Time-array detection

Arataev, V. B. Burrill, P. H. McNitt, K. L. Schmitz, D. A. Enke, C. G. Holland, J. F. High-Speed GC/MS Analysis of Complex Mixtures Using Time-of-Flight Mass Spectrometry with Time-Array Detection. Poster TP 186 presented at the 42nd ASMS Conference on Mass Spectrometry and Allied Topics, Chicago, Illinois, May 29 - June 3, 1994. 

There has been a considerable decline in the number of papers which deal with the details of techniques of measurement of fluorescence decay. This is no doubt due to the fact that the alternative methods are now essentially well established. Nevertheless a microcomputerized ultrahigh speed transient digitizer and luminescence lifeline instrument has been described . A very useful multiplexed array fluorometer allows simultaneous fluorescence decay at different emission wavelength using single photon timing array detection . Data collection rates could approach that for a repetitive laser pulse system and the technique could be usefully applied to HPLC or microscopy. The power of this equipment has been exemplified by studies on aminotetraphenylporphyrins at emission wavelengths up to 680 nm. The use and performance of the delta function convolution method for the estimation of fluorescence decay parameters has been... 

Time-Slice Vs.Time-Array Detection. Holland et al. have referred to this method of data collection as time-slice recordinj. It is shown schematically in... 

FIGURE 2.11 Comparison of time-slice detection and time-array detection. (Reprinted with permission from reference 10). 

C. G. Enke, J. T. Watson, J. AUison, and J. F. Holland, Analysis of data rate requirements for high performance GC/MS the case for TOFMS with time-array detection, Proc. 37th ASMS Conf. Mass Spectrometry and Allied Topics, Miami Beach, Florida, May 21-26, 1989. 

B. D. Gardner and J. F. Holland, High speed, high throughput GC-MS using time-of-flight mass spectrometry with time array detection, Proc. of 44th ASMS Conf. On Mass Spectrometry and AUied Topics, Portland, OR, May 12-16, 1996. 

Where space is not a problem, a linear electron multiplier having separate dynodes to collect and amplify the electron current created each time an ion enters its open end can be used. (See Chapter 28 for details on electron multipliers.) For array detection, the individual electron multipliers must be very small, so they can be packed side by side into as small a space as possible. For this reason, the design of an element of an array is significantly different from that of a standard electron multiplier used for point ion collection, even though its method of working is similar. Figure 29.2a shows an electron multiplier (also known as a Channeltron ) that works without using separate dynodes. It can be used to replace a dynode-type multiplier for point ion collection but, because... 

An array ion collector (detector) consists of a large number of miniature electron multiplier elements arranged side by side along a plane. Point ion collectors gather and detect ions sequentially (all ions are focused at one point one after another), but array collectors gather and detect all ions simultaneously (all ions are focused onto the array elements at the same time). Array detectors are particularly useful for situations in which ionization occurs within a very short space of time, as with some ionization sources, or in which only trace quantities of a substance are available. For these very short time scales, only the array collector can measure a whole spectrum or part of a spectrum satisfactorily in the time available. 

A second use of arrays arises in the detection of trace components of material introduced into a mass spectrometer. For such very small quantities, it may well be that, by the time a scan has been carried out by a mass spectrometer with a point ion collector, the tiny amount of substance may have disappeared before the scan has been completed. An array collector overcomes this problem. Often, the problem of detecting trace amounts of a substance using a point ion collector is overcome by measuring not the whole mass spectrum but only one characteristic m/z value (single ion monitoring or single ion detection). However, unlike array detection, this single-ion detection method does not provide the whole spectrum, and an identification based on only one m/z value may well be open to misinterpretation and error. 

NOTE HPLC detection of test drugs at 200 nm UV. Peak are named for the drugs they represent. Peak identity was discerned by analyzing each dmg individually and observing its retention time and UV spectrum by photodiode array detection between 190 and 360 nm using a Waters Model 990 PDA detector. Retention times are listed in the text. 

A polyethylene-coated (PEE) silica column was used with water-methanol eluents to achieve the separation and retention of 27 pesticides.40 The retention times of 33 commercial pesticides were determined on an octadecyl (ODS)-derivatized alumina column using water-methanol eluents and compared with retention properties on an ODS-silica column packing.41 More recently, RP-HPLC was used in combination with diode array detection for the identification and quantification of 77 pesticides (acidic, basic, and neutral) in groundwater samples.42... 

Cornish,T. J. Antoine, M. Ecelberger, S. A. Demirev, P. A. Arrayed time-of-flight mass spectrometry for time-critical detection of hazardous agents. Anal. Chem. 2005, 77, 3954-3959. 

