Application Notes: GC

The resolution, sensitivity, and mass accuracy of the Agilent 7200 GC/Q-TOF system provide rapid, simple, and reliable analysis of trace levels of sulfur compounds in coffee.

The automated derivatization of fatty acids (FAs) was performed with the Agilent 7696A Sample Prep WorkBench. Since free fatty acids show tailing in gas chromatography, transformation of fatty acids into fatty acid methyl esters (FAMEs) is widely used.

Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are fat-soluble, highly toxic, ubiquitous environmental contaminants found at trace levels in all foodstuffs and animal feed.

Most recently formulated pesticides are smaller in molecular weight and designed to break down rapidly in the environment.

SPME-GC–MS with on-column injection can be successfully employed for flavour profiling of food samples. The on-column injector of the GC-2010 can be used for SPME without any modifications, only an external ring adapter was used to facilitate the injection. The data can be compared with sensorial data of food.

The composition and analysis of fragrance components in home and personal care (HPC) products is very complex and unquestionably time consuming.

The QuEChERS method for pesticide analysis was first introduced by USDA scientists in 2003. The EN method 15662:2007 is a European variation to the QuEChERS method. The method uses acetonitrile extraction, followed by the salting out of water from the sample using anhydrous magnesium sulphate (MgSO4, NaCl and buffering citrate salts to induce liquid–liquid partitioning.

The separation of structurally diverse analytes is often complicated by chance coelutions with other analytes or with matrix related compounds. Often the column is blamed, but while such coelutions make analysis difficult they do not necessarily indicate a faulty column, poor chromatography or method design.

Trace-level chlorinated hydrocarbon analyses using methods such as U.S. EPA Method 551.1 are important tools for assessing organochlorine contamination in water. The wide diversity of target organochlorine compounds can prove chromatographically challenging due mainly to their high volatility and limited retention. This application note shows the benefits of using an Agilent J&W HP-1ms Ultra Inert Capillary GC column as the primary column for detection in this dual-column analysis.

Most U.S. Environmental Protection Agency (U.S. EPA) methods for analysis of volatile organic compounds (VOCs) specify purging with helium for 11 min at 40 mL/min, making purge-and-trap (P&T) one of the biggest consumers of helium in a laboratory. Compared to helium, nitrogen is abundant, inert, and can be purchased at affordable prices.

Over the past 15 years, little has changed for the commercial environmental laboratory's ability to automate U.S. EPA Method 8260 for water and soil purge and trap analysis. As work loads have increased, reporting levels have decreased due to MS sensitivity improvements. However, it has become increasingly difficult for laboratories to run at high levels of productivity due to autosampler reliability, carryover, and internal standard reproducibility challenges. Each of these issues has been addressed in a new Centurion WS autosampler (see Figure 1) designed specifically for the commercial environmental laboratory.

Illegal drug use worldwide is at an all time high. Forensic laboratories are seeing increased sample loads creating an immediate need for fast and accurate analysis to positively identify confiscated materials in criminal investigations. This application highlights the value of gas chromatography with time-of-flight mass spectrometry (GC-TOFMS) for drug testing in forensic laboratories. A method was developed to successfully identify twenty drugs of abuse in 4.5 min. This GC-TOFMS method shows good chromatographic peak shape for even the most challenging drug analytes; even the peak shapes for amphetamine and methamphetamine were exceptional considering they were analyzed underivatized. The total ion chromatogram (TIC) for the twenty drug analytes is shown in Figure 1.

Synthetic fused silica capillary tubing is a vital component in many scientific techniques. The general perception is that most laboratory glass products are fragile and easy to break. The opposite is true of fused silica capillary; with its protective coating it is both strong and durable when handled properly.

GC–MS method is presented for the quantitative determination and confirmation of melamine residues in milk products. The milk sample was cleaned up using Agilent's SampliQ SCX SPE cartridges before derivatization. The derived extracts were analysed by GC–MS with EI in synchronous SIM/scan mode on a Agilent J&W DB-5ms Ultra Inert column.

Thermal agility is a term that describes the ability of an oven to heat up and cool down. Both steps comprise the complete cycle time which, in turn, determines sample throughput. Fast GC accessories provide an attractive means of increasing sample throughput because they are easy to implement and deliver reliable performance at low cost. They require little or no bench space and do not incur additional costs for consumables and support equipment such as autosamplers, data acquisition software, and computers. Fast oven cooling is especially attractive because methods do not have to be re-validated since the separation parameters remain unchanged.

