Many countries and organizations have established maximum residue limits (MRLs) for sulfonamides in foods of animal origin; for example, the European Union (EU) has established a maximum residue limit (MRL) of 100 µg kg-1 for total sulfonamides in foods of animal origin (EC regulation 37/2010).However, for eggs, where no residue limits have been set for sulfonamides there is “zero tolerance” limit, meaning that no residues should be permitted (Forti and Scortichini 2009; Frenich et al. 2010; Saluti et al. 2021).Therefore, monitoring of these compounds at a trace level is very important to comply with the above requirement, especially if the animal product is intended for human consumption.
Sulfonamides (structures ,Kow and pka values are shown in Table 1) have been detected in several matrices over the past years, including water (Garcia-Galan et al. 2010), meat (Chu et al. 2009; Hoff et al. 2015; Huang et al. 2012; Karimi and Aboufazeli 2014; Machado et al. 2013; Mor et al. 2012; Xu et al. 2011; Zhang, 2012), milk (Arroyo – Manzanares etal.2014; Dmitrienko et al. 2015; Koesukwiwa et al. 2007; Msagati, and Nindi 2004; Zhang et al. 2011), egg ( Bekele etal.2022; Forti and Scortichini 2009; Heller etal.2002; Huertas-Perez etal.2016; Lu etal; Summa etal 2015; Suo etal. 2022), infant formulas (Zhan et al. 2013), honey (Bedendo et al. 2010; Hou et al. 2014 ), and animal feed (Lopes et al. 2012).Various analytical methods have been used to determine sulfonamide residues which include liquid chromatography with UV detection (Zhang et al. 2011), diode array detection (Machado et al. 2013), fluorescence detection ( Mor et al. 2012; Zhang et al. 2012), MS or MS/MS detection (Forti, and Scortichini 2009; Frenich et al. 2010; Hoff et al. 2015; Lopes et al. 2012; Msagati and Nindi 2004; Shen et al. 2016), and capillary zone electrophoresis (CZE) (Chu et al. 2009). A number of sample preparation techniques have been used for extraction and clean-up of sulfonamides from various matrices, such as liquid-liquid extraction (LLE) (Koesukwiwat et al. 2007), solid-phase extraction (SPE) (Huang et al. 2012; Koesukwiwat et al. 2007), supported liquid membrane (SLM) (Bekele etal.2022; Msagati and Nindi 2004), molecularly imprinted polymer (MIP) extraction (Xu et al. 2011), pressurized liquid extraction (PLE)(Hoff etal.2015;Yuetal .2011),cloud point extraction (CPE) (Zhang et al. 2011), QuEChERS (Huertas-Perez etal.2016; Lopes et al. 2012), and matrix solid-phase dispersion (MSPD) ( Shen et al. 2016; Zhang et al. 2012).However, current trends are focused on miniaturization of the sample preparation, extraction, and clean-up steps and on the enhancement of the environmental safety of these procedures (Dmitrienko et al. 2014).
Table 1
Linearity, LOD, and LOQ values obtained for 15 SAs
Compound | Regression equation ( n = 6) | Correlation coefficient R2 | Linear range (µg kg− 1) | LOD (µg kg− 1) (n = 10) | LOQ (µg kg− 1) (n = 10) |
SGD | y = 0.003x + 0.030 | 0.9959 | 6.4–1000 | 4.3 | 12.9 |
SAM | y = 0.001x + 0.042 | 0.9918 | 16–1000 | 6.7 | 20.1 |
SAA | y = 0.003x + 0.010 | 0.9930 | 50–1000 | 6.4 | 19.2 |
SDZ | y = 0.010x + 0.189 | 0.9987 | 17–1000 | 7.2 | 21.6 |
STZ | y = 0.001x + 0.305 | 0.9967 | 16–1000 | 7.4 | 22.2 |
SPY | y = 009x + 0.068 | 0.9915 | 14–700 | 6.9 | 20.7 |
SMR | y = 0.075x + 0.404 | 0.9991 | 11–700 | 5.4 | 16.2 |
SMT | y = 0.005x + 0.283 | 0.9982 | 5.4–1000 | 4.5 | 13.5 |
SMM | y = 0.030x + 0.279 | 0.9974 | 10–1000 | 5.9 | 17.7 |
SCP | y = 0.034x + 0.588 | 0.9901 | 7–1000 | 4.7 | 14.1 |
SMX | y = 0.034x + 0.525 | 0.9960 | 8 -1000 | 5.1 | 15.3 |
SSO | y = 0.003x + 0.272 | 0.9976 | 18–1000 | 8.0 | 24.0 |
SBZ | y = 0.010x + 0.514 | 0.9939 | 14–1000 | 6.3 | 18.9 |
SQZ | y = 0.013x + 0.598 | 0.9952 | 13–500 | 6.7 | 20.1 |
SSA | y = 0.0004x + 0.004 | 0.9964 | 9–500 | 5.0 | 15.0 |
The DLLME procedure is an appropriate choice for the analysis of samples with a relatively simple matrix such as water. As a result, the DLLME procedure can be applied directly after simple sample preparation such as filtration, centrifugation, and pH adjustment (Ramos 2012). Since the technique is not suitable for the direct extraction of compounds from solid samples, extensive sample pre-treatment such as homogenisation and extraction (in which analytes are released into a solvent) are required before being subjected to the DLLME procedure. Furthermore, the solvent used to extract the analyte from the sample matrix becomes a disperser solvent in the subsequent DLLME procedure. However, some challenges are encountered when extracting sulfonamides from egg samples; they exist at trace levels, and their extraction is hindered due to the complex nature of the egg matrix whereby some sulfonamides bind to the lipoprotein fraction of the egg. In general, the extent of analyte extraction from the solid sample is influenced by the solubility of the analytes, selectivity of the solvent, and matrix effects (Saraji and Boroujeni 2014).The other challenge is that the method was initially developed for compounds which are neutral or non-polar. Polar compounds such as sulfonamides which have a wide polarity range (most polar to least polar) add to the complexity which means that extraction conditions must be optimized carefully to promote the neutral form of the analyte. Most DLLME applications reported in the literature are for environmental water samples (Herrera-Herrera et al. 2010; Martín et al. 2013) with very few examples of complex biological matrices (Bekele etal.2022; Moema et al. 2012; Ranjbari et al. 2012; Tsai et al. 2009). Therefore, extending the application of the method to complex matrices such as eggs is of great significance for human health and safety as well as for meeting the standards and regulations when exporting such commodities.