Analytical Instrument Documents

Fermenters used for home beer brewing are fitted with an airlock consisting of a liquid barrier that permits the fermentation gases to escape while preventing contamination from atmospheric microbes. Large volumes of carbon dioxide are produced during the most vigorous stages of fermentation, which can occur as early as the first 24 hour period after an ale yeast is added (pitched) to the sweet liquid (wort) produced from barley during the initial mashing step. The gases emitted from the airlock can have a pleasant aroma that can be quite distinctive during the initial stages of fermentation. Solid-phase microextraction (SPME) combined with gas chromatography/mass spectrometry (GC/MS) was used to determine the volatile components contained in the fermentation gas.

Electron ionization (EI), a hard-ionization technique that generates many fragment ions, is the most widely used ionization technique in gas chromatography–mass spectrometry (GC-MS). Since EI mass spectra have good reproducibility, qualitative analysis is possible by comparing an EI mass spectrum of a sample with that of the known compound recorded in the database. However, sometimes EI mass spectra lack molecular ions, which are of key importance to molecular-weight (MW) determination and correct compound assignment. Soft ionization is a useful way to determine MW. The JEOL JMS-Q1500GC offers two soft-ionization techniques: chemical ionization (CI) and photoionization (PI). In this application note, the MW information of diethyl phthalate and n-tetradecane were estimated from measurement results using both of these soft-ionization techniques.

The AccuTOF makes it very easy to obtain exact mass measurements and determine elemental compositions. The mass spectra shown below were acquired with the electrospray ion source operated in negative-ion mode. The mass calibration was acquired the previous day in positive-ion mode. After changing the mass spectrometer polarity and retuning, a stearic acid impurity (present in the methanol) was used as a single-point drift correction “lock mass” to determine the elemental composition of the analyte peak at m/z 256.06242 and the palmitic acid impurity at m/z 256.23104. The error was less than 0.002 u.

JEOL recently introduced a new-generation LC/TOFMS system (the “AccuTOF™”)with a wider dynamic range than conventional LC-TOF MS systems. The increased dynamic range of the AccuTOF provides qualitative and quantitative analysis with the increased accuracy and resolution of an LC/TOFMS system. While the AccuTOF preserves the benefits of TOF MS, such as high sensitivity, high resolution and high mass accuracy, it also features a durable orthogonal API source with long-term stability and easy maintenance. Here, we describe the features of the orthogonal API source. We also demonstrate the ability to operate the AccuTOF for an extended period in the presence of a nonvolatile phosphate buffer often used for LC Analysis.

Sudan dyes are red dyes that are used for coloring solvents, oils, waxes, petrol, and shoe and floor polishes. They are considered to be carcinogens and teratogens. Due to this fact, the US and the EU do not permit the use of these colors as food additives. However, in some countries, these dyes are still occasionally used in order to intensify the color of bell pepper and chili powders. Here, we describe a simple LC/TOF-MS method for sudan dyes I, II, III, and IV analysis.

It has been a decade since Dodonov and his colleagues [1] first announced the electrospray ionization time-of-flight mass spectrometer (ESI-TOF MS). Their initial findings have been enhanced by Standing and others [2,][ 3], and it has been recently reported that a large TOF MS system achieved a mass resolution exceeding 10,000 [4]. Encouraged by the results acquired by Dodonov and Standing, some of the MS manufactures have produced bench top ESI-TOF MS systems. However, most of these commercial models have a narrow dynamic range and are unfit to quantitative analysis because they use a TDC (Time-to-Digital Converter) as a data acquisition system. Their applications were mainly in qualitative analysis with exact mass measurement, and are limited in such fields as environmental studies and chemical dynamics that require only qualitative analysis. Because of detector saturation, these systems only show good mass acuracy when operated within a limited analyte concentration range.

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.