After Cloud Point Extraction

Cloud point extraction (CPE) is related to the conventional liquid-liquid extraction (LLE). CPE based on the solubility and cloud point phenomenon of aqueous solutions of surfactants, upon alteration of the experimental conditions such as pH value of solution, ionic strength, temperature, the solution is separated into phases, which results in the separation of hydrophobe and hydrophile. CPE is an easy, safe, high efficiency and inexpensive methodology for preconcentration and separation. It has been used widely in the study of life sciences and environment sciences, and has also been successfully used in the preconcentration and separation of mental elements. This thesis proposes a new method for determination of trace lead and cadmium in water samples by graphite furnace atomic absorption spectrometry (GFAAS) after cloud point extraction (CPE), in order to achieve more accurate, reliable and sensitive results and lower detection limits.Nonionic surfactant TritonX-114 was chosen , the cloud point temperature(CPT) depends strongly on the degree of polyoxyethylation ie the number of repeating (-CH2-CH2-O-)n units. The CPT increases with the increment of moles of polyoxyethylation. TritonX-114, the mole ratio n=7.5, and has CPT within a narrow range of 22-25 for a concentration range of 0.1-5%. Therefore it is the best one for cloud point extraction for laboratory operation. The effects of electrolytes and organic solvents that could have had on CPT were determined. The CPT range increases with the increase of surfactant concentration and the amount of organic solvents present on the matrix, such as methanol and ethanol. Lower CPT also obverted in the presence ofelectrolytes such as NaCl, KC1 and AlCb. These informations will provide the basic criteria or guidelines in determine the ranges of applications, and allow one to fine-tune the needed experimental conditions under different matrix effects.2-[(5-Bromo-2-pyridyl) azo]-5-diethylamino phenol (5-Br-PADAP) was selected as chelating agent. The effect factors on CPE, such as pH value, concentration of buffer solution, chelating agent, and TritonX-114, equilibration temperature and time, interferences etc. were tested. Most suitable conditions were determined. Effect of pyrolysis and atomization temperatures of GFAAS on absorbance of Pb, Cd was studied. The optimal temperatures were determined.At pH7.0, preconcentration of a 10mL of sample in the presence of 0.05% TritonX-114 and 0.5 10-5mol/L 5-Br-PADAP permitted the detection of 0.04ug/LCd, the concentration factors was 21 for Cd. At pHS.O, preconcentration of a lOmL of sample in the presence of 0.05% TritonX-114 and 0.5 X 10'5mol/L 5-Br-PADAP permitted the detection of 0.04ug/L Pb, the concentration factors was 21 for Pb. The proposed method has been successfully applied for determination of Cd and Pb present in tap water, underground water, surface water samples and the standard addition method was applied to verify the recoveries. The recovery ranges of Pb was 97.8 ~ 104%, and the recovery ranges of Cd was 95 ~ 100%.