A Simple Method for Automated Solid Phase Extraction of Water Samples for Immunological Analysis of Small Pollutants

Summary

A protocol for the extraction and pre-concentration of estradiol from water samples by using an automated and miniaturized system is presented.

Abstract

A new method for solid phase extraction (SPE) of environmental water samples is proposed. The developed prototype is cost-efficient and user friendly, and enables to perform rapid, automated and simple SPE. The pre-concentrated solution is compatible with analysis by immunoassay, with a low organic solvent content. A method is described for the extraction and pre-concentration of natural hormone 17β-estradiol in 100 ml water samples. Reverse phase SPE is performed with octadecyl-silica sorbent and elution is done with 200 µl of methanol 50% v/v. Eluent is diluted by adding di-water to lower the amount of methanol. After preparing manually the SPE column, the overall procedure is performed automatically within 1 hr. At the end of the process, estradiol concentration is measured by using a commercial enzyme-linked immune-sorbent assay (ELISA). 100-fold pre-concentration is achieved and the methanol content in only 10% v/v. Full recoveries of the molecule are achieved with 1 ng/L spiked de-ionized and synthetic sea water samples.

Introduction

Sample preparation is an important step in any analytical process. In particular, removal of matrix effects, diminution of interferences, and enrichment of the analyte are necessary to obtain precise results and reach low limits of detection. Endocrine disrupting compounds (EDCs) are of particular concern due to their action on the living organisms even when present at very low levels in the environment. The natural hormone 17β-estradiol is present on the EU water pollution Watch List and prone to be added to the list of priority substances regulated under the European Water Framework Directive. Solid phase extraction (SPE) is commonly applied for the analysis of....

Protocol

Note: The following protocol describes the SPE performed on 100 ml water sample with C18 sorbent and elution with 50% v/v methanol. The enriched sample is diluted to reach 10% v/v methanol before analysis with an enzyme linked immunosorbent assay (ELISA) kit.

1. Preparing the Reagents

1. Prepare the water samples
   1. Prior to any other step, filter each 100 ml water sample with 0.2 µm pore size filters.
   2. Spike the sample with desired concentration by diluting appropriate volume of reference solution into a volume of water. For example, prepare 100 ml of water sample with 100 ng/L of E2 by diluting 3.3 µl....

Results

Reproducibility of sorbent packing was evaluated by drying and weighting the pipetted sorbent in glass vials and the result is shown in Figure 1. Reproducibility of the time of injection was tested for 100 ml samples, as shown in Figure 2. Concentration in initial and pre-concentrated spiked samples were determined by using a commercial ELISA kit for 17β-estradiol and are shown in Figure 3.

Discussion

A new method for the preparation of water samples followed by analysis using immunoassay was proposed. The instrument enables to perform solid phase extraction in an automated and user-friendly way.

The filtration of the water sample prior to its injection into the system is critical. Any particulates still present in the solution would potentially cause clogging of the fluidic network and obstruct the SPE column. Another important step is the preparation of the SPE column. The amount of parti.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Filter membrane 0.2 μm pore size	Merck Millipore	GNWP04700	For sample filtration
Nylon membrane 11 μm pore size	Merck Millipore	NY1104700	For SPE column
Disposable biopsy punch 5 mm	Medical Budget	39302439
Nucleodur C18 ec	Macherey Nagel	713550.01	50 μm particle diameter
Synthetic sea water	Sigma Aldrich	SSWS500-500ML
Methanol	VWR
17beta-estradiol standard	Enzo Life Science		300 ng/ml
17beta-estradiol ELISA kit	Enzo Life Science	ADI-900-008	96 wells, range 30 - 3,000 ng/L