New Advanced Materials and Sorbent-Based Microextraction Techniques as Strategies in Sample Preparation to Improve the Determination of Natural Toxins in Food Samples.

Natural toxins are chemical substances that are not toxic to the organisms that produce them, but which can be a potential risk to human health when ingested through food. Thus, it is of high interest to develop advanced analytical methodologies to control the occurrence of these compounds in food products. However, the analysis of food samples is a challenging task because of the high complexity of these matrices, which hinders the extraction and detection of the analytes. Therefore, sample preparation is a crucial step in food analysis to achieve adequate isolation and/or preconcentration of analytes and provide suitable clean-up of matrix interferences prior to instrumental analysis. Current trends in sample preparation involve moving towards "greener" approaches by scaling down analytical operations, miniaturizing the instruments and integrating new advanced materials as sorbents. The combination of these new materials with sorbent-based microextraction technologies enables the development of high-throughput sample preparation methods, which improve conventional extraction and clean-up procedures. This review gives an overview of the most relevant analytical strategies employed for sorbent-based microextraction of natural toxins of exogenous origin from food, as well as the improvements achieved in food sample preparation by the integration of new advanced materials as sorbents in these microextraction techniques, giving some relevant examples from the last ten years. Challenges and expected future trends are also discussed.

Mesostructured Silicas as Cation-Exchange Sorbents in Packed or Dispersive Solid Phase Extraction for the Determination of Tropane Alkaloids in Culinary Aromatics Herbs by HPLC-MS/MS.

In this work, Hexagonal Mesoporous Silica (HMS) and Santa Barbara Amorphous-15 (SBA-15) mesostructured silicas were synthesized and functionalized with sulfonic acid groups. The materials (HMS-SO3− and SBA-15-SO3−) were evaluated as strong cation exchange sorbents for sample extract clean-up, by solid phase extraction (SPE) and dispersive solid phase extraction, to determine atropine (At) and scopolamine (Sc) in commercial culinary aromatic herbs. Under optimized conditions, 0.25 g of sample was subject to solid−liquid extraction with acidified water (pH 1.0), and good recovery percentages were achieved for At and Sc using 75 mg of HMS-SO3− in SPE as the clean-up stage, prior to their determination by HPLC-MS/MS. The proposed method was validated in a thyme sample showing recoveries in the range of 70−92%, good linearity (R2 > 0.999), adequate precision (RSD ≤ 14%) and low limits (MDL 0.8−2.2 µg/kg and MQL 2.6−7.2 µg/kg for both analytes). Sixteen aromatic herbs samples (dried thyme, basil and coriander leaves) were analysed and At was found in fourteen samples over an interval of <5−42 µg/kg, whereas Sc was found in three of the sixteen samples studied (between <5−34 µg/kg). The amount of At and Sc found in some analysed samples confirms the importance of setting maximum levels of At and Sc in culinary aromatic herbs.

Sulfonic Acid-Functionalized SBA-15 as Strong Cation-Exchange Sorbent for Solid-Phase Extraction of Atropine and Scopolamine in Gluten-Free Grains and Flours.

A novel method was developed and applied to the determination of the most representative tropane alkaloids (TAs), atropine and scopolamine, in gluten-free (GF) grains and flours by HPLC-MS/MS. Accordingly a suitable sample treatment procedure based on solid-liquid extraction (SLE) and followed by strong cation-exchange solid-phase extraction (SCX-SPE) was optimized. SBA-15 mesostructured silica functionalized with sulfonic acids was evaluated as sorbent. The proposed method was fully validated in sorghum flour showing good accuracy with recoveries in the range of 93-105%, good linearity (R2 > 0.999) and adequate precision (RSD < 20%). Low method quantification limits (MQL) were obtained (1.5 and 2.4 µg/kg for atropine and scopolamine, respectively) and no matrix effect was observed thanks to the extraction and clean-up protocol applied. The method was applied to 15 types of GF samples of pseudocereals (buckwheat, quinoa and amaranth), cereals (teff, corn and blue corn, sorghum and millet) and legumes (red and green lentil, chickpea and pea). Atropine was found above the MQL in eight of them, with values between 7 and 78 µg/kg, while scopolamine was only found in teff flour, its concentration being 28 µg/kg. The method developed is an interesting tool for determining TAs in a variety of samples of GF grains and flours.

On-line flow injection molecularly imprinted solid phase extraction for the preconcentration and determination of 1-hydroxypyrene in urine samples.

New analytical strategies tend to automation of sample pre-treatment and flow analysis techniques provided a number of enhanced analytical methods allowing high throughput. Flow techniques are usually faster, more robust and more flexible than their batch equivalents. In addition, flow methods use less sample and reagent amounts and reduce analytical costs and waste. A flow injection solid-phase extraction pre-concentration system using a molecularly imprinted polymer (MIP) packed micro-column was developed for the determination of 1-hydroxypyrene in human urine with fluorescence detection. The pre-concentration of 1-hydroxypyrene on the MIP was carried out based on the specific retention of analyte by on-line introducing the sample into the micro-column system. Methanol and dichloromethane mixture was used to elute the retained analyte for fluorometric analysis. Important influencing factors were studied in detail, in batch and in flow (MISPE procedure optimisation, sample and eluent volumes, flow rate, dimensions of MIP micro-column and amounts of packing material, etc). To the best of our knowledge, this is the first on-line flow injection molecularly imprinted solid phase extraction for the pre-concentration and determination of hydroxylate PAH metabolite in urine samples. The optimised method was successfully applied to the determination of 1-Hydroxypyrene in spiked urine samples, with recoveries in the range of 74-85% and RSD<4.6%. Under optimum experimental conditions, the linearity concentration range used was 10-400µgL-1, R2>0.996. We obtained limit of detection and quantification of 3.1µgL-1 and 10.5µgL-1, respectively.

