The Institute of Global Food Security at Queen’s University Belfast successfully identifies food fraud in the ever more complex food supply chain by developing and applying reliable analytical tests. Chris Elliott, professor of food safety and founder of the Institute, points out a two-tier approach of untargeted analysis and targeted analysis. Tier One is low cost and easy-to-use with 80–90% reliability. The second tier of highly sophisticated analytical methods, like mass spectrometry, gas chromatography and others, can identify a food item with a 99.999% certainty. These analytical methods combined with correct data are able to identify even details like type of fish, country of origin of a food item, added ingredients, and much more.
Vitamins play a critical role in the regulation of key physiological processes, such as blood clotting, metabolism and maintaining our vision. These biologically important compounds can be divided into two broad classes based on their solubility and differ in the way they are handled in the body—and in food safety laboratories. While excess amounts of water-soluble vitamins (including B1, B2, B3, B6 and B12) are excreted, fat-soluble vitamins (including vitamin A, D, E and K) can be stored in the liver or fatty tissue for later use. The simultaneous analysis of water- and fat-soluble vitamins in traditional liquid chromatography is difficult, and is compounded by the presence of biologically important vitamin isomers, which exist at lower concentrations and demand greater sensitivity from analytical techniques.
Food analysis laboratories support food manufacturers by assessing food safety and authenticity, and have a responsibility to produce precise and reliable data. Vitamins are among a number of compounds assessed in infant formulas, energy drinks and other supplements, and are added to fortify the nutritional value of these products. Given the critical nutritional role of vitamins, especially during early developmental periods, their characterization is highly important. This, along with the challenging and cumbersome nature of vitamin analysis, has spurred the development of innovative high-performance liquid chromatography (HPLC) methods for food safety testing.
Unique Challenges of Vitamin Analysis
The simultaneous analysis of water- and fat-soluble vitamins is difficult to achieve with reversed-phase high-performance liquid chromatography, due to the wide range of hydrophobicity among vitamins. Highly hydrophobic fat-soluble vitamins are retained strongly by chromatography columns and are only eluted with high-strength mobile phases. In contrast, water-soluble vitamins are usually poorly retained, even with very weak mobile phases. As the ideal conditions for chromatographic separation are very different for the two vitamin classes, there have been efforts to explore the possibility of operating two columns sequentially in one system. The early versions of this approach, however, were not well suited to high-throughput food safety laboratories, requiring complex hardware setup and even more complicated chromatography data system programming.
Prior to liquid chromatography analysis, food samples must be purified and concentrated to ensure target analytes can be detected without matrix interference. Liquid-liquid extraction is one purification method used to prepare for the analysis of vitamins and other compounds; it was one of the first methods developed for purification and enables compounds to be separated based on their relative solubilities in two different immiscible liquids.1 It is a simple, flexible and affordable method, yet has several major disadvantages.2 Liquid-liquid extraction consists of multiple tedious steps and requires the use of large volumes, therefore the time for completion is highly dependent on the operator’s skills and experience. Consequently, the duration of sample exposure to unfavorable conditions can vary greatly, which compromises reproducibility and efficiency of the method. This is of concern for vitamins that are particularly prone to degradation and loss when exposed to heat and light, such as vitamin D in milk powder.
Two-Dimensional Liquid Chromatography Enables Deeper and Faster Analysis
Analysts in the food industry are under pressure to process high volumes of samples, and require simple, high-throughput and high-resolution systems. Fortunately, two-dimensional liquid chromatography (2D-LC) systems have evolved markedly in recent years, and are ideally suited for the separation of vitamins and other compounds in food and beverages. There are two main types of systems, known as comprehensive and heart-cutting 2D-LC. In comprehensive 2D-LC, the sample is separated on the first column, as it would be in 1D-LC. The entire eluate is then passed in distinct portions into a second column with a different selectivity, enabling improved separation of closely eluting compounds. In contrast, heart-cutting 2D-LC is more suited to targeted studies as only a selected fraction (heart-cut) of the eluate is transferred to the second-dimension column.
