SIMS detection limits Table

Table 7.2 Comparison of SIM detection limits in ng (quantitation ion) of some carbamates [11] ...

SALI compares fiivorably with other major surface analytical techniques in terms of sensitivity and spatial resolution. Its major advantj e is the combination of analytical versatility, ease of quantification, and sensitivity. Table 1 compares the analytical characteristics of SALI to four major surfiice spectroscopic techniques.These techniques can also be categorized by the chemical information they provide. Both SALI and SIMS (static mode only) can provide molecular fingerprint information via mass spectra that give mass peaks corresponding to structural units of the molecule, while XPS provides only short-range chemical information. XPS and static SIMS are often used to complement each other since XPS chemical speciation information is semiquantitative however, SALI molecular information can potentially be quantified direedy without correlation with another surface spectroscopic technique. AES and Rutherford Backscattering (RBS) provide primarily elemental information, and therefore yield litde structural informadon. The common detection limit refers to the sensitivity for nearly all elements that these techniques enjoy. 

The advantages of SIMS are its high sensitivity (detection limit of ppms for certain elements), its ability to detect hydrogen and the emission of molecular fragments that often bear tractable relationships with the parent structure on the surface. Disadvantages are that secondary ion formation is a poorly understood phenomenon and that quantification is often difficult. A major drawback is the matrix effect secondary ion yields of one element can vary tremendously with chemical environment. This matrix effect and the elemental sensitivity variation of five orders of magmtude across the periodic table make quantitative interpretation of SIMS spectra oftechmcal catalysts extremely difficult. 

Table 3.1.10 (continued) Reference ranges of organic acids and acylglycines in urine in children of different ages. Values are presented as mmol/mol creatinine. TIC average detection limit 0.1 mmol/mol creatinine SIM average detection limit (with stable-isotope-labeled internal standard 0.01 mmol/mol creatinine. Reproduced from reference [32], with permission. nd Not detected... 

As a surface analytical tool, SIMS has several advantages over X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). SIMS is sensitive to all elements and isotopes in the periodic table, whereas XPS and AES cannot detect H and He. SIMS also has a lower detection limit of 10 5 atomic percent (at.S) compared to 0.1 at.S and 1.0 at.% for AES and XPS, respectively. However, SIMS has several disadvantages. Its elemental sensitivity varies over five orders of magnitude and differs for a given element in different sample matrices, i.e., SIMS shows a strong matrix effect. This matrix effect makes SIMS measurements difficult to quantify. Recent progress, however, has been made especially in the development of quantitative models for the analysis of semiconductors [3-5]. 

A comparison of various LC-MS interfaces in the analysis of carbofuran was reported by Honing et al. [10], The progress in LC-MS interface performance can be read from a comparison of absolute detection limits in selected-ion monitoring (SIM) of three representative carbamates, as collected by Pleasance et al. [11], using data from various other authors as well (see Table 7.2). 

SIMS Is more sensitive than the other common surface or Interface analysis techniques of Auger X-ray Photoelectron Spectroscopy Rutherford BackscatterIng Spectroscopy or Energy Dispersive X-ray Analysis. Detection limits and background signal levels for a large number of semiconductor materials have been reported under typical operating conditions (Ji). Table I lists the detection limits for a number of dopants used In semiconductors obtained under optimized conditions. 

Figure 7-9 shows the ion sets in single-ion monitoring (SIM) for the determination of the detection limits. A bovine blood was spiked with the unlabeled and the deuterated compounds in the concentrations shown in Table 7-1 derivatized with PFP. 

Quantitative analyses of trace oxygenated compounds with a detection limit of 1 or 10 ppm in jet fuel derived from coal liquids with GC-MS had been reported in 1988 [31], A Hewlett-Packard model 5988 GC-MS equipped with a 60-m DB-5 capillary column (250-pm i.d., 0.25-pm film thickness) was used, and two methods were applied in the GC-MS analyses. In method 1,20-nL neat sample of each fuel was injected with a split ratio of 1 50, and selected ion monitoring (SIM) was used to selectively detect each of the oxygenated standards as shown in Table 32.6. Two mass ions characteristic of each of the standard oxygenates were monitored at appropriate time intervals. Petroleum-derived JP-8 was used to prepare standard concentrations of oxygenates, because no oxygenated compounds were detected in it. Standards in petroleum-derived JP-8 were prepared at 100, 10, and 1 ppm (wt/wt) concentrations. Each standard solution... 

When comparing samples A, B and C, simple signatures of the molecules such as fluorine, CF3 among others, should allow one to test easily the efficiency of their immobilization on PS with XPS and ToF-SIMS. Table 2 illustrates the case of lactose aryl diazirine. The residual level of molecules observed on sample B by ToF-SIMS was below the XPS instrument detection limit. It confirms that the washing procedure was able to remove physlsorbed molecules. For sample C, after washing, covalently attached molecules were expected to remain bound to the surface, in contrast with sample B [94,96). XPS fluorine atomic percentage, as well as CF3 and F normalized intensities (Table 2), illustrate in the same way the successful immobilization of the molecule at the surface of polystyrene. These results are... 

