Paraquat is a bipyridyl herbicide and organic divalent cation which due to its high polarity and water solubility cannot be readily extracted by common organic solvents from body fluids. Dithionite color test for qualitative and quantitative determination of paraquat in urine has been proposed and used for many years. Although some methods were proposed for solvent extraction of paraquat from blood, they are less practical in clinical laboratories and lack high extraction recovery. Clinoptilolite is a highly porous natural zeolite with cation-exchange property and high surface area. In the present work, extraction of paraquat from human blood by clinoptilolite was investigated and compared with Amberlite CG-50 I, a well-known weak cation-exchanger. Blood paraquat was adsorbed by adsorbents (clinoptilolite or Amberlite) and extracted from them by saturated sodium chloride solution. Extracted paraquat was spectrophotometrically measured by means of sodium dithionite reagent at 394.5？nm. Recovery, limit of detection, considering signal-to-noise (S/N) ratio of 3, and limit of quantification, regarding S/N of 10, of paraquat extraction by clinoptilolite and Amberlite CG-50 were 81.7%？±？3.4%, 0.58？μg, and 1.93？μg and 83.6%？±？3.2%, 0.49？μg, and 1.63？μg, respectively. Repeatabilities (within-laboratory error) of paraquat extraction by clinoptilolite and Amberlite CG-50 I were 7.1% and 6.3%, respectively. 1. Introduction Paraquat, 1,1′-Dimethyl–4,4′-bipyridinium, is a bipyridyl herbicide and divalent organic cation [1] which due to its high polarity and water solubility cannot be readily extracted by common organic solvents from body fluids [2]. Dithionite color test for qualitative and quantitative determination of paraquat in urine has been proposed and used for many years [3]. Although some methods were proposed for solvent extraction of paraquat from blood [4, 5], they are less practical in clinical laboratories and lack high extraction recovery. Zeolites are microporous hydrated aluminosilicate materials which are available as naturally occurring materials or as synthetically manufactured substances [6]. They are used in industries and medicine for their high surface area/volume ratio. Clinoptilolite as a natural zeolite due to its high availability, low cost, and high surface area/volume ratio has found many applications in agriculture [7, 8], animal husbandry [9], industries [8, 10], and medicine [11–16]. It has been found to be an efficient adsorbent of cations [10, 17] and a nontoxic carrier for drugs [11]. It has high negative charge which is
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