Analytical Instrument Documents

Recently, matrix assisted laser desorption/ionization (MALDI) imaging techniques have been developed for biological sciences to evaluate and understand the distribution of various chemicals on biological surfaces. In particular, this technique provides useful visual information about the locations of specific chemicals on surfaces. In this work, we explored the use of laser desorption/ionization (LDI) imaging for forensically applicable samples such as a handwriting sample with a ballpoint ink. These measurements were done using a spiral-trajectory ion optics time-of-flight mass spectrometer (SpiralTOF-MS). This TOF system has a 17m flight path that provides high resolution capabilities even down into the lower m/z region. Additionally, we looked at the SEM/EDS imaging using the JEOL JSM-6510LV scanning electron microscope.

Industrial materials are often evaluated by surface analysis instruments that provide information on surface elements, bonding states, and functional groups. However, there are limited options for surface analysis techniques that provide molecular weight and molecular structure information for organic compounds present on surfaces. Matrix Assisted Laser Desorption Ionization - Time of Flight Mass Spectrometry (MALDI-TOFMS) is a soft ionization technique that can be used to analyze surfaces in order to estimate elemental compositions with accurate mass measurements, obtain structural information by using MS/MS, and map surface compounds by using MS imaging. MALDI-TOFMS uses a high voltage on the target plate to accelerate the ions into the TOFMS analyzer. Therefore, the target plates are conductive and are typically made of stainless steel. MALDI imaging mass spectrometry is widely used for analyzing organic substances on frozen tissue sections. In this case, a frozen tissue section with a thickness of about 10 μm is placed on a conductive glass slide coated with an indium tin oxide (ITO) film. However, for the analysis of industrial products, the target organic compounds are on nonconductive substrates such as resins with millimeter thicknesses. MALDI-TOFMS surface measurements using nonconductive substrates lead to a reduction in mass resolution and a significant decrease in ion intensity due to surface charging. This problem can be solved by pretreating the surface with gold vapor deposition in order to change it from nonconductive to conductive. This method was previously shown to work well in MSTips No. 204 in which the gold vapor deposition method was applied to the MALDI-MS imaging analysis of inks on paper. In this report, we used gold vapor deposition to look at samples on the surface of a 1 mm thick acrylic plate.

Biological markers (biomarkers) are compounds such as terpanes, steranes, and steroids that are derived from organisms present in the original biomass from which organic-rich sediments and oils were formed. These compounds can be measured in both oils and source rock bitumens, and they can be used to establish a correlation between an oil sample and the original petroleum source rock. Combined gas chromatography / mass spectrometry (GC/MS) can be used to analyze for biomarkers in oil samples. However, there are numerous interferences present that have the same integer mass as biomarkers, but different elemental compositions. Because these isobaric compounds have different exact masses than the biomarkers, the interferences can be separated by high-resolution mass spectrometry. Some examples of compounds that interfere with the detection of biomarkers are given in Table I.

Most familiar applications of high resolution mass spectrometry relate to exact mass measurements for elemental composition determination of compounds such as natural products, environmental contaminants, petrochemicals and synthetic organic compounds. However, high resolution can also be useful at the very low end of the mass scale for monitoring gases and isotopes. The GCmate has a mass range that extends as low as m/z 1 and as high as m/z 3000 (at reduced accelerating voltage) and is capable of a resolving power up to 5,000. This is more than sufficient for analyzing low-mass species such as CO and N2 as well as H+, D+, H2+, HD+ etc. The example shown above was obtained by monitoring H2+ (m/z 2.01565) and D+ (m/z 2.0141) from a mixture of D2O and H2O at a resolving power of 3400. The difference in mass between these two species is only 0.00155 u.

A few needles from the holiday tree in the lobby of our Peabody office were extracted with dichloromethane and analyzed with the JEOL GCmate GC/MS system. Components were identified by a library search of the mass spectra. The fragrance comes from a complex mixture of terpenes such as alpha-pinene (familiar pine aroma) and limonene (citrus aroma) and other compounds, such as maltol (fresh-baked bread aroma).

The GCmate and LCmate benchtop mass spectrometers can be fitted with an optional fast atom bombardment (FAB) ion source that provides a means for rapid and convenient analysis of polar or thermally labile molecules. The FAB source can be operated in positive and negative-ion mode, and it can be used for high-resolution or MS/MS measurements (with the linked scan MS/MS option). The LCmate can be fitted with an optional frit-FAB LC/MS interface, and an auto-probe has also been developed that can allow unattended analysis of up to 40 direct-probe FAB samples at a time. Some examples of FAB analysis with GCmate are shown here.

A high chemical background or the continuous introduction of a reference compound can make it difficult to locate and identify trace components in a total ion current chromatogram in a GC/MS or LC/MS experiment. The Shrader System for Windows™ software1 available with the JEOL GCmate, LCmate, and RSVP mass spectrometers provides a solution to this problem based on the Component Detection Algorithm (CODA), developed by Windig et. al.2 The CODA algorithm identifies significant peaks by comparing a smoothed, mean-subtracted reconstructed ion chromatogram (RIC) with the original RIC.

Solid-phase microextraction (SPME) is a convenient sample preparation method for extracting organic compounds from aqueous samples. The combination of SPME with gas chromatography and high-resolution mass spectrometry provides powerful capabilities for the analysis of alcoholic beverages. Two samples of Scotch whiskey and one tequila sample were sampled by using solid-phase microextraction for analysis by high-resolution GC/MS. Sample 1 was a blended 12-year old light Scotch whiskey, while sample 2 was a 12-year old single-malt light Scotch whiskey. The tequila sample was a popular brand that is widely sold in the USA. Compounds were extracted and identified by GC/MS with library search. Exact mass measurements provided elemental compositions for molecular ions and fragment ions.

Polychlorinated biphenyl’s (PCBs) have been in use in industry since the early 1900's. These compounds are relatively stable and have properties have led to their use in a variety of applications ranging from electrical insulators to flame retardants. Exposure to PCBs can cause irritation, acne, and rashes. PCBs have demonstrated carcinogenic activity in animal studies. Because of potentially adverse health effects, PCB manufacture was banned in the United States in the 1970's. Because of their stability, PCBs resist degradation and can accumulate in the environment. Quantities of PCBs also exist in transformers and capacitors and hazardous waste sites. Their volatility and thermal stability make PCBs suitable for analysis by GC/MS methods. However, lowresolution mass selected-ion monitoring (LRSIM) is not selective enough to unequivocally identify PCBs in complex mixtures. High-resolution SIM (HRSIM), available with the JEOL GCmate, provides additional selectivity which can greatly simplify the identification of PCBs in complex mixtures and environmental samples.

The Japanese government, through various guidelines and the JIS standard, regulates analytical methods for dioxins from preliminary treatment to data acquisition to data processing. The guidelines specify a high resolution gas chromatograph – high resolution mass spectrometer system (HRGC/HRMS) as a final analytical instrument and a resolution of 10,000 for the mass spectrometer. These methods, however, are quite costly if executed as the government recommends. Since the Law Concerning Special Measures Against Dioxins went into effect in January 2000, dioxin samples to be analyzed are expected to multiply in a few years to come. Researchers are concerned that the high cost of analysis per sample will affect the scope and quality of their studies. As a result, simplified methods for dioxin analysis are in dire need to streamline the analytical process and reduce the cost.


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