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Recipes with Raman

Recipes with Raman

Many of us have spent more time in the kitchen in the past year than usual, (re)discovering our culinary skills with varying degrees of success. Our pantries have been kept full, and our stoves on for a year (and counting) since our normal, social ways of life have been curtailed by home office regulations, online schooling, and the sweeping closures of bars and restaurants.

Cooking at home can mean a number of things. Some people rely on «Chef Mike» (i.e., the microwave) to prepare their meals, while others turn humble ingredients into haute cuisine dishes. However, most people would probably agree that the keys to delicious and nutritious meals are fresh, high quality ingredients.

What is on your menu today? For breakfast, perhaps toast and some fresh pressed orange juice, lunch is maybe a quiche with tomatoes and cheese, and for dinner, stir-fried vegetables accompanied by a glass of good wine. Hungry yet?

With all of this talk about food, how can you be certain that the ingredients you are using in the kitchen are of the highest quality? You may trust in the grocery store, the brand, or the farmer at your local market, but do you know how different food quality parameters are measured?

One technique provides rapid, non-destructive and specific food quality testing: Raman spectroscopy. Whether you are looking to determine the ripeness of fruits or vegetables, the adulteration of spices or dairy products, or contamination of foods with banned pesticides, Raman spectroscopy is at the cutting edge of food quality analysis.

If you want to refresh your knowledge about Raman spectroscopy, have a look at our previous blog post about Mira, which includes some history about the technique.

To learn more about the analysis of trace adulterants in foods and beverages, read our blog post all about measurement with SERS (surface‐enhanced Raman scattering).

Are you confused about the differences between Raman spectroscopy and SERS? You’re not alone! Check out our blog post about these two techniques and learn about their benefits.

Here, we share a selection of peer-reviewed articles from the scientific community using Raman spectroscopy and portable instrumentation from B&W Tek, a Metrohm Group Company and Metrohm Raman to address quality issues of food. Enjoy your meal! Bon appetit!

~~ Starter ~~

To begin, maybe you would be interested in sharing a bottle of red wine with your companion as you snack on some crispy bread sticks. Red wines are made from red varieties of grapes, whose color is imparted through the crushing process as the skins soak in the sugary juices. Phenolic compounds derived from the grape skins can be beneficial to human health, and can be determined with Raman spectroscopy [1].

It’s not only beneficial compounds but also harmful contaminants that can be measured in beverages with Raman spectroscopy. Fungicides can also be detected in wine with SERS. Download our free Application Note if you want to find out more.

Watch our video below to see how methanol in alcoholic drinks is quantified rapidly without sample preparation – right at the bottle!

Snacking on prepackaged foods when you are on the go, or when you don’t feel like cooking at the moment, is something we have all done. The moisture levels in most of these foods is kept to a minimum, especially in those meant to have long shelf lives. Water content above certain levels allows harmful bacteria to grow, which is one of the major reasons to always consult the date of packaged foods before consumption. Eating contaminated foods can cause severe sickness and even death. It is possible to determine whether such low moisture foods (LMFs) contain harmful levels of these bacteria with SERS [2].

What else do both of these applications have in common? Both of them utilize the portable i-Raman Plus instrument from B&W Tek. For more information, download our free application note: Portable Raman for Quantification of Methanol in Contaminated Spirits.

~~Main Course~~

Depending on what you are in the mood for, anything is possible. Some tomatoes, vegetables, spices, perhaps meat (if you eat it) and a starch are on the menu today, ready to be turned into almost any dish.

Determining whether fresh foods are at peak ripeness can be a tricky process, not necessarily just the change of a color. The ripeness of a fruit or vegetable indicates its antioxidant content, as well as nutrients and other beneficial compounds. Monitoring the ripening process is possible with portable Raman spectroscopy [3], such as the B&W Tek i-Raman Pro.

Some of us like a little heat in our meals. Unfortunately, the adulteration of spices like chili powder (sometimes known as cayenne powder) is common, as cheap and harmful coloring agents are added to achieve more profits at the cost of human health. These synthetic dyes are able to be determined easily even at trace levels with SERS [4].

Download our free Application Note to learn more about the detection of trace levels of Rhodamine B in cayenne powder with SERS.

Some types of cheese command a high price for what seems like just a small pinch. One such type is Parmigiano Reggiano, an Italian cheese with a protected denomination of origin (PDO) quality marker, made in compliance with several production rules. These cheeses are subject to counterfeiting, but luckily this is easy to determine on-site without damaging the sample using handheld Raman spectroscopy [5].

The price of meat varies according to several reasons, even for the same animal source, section (cut), and portion size. Among these is the origin of the meat, as well as how it was produced (e.g., organic or a factory farm). Determining the difference between premium meat products and lower quality ones is possible with handheld Raman systems [6] such as Mira from Metrohm Raman. Not only these differences but also the freshness of meat during the production process can be measured with portable Raman devices [7] like the i-Raman Plus from B&W Tek.

