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Articles

Accurate and Rapid Metabolomics Strategies Using GC-MS/MS-MRM Technology

This article explores the use of this technology for the investigation of plant metabolism and phytohormone profiling. Plants are unique in that they are sessile organisms and cannot escape environmental pressures. As a result, they represent one of the richest sources of novel bioactive compounds. Using GC-MS/MS-MRM technology, physiological markers are selectively identified and quantified from complex metabolomics samples in a high sample throughput manner. This article will also highlight significant additional benefits gained from GC-MS/MS-MRM technology, including accelerated processes through using a single instrument when performing screening, as well as guaranteed reproducibility in fragmentation pattern, peak intensities and mass accuracies.

 

GC Solutions #30: Pay Attention to Acquisition Rate and Detector Range

Last month we talked about determining limit of detection (LOD) and limit of quantitation (LOQ). I mentioned that it is important to pay attention to the detector acquisition rate and amplifier settings (if they are adjustable) since these can impact the ability to detect small peaks. This month we look at the impact of those factors in more detail.

 

GC Solutions #25: Is it Working?

This month we talk about avoiding problems through routine maintenance and verifying that your instrument is working through the use of a performance verification method.

 

GC Solutions #26: Too Fast GC -- What is Too Fast in GC?

Commercialization of technologies to produce faster temperature ramps in GC have been some of the few GC advances in recent decades. This article will take a look at the utility and ultimate areas of practical application for these technologies.

 

GC Solutions #22: Inlet Activity

In this article we discuss issues related to inlet and liner activity. 

 

GC Solutions #19: Calibration Curves – Part 1

In this article we discuss general approaches to GC response calibration and focus on the simplest; external calibration.

 

GC Solutions #14: Post Column Backflush

We continue last month’s backflush discussion with a description of the most common form of backflush: post-column backflush. 

 

GC Solutions #16: Uncoated Pre-Column Backflush Configuration

Under discussion is one of the newer approaches to capillary column backflush: the uncoated pre-column configuration.

 

GC Solutions #15: Coated Pre-Column Backflush

Continuing our discussion of the three configurations of capillary column backflush, we cover the coated pre-column configuration.

 

GC Solutions #13: Capillary Column Backflush

In this article we introduce the concepts of backflushing capillary columns.

 

GC Solutions #12: The Flame Ionization Detector – Part 2

Continuing the previous discussion of the most popular GC detector, the FID, we cover deviations from typical unit carbon response, optimization and troubleshooting.

 

How to Increase the Linear Application Range of Your GC–MS Method Using Smart Ion Selection?

With the introduction of lean thinking, 6-sigma and other related strategies*, laboratory managers have to apply new approaches in order to meet the stringent requirements imposed by these management philosophies. Particularly the large day-to-day variability in volume and mix of samples arriving in an analytical laboratory is often hard to address appropriately. A common approach to reduce the ‘waste’ of applying too many different methods is based on the use of generic methods. 

 

How to Analyse Unknown Samples by Pyrolysis GC/MS?

Although GC/MS and LC/MS are very powerful analytical techniques, they generally lack the ability to analyse and characterize insoluble materials, such as polymers and other high molecular weight products. An elegant approach to cope with this type of samples involves a combination of thermal decomposition and online chromatographic analysis of the released breakdown products. This approach is called analytical pyrolysis.

 

Activity in the FID Detection Port: A Big Problem if Underestimated

It is commonly known in gas chromatography, that many problems can be traced to the injection system (e.g. sample, syringe, inlet), which is often a primary place to look at possible issues. This is a valid statement, as 80% of “trouble” is related to injection conditions. One must also be aware that activity may be caused by other contributions. For instance, if we look at non-symmetrical peaks, there are more important area’s to look at. Not only the columns used can be overloaded or poorly deactivated, also the contribution of the detector has a huge impact on peak shape and response.Here it is shown that flame tips can adsorb up to 90% of component and cause tailing on polar as well as base/acidic components. Though it looks columns are not performing, it’s the detector that is the problem.

 

GC Solutions #24: What’s New?

As I prepare to attend PittCon 2012, I suspect that the answer to the question “what’s new in gas chromatography?” is “not much”. Is that because there is nothing left for instrument manufacturers and researchers to do in the area or is there something else going on?

 

GC Solutions #23: Sandwich Injections

In this article we discuss the merits and deficiencies of sandwich injection techniques.

 

GC Solutions #11: The Flame Ionization Detector

In this article we initiate a discussion on the workhorse detector of gas chromatography: the flame ionization detector.

 

Chromatographic Method Validation

An analytical method must be able to deliver valid results. Method validation involves performing the scientific experiments that demonstrate a method is fit for its intended purpose – only when this is done can one be assured that the method will produce valid data. Validation can unearth surprises that can indicate a method vulnerability that didn’t show up during development. While method development and method validation should be integrated oftentimes a method is hastily constructed because of time pressures and later falls down at the validation stage. Every method development project is unique with specific issues such as resolution of impurities, stability of the analytes, inadequate sensitivity, poor sample extraction, poor recovery data and so forth – validation of the method proves that you have solved these issues.

