Atmospheric pressure ionization mass spectrometry techniques for the analysis of alkyl ethoxysulfate mixtures.

This paper compares two liquid introduction atmospheric pressure ionization techniques for the analysis of alkyl ethoxysulfate (AES) anionic surfactant mixtures by mass spectrometry, i. e., electrospray ionization (ESI) in both positive and negative ion modes and atmospheric pressure chemical ionization (APCI) in positive ion mode, using a triple quadrupole mass spectrometer. Two ions are observed in ESI(+) for each individual AES component, [M + Na](+) and a "desulfated" ion [M - SO3 + H](+), whereas only one ion, [M - Na](-) is observed for each AES component in ESI(-). APCI(+) produces a protonated, "desulfated" ion of the form [M - NaSO3 + 2H](+) for each AES species in the mixture under low cone voltage (10 V) conditions. The mass spectral ion intensities of the individual AES components in either the series from ESI(+) or APCI(+) can be used to obtain an estimate of their relative concentrations in the mixture and of the average ethoxylate (EO) number of the sample. The precursor ions produced by either ESI(+) or ESI(-), when subjected to low-energy (50 eV) collision-induced dissociation, do not fragment to give ions that provide much structural information. The protonated, desulfated ions produced by APCI(+) form fragment ions which reveal structural information about the precursor ions, including alkyl chain length and EO number, under similar conditions. APCI(+) is less susceptible to matrix effects for quantitative work than ESI(+). Thus APCI(+) provides an additional tool for the analysis of anionic surfactants such as AES, especially in complex mixtures where tandem mass spectrometry is required for the identification of the individual components.

Development of electrophoretic conditions for the characterization of protein glycoforms by capillary electrophoresis-electrospray mass spectrometry.

A capillary electrophoresis (CE) method using acidic buffers and capillaries coated with Polybrene, a cationic polymer has been developed for the separation of glycoproteins and glycopeptides. Electrophoretic conditions have been optimized to provide resolution of individual glycoforms observed for different glycoprotein preparations. These conditions were found to be entirely compatible with the operation of electrospray mass spectrometry (ESMS), which facilitated the assignments of possible carbohydrate compositions of glycopeptides arising from digests of glycoproteins. By using operating conditions enhanced the formation of oxonium fragment ions prior to mass spectral analysis, selective identification of glycopeptides was achieved for complex samples such as those from proteolytic digests or chemical cleavages. Examples of applications are presented for ribonuclease B, ovalbumin, horseradish peroxidase, and a lectin from Erithrina corallodendron using both CE-ESMS and CE with ultraviolet detection (CE-UV).

Use of a moving-belt interface for on-line high-performance liquid chromatography/mass spectrometry characterization of polycyclic aromatic compounds of molecular weight up to 580 Da in environmental samples.

The applicability of the moving belt high-performance liquid chromatography/mass spectrometry (HPLC/MS) interface to the analysis of high molecular weight polycyclic aromatic compounds (PACs) in a complex sample derived from coal tar is investigated. This interface provides good preservation of chromatographic integrity and useful electron ionization spectra of thermally stable PACs of low to moderate volatility up to molecular masses of at least 580 Da. It is concluded that this HPLC/MS technique will be useful in the analysis of such complex samples, provided a large enough suite of standard compounds can be made available.

Digital laser Raman spectrometer system with on-line computer control of data acquisition and reduction.

An interface for coupling a laser Raman spectrometer employing photon counting detection to an on-line programmable calculator or minicomputer is described. The resulting system provides both background and spectral data in digital form that allows data manipulation to be easily performed. In addition online computer control allows the enhancement of the signal-to-noise ratio by signal averaging. The spectrum of gaseous N(2) and O(2) taken with the system illustrates the capability of the interface and computer when coupled with the spectrometer to make precise and sensitive measurements.