Determination of tetracyclines in surface water and milk by the magnesium hydroxide coprecipitation method

doi:10.1016/j.chroma.2009.12.006

Journal of Chromatography A

Volume 1217, Issue 3, 15 January 2010, Pages 415-418

https://doi.org/10.1016/j.chroma.2009.12.006 Get rights and content

Abstract

A simple coprecipitation method was developed for the determination of tetracyclines (TCs) in surface water and milk by high-performance liquid chromatography with diode-array detection (HPLC–DAD). Magnesium ion was added into the surface water or the acetonitrile (MeCN) extract of milk. After alkalinization, magnesium hydroxide precipitates which had been formed can be separated from the matrix solution easily by centrifuging and then a dissolution step was performed by adding a small amount of acid. The final solution could be introduced directly into HPLC system for the determination of the analytes. Under optimal conditions, recoveries for the analysis of spiked surface water samples ranged from 83.6% to 95.1% with relative standard deviation of 2.0–5.5%. For milk samples, relative recoveries were 95.9–104.6% with relative standard deviation of 3.4–6.7%. The enrichment factors ranged from 41.5 to 48.1 for 10 mL water samples, and from 3.6 to 4.4 for 1 mL MeCN extracts of milk. Limits of detection ranged from 0.13 to 0.51 ng/mL, and from 3.0 to 8.5 ng/g for four TCs in surface water and milk samples, respectively.

Introduction

Tetracyclines are broad-spectrum antibiotics that are active against both gram-positive and gram-negative bacteria. Improper use of these compounds may result in unsafe residue levels in the tissues of food-producing animals. Moreover, the widespread use of TCs in food animals has led to concerns regarding the public health impact of the occurrence of these antibiotics in the aquatic environment [1], [2] due to the possible enhancement of resistance formation in bacteria.

Liquid–liquid extraction (LLE) is one of the oldest preconcentration and matrix isolation techniques in analytical chemistry and it remains a popular choice. However, conventional LLE is time-consuming, tedious and requires large amounts of organic solvent. Solid-phase extraction (SPE) has gradually replaced classical LLE to become the most common sample preparation technique [3], [4], but this can be relatively expensive and it normally requires an extra step of concentrating the extract down to a small volume. Moreover, using parent TCs as model compound, a number of solvent-minimized sample extraction methods include using in-tube solid-phase microextraction (SPME) [5], molecularly imprinted SPME [6], hollow fiber based liquid phase microextraction (HF-LPME) [7], magnetic molecularly imprinted polymers [8], carbon nanotubes [1], restricted access materials (RSM) [2] and dispersive micro solid-phase extraction [9] for the determination of TCs have been developed. Despite their advantages, these methods are usually instrument-based techniques or still require time-consuming extraction steps.

Recently, coprecipitation has been accepted as a useful technique to preconcentrate traces of heavy metals rapidly and easily because it has some advantages including, simplicity, rapidity, low expense, high preconcentration factor and low consumption of organic solvent. Unlike traditional methods, the coprecipitation method does not entail a solvent evaporation step to further concentrate the analytes in the final extract prior to analysis. Moreover, the final aqueous solution could also be directly introduced into the HPLC system. However, the determination of organic compounds by coprecipitation has undergone only limited application [10]. Several studies have revealed that TCs could form chelate complexes with multivalent cations and have the greater complex formation with magnesium [11], therefore, the aim of this study was to assess the feasibility in the application of coprecipitation with magnesium hydroxide to determine TCs in surface water and milk samples by HPLC–DAD.

Section snippets

Reagents and materials

Analytical standards of oxytetracycline (OTC) hydrochloride and doxycycline (DC) hyclate and analytical grade oxalic acid dehydrate were obtained from Riedel-de Haen (Sigma–Aldrich Laborchemikalien, Seelze, Germany). Tetracycline hydrochloride (TC) and Chlortetracycline (CTC) hydrochloride were supplied by Sigma–Aldrich Chemie (Steinheim, Germany). HPLC-grade acetonitrile (MeCN), methanol, sodium hydroxide solution (1 M), phosphoric acid (85%) and perchloric acid (70–72%) were purchased from

Influences of amounts of magnesium as carrier element

Magnesium (II) was selected as carrier element for the present work and the influences of magnesium (II) on the coprecipitation of TCs were investigated in the range of 0.1–0.6 mg for 10 mL deionized water. Increasing recoveries for TCs were observed with increased amounts of magnesium (II). After 0.4 mg of magnesium (II), the recoveries of TCs were kept constant and high enough for the quantitative extraction of analytes. However, the use of a large amount of magnesium (II) increased the volume

Conclusions

The proposed extraction technique based on the magnesium hydroxide coprecipitation system was demonstrated to be an excellent strategy for the rapid concentration of traces of TCs in water. For milk sample, the coprecipitation method could be also applied to the MeCN extract after a SALLE step. Compared with conventional methods, the proposed method was simple and the final solution from dissolving the hydroxide precipitates could be introduced directly into HPLC system for the determination of

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Development and optimization of an ultra-fast microextraction followed by HPLC-UV of tetracycline residues in milk products
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Short communicationDetermination of tetracyclines in surface water and milk by the magnesium hydroxide coprecipitation method

Abstract

Introduction

Section snippets

Reagents and materials

Influences of amounts of magnesium as carrier element

Conclusions

J. Chromatogr. A

J. Chromatogr. A

J. Chromatogr. A

Rapid Commun. Mass Spectrom.

Talanta

J. Chromatogr. A

J. Chromatogr. B

J. Chromatogr. A

J. Chromatogr. A

Short communication
Determination of tetracyclines in surface water and milk by the magnesium hydroxide coprecipitation method