The Clean Air Act (CAA) (1) provides the U.S. Environmental Protection Agency authority to enforce regulations limiting emissions of volatile organic compounds (VOCs) and other air pollutants. The Compendium of Methods for the Determination of Toxic Compounds in Ambient Air includes a variety of sampling and analysis methods (2, 3), including use of single- and multi-sorbent tubes. Concentrating a large volume of sample onto a sorbent tube, followed by thermal desorption onto a GC column provides an efficient, cost-effective means of monitoring VOCs at parts per billion (ppb) or parts per trillion (ppt) levels.

Hydrogen, commonly used as a carrier gas instead of Helium for gas chromatography (GC) can be supplied via cylinders or by the electrolysis of water using an in-house generator containing metallic electrodes or an ionomeric membrane. An in-house generator can provide a significant increase in safety and convenience with a reduction in operating costs.

Melamine is an industrial chemical with a high nitrogen content that can cause kidney stones and lead to renal failure. In some instances, melamine has been added to baby formula and dairy products as a substitute for protein. This paper presents an efficient and definitive gas chromatography–mass spectrometry (GC–MS) method to identify melamine and related compounds based on the released US Food and Drug Administration (FDA) method.

This application details a fast, reliable and highly selective trace-level screening method for the quantification of polychlorinated biphenyls (PCBs) in environmental, food and biological samples, using gas chromatography and a triple stage quadrupole mass spectrometer. The analytical strategy is analogous to the well-established US Environmental Protection Agency (USEPA) Method 1668A.

QC test probes serve a vital function in ensuring the reproducibility of modern GC columns. These probes ensure that the columns have been properly deactivated, contain the correct amount of stationary phase, and have the same relative retention as the last column purchased. The choice of individual compounds in these test mixes varies widely and can have profound consequences on the performance of a column in the users' applications.

Synthetic fused silica capillary tubing is commonly used as the preferred substrate for chromatographic separation columns. In limited instances the absorption and diffusion of molecules into and through the fused silica deserves consideration.

Escalating costs and increasing demands for helium, coupled with diminishing helium supply, have given rise to the investigation and use of hydrogen as an alternate choice of carrier gas for use in gas chromatography (GC) applications. This application note illustrates that the use of hydrogen as a carrier gas as an alternative to helium in refinery gas applications is not only possible, but also results in improved performance and higher sample throughput.

Mycotoxins, toxic secondary metabolites of several fungal species, represent food safety issues of high concern. Deoxynivalenol, the most abundant trichothecene mycotoxin, can be found worldwide as a contaminant of wheat, barley, maize and other cereals (1,2). The transmission of deoxynivalenol from barley into beer has been reported in several studies (3,4). Therefore, its levels should be controlled.

Semivolatile analyses using methods similar to US EPA method 8270 (1) are important in environmental laboratories worldwide. A number of acidic compounds such as benzoic acid or 2,4-dinitrophenol and strong bases such as pyridine or benzidine are active species found in the semivolatile sample set. These highly polar species are particularly susceptible to adsorption into active surfaces in the sample flow path, including the column itself. System and column inertness are critical for effective analysis of these active chemical species.

Political priorities as well as economic interests have fueled a dramatic growth in the biofuel industry, due much in part to research funding and tax incentives. Currently the world's ethanol production is estimated to be over 16 billion gallons a year. This number is expected to increase in the next few years, reaching an estimated yearly production of 20 billion gallons by 2012. Today, many ethanol producers add fermentors to expand their production capacity. In order to continue using existing HPLC equipment for the increased monitoring, increased analytical throughput is needed.

Capillary flow technology (CFT) devices are microfluidic components that extend capillary GC capabilities through simple and robust connections between pressure/flow modules and columns. One of the most powerful and simple is the CFT Tee. This is especially useful in GC–MS analysis providing (1) rapid column and inlet maintenance without MSD venting and (2) the capability of rapidly removing late eluting interferences from the column by forcing their retreat into the injection port through "backflushing". Removing these interferences improves column and detector longevity and analytical integrity. Backflushing is very valuable for trace GC–MS analysis in samples from complex matrices like soil, foods or tissues. The CFT Tee uses pressure-pulsed injections and constant flow mode with minimal loss in the MS signal. This approach will be useful to all GC–MS users who want to improve their instrument uptime.

A new APCI/APLI source enables a high resolution TOF-MS to be coupled on LC and GC, thus increasing flexibility and performance of TOF-MS in combination with GC.

Synthetic fused silica capillary tubing has proven to be a vital component in many separation science techniques. Recently, it has expanded to serve an array of scientific markets. In most cases, an understanding of the internal surface chemistry is of fundamental importance.