Using lower quality cooking oil with a low smoke point at high temperatures can result in consumption of harmful byproducts formed during cooking. Older oils have a lower antioxidant content as a result of the aging process, and can become rancid when the antioxidant properties vanish. For these reasons, high quality edible oils full of antioxidants are worth much more, but are also susceptible to adulteration with cheaper ingredients. It is possible to not only determine the purity of edible oils by Raman spectroscopy [8] but also the heat stability of different types of oils [9].

For more information about the analysis of edible oils by Raman spectroscopy, download our free Application Notes and our White Paper below!

~~ Dessert ~~

After dinner is over, a hot beverage like tea can be nice to cleanse the palate. How can you be sure that the tea is free of banned pesticides, other than buying from a trusted organic label? SERS allows rapid identification of such substances in tea leaves [10].

To learn more about detecting illegal compounds such as herbicides on tea leaves, download our free Application Note.

The honey you put in your tea or drizzle over your dessert can also be subjected to tampering. Depending on the type of flower or the origin of the honey, costs can vary widely for the same volume. Some honeys (e.g., Manuka) claim to impart certain health benefits, and therefore many lower quality products with cheap sweeteners (e.g., high fructose corn syrup) are falsely labeled as such and sold at a higher price point to unsuspecting consumers. It is possible to detect honey adulteration [11] and even its botanical origin [12] with Raman spectroscopy.

Not only tea and honey, but also coffee and the milk added to it can be analyzed with Raman spectroscopy to determine various quality markers and adulterants.

The protein content of milk can be falsely enhanced with the addition of melamine. This compound is now monitored in dairy products due to scandals which led to deaths from kidney damage. Melamine [13] and other substances which can contribute to ill health effects [14] can be easily determined in milk with SERS.

Want to learn more about Melamine and how to measure it with SERS? Check out our free Application Note for further information.

Download our free Application Note to learn about the rapid detection of the alkaloid trigonelline in coffee, which reduces in concentration the darker the beans are roasted.

The ripeness of fruits and vegetables is not just important information when planning meals, but it is also critical for food transport. Perishable fruits and vegetables are often shipped in an unripened state so they arrive at their destination in top condition.

Freshness in citrus fruits can be determined with portable Raman instruments by measuring the carotenoid content [15].

Aside from the freshness, it is also possible to detect if pesticides, fungicides, herbicides or other harmful substances have been sprayed onto fruits using SERS [16].

Check out our selection of free Application Notes below about the determination of these kinds of substances on different fruits with Misa.

Several food quality parameters can be measured quickly and easily with Raman spectroscopy without the need to open bottles or destroy samples. Portable and handheld instruments make measurements simple to perform nearly anywhere. Visit the Metrohm website to learn more about the possibilities with Raman!

Learn more about rapid food analysis with Raman spectroscopy

Download free applications directly from our website.

References

[1] Dranca, F.; Oroian, M. Kinetic Improvement of Bioactive Compounds Extraction from Red Grape (Vitis vinifera Moldova) Pomace by Ultrasonic Treatment. Foods 2019, 8, 353. doi:10.3390/foods8080353

[2] Pan, C.; Zhu, B.; Yu, C. A Dual Immunological Raman-Enabled Crosschecking Test (DIRECT) for Detection of Bacteria in Low Moisture Food. Biosensors 2020, 10, 200. doi:10.3390/bios10120200

[3] Trebolazabala, J.; Maguregui, M.; Morillas, H.; et al. Portable Raman spectroscopy for an in-situ monitoring the ripening of tomato (Solanum lycopersicum) fruits. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2017, 180, 138–143. doi:10.1016/j.saa.2017.03.024

[4] Lin, S.; Hasi, W.-L.-J.; Lin, X.; et al. Rapid and sensitive SERS method for determination of Rhodamine B in chili powder with paper-based substrates. Analytical Methods 2015, 7, 5289–5294. doi:10.1039/c5ay00028a

[5] Li Vigni, M.; Durante, C.; Michelini, S.; et al. Preliminary Assessment of Parmigiano Reggiano Authenticity by Handheld Raman Spectroscopy. Foods 2020, 9(11), 1563. doi:10.3390/foods9111563

[6] Logan, B.; Hopkins, D.; Schmidtke, L.; et al. Authenticating common Australian beef production systems using Raman spectroscopy. Food Control 2021, 121, 107652. doi:10.1016/j.foodcont.2020.107652

[7] Santos, C; Zhao, J.; Dong, X.; et al. Predicting aged pork quality using a portable Raman device. Meat Science 2018, 145, 79–85. doi:10.1016/j.meatsci.2018.05.021

