Static mode

Ions are also used to initiate secondary ion mass spectrometry (SIMS) [ ], as described in section BI.25.3. In SIMS, the ions sputtered from the surface are measured with a mass spectrometer. SIMS provides an accurate measure of the surface composition with extremely good sensitivity. SIMS can be collected in the static mode in which the surface is only minimally disrupted, or in the dynamic mode in which material is removed so that the composition can be detemiined as a fiinction of depth below the surface. SIMS has also been used along with a shadow and blocking cone analysis as a probe of surface structure [70]. 

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. 

TOF-SIMS was pioneered by Professor Benninghoven and his group in the early 1980s [109], originally developed in static mode and applied for the chemical analysis (elemental as well as molecular) of the uppermost monolayer of solid surfaces [110]. By the introduction and further development of the dual beam technique, the TOF-SIMS can... 

Long equilibrium time required (for static mode)... 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

Discussed earlier in the Ionization section, FAB was most commonly used in what was referred to as a static mode, in which the sample was dissolved in a suitable matrix and applied to a target that was inserted into the ion source using a probe. Once the analysis was complete (or the matrix evaporated or was sputtered away), the process was repeated as necessary. The initial FAB targets that supported the glycerol/sample droplet were solid, stainless surfaces. The earliest attempts at using FAB as an ionization mode for use in conjunction with HPLC introduced the eluent into the mass spectrometer by means of the probe that supported the target. The target was modified in order... 

PLE using methanol was applied for extraction of NP [48,49] and NPEO [49] from sediments. With 5-6 g sample, PLE was performed at 100-150°C, and 100-150 atm, with two static mode cycles [49] or one static and three dynamic cycles with subsequent elution [48]. Although... 

CORRECTION OF THE NON-MASS DEPENDENT INSTRUMENTAL BIAS IN STATIC MODE... 

The performance of the NIR analyzer in static mode is shown in Table 15.3. The use of second-derivative spectra in developing the identihcation method, along with the inclusion of sufficient diversity in color and construction, allowed for 100% accurate identihcation of unknown samples. 

A laboratory robot can operate unattended for 24 hours a day, releasing skilled technicians and scientists for more important and challenging work. Process workers can often be trained to bring the samples to the robot for analysis on a static mode operation. This provides valuable results with a fast timescale. 

Multi-collection mass spectrometers can analyze isotope ratios in a static mode to eliminate the errors from beam instability. However, the static multi-collection method depends on the extent to which the collectors (e.g., Faraday cups) are identical and to the extent to which the gain of each collector is stable. An alternative approach is to use the so-called dynamic multi-collector mode, to cancel out beam instability, detector bias, and performing a power-law mass fractionation correction. The following descriptions are modified from the Finnigan MAT 262 Operating manual (Finnigan, 1992). 

Blasco, L., Duracher, L., Forestier, J. P., Vian, L., and Marti-Mestres, G. (2006). Skin constituents as cosmetic ingredients. Part I A study of bio-mimetic monoglycerides behavior at the squalene-water interface by the pendant drop method in a static mode. J. Dispers. Sci. Technol. 27, 799-810. 

The scattered light intensity from a polymer solution arises from the fluctuations in both the solvent density and the polymer concentration. These fluctuations are considered as stable during the timescale of the measurement in the static mode of light scattering (for more details, see Evans (1972)). The light scattered from just the polymer (in excess of the light scattered from the pure solvent) is given by (Burchard, 1994)... 

Extractions can be carried out in dynamic, static, or combination modes. In the dynamic mode, the supercritical fluid continuously flows through the sample in the extraction vessel and out the restrictor to the trapping vessel. In the static mode, the supercritical fluid circulates in a loop containing the extraction vessel for some period of time before being released through the restrictor to the trapping vessel. In the combination mode, a static extraction is performed for some period of time, followed by a dynamic extraction. 

Static mode the sample (liquid or solid matrix) is placed in a glass phial capped with a septum such that the sample occupies only part of the phial s volume. After thermodynamic equilibrium between the phases has been reached (1/2 to 1 h), a sample of the vapour at equilibrium is taken (Fig. 20.4). Under these conditions, the quantity of each volatile compound present in the headspace above the sample is proportional to its concentration in the matrix. The relationship between the amount of sample injected into the gas chromatograph and its concentration in the matrix can be obtained by calibration (using internal or external standards). 

