Abstract
An ion-associate phase (IAP) microextraction/ back-microextraction system was applied for the enrichment, separation, and detection of trace amounts of nickel from environmental water samples. Thenoyltrifluoroacetone (HTTA) acted not only as a chelating reagent for nickel, but also as a component of the extraction phase, i.e., IAP. Nickel in a 40 mL sample solution was pH-adjusted with phenolsulfonate (PS−) and tetramethylammonium hydroxide and converted by chelation reaction in the presence of thenoyltrifluoroacetonate (TTA−). When benzyldodecyldimethylammonium ion (C12BzDMA+) was added, a suspension of IAP formed in the solution. The IAP consisted of TTA−, a chelating reagent, the PS−, a component of pH buffer, and C12BzDMA+, which helps extract the chelating complex. When the solution was centrifuged, the IAP separated from the suspension and the nickel-TTA chelate was extracted into the bottom phase of the centrifuge tube. After the aqueous phase was taken away, 100 µL of nitric acid (2 M) solution containing phosphate was used to back-microextract nickel from the IAP. The acid phase was measured via graphite-furnace atomic-absorption spectrometry (GF-AAS). The proposed method facilitated a 400-fold enrichment. The limit of detection was 0.02 µg L−1. The proposed method was applied for the determination of nickel in river water and seawater samples.
Highlights
Nickel is ubiquitous in our daily live s and is found in trace amounts in environmental water [1]
HTTA and benzoylacetone (BzA) were used as chelating reagents because they make stable complexes with nickel and are β-diketones [26], which are a constituent of the ion-associate phase (IAP) and an OA−
The recoveries of both HTTA and BzA decrease with increasing acidity or basicity. β-Diketones cannot be coordinated in metals unless they are deprotonated to the enol form [26]
Summary
Nickel is ubiquitous in our daily live s and is found in trace amounts in environmental water [1]. We propose an ion-associate phase (IAP) extraction technique [15,16] that improves sensitivity and removes interfering components, and use it as a pretreatment technique for atomic spectroscopy [17,18,19,20]. HDPM reacts selectively with lithium to form a chelating complex, and acts as an OA− for the proposed IAP extraction/back-microextraction [20]; it is inexpensive. The standard solution of nickel, 1000 mg L−1, was prepared by dissolving nickel(II) nitrate hexahydrate (99.9%, Wako Pure Chemical, Osaka, Japan) in 0.1 M nitric acid. An ultrapure water with a specific resistance of 18.2 MΩ cm (Direct-Q3 UV system, Millipore, Tokyo, Japan) was used throughout
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