[8] Liu, Z.; Yu, S.; Xu, S.; et al. Ultrasensitive Detection of Capsaicin in Oil for Fast Identification of Illegal Cooking Oil by SERRS. ACS Omega 2017, 2, 8401–8406. doi:10.1021/acsomega.7b01457

[9] Alvarenga, B.; Xavier, F.; Soares, F.; et al. Thermal Stability Assessment of Vegetable Oils by Raman Spectroscopy and Chemometrics. Food Analytical Methods 2018, 11, 1969–1976. doi:10.1007/s12161-018-1160-y

[10] Yao, C.; Cheng, F.; Wang, C.; et al. Separation, identification and fast determination of organophosphate pesticide methidathion in tea leaves by thin layer chromatography–surface-enhanced Raman scattering. Analytical Methods 2013, 5, 5560. doi:10.1039/c3ay41152d

[11] Li, S.; Shan, Y.; Zhu, X.; et al. Detection of honey adulteration by high fructose corn syrup and maltose syrup using Raman spectroscopy. Journal of Food Composition and Analysis 2012, 28, 69–74. doi:10.1016/j.jfca.2012.07.006

[12] Oroian, M.; Ropciuc, S. Botanical authentication of honeys based on Raman spectra. Journal of Food Measurement and Characterization 2017, 12, 545–554. doi:10.1007/s11694-017-9666-3

[13] Nieuwoudt, M.; Holroyd, S.; McGoverin, C.; et al. Rapid, sensitive, and reproducible screening of liquid milk for adulterants using a portable Raman spectrometer and a simple, optimized sample well. Journal of Dairy Science 2016, 99, 7821–7831. doi:10.3168/jds.2016-11100

[14] Lin, X.; Hasi, W.-L.-J.; Lou, X.-T.; et al. Rapid and simple detection of sodium thiocyanate in milk using surface-enhanced Raman spectroscopy based on silver aggregates. Journal of Raman Spectroscopy 2014, 45, 162–167. doi:10.1002/jrs.4436

[15] Nekvapil, F.; Brezestean, I.; Barchewitz, D.; et al. Citrus fruits freshness assessment using Raman spectroscopy. Food Chemistry 2018, 242, 560–567. doi:10.1016/j.foodchem.2017.09.105

[16] Xie, J.; Li, L.; Khan, I.; et al. Flexible paper-based SERS substrate strategy for rapid detection of methyl parathion on the surface of fruit. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2020, 231, 118104. doi:10.1016/j.saa.2020.118104

Post written by Dr. Sara Seiffert (Product Specialist Spectroscopy at Metrohm Deutschland) and Dr. Alyson Lanciki (Scientific Editor at Metrohm International Headquarters).

Chemistry of Chocolate

Chemistry of Chocolate

Swiss… Belgian… Pure… Milk…

Here we are in mid-February again, bombarded by chocolate from all sides in preparation for Valentine’s Day on the 14th. Whether in a solid bar, as a chewy truffle, or as a luxurious drink, chocolate has completely infiltrated our lives. Most people can agree that this confectionary treat is fantastic for any occasion – to be given as a gift, to recover after having a bad day, as well as to celebrate a good one – chocolate is certainly meant to be enjoyed.

Even if you don’t like the taste, the chances are high that someone close to you does. So how can you be certain of its quality?

Components of a chocolate bar

For the sake of this article, let us consider the humble chocolate bar, without any extra additions (not to mention any Golden Tickets). This form can be found worldwide in nearly any grocery store or candy shop, generally designated as white, milk, or dark.

All of this variability comes from the edible seeds in the fruit of the cacao tree, which grows in hot, tropical regions around the equator. They must be fermented and then roasted after cleaning. From this, cocoa mass is produced, which is a starting base for several uses. Cocoa butter and cocoa solids are prepared from the cocoa mass and are utilized in products ranging from foods and beverages to personal care items.

As for chocolate bars, these are generally sweetened and modified from the pure form, which is very bitter. Milk (liquid, condensed, or powdered) is added to many types, but does not necessarily have to be present. Varying the content of the cocoa solids and cocoa butter in chocolate to different degrees results in the classifications of dark to white. While some dark chocolates do not contain any milk, white chocolates do to add to the significant amounts of cocoa fat used to produce them.

In general, dark chocolate contains a high ratio of cocoa solids to cocoa butter and may or may not contain any milk. It may be sweetened or unsweetened. Milk chocolate is a much broader category, containing less cocoa solids but not necessarily a different cocoa butter content compared to dark chocolate, as milk fats are also introduced. Milk chocolate is also sweetened, either with sugar or other substitutes. White chocolate contains no cocoa solids at all, but a blend of cocoa butter and milk, along with sweeteners.

Depending on the country, there are different regulations in place regarding the classification of the type of chocolate. If you are interested, you can find a selection of them here.

What makes your favorite chocolate unique?