Multiple mass analyzers exist that can perform tandem mass spectrometry. Some use a tandem-in-space configuration, such as the triple quadrupole mass analyzers illustrated (Fig.3.9). Others use a tandem-in-time configuration and include instruments such as ion-traps (ITMS) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS or FTMS). A triple quadrupole mass spectrometer can only perform the tandem process once for an isolated precursor ion (e.g., MS/MS), but trapping or tandem-in-time instruments can perform repetitive tandem mass spectrometry (MS ), thus adding n 1 degrees of structural characterization and elucidation. When an ion-trap is combined with HPLC and photodiode array detection, the net result is a profiling tool that is a powerful tool for both metabolite profiling and metabolite identification. 

The greatest disadvantage of all detector systems such as, e.g. FID, UV, diode array detection (UV-DAD), FL, refractory index (RI), light scattering detector (LSD) or conductivity, applied in combination with GC, LC or CZE, is that they only provide an electric signal at the detector. The retention time alone of standard compounds, if available, is not sufficient for a reliable identification. LC separation of surfactant-containing extracts may often result in non-reproducible retention... 

For the characterisation of the biodegradation intermediates of C12-LAS, metabolised in pure culture by an a-proteobacterium, Cook and co-workers [23] used matrix-assisted laser desorption/ionisation (MALDI)-time of flight (TOF)-MS as a complementary tool to HPLC with diode array detection and 1H-nuclear magnetic resonance. The dominating signal in the spectrum at m/z 271 and 293 were assigned to the ions [M - H] and [M - 2H + Na]- of C6-SPC. Of minor intensity were the ions with m/z 285 and 299, interpreted to be the deprotonated molecular ions of C7- and C8-SPC, respectively. 

E.N. Lewis and I.W. Levin, I.W., Real-time, mid-infrared spectroscopic imaging microscopy using indium antimo-nide focal-plane array detection, Appl. Spectrosc., 49(5), 672-678 (1995). 

As shown in Fig. 22, the resulting procedure, referred to as a multi-block experiment, produces a two-dimensional data set, such as an array of FIDs (its exact nature depends upon the signal acquisition method). The data of each x-block are then reduced to a single quantity, S(t) which should be proportional either to the total sample magnetization Ma(x) or to one of its components. Since the vertical scale of the relaxation curve is irrelevant, we can identify S(t) with Ma(x) at the exact time of detection (usually just after the first excitation pulse). 

Two predominant phenolic compounds (neochlorogenic and chlorogenic acids) in prunes and prune juice can be analyzed by reversed-phase HPLC with diode array detection along with other phenolic compounds (65). Phenolic compounds were extracted from prunes with methanol and aqueous 80% methanol and analyzed by HPLC. Ternary-gradient elution (a) 50 mM NaH4H2P04, pH 2.6, (b) 80% acetonitrile/20% (a), and (c) 200 mM phosphoric acid, pH 1.5, was employed for an 80-min run time. Four wavelengths were monitored for quantitation 280 nm for catechins and benzoic acids, 316 nm for hydroxycinnamates, 365 nm for flavonols, and 520 nm for anthocyanins. Phenolic analysis of pitted prune extract is presented in an HPLC chromatogram in Fig. 9, which is based on work done by Donovan and Waterhouse (65). 

An HPLC method for chlorogenic acids with lactones in six different commercial brands of roasted coffee was developed by Schrader et al. (143). Hydroxycinnamic acid derivatives, including mono- and di-caffeoylquinic acids, corresponding lactones, and feruloylquinic acids were extracted from coffee with methanol at 80°C for 1 h under reflux. An HPLC method using step-gradient elution with 2% aqueous acetic acid (eluent A) and ACN (eluent B) for a 75-min run time was developed. Determination was carried out by HPLC with UV detection at 324 nm, and further confirmation was conducted by HPLC-thermospray (TSP)-MS and HPLC-diode array detection. Elution order for mono-caffeoylquinic acid (CQA) was 3-CQA, 5-CQA, followed by 4-CQA, which was different from the usual elution order of mono-CQA (Fig. 17). These results indicate that it is currently not possible to predict the elution order of different reversed-phase packings due to the different selectivity (143). 

Photolyses were performed at room temperature using a Nagano Science LT-120 irradiatior equipped with a Toshiba chemical lamp FIR-20S-BL/M (800 mW cm-2). The crystalline samples were packed between two glass plates and placed in the irradiator. The time course of the reaction was checked by HPLC periodically. Irradiation of 1 for 3 h afforded the photoproduct 2 in 100% yield. The pyridine derivatives of 1 and 3 were identified by means of HPLC analyses using photodiode array detection by comparison of the retention time and the UV spectra to those of the authentic samples. 

Here, the outlet of the chromatographic system is connected to an NMR detection cell. The NMR spectra are acquired continuously while the sample is flowing through the detection cell. The result is a set of one-dimensional (ID) NMR spectra which cover the whole chromatogram and are typically displayed as a two-dimensional (2D) matrix showing NMR spectrum against retention time, similar to an LC-diode array detection (DAD) plot. 

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