Recently, another novel approach has emerged which utilizes two independent LC flow paths. In dual workflows, each sample is processed by two columns in parallel, which are integrated in a single instrument for ease of use. The columns may offer identical or different analyses to enable a higher throughput or deeper insights on each sample. This approach is highly suited to vitamin analysis, as the two reversed-phase columns enable simultaneous analysis of water- and fat-soluble vitamins. A simple, optimized preparation method is required for each of the two vitamin classes to ensure samples are appropriately filtered and concentrated or diluted, depending on the expected amount of analyte in the sample. The dual approach enables a broad range of ingredients to be assessed concurrently in supplement tablets, energy drinks, and other food and beverages containing both water- and fat-soluble vitamins. For analysts working to validate claims by food vendors, these advances are a welcome change.
Refined Detection and Extraction Methods Create a Boost in Productivity
Analysts in food analysis laboratories now have a better ability to detect a wide range of components in less time, due to improved detection and extraction methods. Modern LC systems utilize a wide range of analytical detectors, including:
Mass spectrometry (MS)
Diode array detection (DAD)
Charged aerosol detection (CAD)
Fluorescence detection (FLD)
The optimal detector technology will depend on the molecular characteristics of the target analyte. Infant formula, for example, can be analyzed by DAD and FLD, with detection and separation powerful enough to accurately quantify the four isomers of vitamin E, and separate vitamin D2 and D3. Highly sensitive 2D-LC methods are also particularly favorable for the trace level quantitation of toxins in food, such as aflatoxins in nuts, grains and spices.
Given the limitations of liquid-liquid extraction, an alternative, simplified approach has been sought for 2D-LC analysis. Liquid-liquid extraction, prior to chromatography analysis, involves many tedious separation steps. In contrast, the use of solid phase extraction for infant formula testing reduces pre-treatment time from three hours to one hour, while improving detection. This is of great significance in the context of enterprise product quality control, where a faster, simpler pre-treatment method translates into a greater capacity of product testing and evaluation.
HPLC Toolkit for Food Safety Analysis Continues to Expand
Several other HPLC approaches have also been utilized in the field of food safety and authentication. For example, ultra-high-performance liquid chromatography (UHPLC) with detection by CAD followed by principal component analysis (PCA) can be used to investigate olive oil purity. In contrast to conventional approaches (fatty acid and sterol analysis), this revised method requires very little time and laboratory resources to complete, enabling companies to significantly reduce costs by implementing in-house purity analysis. With a reduced need for chemicals and solvents compared with fatty acid and sterol analyses, UHPLC-CAD provides a more environmentally friendly alternative.
Analyzing amino acid content in wine is an important aspect of quality control yet requiring derivatization to improve retention and separation of highly hydrophilic amino acids. Derivatization, however, is labor-intensive, error-prone, and involves the handling of toxic chemicals. To overcome these limitations, hydrophilic interaction liquid chromatography (HILIC) combined with mass detection has been identified as an alternative method. While HILIC is an effective technique for the separation of small polar compounds on polar stationary phases, there still may be cases where analytes in complex samples will not be completely separated. The combination of HILIC with MS detection overcomes this challenge, as MS provides another level of selectivity. Modern single quadrupole mass detectors are easy to operate and control, so even users without in-depth MS expertise can enjoy improved accuracy and reproducibility, while skipping derivatization steps.
Recent innovations in 2D- and dual LC technology are well suited to routine vitamin analysis, and the assessment of other components important in food safety evaluation. The concurrent and precise assessment of water- and fat-soluble vitamins, despite their markedly different retention and elution characteristics, is a major step forward for the industry. Drastic improvements in 2D-LC usability, flexibility and sensitivity also allows for biologically important vitamin isomers to be detected at trace levels. A shift towards simpler, high-throughput systems that eliminate complicated assembly processes, derivatization and liquid-liquid extraction saves time and money, while enabling laboratories to produce more reliable results for food manufacturers. In terms of time and solvent savings, solid phase extraction is superior to liquid-liquid extraction and is one of many welcome additions to the food analysis toolkit.
Schmidt, A. and Strube, J. (2018). Application and Fundamentals of Liquid-Liquid Extraction Processes: Purification of Biologicals, Botanicals, and Strategic Metals. In John Wiley & Sons, Inc (Ed.), Kirk-Othmer Encyclopedia of Chemical Technology. (pp. 1–52).