Of course, more ingredients are added to chocolate bars to affect a number of things like the aroma, texture/mouthfeel, and certainly to enhance the flavor. The origin of the cacao beans, much like coffee, can impart certain characteristics to the resulting chocolate. The manufacturing process also plays a major part in determining e.g., whether the chocolate has a characteristic snap or has a distinct scent, setting it apart from other brands.

In some cases, vegetable fats are used to replace a portion of the cocoa fats, although this may not legally be considered «chocolate» in some countries. The adjustment of long-standing recipes for certain chocolate brands has sometimes led to customer backlash, as quality is perceived to have changed. Truly, chocolate is inextricably tied to our hearts.

Applications for chocolate quality analysis

Nobody wants to give their Valentine a bad gift, especially out-of-date chocolate from a dubious source. Here, we have prepared some interesting analyses for different chocolate quality parameters in the laboratory.

Sugar analysis via Ion Chromatography (IC)

Most types of chocolate contain sugars or sugar substitutes to sweeten the underlying bitterness. Considering different regulations regarding food labeling and also nutritional content, the accurate reporting of sugars is important for manufacturers and consumers alike.

Sugar analysis in chocolate can be performed with Metrohm IC and Pulsed Amperometric Detection (PAD). An example chromatogram of this analysis is given below.

A small amount of commercially produced sweetened milk chocolate was weighed and dissolved into ultrapure water. After further sample preparation using Metrohm Inline Ultrafiltration, the sample (20 µL) was injected on to the Metrosep Carb 2 – 150/4.0 separation column and separated using alkaline eluent. As shown, both lactose and sucrose elute without overlap in less than 20 minutes.

Learn more about Metrohm Inline Ultrafiltration for difficult sample matrices and safeguard your IC system!

In this example, the sugar content was listed on the label as 47 g per 100 g portion (470 g/kg). Lactose was determined to be 94.6 g/kg, and sucrose was measured at 385.6 g/kg. To learn about what other carbohydrates, sweeteners, and more can be determined in chocolate and other foods with Metrohm IC, download our free brochure about Food Analysis and check out the table on page 25!

Lactose content in lactose-free chocolate

The accurate measurement of lactose in lactose-free products, including chocolate, is of special importance to consumers who are lactose-intolerant and suffer from digestive issues after eating it. Foods which are labelled as lactose-free must adhere to guidelines concerning the actual non-zero lactose content. Foodstuff containing less than 0.1 g lactose per100 g (or 100 mL) is most frequently declared as lactose-free.

Determination of lactose in chocolate is possible with IC. Here is an chromatographic overlay of a dissolved chocolate sample with lactose spikes which was analyzed via Metrohm IC using the flexiPAD detection mode.

Milk chocolate, labelled lactose-free measured via Metrohm IC (0.57 ± 0.06 mg/100 g lactose, n = 6).

The sample contained 0.6 mg lactose per 100 g, with measurement of the lactose peak occurring at 13.2 minutes. The black line is the unspiked lactose-free chocolate sample, red and blue are spiked samples of increasing concentration. To prepare the samples, approximately 2.5–5 g chocolate was dissolved in heated ultrapure water, using Carrez reagents to remove excess proteins and fats from the sample matrix. Afterward, centrifugation of the samples was performed, followed by the direct injection of the supernatant (10 µL) into the IC system. Measurement was performed with the Metrosep Carb 2 – 250/4.0 separation column and an alkaline eluent.

Interested in lactose determinations with ion chromatography? Download our free Application Notes on the Metrohm website!

Water determination with Karl Fischer Titration

The amount of water in foods, including chocolate, can affect their shelf life and stability, as well as contribute to other physical and chemical factors. Aside from this, during the processing stage, the amount of water present affects the flow characteristics of the chocolate mass.

AOAC Official Method 977.10 lists Karl Fischer titration as the accepted analysis method for moisture in cacao products.

The determination of moisture in different chocolate products is exhibited in the following downloadable poster. As an example, several samples (n = 10) of dark chocolate (45% cocoa content) were analyzed for their moisture content with Metrohm Karl Fischer titration.  Results were found to be 0.96% water with a relative standard deviation (RSD) of 2.73%. More information about this analysis can be found in our poster about automated water determination in chocolate, or in chapter 11.6 of our comprehensive Monograph about Karl Fischer titration.

Oxidation stability with the Rancimat test

Oxidation stability is an important quality criterion of chocolate as it provides information about the long-term stability of the product. Cocoa contains various flavonoids that act as antioxidants. Although the flavonoid content may vary amongst chocolate type, in general, the greater the content of cocoa solids in the chocolate, the greater its antioxidant effect.

The 892 Professional Rancimat from Metrohm determines the oxidation stability of fat-containing foods and cosmetics. The Rancimat method accelerates the aging process of the sample and measures the induction time or oxidation stability index (OSI).

