Analytical Instrument Documents

Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) tend to produce mass spectra with minimal fragmentation. Positive-ion mass spectra are dominated by protonated molecules and cation attachment, while negative-ion mass spectra usually show molecular anions or ions produced by hydride abstraction. However, by varying the potentials in the atmospheric pressure interface, collision-induced dissociation (CID) can produce mass spectra with extensive fragmentation. This is sometimes referred to as “in-source CID”. Because the ionization process and ion energies are different for ESI or APCI compared to electron ionization (EI), the fragmentation is often different from the EI mass spectra in common mass spectral databases. Furthermore, the fragmentation pattern can vary depending on in-source CID conditions. This leads one to question whether there is any value to searching an EI mass spectral database for ESI or APCI mass spectra. The NIST 02 Mass Spectral Search software provides functions for a structure similarity search. This search can be used to search the library for compounds with similar structures based on neutral losses, which is a more suitable method for searching ESI or APCI mass spectra against the library. Compounds that have mass spectra in the library database can often be identified from the search results. The similarity search can provide structural information about compounds that do not have mass spectra in the library by displaying the structures of similar compounds identified by the search.

We have developed two new ion sources, the Dual ESI and Corona ESI, for the AccuTOF LC-TOF MS system that was introduced in the spring of 2002. The Dual ESI (Figure 1) provides two ESI (electrospray ionization) sprayers. This permits the introduction of a reference compound without disturbing or suppressing the spray of the analyte. In addition, the dual-probe system can be useful for high-throughput analysis. The Corona ESI ion source (Figure 2) is equipped with both an ESI sprayer and a corona-discharge electrode. The combination of ESI and APCI (atmospheric pressure chemical ionization) in a single source is useful for rapid analysis of unknown elements, and for improved efficiency in determining optimal analysis conditions. In addition, the orthogonal spray ion sources feature long-term stability and easy maintenance. For further details about the orthogonal-spray API source, refer to applications note MS-021024B.

Nanoelectrospray (nanoESI) has become a powerful tool in bioanalytics and is now used as a routine analytical method1. The advantages of nanoelectrospray as compared to conventional electrospray (ESI) include very low flow rate and more tolerance toward salt contamination in the analyte solution2. Thus, a few μL of analyte solution suffice for extended mass spectrometric studies. This applications report demonstrates the use of nanoESI for protein identification. A commercially available replication protein A3 is in-gel digested with trypsin and desalted with ZipTip C18 tip. The analysis is performed using nanoESI coupled with the AccuTOF™ time-of-flight MS system to obtain the peptide fingerprint followed by a database search with ProFound3 software.

Lysergic acid diethylamide (LSD) is a psychoactive drug with a long history of abuse. It is one of the most difficult drugs of abuse to detect in urine since the parent drug is excreted at very low concentration. Less than 1% of the ingested LSD dose is eliminated unchanged [1]. Analysis is further complicated because the isomeric compound iso-LSD, N-n-propylamide (LAMPA), which is itself a controlled drug, has a virtually identical mass spectrum [2]. Several GC/MS or GC/MS/MS methods have been developed for confirmation of LSD in urine, but a tedious and unstable derivatization procedure is required. The use of LC/MS for the analysis of LSD does not require derivatization of the analytes, thus simplifying the procedure. This application note demonstrates the feasibility by using the AccuTOF™ LC/MS for identification of LSD and related compounds. Additional method development and validation may be required for routine analysis.

Coldspray ionization (CSI) mass spectrometry (MS) has been developed and applied to characterize labile organometallic compounds. While conventional ESI is not applicable to those compounds because of their instability to heat and/or air, CSI affords multiply charged molecular ions with many solvents molecules attached. Here we describe the CSI method and its application to several labile organometallic compounds.

Time-of-flight mass spectrometry has the advantages of high resolution, high sensitivity, and high mass accuracy but with relatively narrow dynamic range if a TDC (Time-to-Digital Converter) is used as a data acquisition system. This disadvantage of narrow dynamic range hinders the applications for isotope ratio enrichment measurement. Recently, a new LC/TOF-MS system was introduced that achieved a wide dynamic range by using an ADC (Analog-to-Digital Converter) instead of a conventional TDC. We used this system to evaluate the measurement of phenylalanine (Phe) isotope ratio enrichment. The accuracy, reproducibility, and sensitivity for the method were determined. The method is simple, rapid, and accurate and presents an attractive alternative to traditional GC/MS applications.

Haloacetic acids (HAAs) are disinfection byproducts (DBPs) of the chlorination of drinking water. Dichloroacetic acid and trichloroacetic acid are animal carcinogens. We present an ion-pair HPLC and negative electrospray ionization mass spectrometry (ESI-MS) method with a “function-switching” feature for analysis of all 9 haloacetic acids, monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), monobromoacetic acid (MBAA), bromochloroacetic acid (BCAA), dibromoacetic acid (DBAA), bromodichloroacetic acid (BDCAA), trichloroacetic acid (TCAA), chlorodibromoacetic acid (CDBAA), and tribromoacetic acid (TBAA). JEOL MassCenter™ software can switch different MS settings by the time course. This “function-switching” feature enables each HAA to be analyzed under its optimized MS conditions so that the highest sensitivity can be achieved. Using triethylamine (TEA) as an ion-pairing reagent, a good HPLC separation of all 9 HAAs has been achieved. The optimized MS conditions for each HAA were evaluated.

Nano-LC/MS has demonstrated many advantages, including lower sample consumption, higher mass sensitivity and less matrix effect. Here, we introduce a very simple method to convert regular AccuTOF™ LC system into a nano-LC/MS system without high cost. An application of peptide analysis was used as an example to test the nano-LC/MS system. The RSD of retention time for gradient elution is less than 1%.

The JEOL AccuTOF™ LC/MS system offers easy exact-mass measurements and elemental composition determinations. A robust design and stable time-of-flight mass analyzer are combined with a detection system that provides high sensitivity and high dynamic range. Unlike other API/TOF mass spectrometer systems, the AccuTOF™ provides excellent linearity and mass accuracy over a wide range of analyte concentrations. To demonstrate the potential of the AccuTOF™ for automated exact mass measurements, a variety of small-molecule drug samples were measured by using a macro that allows the user to submit samples for unattended elemental composition determinations. Samples were introduced by using the LC autosampler. The macro applied an automatic drift (“lock mass”) correction to the reserpine reference standard and printed out elemental compositions for user-specified elemental limits. The results show high accuracy and stability regardless of sample concentration.

The AccuTOF™ high-resolution time-of-flight mass spectrometer provides powerful qualitative and quantitative tools that can be applied to HPLC/MS analysis of polyphenols and other compounds in tea. The combination of high-pressure liquid chromatography (HPLC) with high-resolution time-of-flight mass spectrometry (TOFMS) provides powerful capabilities for chemical analysis. HPLC with UV detection relies on wavelength and retention time for peak identification. Here we show how the AccuTOF™ TOFMS with its unique high dynamic range detection system can be used to determine polyphenols (such as catechins), caffeine and related compounds, amino acids, and vitamins in different teas.


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