Musteata, M. and Musteata, F. (2011). Overview of extraction methods for analysis of vitamin D and its metabolites in biological samples. Bioanalysis, 3(17), 1987–2002.
In the modern world, it’s often taken for granted that consumers can head to their local grocery store and fill their baskets with a broad range of meat, poultry, fish and dairy produce. Yet the plentiful availability of these products is possible, to a large extent, thanks to modern farming methods that rely on veterinary drugs to promote healthy animal growth, protect livestock from contracting diseases, and in some cases provide aesthetic qualities to food.
Despite the important role veterinary drugs play in farming and food production, usage must be carefully controlled, as their inappropriate administration can have adverse effects on animals, the environment and human health. A particular concern is the growing problem of antimicrobial resistance, which can be promoted in the environment by the overuse of some of these veterinary drugs.
As a result, the analysis of veterinary drugs forms an important part of routine food safety and quality control testing. However, the wide range of residue concentrations required to be quantified, along with the diverse sample matrices and chemical properties of multiple classes of veterinary drugs placed in a single analytical method, pose significant analytical challenges. The latest multi-residue, multi-class analytical workflow solutions using a generic sample preparation method and liquid chromatography tandem mass spectrometry (LC-MS/MS) are overcoming these issues to provide a robust, sensitive method for the extraction, detection, confirmation, and quantitation of veterinary drugs below their required maximum residue limits (MRLs).
Meeting the Needs of Veterinary Drug Analysis Workflows
Given the need to accurately and reliably quantify veterinary drugs in food, testing workflows must be both sensitive and operationally robust. Importantly, workflows must be amenable to a variety of different matrices, including meat, fish and dairy, and should be capable of screening for drug molecules with a broad range of physicochemical properties. The sample preparation protocols that are employed must minimize the loss of analytes and be sufficiently simple and cost effective to enable routine laboratory use. Additionally, the separation steps that are employed must be sufficiently rugged and should ideally be able to handle any analyte and matrix. Finally, the methods used to identify and quantify samples must be sufficiently selective and sensitive to detect and confirm drug molecules and their metabolites at trace levels.
Developing methods that can meet all of these criteria for a wide range of drug molecules and food matrices, while minimizing the potential for false positive and negative results, is not straightforward and has proven challenging for the industry. As a result, many analytical methodologies have emerged that are typically limited in scope to a limited number of residues or specific chemical classes, are labor intensive, and require extensive sample preparation and clean-up. Fortunately, ongoing advances in veterinary drug analysis workflows are helping to drive the adoption of standardized protocols that have universal applicability.
QuEChERS: Making Sample Preparation Quick, Easy and Reliable
Sample preparation is a key first step in veterinary drug analysis workflows, but its importance is often overlooked. Even with the most advanced downstream separation and detection technologies, workflows are liable to generate poor quantitative results without reliable residue extraction methods.Having robust sample preparation protocols is especially important given the heterogeneous nature of the sample matrix and the different physicochemical properties of the residues that must be extracted.
Traditional approaches, based on sample homogenization and multi-step solvent extraction procedures, were time-consuming and did not always produce consistent results. The loss of residues during sample grinding or through the formation of insoluble drug-matrix complexes would often impact the accuracy of measurements. Moreover, the need for labor-intensive sample cleanup steps, based on separation methods such as gel permeation chromatography, added additional complexity to workflows.
The widespread adoption of universal sample preparation protocols based on QuEChERS (Quick, Easy, Cheap, Effective, Rugged and Safe) methods has simplified the process of extracting veterinary drugs from matrix samples. These approaches have been specifically designed to be quick and easy to implement, and enable high extraction efficiency with a very broad range of chemical properties from a variety of matrices. As a result, QuEChERS has proven to be a very reliable means of preparing samples for veterinary drug analysis.
The universal suitability of the QuEChERS approach has reduced the complexity of sample preparation workflows to such an extent that many suppliers now offer kits containing pre-weighed reagents that can be used straight from the box. Moreover, because they only require small amounts of sample and solvent, and little in the way of equipment, these easy-to-use methods are helping laboratories minimize waste and make workflows more cost-effective.