Chocolate cannot be measured directly with the classical Rancimat method, as no evaluable induction time is obtained. There are many reasons for this: e.g., the fat content is too low. Traditionally, extraction of the fat from the chocolate is necessary, but not always.

Learn more about the Rancimat method on our website, and download our free Application Note about the oxidation stability of chocolate. In this Application Note, the oxidation stability of white, milk and dark chocolate is determined without extraction.

Cadmium in chocolate by Voltammetric analysis

The toxic element cadmium (Cd) can be found in elevated concentrations with high bioavailability in some soils. Under such conditions, cacao trees can accumulate cadmium in the beans. Chocolate produced from the affected beans will contain elevated cadmium levels.

Typical limit values for Cd in chocolate in the European Union are between 100 µg/kg and 800 µg/kg (EU Commission Regulation 1881/2006) depending on the cocoa content of the chocolate. Anodic stripping voltammetry (ASV) can be used to accurately determine trace quantities of cadmium in chocolate down to approximately 10 µg/kg. The method is simple to perform, specific, and free of interferences.

Chocolate samples are first mineralized by dry ashing in a furnace at 450 °C for several hours. The remaining ash is then dissolved in an acidified matrix. The cadmium determination is then carried out on the 884 Professional VA instrument from Metrohm. To learn more about how to perform the analysis, download our free Application Note.

Happy Valentine’s Day from us all at Metrohm!

Post written by Dr. Alyson Lanciki, Scientific Editor at Metrohm International Headquarters, Herisau, Switzerland.

Raman vs SERS… What’s the Difference?

Raman vs SERS… What’s the Difference?

If you’ve ever had a conversation with a Raman spectroscopist about the feasibility of a low-concentration sensing application, chances are you’ve heard them say “well, Raman may not be sensitive enough…but maybe SERS will work!” But what’s the actual difference between these two techniques, and why is SERS (surface-enhanced Raman scattering, or alternatively surface-enhanced Raman spectroscopy) recommended for low-concentration applications? Let’s explore the technical differences between Raman and SERS spectroscopies, as well as some of the practical considerations for how we regard the data for each.

In normal Raman spectroscopy, a laser source is incident directly on a sample (Fig. 1a). The laser light is scattered by the bonds of the analyte, and the inelastically scattered light is collected and processed into a Raman spectrum. The non-destructive nature of the technique, the selectivity of Raman bands, and the insensitivity to water make Raman a useful analytical tool for both qualitative and quantitative studies of both organic and inorganic systems.

Figure 1. 

However, for decades Raman spectroscopy was an underutilized technique in real-world applications. This can be attributed to its two major limitations: 1) the inherent insensitivity of Raman, as only ~1 in 106 incident photons are Raman scattered; and 2) fluorescence emission interference, which depends on the nature of the analyte molecule and the excitation wavelength used. Fluorescence is a competing phenomenon that is much more efficient than Raman scattering, and can thus completely overwhelm the Raman signal.

Though they depend on the scattering strength of the analyte molecule and the sample matrix in question, typical limits of detection for normal Raman scattering can range from ~1–10% in concentration. For certain applications such as disease detection or narcotics identification, this limit may be several orders of magnitude higher than what is required! In this case, an application scientist might recommend a SERS measurement. The hardware required would be the same as for a normal Raman measurement, but different sampling is required for SERS analysis. To understand the difference, let’s discuss a bit about the SERS effect.

In the 1970s, several research groups observed that the Raman signal from organic molecules like pyridine was greatly enhanced when adsorbed to a roughened metallic substrate (Fig. 1b) [1–3]. While several theories emerged to account for this observation, it is today generally accepted that the mechanism for enhancement is two-fold: the electromagnetic enhancement mechanism accounts for the dominant contribution, while a chemical mechanism accounts for a smaller portion of the enhancement.

Figure 2.

The electromagnetic enhancement mechanism is enabled by the use of a roughened nanometallic substrate made of a noble metal (usually silver or gold), and the presence of localized surface plasmons, which are quantized oscillations of the valence electrons of the chosen metal. When the laser excites the sample/nanosubtrate complex, it drives the localized surface plasmons into resonance, or excites the “LSPR” (Fig. 2). At this condition, both the laser excitation radiation and the scattered radiation from the sample are amplified. The arrows in Fig. 1b are bolded to show this increase in magnitude. This mechanism can theoretically account for signal enhancement by factors as large as 1011 [4]. The chemical mechanism involves charge-transfers in resonance with the laser excitation wavelength, and typically accounts for a theoretical enhancement factor of up to 104 [5]. Interfering fluorescence can also be quenched by these charge transfers. With the combined enhancement mechanisms we are able to overcome both the inherent insensitivity and fluorescence interference that limits normal Raman scattering. In fact, there are studies which have demonstrated that SERS is able to detect single molecules [6,7]!