Figure 20.4—Static mode of headspace sample analysis. The sampling phial is pressurised with the carrier gas of the chromatograph. After equilibrium, a small volume of the gas containing the volatile compounds is inserted into a sample loop. Rotation of the six-way valve allows introduction of the sample into the injector of the chromatograph. Consequently, this set-up combines sample preparation with sample introduction into the chromatographic column. (Reproduced by permission of Tekmar.)...

Functionality. Surface affinity to different solutes is the most important characteristic of solid adsorbents. These affinities depend on the chemical functionality and the surface orientation of the polymer. Affinity can be estimated in the static mode by measuring adsorption isotherms for different organic solutes. 

TIMS analysis was performed on a fully automated VG Sector 54 mass spectrometer with eight adjustable faraday cups and a Daly ion-counting photomultiplier system. Analysis was performed in static mode. Each sample was analyzed 50 times to ensure acceptable precision. The TIMS analysis was standardized by use of the NIST SRM981 common lead standard. Multiple analyses of the SRM981 standard were used to determine a fractionation correction of 0.12% per amu and an overall error 0.06% per amu. Errors between runs of the same sample were below 0.01% per amu. This level of precision is comparable to the archaeometry database for lead isotopes (8). 

With the fundamental apparatus established, normal operation above 273 K proceeds in one of three static modes ... 

In addition, our design has eliminated the use of a restrictor. Restrictors are the most common means of controlling the pressure or density of a supercritical process. With no restriction, flow is dead-ended (i.e. restricted) via a switching valve in our invention. Supercritical fluid extractions are then conducted in a static mode (no flow). 

With the 12-vessel extractor, the 1/8" valve receives the extraction effluent from the vessels in tandem column selectors 1 and 2 (TCS-1 and TCS-2) into two separate ports 1 and 4 as shown in Figure 7. During the static mode, the counter-current valves, i.e. modifier pump valves (MP-3 and MP-4) are closed. Pressure build-up for static extraction then follows. Valves MP-3 and MP-4 are mounted close to the ports so that no accumulation of extract occurs. The valves are connected via a stainless steel tee (T2), to the modifier pump which is also used for flushing the lines after the extractions have been conducted. In the dynamic mode, extract flows from the unblocked ports of 1 and 4 to ports 5 and 6 then through to the delivery nozzles. 

Delivery of Extract Delivery Nozzle. Delivery of the extraction effluent is conducted via the six port static/dynamic valve while in the dynamic mode. Generally, extractions are conducted at a high density in the static mode. Once the extraction is complete, the valve is re-positioned into a dynamic evacuation, pressure or density is reduced rapidly to prevent significant losses of the supercritical fluid and the extraction effluent is transferred for collection. The extract leaves through the heated static/dynamic valve to the heated lines then to the delivery nozzle(s). Figure 8 shows a diagram of the delivery nozzle and its components. 

The premixed modifiers enter the extraction cell already in the CO2 fluid phase. The modifier stays in the fluid phase during the extraction, therefore has less interaction with the matrix itself compared to the liquid modifier being placed directly on the sample(70). This reduced interaction with the matrix is probably responsible for the lower recoveries. All of these experiments were done in a dynamic mode, the results might have been quite different if the experiments with the modified tanks were run in a static mode. Under static conditions the modified C02 would have a longer time to interact with the matrix and potentially produce higher recoveries. 

Extreme surface sensitivity for some elements (10 6 monolayer). Probing depth restricted to top monolayer in the nondestructive static mode. 

Sensitivity to First Monolayer Profiling Capability with Depth Possible Operation in Near Static Mode... 

To enhance extraction efficiency in the SME system (also called single-drop microextraction [SDME]), He and Lee developed a procedure termed liquid-phase microextraction (LPME),89 which, in its static mode, resembles the SME system. 

Determine the molecular masses of the alkylated peptide samples by nanoESI-MS in static mode using 2-p,L sample or by MALDI-MS using either CHCA matrix or DHB matrix (see Subheadings 3.2.1. and 3.2.2.),... 

Poole, J. C., McNeil, G. W., Langman, S. R., Dennis, F. (1997) Analysis of noble gases in water using a quadrupole mass spectrometer in static mode. Appl. Geochem., 12, 707-14. 

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