 

Characterization of Chinese Medicines by Comprehensive Two-Dimensional Gas Chromatography and Time-of-Flight Mass Spectrometry (GC×GC-TOFMS) with Assistance of Multivariate Data Analyses

A comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) system was applied for profiling the complex chemical composition of Chinese herbs (Radix Angelicae Pubescentis and Radix Angelicae Dahuricae ). The two-dimensional GC and deconvolution algorithm largely enhances selectivity and sensitivity of analysis. Over 300 compounds were identified in each herbal. The data obtained were then processed by multivariate data analyses. Based on their fingerprint chromatograms, herbs could be distinguished; e.g., by their species, geographical origins. GC×GC-TOFMS has shown great potential as a powerful tool for metabolomics studies.

 

Peak Elution Order

Recently I spoke with a customer who was trying to speed up an analysis. He had decided to use a shorter column with a smaller diameter, to maintain separation efficiency and decrease run times by a factor of 2. However, using this approach the customer did not get the same separation as peaks moved, even swapping direction. What was happening and how could the risk of peak swapping be reduced? In this article we discuss the phenomena of relative peak-shifting which can occur because of a possible change in the elution temperature.

 

Multi-residue Pesticide Analysis in Rice by QuEChERS and GC/MS Analysis

This article discusses current legislation governing the concentration of pesticide residues in foods and describes the QuEChERS sample preparation method. An application example is used to highlight the efficiency of the QuEChERS/ion trap GC/MSn technique, covering preparation of extracts and optimization of analytical parameters for injection, separation and detection.

 

Combining Time of Flight Mass Spectrometry with Gas Chromatography for Increased Sensitivity in Beer Analysis

Beer is derived from natural plant products, mainly cereal grains such as barley, rice, wheat and corn. Beer samples are very complex and contain many hundreds of organic components including vitamins, amino acids, proteins and bitter acids. The ‘signature’ flavour and aroma of each particular beer brand is characterized by a vast array of volatile compounds, which often have very low olfactory thresholds. This means that the actual concentrations of signature compounds can be extremely low, posing significant analytical challenges. In addition, some compounds may exist at very high concentrations. As a result, beer samples can be very difficult to analyse.

 

Application and Limitation of using Adsorbents as Stationary Phases in Gas Chromatography for the Separation of Volatile Compounds

Adsorbents have unique separation characteristics. The adsorption process allows very volatile components to be retained at higher temperatures that create easier conditions to quantify very volatile compounds.

 

Method 8260C by Purge and Trap Gas Chromatography–Mass Spectrometry

The improvement and protection of the environment from human activity is recognized by many as a duty we owe to future generations. Organizations such as the US Environmental Protection Agency (EPA) are created to provide guidance for the protection of the natural environment through regulation of pollution and analytical methodology.

 

Peak Tailing in GC Trace Analysis

In chromatography the analysis methods are becoming more and more challenging. Lower detection limits are required especially if quantification is required at trace levels. As soon as activity develops in a GC system, the first component that starts to loose response, will be ones that have polar functionality. This can be hydroxyl, amine, carboxyl groups or combinations. Peaks usually start to tail and even retention times can change.

 

GC and HPLC Detection of Adulterations in Citrus Oils

Citrus essential oils are valuable products in the international market for their use in the food and cosmetic industries. They have always been employed as natural flavourings in food, as whole extracts or as part of their constituents. Conventional extraction is based on cold pressing of the fruit peels by means of suitable machinery which ensures breaking of the glands containing the essential oils. The quality and amount of the final product depends upon many factors such as the Citrus species and the accuracy of the extraction process. Production of some types of Citrus oils is definitely limited by low availability of the raw material, e.g., bergamot oil, which only finds its optimum habitat in a tiny strip of land in Calabria (South Italy). This makes bergamot oil more valuable than other Citrus oils and, therefore one of the most expensive worldwide. In contrast, high production of other Citrus species, i.e., sweet orange, makes this one of the cheapest oils available in the market.

 

Multidimensional Gas Chromatography — A Technology For Today’s Analytical Challenges

Today, the discerning chromatographer should expect that with modern instrumentation, the gas chromatography (GC) method should deliver an advanced capability to assess the chemical constituents of a sample, with precision, and a significant coverage of sample components present in trace to major amounts.

 

GC Solutions #1: Helping You Get the Most Out of GC Analysis

In the monthly series of articles that will follow in GC Solutions I aspire to make the time you spend as rewarding as possible by presenting concise, clear, straightforward and practical articles on gas chromatographic (GC) analysis.

 

GC Solutions #3: The Function of GC Columns

This month I present a general overview of the purpose of GC columns, key processes involved and high-level description of differences between them.

 

GC Solutions #5: Hot Split Injections – Part 1

This  article will discuss split injections with a hot split/splitless inlet. This is the most popular inlet and sampling mode for capillary GC. 