Fabrication of these nanostructures has been an increasing area of academic research in the last two decades. SERS substrates can include colloidal suspensions, solid nanospheres, and metal coated on silicon chips. The enhancement tends to be at its height when the analyte molecule is placed at a junction of nanostructures (otherwise known as a SERS “hotspot”), so researchers can tailor the shapes and the plasmonic activity of these substrates to reach even greater levels of enhancement for their research purposes.

There are also commercial SERS substrates that are available for purchase to use for real-world applications. These substrates are designed to be easy-to-use, flexible, and low-cost, but may not be as sensitive as highly ordered substrates. We offer both a paper-based SERS substrate and a chip-based SERS substrate mounted to a glass slide.

After discussion with an application scientist, users may determine that a commercially available SERS substrate is suitable for their application. However, in others greater sensitivity may be required to meet the limits of detection for the application. In this case, local university labs who work on nanofabrication may be able to collaborate on measurements.

Figure 3.

We often get questions such as “Can we use our existing Raman reference library to analyze our SERS spectrum?” Figure 3 shows the difference between a normal Raman spectrum of fentanyl HCl (Fig. 3a), and a SERS spectrum of a saturated solution of fentanyl HCl on a commercial SERS substrate (Fig. 3b). The normal Raman spectrum for fentanyl contains significantly more peaks than the corresponding SERS spectrum. The SERS bands are also noticeably broader than the normal Raman bands. In the case of the SERS spectra, it is not solely the vibrational modes of the molecule that are being probed, but the sample as adsorbed to the substrate. Hence, we may also observe some peaks in a SERS spectrum that can be attributed purely to the substrate. Because of the differences between a SERS spectrum and a normal Raman spectrum, it may be difficult in some cases to use commercial Raman libraries for analysis of SERS spectra. We encourage users who require SERS identification to create their own SERS spectral databases using their substrates. We also include SERS-specific narcotics libraries on some of our TacticID handheld Raman products. For more complicated data analysis, there is also an expansive SERS literature base to draw on.

In low-concentration sensing applications, or instances where fluorescence overwhelms your Raman signal, SERS is an invaluable technique for both researchers and real-world problem solvers alike. For more information, visit our website.

Learn more about SERS

Download free applications, white papers, and more from our website.

References

[1] D.L. Jeanmaire and R.P. Van Duyne, J. Electroanal, Chem84, 1–20 (1977).
[2] M.FleischmannP.J.Hendra, and A.J. McQuillanChem. Phys. Lett. 26, 163-166 (1974).
[3] M.G. Albrecht and J.A. Creighton, J. Am. Chem. Soc. 99, 5215-5217 (1977).
[4] J.P  Camden J. A. DieringerY. WangD.J. MasielloL.D. MarksG.C. Schatz, and R.P. Van DuyneJ. Am. Chem. Soc. 130, 12616–12617 (2008).
[5] R. Pilot, R. Signorini, and L Fabris, “Surface-Enhanced Raman spectroscopy: Principles, Substrates, and Applications”. In: Deepak F.L., editor. Metal Nanoparticles and Clusters: Advances in Synthesis, Properties and Applications. Springer; Cham, Switzerland: 2018. pp. 89–164.
[6] J.A. Dieringer, R.B. Lettan, K.A. Scheidt, and R.P Van Duyne, J. Am. Chem. Soc.129, 16249–16256 (2007).
[7] K. Kneipp, Y. Wang, H. Kneipp, L.T. Perelman, I. Itzkan, R.R. Dasari, and M.S. Feld, Phys. Rev. Lett. 78, 1667-1670 (1997).

Post written by Kristen Frano, Applications Manager at B&W Tek, Newark, DE, USA.

History of Metrohm IC – Part 5

History of Metrohm IC – Part 5

In the fifth part in our ongoing series about the history of ion chromatography development at Metrohm, we now focus on automated air quality monitoring with the 2060 MARGA instrument.

Did you miss the other parts in this series? Find them here!

The importance of clean air cannot be understated. Air pollution is one of the major environmental risks to human health; it can cause strokes, heart disease, lung cancer, and both chronic and acute respiratory diseases. Additionally, the contribution of such pollution to climate change is of significant scientific interest.

Monitoring air quality is of increasing concern, and thankfully more and more companies are taking responsibility for their input and looking for ways to measure and mitigate their environmental contribution.

What is MARGA?

MARGA (Monitor for AeRosols and Gases in ambient Air) was developed in the 1990s by Metrohm Process Analytics in cooperation with the Energy Research Centre of the Netherlands (ECN) (Figure 1).

Figure 1. The original MARGA 1S air monitoring system, developed in the 1990s by Metrohm Process Analytics.

This instrument application offered a new approach in which gases and aerosols sampled from the same air mass are separated from each other by selectively dissolving them in water. The resulting solutions (available every hour) are then analyzed using ion chromatography with conductivity detection. Separating the two fractions from each other allows for the detection of important precursor gases and ionic species found in the aerosols.