One-pot synthesized functionalized mesoporous silica as a reversed-phase sorbent for solid-phase extraction of endocrine disrupting compounds in milks.

A new procedure for the determination of 12 naturally occurring hormones and some related synthetic chemicals in milk, commonly used as growth promoters in cattle, is reported. The method is based on liquid-liquid extraction followed by solid-phase extraction (SPE) using a new one-pot synthesized ordered mesoporous silica (of the SBA-15 type) functionalized with octadecyl groups (denoted as SBA-15-C18-CO) as reversed-phase sorbent. The analytes were eluted with methanol and then submitted to HPLC with diode array detection. Under optimal conditions, the method quantification limit for the analytes ranged from 0.023 to 1.36µg/mL. The sorbent affored the extraction of estrone, 17ß-estradiol, estriol, progesterone, hexestrol, diethylstilbestrol, 4-androstene-3,17-dione, ethinylestradiol, 17α-methyltestosterone, nandrolone, prednisolone and testosterone with mean recoveries ranging from 72% to 105% (except for diethylstilbestrol) with RSD<11%. These results were comparable and, in some cases, even better than those obtained with other extraction methods, therefore SBA-15-C18-CO mesoporous silica possess a high potential as a reversed-phase sorbent for SPE of the 12 mentioned endocrine disrupting compounds in milk samples.

Novel supports in chiral stationary phase development for liquid chromatography. Preparation, characterization and application of ordered mesoporous silica particles.

Recent advances in the development of new materials are having a major impact on analytical chemistry. For example, the unique properties of ordered mesoporous silicas (OMSs) have been shown to enhance the analytical performance of many existing techniques or allow new, exciting ones to be developed. Likewise, the introduction of organo-functional groups makes OMSs highly versatile and enables them to perform specialized tasks, such as the separation of chiral compounds. This review provides an overview with the most relevant achievements in the preparation of OMS particles functionalized with chiral selectors. In addition, some examples from the last fifteen years regarding the analytical applications of functionalized OMS for chiral separations by high-performance liquid chromatography, ultra-high pressure high-performance liquid chromatography and capillary electrochromatography have been reviewed.

Evaluation of a molecularly imprinted polymer for determination of steroids in goat milk by matrix solid phase dispersion.

A molecularly imprinted polymer-matrix solid-phase dispersion methodology for simultaneous determination of five steroids in goat milk samples was proposed. Factors affecting the extraction recovery such as sample/dispersant ratio and washing and elution solvents were investigated. The molecularly imprinted polymer used as dispersant in the matrix solid-phase dispersion procedure showed high affinity to steroids, and the obtained extracts were sufficiently cleaned to be directly analyzed. Analytical separation was performed by micellar electrokinetic chromatography using a capillary electrophoresis system equipped with a diode array detector. A background electrolyte composed of borate buffer (25mM, pH 9.3), sodium dodecyl sulfate (10mM) and acetonitrile (20%) was used. The developed MIP-MSPD methodology was applied for direct determination of testosterone (T), estrone (E1), 17ß-estradiol (17ß-E2), 17α-ethinylestradiol (EE2) and progesterone (P) in different goat milk samples. Mean recoveries obtained ranged from 81% to 110%, with relative standard deviations (RSD)≤12%. The molecularly imprinted polymer-matrix solid-phase dispersion method is fast, selective, cost-effective and environment-friendly compared with other pretreatment methods used for extraction of steroids in milk.

Comparison of different mesoporous silicas for off-line solid phase extraction of 17ß-estradiol from waters and its determination by HPLC-DAD.

Functionalized (SBA-C18 and SM-C18) and non-functionalized (SBA-15 and SM) mesoporous silicas were then examined as sorbents for solid-phase extraction of 17ß-estradiol in aqueous media. Experiments were run in order to test critical factors affecting the procedure extraction efficiency, including the type of sorbent, the analyte concentration, the solvent and volume used for elution and the sample volume. Among the prepared materials, SBA-C18 had the highest adsorption affinity towards 17ß-estradiol and under optimized conditions (200mg of sorbent, 150 mL of water sample, elution with 3 × 2 mL of methanol) this sorbent proved good extraction capacity and elution efficiency for this hormone from aqueous media (recovery near 100%). To evaluate the analytical applicability of the proposed method, it was applied to the determination of 17ß-estradiol in drinking water by high performance liquid chromatography with a photodiode array detector. Calibration curves were shown to be linear between 1.25 and 100 mg L(-1)with correlation coefficients ≥0.999 (n=5) for 17ß-estradiol. The instrumental detection and quantitation limits calculated were 0.38 and 1.25 mg L(-1), respectively. The relative standard deviation obtained values were ≤3% and the mean recoveries obtained were of 82%. The results suggest that SBA-C18 is a promising material for the off-line solid phase extraction of 17ß-estradiol from waters.