Contaminants, laser probe

Single-step LDI/FTMS was used in the analysis of the source and chemical identity of chro-mophores present in PE lamination [216]. The technique allowed both sampling the surface and depthprofiling with high spatial resolution and accurate mass determination. Also laser-induced thermal desorption FTMS of multilayer thin films of a computer hard disk has been reported [217]. LD-FTMS could be used for the identification of fluorinated lubricants on magnetic storage media [188]. Laser Probe FTMS analysis may also probe surface and interstitial contaminants. 

The laser-based methods discussed thus far can be used to probe surface and interstitial contaminants as well as for the direct determination of additives in a complex matrix. It is now common to have a CCD camera and video display that gives a microscopic view of the sample when it is in the mass spectrometer. This allows contaminants, defects, and areas of interest to be observed and manipulated while under the probing beW of the laser (25). A number of industrial examples have I ved that direct Laser Probe FT/MS analyses can rapidly determine many additives directly, even when the combination of laborious classical wet chemical techniques with other modem instrumental methods have proved difficult and time consuming. 

MALDI/TOF provides cost-effective measurements for low molecular weights (less than 100 Daltons) to over 250,0(X) Daltons. Today, the Laser Probe FT S technique can provide accurate molecular weight information for polymers that are less than 20,000 Daltons. Additionally, the FT/MS has features that allow molecular structures and substmctures of most classes of polymers to be probed. These mass spectrometry techniques are also directly applicable to contaminant and additive analysis. 

Laser ionization mass spectrometry or laser microprobing (LIMS) is a microanalyt-ical technique used to rapidly characterize the elemental and, sometimes, molecular composition of materials. It is based on the ability of short high-power laser pulses (-10 ns) to produce ions from solids. The ions formed in these brief pulses are analyzed using a time-of-flight mass spectrometer. The quasi-simultaneous collection of all ion masses allows the survey analysis of unknown materials. The main applications of LIMS are in failure analysis, where chemical differences between a contaminated sample and a control need to be rapidly assessed. The ability to focus the laser beam to a diameter of approximately 1 mm permits the application of this technique to the characterization of small features, for example, in integrated circuits. The LIMS detection limits for many elements are close to 10 at/cm, which makes this technique considerably more sensitive than other survey microan-alytical techniques, such as Auger Electron Spectroscopy (AES) or Electron Probe Microanalysis (EPMA). Additionally, LIMS can be used to analyze insulating sam-... 

On-probe purification using derivatized MALDI probe surfaces has been described to simplify the sample preparation process. Various developments in this field have allowed the introduction of new techniques such as the surface-enhanced laser desorption ionization (SELDI) [42], The surface of the probe plays an active role in binding the analyte by hydrophobic or electrostatic interactions, while contaminants are rinsed away. In the same way, this technique uses targets with covalently coupled antibodies directed against a protein, allowing its purification from biological samples as urine or plasma. Subsequent addition of a droplet of matrix solution allows MALDI analysis. 

We have developed an analogous, but more robust system which is not necessarily constraint by the aforementioned limitations. The obvious extension has been to couple an affinity-based separation with mass spectrometry. Hutchens et al. have shown that affinity probe surfaces can be ust to capture specific protein ligands allowing detection by laser desorption mass spectrometry (. The limitations to their technique have been that the surface area for ligand capture is quite small and salt (or detergent) contaminants are still problematic. Perfusive affinity resins, on the other hand, provide a tremendous surface area for binding. The nature and composition of the solvents required for affinity chromatography, however, are not directly compatible with mass spectrometric analysis. 

Fluorescein structural formula and molecular model. This strongly fluorescent dye has many applications. It is widely used to study retinal circulation and various diseases involving the retina. The technique is known as fluoi escein angiography. Fluorescein can be bound to DNA and other proteins and its fluorescence used as a probe of these molecules and their interactions. Fluorescein is also used for water tracing to provide information on the contamination of underground wells. In addition, it has been used as a laser dye. 

Also the contamination of soil by oil or other toxic material can be probed either by LIBS or by laser-induced fluorescence. 

Surface enhanced laser desorption/ionization (SELDI) SELDI is a variant of MALDI in which the MALDI probe is derivatized with various substances that have affinity for the analyte. The probes are then used to extract the analyte directly from mixtures thus avoiding sample loss through more complicated cleanup procedures. Contaminants can... 

Surface enhanced laser desorption/ionization (SE-LDI) is a variant of MALDI in which the MALDI probe is derivatized with various substances that have affinity for the analyte. The probes are then used to extract the analyte directly from mixtures thus avoiding sample loss through more complicated procedures such as column chromatography. Contaminants can be washed from the probe with appropriate buffers or solvents leaving the purified analyte ready for analysis. Many adsorbents have been used typical examples are hydrophobic or ionic compounds, enzymes, various receptors, antibodies, and nucleic acids. Although most applications have been reported with proteins, the technique is potentially applicable to any type of compound for which a specific adsorbent can be attached to the probe. 

The SWNTs produced by laser-vaporization and arc discharge are usually capped by fullerene-like structures. Those from catalytic decomposition are usually capped by metal particles. Ye et al. (1999) and Dillon et al. (2000) both used ultrasonication to open the tubes. In the work of Dillon et al. (2000), it was reported that by using the ultrasonic probe of Ti-alloy (with 9 wt % Ti, 6 wt % Al, and 4 wt % V), the alloy (T1AI0.1V0.04) was incorporated into the SWNTs as contamination. The maximum adsorption capacity was 7 wt %, and upon TPD, two desorption peaks occurred approximately 2.5% evolved at 300 K, while the remainder evolved between 475-850 K. It was suspected that the alloy contaminant acted as a catalyst that stimulated the adsorption and desorption. This... 

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