Collection of water-soluble ions and analysis by ion chromatography:
  • Gases: HCl, HNO3, HNO2, SO2, NH3
  • Aerosols: Cl, NO3, SO42-, NH4+, Na+, K+, Ca2+, Mg2+, *F

*also possible with the 2060 MARGA (Figure 2)

This new analyzer application was a huge success at that time. However, in the meantime Metrohm Process Analytics was busy implementing more modular flexibility to their process analyzers. That’s why in 2018, based on the all-new 2060 online analysis platform from Metrohm Process Analytics, the 2060 MARGA (Figure 2) was introduced.

To learn more about how MARGA is used in real life situations, download our free technical notes on the Metrohm website.

Figure 2. The Metrohm Process Analytics solution to unattended, automated air quality analysis: the 2060 MARGA M.

Featuring state of the art 2060 software to automate analysis 24/7, brand new hardware adaptable for modular flexibility, and the dependable and well-known MagIC Net software, the 2060 MARGA is the right solution to gain insight of the effects of particulate matter on health and the environment. This instrument is available in two versions:

2060 MARGA M (Monitoring)

The 2060 MARGA M (Figure 2) is ideal for unattended routine monitoring at a permanent site.

Everything is packed into a single instrument, with separate subcabinets for the sample collection wet part, ion analysis cabinet (with two IC channels and column oven for anion and cation determinations), plus reagent containers with level sensors.

2060 MARGA R (Research)

A flexible version, ideal for research applications, features the 2060 user interface and sample collection wet part.

Sample analysis is carried out on a stand-alone Metrohm 940 Professional IC Vario TWO/SeS/PP, including sequential suppression for the anion analysis channel. Installed on-site for a limited time campaign, the 2060 MARGA R works unattended in the same way as the 2060 MARGA M. When not required for field use, the 940 Ion Chromatograph can be put to work in the laboratory, using an external PC and MagIC Net, to run any of the multitude of applications available from Metrohm.

Figure 3. The 2060 MARGA offers hourly data and easy to read trend charts for a full overview of gas and aerosol analysis.

The 2060 MARGA is designed for monitoring in remote locations but it’s never far from home. By using a direct internet connection, the 2060 MARGA performance can be checked remotely, adjustments can be made, and results can be evaluated at any time.

Monitoring air quality around the world

MARGA systems from Metrohm have been used by many official agencies and research organizations globally to monitor air quality in a completely autonomous way.

Figure 4. World map showing the locations of installed MARGA instruments from Metrohm Process Analytics.
Scotland

The MARGA participated in a program focusing on measurement and evaluation of the long-range, transboundary transmission of air-polluting substances in Europe (European Monitoring and Evaluation Programme, «EMEP»). 

This research was performed in Auchencorth Moss, approximately 20 kilometers south of Edinburgh in Scotland, with the objective of analyzing to what degree crops and natural ecosystems, as well as the rural population, are exposed to airborne pollutants.

Learn more about this application here.

Netherlands

Fireworks are full of water-soluble ions and trace metals. The different colors are produced through the combustion of these chemical compounds. After combustion, the air is full of toxic gases and particles which can linger for a significant time, depending on weather patterns.

The 2060 MARGA can determine detailed gas and aerosol concentrations on an hourly basis completely autonomously, offering valuable scientific information about the effect of fireworks on local air quality (Figure 5).

Figure 5. Air pollution due to New Year’s Eve fireworks celebrations in the Netherlands: aerosol concentrations of selected compounds.

For more information about this application, download our free technical note here.

If you would like to read more scientific literature featuring the MARGA, please download our free overview: Air monitoring with ion chromatography: An overview of the literature references.

Download our free monograph:

Practical Ion Chromatography – An Introduction

Post written by Andrea Ferreira (Technical Writer at Metrohm Applikon, Schiedam, The Netherlands) and Dr. Alyson Lanciki (Scientific Editor at Metrohm International Headquarters).

Introduction to Analytical Instrument Qualification – Part 2

Introduction to Analytical Instrument Qualification – Part 2

Welcome back to our blog, and happy 2021! We hope that you and your families had a safe and restful holiday season. To start the year, we will conclude our introduction to Analytical Instrument Qualification. 

Metrohm’s approach to Analytical Instrument Qualification (AIQ)

Metrohm’s answer to Analytical Instrument Qualification is bundled in our Metrohm Compliance Services. The most thorough level of documentation offered for AIQ is the IQ/OQ.

Metrohm IQ/OQ documentation provides you with the required documentation in strict accordance to the major regulations from the USP, FDA, GAMP, and PIC/S, allowing you to document the suitability of your Metrohm instruments for your lab’s specific intended use.

With our test procedures (described later in more detail), we can prove that the hardware and software components function correctly, both individually and as part of the system as a whole. With Metrohm’s IQ/OQ, you are supported in the best possible way to integrate our systems into your current processes.

