Tag Archives: compounds


Revamped Liquid Chromatography Enhances Analysis of Vitamins and Beyond

By Maria Grübner
No Comments

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)
  • Multi-wavelength detection
  • 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.


  1. 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).
  2. 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.


Crop spraying, Ellutia

From Farm to Fork: The Importance of Nitrosamine Testing in Food Safety

By Andrew James
No Comments
Crop spraying, Ellutia

N-nitroso compounds (NOCs), or nitrosamines, have once again made headline news as their occurrence in some pharmaceuticals has led to high profile product recalls in the United States.1 Nitrosamines can be carcinogenic and genotoxic and, in the food industry, can compromise a food product’s quality and safety. One nitrosamine in particular, N-nitrosodimethylamine (NDMA), is a highly potent carcinogen, traces of which are commonly detected in foods and may be used as an indicator compound for the presence of nitrosamines.2

NOCs can potentially make their way into the food chain in a number of ways, including (but not limited to): Via the crop protection products used to maximize agricultural yields; via the sodium and/or potassium salt added to preserve certain meats from bacterial contamination; as a result of the direct-fire drying process in certain foods; and via consumption of nitrates in the diet (present in many vegetables due to natural mineral deposits in the soil), which react with bacteria and acids in the stomach to form nitrosamines.3

The crop protection and food manufacturing industries are focused on ensuring that levels of nitrosamines present in foods are minimal and safe. Detection technology for quantitating the amount of nitrosamines (ppm levels) in a sample had not advanced in nearly 40 years—until recently. Now, a thermal energy analyzer (TEA) —a sensitive and specific detector—is being relied on to provide fast and sensitive analysis for players throughout the food supply chain.

Regulatory Landscape

Both NDMA and the nitrosamine N-nitrososodiethylamine (NDEA) have been classified by national and international regulatory authorities as ‘probable human carcinogens’.3 NDMA in particular is by far the most commonly encountered member of this group of compounds.7

In the United States there are limits for NDMA or total nitrosamines in bacon, barley malt, ham and malt beverages, yet there are currently no regulatory limits for N-nitroso compounds (NOC) in foods in the EU.7

Developers of crop protection products are required to verify the absence of nitrosamines or quantify the amount at ppm levels to ensure they are within the accepted guidelines.

Crop Protection

The presence of nitrosamines must be traced and risk-managed along the food’s journey from farm to fork. The issue affects testing from the very beginning – particularly at the crop protection stage, which is one of the most highly regulated industries in the world. Without crop protection, food and drink expenditures could increase by up to £70 million per year and 40% of the world’s food would not exist.7

Development of a new crop protection product (herbicide, fungicide, insecticide or seed treatment) involves several steps: Discovery and formulation of the product, trials and field development, toxicology, environmental impacts and final registration. New product registration requires demonstration of safety for all aspects of the environment, the workers, the crops that are being protected and the food that is consumed. This involves comprehensive risk assessments being carried out, based on data from numerous safety studies and an understanding of Good Agricultural Practice (GAP).

One global producer of agrochemicals uses a custom version of the TEA to verify the absence of nitrosamines or quantitate the amount of nitrosamines (ppm levels) in its active ingredients. The LC-TEA enables high selectivity for nitro, nitroso and nitrogen (when operating in nitrogen mode), which allows only the compounds of interest to be seen. Additionally, it provides very high sensitivity (<2pg N/sec Signal to Noise 3:1), meaning it is able to detect compounds of interest at extremely low levels. To gain this high sensitivity and specificity, it relies on a selective thermal cleavage of N-NO bond and detection of the liberated NO radical by the chemiluminescent signal generated by its reaction with ozone.

The customized system also uses a different interface with a furnace, rather than the standard pyrolyser, to allow for the additional energy required and larger diameter tubing for working with a liquid sample rather than gas.

The system allows a company to run five to six times more samples with increased automation. As a direct result, significant productivity gains, reduced maintenance costs and more accurate results can be realized.

Food Analysis

Since nitrite was introduced in food preservation in the 1960s, its safety has been debated. The debate continues today, largely because of the benefits of nitrite in food products, particularly processed meats.6 In pork products, such as bacon and cured ham, nitrite is mostly present in the sodium and/or potassium salt added to preserve the meat from bacterial contamination. Although the meat curing process was designed to support preservation without refrigeration, a number of other benefits, such as enhancing color and taste, have since been recognized.

Analytical methods for the determination of N-nitrosamines in foods can differ between volatile and non-volatile compounds. Following extraction, volatile N-nitrosamines can be readily separated by GC using a capillary column and then detected by a TEA detector. The introduction of the TEA offered a new way to determine nitrosamine levels at a time when GC-MS could do so only with difficulty.

To identify and determine constituent amounts of NOCs in foods formed as a direct result of manufacturing and processing, the Food Standards Agency (FSA) approached Premier Analytical Services (PAS) to develop a screening method to identify and determine constituent amounts of NOCs in foods formed as a direct result of manufacturing and processing.

A rapid and selective apparent total nitrosamine content (ATNC) food screening method has been developed with a TEA. This has also been validated for the known dietary NOCs of concern. This method, however, is reliant on semi-selective chemical denitrosation reactions and can give false positives. The results can only be considered as a potential indicator rather than definitive proof of NOC presence.

In tests, approximately half (36 out of 63) samples returned a positive ATNC result. Further analysis of these samples by GC-MS/MS detected volatile nitrosamine contamination in two of 25 samples.

A key role of the TEA in this study was to validate the alternative analytical method of GC-MS/MS. After validation of the technique by TEA, GC-MS/MS has been proven to be highly sensitive and selective for this type of testing.

The Future of Nitrosamine Testing

Many countries have published data showing that toxicological risk from preformed NOCs was no longer considered an area for concern. Possible risks may come from the unintentional addition or contamination of foods with NOCs precursors such as nitrite and from endogenous formation of NOCs and more research is being done in this area.

Research and innovation are the foundations of a competitive food industry. Research in the plant protection industry is driven by farming and the food chain’s demand for greater efficiency and safer products. Because the amount of nitrosamines in food that results in health effects in humans is still unknown, there is scope for research into the chemical formation and transportation of nitrosamines, their occurrence and their impact on our health. Newer chromatographic techniques are only just being applied in this area and could greatly benefit the quantification of nitrosamines. It is essential that these new approaches to quality and validation are applied throughout the food chain.


  1. Christensen, J. (2020). More popular heartburn medications recalled due to impurity. CNN.
  2. Hamlet, C, Liang, L. (2017). An investigation to establish the types and levels of N-nitroso compounds (NOC) in UK consumed foods. Premier Analytical Services, 1-79.
  3. Woodcock, J. (2019). Statement alerting patients and health care professionals of NDMA found in samples of ranitidine. Center for Drug Evaluation and Research.
  4. Scanlan, RA. (1983). Formation and occurrence of nitrosamines in food. Cancer res, 43(5) 2435-2440.
  5.  Dowden, A. (2019). The truth about nitrates in your food. BBC Future.
  6.  Park, E. (2015). Distribution of Seven N-nitrosamines in Food. Toxicological research, 31(3) 279-288, doi: 10.5487/TR.2015.31.3.279.
  7.  Crews, C. (2019). The determination of N-nitrosamines in food. Quality Assurance and Safety of Crops & Foods, 1-11, doi: 10.1111/j.1757-837X.2010.00049.x
  8. (1989) Toxicological profile for n-Nitrosodimethylamine., Agency for Toxic substances and disease registry.
  9. Rickard, S. (2010). The value of crop protection, Crop Protection Association.