 

GC Solutions #6: Hot Split Injections, Part 2 – Sources of Discrimination

This article continues our discussion of the process of hot split injection; the most popular form of sample introduction into capillary columns.

 

GC Solutions #8: Basis of Interactions in Gas Chromatography, Part 1 – Non-Polar Interactions

To fully grasp the concepts of retention and selectivity of GC stationary phases, one must first understand the fundamental intermolecular interactions that lead to retention. In this article we discuss the most dominant of those interactions – dispersive, non-polar interactions.

 

How to Develop a Method using In-tube Extraction (ITEX) For GC and GC/MS?

Throughout our lives we are continuously exposed to substantial quantities of volatile organic components (VOC). Residual solvents from carpets, paints and glues largely determine the quality of the indoor air we daily inhale. Offices, workspaces and even our living rooms, it’s practically impossible to breathe clean air nowadays. Perhaps we are luckier with the food we eat and the beverages we drink? Unfortunately, I am afraid not. Solvents from packaging foils and printing inks may pose a severe risk for the foodstuff they contain, while the water we drink or use to make soda, beers, etc. is polluted with traces of disinfection agents and other environmental contaminants. No wonder ‘VOC analysis’ plays such a vital role in many QC laboratories around the globe.

 

How to Get More Analysis Out of Your GC System?

A common question we get asked by our customers is how they can get a longer column lifetime. This can be from a cost perspective (column price) or from a maintenance perspective (downtime, labour, calibration).

 

The Impact of Using Guard Columns in Gas Chromatography

Gas chromatography is a technique which can be used for a wide class of sample types. If the components to analyse can be transferred in the gas-phase by increasing the temperature, then there is a high probability that they can be analysed by gas chromatography.

 

GC Solutions #2: The Function of GC Inlets

This article will cover the general function of GC inlets describing some common attributes and differences. It will also provide a context for future articles covering inlets in more detail.

 

GC Solutions #4: GC Detectors

This article presents an overview of GC detectors.

 

GC Solutions #7: Hot Split Injections, Part 3 – Decomposition

In this article, we tackle another potential problem of hot split injection: sample decomposition. Decomposition changes the nature of components in the original sample, affecting the “recovery” of target compounds. 

 

GC Solutions #9: Basis of Interactions in Gas Chromatography – Part 2: Polar Interactions

To fully grasp the concepts of retention and selectivity of GC stationary phases, one must first understand the fundamental intermolecular interactions that lead to retention. This month we discuss polar interactions; the interactions responsible for any observed selectivity in GC.

 

Identification of Pesticide Residues in Orange Essential Oils by GC/MS

Determining the presence of pesticide residues in essential oils is very important for ensuring their quality, especially because many essential oils are used in food, pharmaceutical and cosmetic industries.

 

Characterizing (bio-)Macromolecules Using Hyphenated and Comprehensively Coupled Gas Chromatography-Based Techniques

Polymers are important materials in modern life. Synthetic polymers are used for clothing, to provide housing and shelter, for packaging materials, biomedical implants etc.

 

GC Solutions #10: Basis of Interactions in Gas Chromatography – Part 3: Stationary Phase Selectivity, Glass Half Full?

In Part 3 we bring together the retention mechanism concepts discussed earlier to form a simple view of the nature of selectivity in liquid stationary phases used in gas chromatography.

 

GC Solutions #28: Why Don’t More People do Fast GC?

In this article I discuss the dichotomy between the often touted benefits of fast GC methods and the proportion of GC methods actually in use.

 

GC Solutions #31: Hydrogen vs. Helium as Carrier Gas – Hot Discussions

There has been a recent surge in discussions amongst gas chromatographers about switching from helium to hydrogen for carrier gas. Most GC manufacturers, column suppliers, and suppliers of bottled gases and/or gas generators have been feeding the discussions (mostly in a positive, informative way) through publications, webinars, and/or advertising pushes.  So what prompted the current fervor and where is it headed?

 

GC Solutions #32: Saturation of GC Detectors

I recently received a question relating to the saturation of GC detectors. The GC user was unsure of the causes of saturation, what effect saturation might have on analytical results, how to know when it is happening, and how to avoid it.

 

Ghost Peaks in Gas Chromatography Part I: The Carrier Gas and Carrier Gas Lines

We get always a number of inquiries from customers that see peaks show up in their chromatogram when they do not inject them. There are several sources for these “ghost peaks” which we will discuss in several articles.

 

Ghost Peaks in Gas Chromatography Part 2: The Injection Port

In last article we discussed the problem of “flash back”, which is a serious source for creating ghost peaks or “carryover”. It is important not to exceed the liner volume when the sample is introduced.

 

GC Solutions #29: How do I Determine Limits of Detection and Quantification?

I received this question from Ask the Doctor . “I am doing some research trying to quantify an illicit drug using external calibration and I was wondering if you could help me understand the best way I can obtain my limit of detection and quantification? I was unable to run blank samples. Is that the only way? Really confused.”