Our high quality documentation will have you «audit ready» all the time.

The flexibility of a modular document structure

Depending on the environment you work in and your specific demands, Metrohm can offer a tailored qualification approach thanks to documentation modularity. If you need a lower level of qualification, only the required modules can be executed. Our documentation consists of different modules, each of which documents the identity of the Metrohm representative along with the qualification reviewer, combined with the details of each instrument, software, and document involved in the qualification.  Thanks to this, each module is independent, which guarantees both full traceability and reliability for your system setup.

Cost-effective qualification from Metrohm

Metrohm supports you by implementing a cost-effective qualification process, depending upon your requirements and the modules needed. This means that a qualification is not about performing unnecessary actions, qualification is about completing the required work.

The risk assessment analysis defines the level of qualification needed and based on it, we focus on testing only what needs to be tested. In case you relocate your device to another lab, which qualification steps (DQ, IQ, OQ, PQ) are really needed in order to fulfill your requirements? Contact your local Metrohm expert for advice on this matter.

A complete Metrohm IQ/OQ qualification includes…

Metrohm IQ/OQ documentation is based on the following documentation tree, beginning with the first module, the Master Document (MD), followed by the Installation Qualification (IQ) and eventually the Operational Qualification (OQ). The OQ is then divided again into individual component tests (Hardware and Software) and a holistic test to validate your complete system.

Master Document (MD)

Each qualification starts with the Master Document (MD) – the central organizing document for the AIQ procedures. It not only describes the process of installing and qualifying the instruments, but also the competence and education level of the qualifying engineer. The MD identifies all other components to be added to the qualification, resulting in a flexible framework on which to build up a set of documentation.

Installation Qualification (IQ)

Once the content of the documentation is defined in the MD, the Installation Qualification (IQ) follows. This set of documentation is designed to ensure that the instrument, software, and any accessories have been all delivered and installed correctly. The IQ protocol additionally specifies that the workplace is suitable for the analytical system as stipulated by Metrohm.

Operational Qualification (OQ)

After a correct installation comes the main part of the qualification: the Operational Qualification (OQ). In the first part of the OQ, the functionality of the single hardware components is tested and evaluated according to a set of procedures. This is to ensure that the instrument is working perfectly as designed, and is safe to use. Rest assured that you can rely on the expertise of our Metrohm certified engineers to conduct these comprehensive tests on your instruments using the necessary calibrated and certified tools.

The second part of the OQ consists of a set of Software Tests to prove that the installed Metrohm software functions correctly and reliably on the computer it was installed on. The importance of maintaining software in a validated state is also related to the data integrity of your laboratory. Therefore these software tests can be repeated periodically or after major changes. In particular, these functionality tests cover verifications on user management, database functionalities, backups, audit trail review, security policy, electronic signatures, and so on.

At Metrohm, we constantly work to improve our procedures and use state of the art tools and technologies.  For this reason, we have implemented a completely automated test procedure for validating the software of our new OMNIS platform. This ensures full integrity in the execution and delivers consistent results with a faster and completely error-free test execution. This innovative and automated software validation eliminates manual activities that are labor intensive and time consuming. This therefore expedites testing and removes the inefficiencies that plague the paper-based software validation.

Your benefit is clear: save valuable time and reduce unnecessary laboratory start-up activities during qualification. That’s time you can spend on other work in your lab!

Holistic Test (Performance Verification, PV)

Once each individual component has been separately tested, the performance of the system as a whole is proven by means of a holistic test (OQ-PV).

This includes a series of «wet-chemical» tests, performed using certified reference materials, to prove the system is capable of generating quality data, i.e. results that are accurate, precise, and above all fit for purpose. Based on detailed, predefined instructions (SOPs), a series of standard measurements are performed, statistically evaluated, and compared to the manufacturer’s specifications.

Differences between Performance Verification (PV) and Performance Qualification (PQ)

The Performance Verification (PV) is a set of tests offered by Metrohm in order to verify the fitness for purpose of the instrument. As mentioned in the previous paragraph, the PV includes standardized test procedures to ensure the system operates as designed by the manufacturer in the selected environment.

On the other hand, the Performance Qualification (PQ) is a very customer specific qualification phase (see the «4 Q’s» Qualification Phases found in Part 1). PQ verifies the fitness for purpose of the instrument under actual condition of use, proving its continued suitability. Therefore, PQ tests are defined depending on your specific analysis and acceptance criteria.

Now my questions to you—is your analytical instrument qualified for its intended use? Is your lab in compliance with the latest regulations for equipment qualification and validation? Get expert advice directly from your local Metrohm agency and request your quote for Metrohm qualification services today!

Check out our online material:

Metrohm Quality Service

Post written by Lara Casadio, Jr. Product Manager Service at Metrohm International Headquarters, Herisau, Switzerland.