Table 4.11 compares SIMS and SNMS (cfr. also Table 8.57 of ref. [110a]). Detection limits in the sub-ppm range are accessible under optimised analytical conditions. A lateral resolution of less than 100 nm and an in-depth resolution of a few nm can be achieved. One of the unique features of SNMS is the ease of analysis of insulators. This is at variance to SSMS, GD-MS and SIMS, which are handicapped by electrical charging effects. Laser SNMS is not strictly restricted to elemental analysis, but can also be applied to the characterisation of molecular surfaces. For an optimum yield of intact molecular ions and characteristic fragments it is necessary to optimise laser power density, wavelength, and pulse width [112],... 

A summary of some selected literature data is provided in Table 3, where some HRGC-ECNI-MS methods in SIM mode are given. Detection limits for the individual congeners (Parlar No. 26,50, and 62] between 0.3 and 7 pg injected are achieved and a wide range of toxaphene concentrations in environmental and biological samples is found. Some authors used the technical toxaphene as standard to estimate total concentration [58,90-92]. Recently, the individual determinations of Parlar No. 26 and 50 for marine mammals [63,88] and Parlar No. 26, 50, and 62 for fish and fish products [42,63,64,70] have been used as indicators of the level of toxaphene contamination. 

In the use of conventional mass spectrometers (beam instruments), the detection limit in the full scan mode is insufficient for trace analysis because the analyser only has a very short dwell time per ion available during the scan. Additional sensitivity is achieved by sharing the same dwell time between a few selected ions only by means of individual mass recording (SIM, MID) (Table 2.53 and Figure 2.221). 

The QIT has a commercial mass range typically from 50-2000 Th, although some manufacturers provide two or three mass ranges up to 4000 Th. Scan rates vary from 500 Th/s to 27,000 Th/s and allow for resolution specifications of up to 5000. The typical mass accuracy is 50 ppm to 100 ppm at m/z 1000. Detection limits can be at the attomole level. Scan modes include the full scan, SIM, SRM, rapid high sensitivity and high resolution, and MS". Some QITs have a high charge capacity, which has increased the sensitivity by 10-fold. See Table 9.A in the Appendix. 

Detection limits of analytes measured in ESI and MALDI using the mass analyzers covered in this chapter are quite noteworthy. Table 9.3 lists detection limits for various molecules analyzed by LC, CE, and EIA coupled to ESI QIT, LQIT, and the orbitrap or with the use of MALDI. The lowest limits of detection are measured when an isolation step is used to accumulate and/or isolate only the ion(s) of interest. For example, in Table 9.3, the detection limits for reserpine in SIM and SRM scan modes are better than in the full-scan mode. Although ion trap full MS scans have a higher duty cycle over QMF ion beam instruments, detection limits can be reduced in the full-scan MS mode due to matrix effects. In this latter case, at low analyte amounts, the QIT is filled up primarily with unwanted matrix ions, leaving little space to store the ions of interest. The advantage of the high-charge-capacity... 

The limitations of SIMS - some inherent in secondary ion formation, some because of the physics of ion beams, and some because of the nature of sputtering - have been mentioned in Sect. 3.1. Sputtering produces predominantly neutral atoms for most of the elements in the periodic table the typical secondary ion yield is between 10 and 10 . This leads to a serious sensitivity limitation when extremely small volumes must be probed, or when high lateral and depth resolution analyses are needed. Another problem arises because the secondary ion yield can vary by many orders of magnitude as a function of surface contamination and matrix composition this hampers quantification. Quantification can also be hampered by interferences from molecules, molecular fragments, and isotopes of other elements with the same mass as the analyte. Very high mass-resolution can reject such interferences but only at the expense of detection sensitivity. 

Tables 6.27 and 6.31 show the main characteristics of ToF-MS. ToF-MS shows an optimum combination of resolution and sensitivity. ToF-MS instruments provide up to 40000 spectra s-1, a mass range exceeding 100000 (in principle unlimited), a resolution of 5000, and peak widths as short as 200 ms. This is better than quadruples and most ion traps can handle. Unlike the quadrupole-type instrument, the detector is detecting every introduced ion (high duty factor). This leads to a 20- to 100-times increase in sensitivity, compared to QMS used in scan mode. The mass range increases quadratically with the time range that is recorded. Only the ion source and detector impose the limits on the mass range. Mass accuracy in ToF-MS is sufficient to gain access to the elemental composition of a molecule. A single point is sufficient for the mass calibration of the instrument. ToF mass spectra are commonly calibrated using two known species, aluminium (27 Da) and coronene (300 Da). ToF is well established in combination with quite different ion sources like in SIMS, MALDI and ESI.

Numerous publications in earlier years dealing with the kinetics of this reaction were limited by the analytical determination in ECH concentration ranges of 0.01-0.2 mol/l. The control of these residual monomers, however, requires methods and knowledge of the reaction process in the trace amount concentration region of approximately 1 10"6 mol/l for pH values from 2 to 12. Combined GC/MS using headspace and SIM techniques allows the quantitative determination of ECH at a limit of detection of 0.5 10 6 mol/l (40 ppb ECH in aqueous solution). Values obtained for halflife times 11/2 of the hydrolysis using this method are given in Table 10-6. 

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