LC-MS/MS has rapidly established itself as the go-to technique for sensitive and reliable veterinary drug analysis, with set-ups based on ultra-high performance liquid chromatography (UHPLC) systems and triple quadrupole mass spectrometers proving to be particularly effective. With drug residues typically on the parts per billion scale, these systems have proven to be more than capable of delivering the level of performance that’s required when working with analytes that require low detection limits.
What’s more, recent advances in triple quadrupole mass spectrometer technologies are pushing the limits of quantitation even further. Improved instrument designs based on segmented quadrupoles, more powerful electron multipliers and enhanced ion transmission optics are enabling food analysis laboratories to achieve even greater levels of experimental sensitivity, mass accuracy, selectivity and precision. These performance improvements are allowing analysts to make more confident decisions around every sample.
The capabilities of the latest generation of triple quadrupole LC-MS/MS systems for quantitative veterinary drug analysis were put to the test in a recent study. More than 170 veterinary drugs were added directly to a variety of homogenized matrices, including bovine muscle, milk, and salmon fillet using a QuEChERS sample preparation protocol to create a series of matrix extracted spikes (MES). The concentration of residues in the MES samples referenced a chosen screening target concentration (STC), which was typically one-third to one-quarter of the defined European Union MRL for each residue/matrix combination. Figure 1 presents the total extracted ion chromatogram for an MES sample of salmon fillet at the STC, obtained with a binary UHPLC system and a triple quadrupole mass spectrometer.
For each analyte, calibration curves were constructed using replicate measurements of each of the MES samples at seven concentrations ranging from one-fifth to five times that of the STC. Figure 2 highlights the calibration curve constructed for ethyl violet, a therapeutic dye used in aquaculture, in
the range 0.2 to 5.0 ng/g (STC = 1 ng/g). The calculated method detection limit of 0.03 ng/g for this compound in salmon fillet demonstrates confidence in the results well below the minimum required performance limit (MRPL).
LC-MS/MS: Leading the Way in Workflow Robustness
With potentially hundreds of samples to analyze every week, veterinary drug analysis workflows not only demand the highest levels of sensitivity, but also exceptional speed and robustness.
One way in which greater throughput can be achieved is by using shorter instrument dwell times, an experimental optimization that allows more compounds to be analyzed within a given timeframe during a chromatographic separation. Traditionally, the use of shorter dwell times would typically require sacrificing some measurement sensitivity. However, the latest advances in triple quadrupole instrument design are ensuring short dwell times no longer come at the expense of analytical performance.
Timed selected dreaction monitoring (SRM) is an effective strategy that allows analysts to overcome this challenge to achieve sensitivity with high throughput. Using timed SRM, data acquisition occurs within a short retention time window. This reduces the number of transitions that are monitored in parallel for each residue peak, while ensuring consistent quantitation even at low concentrations. Instrument control system software can automatically optimize the SRM conditions across the chromatographic run, maximizing operational efficiency with minimal need for manual input.
Instrument uptime is another factor that is of paramount importance for veterinary analysis workflows. With large workloads and tight turnaround times, regular instrument recalibration and frequent maintenance can be a major frustration for busy food testing laboratories. UHPLC is renowned for its operational robustness and suitability for fast-paced routine screening workflows, and the latest instruments are taking this reputation to an even higher level.
Figure 3 compares injections of bovine muscle extract at 3× STC over a 500-injection run that took place over a period of one week, obtained using the experimental set-up described earlier. Despite continuous operation over this extended period, the peak shape, intensity and retention time stability are maintained. These results further highlight the robustness of the LC-MS/MS system for routine veterinary drug testing.
Enforcing the responsible use of veterinary drugs in farming and food production depends upon comprehensive, sensitive, robust and reliable workflows capable of delivering quantitative results. Advances in sample preparation techniques and LC-MS/MS technologies are setting new standards when it comes to confident multi-residue veterinary drug analysis. From the development of reliable easy-to-use QuEChERS protocols, through to robust UHPLC separation methods and sensitive triple quadrupole mass spectrometers, improvements across the workflow are driving exceptional performance—whatever the matrix, whatever the residue.
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