A VARIABLE TEMPERATURE, U.V. LUMINESCENCE SPECTROGRAPH FOR SMALL SAMPLES

Abstract— A variable temperature spectrometer suitable for recording phosphorescence, fluorescence and luminescence spectra is described. The instrument has been chiefly used for emission spectroscopy at temperatures between 80° and 370°K but may be used for excitation spectroscopy as well. The samples are contained in quartz tubes with inside diameters of 1.5 mm and are generally optically thick at the excitation wavelength. The sample volume can be as small as 10μl. Absolute quantum yields may be obtained with ease and the use of phase sensitive detection makes it possible to record in 30 sec a fluorescence spectrum with 30 Å resolution and a quantum yield of 10^--⁴ with a signal to noise ratio of 20. The instrument has also been useful for photochemical irradiations.     

Subtraction of atmospheric water contribution in Fourier transform infrared spectroscopy of biological membranes and proteins

The contribution of the absorption of H₂O vapor in the IR spectrum of proteins Interferes with the analysis of the shape of amide I and II bands and prevents correct assignments to be performed, in particular after Fourier self-deconvolution of the spectra Mathematical treatments of the spectra have previously been proposed to subtract the water vapor contribution from the sample spectrum. Here we propose to take advantage of the intrinsic bandwidth difference existing between the absorption bands of the water vapor and these of the liquid or solid sample. When a nominal resolution of 8 or 4 cm⁻¹ is chosen, atmospheric water bands are broad and rather featureless. The subtraction coefficient applied may vary by about 50% according to the operator. Conversely, when the spectrum of the same sample in the same conditions is recorded with a nominal resolution of 0.5 cm⁻¹, subtraction coefficients are exactly evaluated by integration and the visual evaluation can not be mistaken by more than 5%. The very sharp features arising from imperfect matching between the atmospheric water band shapes in the reference and in the sample spectrum completely disappear if the difference spectrum is now convoluted to a final resolution of 4 cm⁻¹. Incidence of the subtractions obtained at different resolutions on the evaluation of protein secondary structure is evaluated.     

Use of a novel array detector for the direct analysis of solid samples by laser ablation inductively coupled plasma sector-field mass spectrometry

The use of laser ablation (LA) as a sample-introduction method for inductively coupled plasma mass spectrometry (ICP-MS) creates a powerful tool for trace elemental analysis. With this type of instrument, high analyte spatial resolution is possible in three dimensions with ng/g limits of detection and minimal sample consumption. Here, simultaneous detection is used to eliminate the correlated noise that plagues the ablation process. This benefit allows analyses to be performed with single laser pulses, resulting in improved depth resolution, even less sample consumption, and improved measurement precision. The new instrument includes an LA sample-introduction system coupled to an ICP ionization source and a Mattauch-Herzog mass spectrograph (MHMS) fitted with a novel array detector. With this instrument, absolute limits of detection are in the tens to hundreds of fg regime and isotope-ratio precision is better than 0.02% RSD with a one-hour integration period. Finally, depth-profile analysis has been performed with a depth resolution of 5 nm per ablation event.     

High energy resolution Auger spectroscopy on a CMA instrument

An experimental method that increases the analyzer resolution of cylindrical mirror analyzer CMA‐based Auger spectrometers is described. By means of electrically biasing the sample, the effective energy resolution obtainable from the CMA instrument is improved from the native 0.5 to 0.1% or even better for higher kinetic energy Auger transitions. In addition, the maximum kinetic energy Auger transition observable by the CMA Auger instrument is increased from 3200 to 5700 eV, in the current realization. It is also shown that the sensitivity of the energy scale calibration to sample working distance with respect to the analyzer is simultaneously reduced, making the method suitable for chemical surface analysis. The biasing is accomplished using a special sample holder with electronics and software that can be added to an existing instrument. The overall capability of the Auger instrument for chemical analysis is, therefore, increased, while preserving all the analytical functionality and features of the CMA. Copyright © 2011 John Wiley & Sons, Ltd.     

AUTOMATIC RECORDING OF ACTION SPECTRA OF PHOTOBIOLOGICAL PROCESSES, SPECTROPHOTOMETRIC ANALYSES, FLUORESCENCE MEASUREMENTS AND RECORDING OF THE FIRST DERIVATIVE OF THE ABSORPTION CURVE IN ONE SIMPLE UNIT

Abstract— A compact, rugged and simply constructed instrument has been designed which measures action spectra of photosynthesis by delivering equal numbers of quanta between 400 and 720 nm to a sample placed upon the cathode of an oxygen sensor. The absorption spectrum is measured delivering equal numbers of quanta over the spectrum to a sample placed directly above a photoreceiver that has been adjusted in wavelength sensitivity to function as a quantum counter. All the details that are recorded by conventional high precision spectro-photometers for samples with relatively broad absorption bands (e.g. chlorophyll, carotenoids, phycobilins and living material such as algal suspensions) are resolved by the instrument. Corrected excitation spectra of fluorescence are obtained with the same instrument. Likewise the first derivative of the absorption curve may be scanned. Such recordings amplify details in the absorption spectrum, and they are particularly useful in analyses of small changes in slope. The functions described above may be operated separately or combined. The instrument has a total weight of about 10 kg, and the dimensions are ca . 60 × 40 × 30 cm. It is constructed for use in field laboratories and on board research vessels, and also for courses in biology where the principles behind photobiological analyses are illustrated. It is possible that a device of this type could be used for investigations of photosynthesis on other planets.     

AN INSTRUMENT FOR SIMULTANEOUS ACQUISITION OF FLUORESCENCE SPECTRA AND FLUORESCENCE LIFETIMES FROM SINGLE CELLS

Abstract— An instrument is described that has the capability of acquiring both the spectrum and lifetime(s) of fluorescent species dispersed in biological cells. It operates at the single cell (or organelle) level and the spectral and temporal data collection can be performed simultaneously. A synchronously pumped, mode-locked dye laser provides the excitation light, time-correlated single-photon counting is used for lifetime measurements, and a diode array spectrograph is used for spectral work. Spatial resolution of sub-micrometer is obtained using a fluorescence microscope. The temporal resolution is better than 300 ps and wavelength resolution is less than 1 nm per channel. The instrument has been used for observing the spectral and temporal characteristics of hematoporphyrin in mouse myeloma cells.     

Measurement and calibration of the He(I) photoelectron spectra of gaseous and liquid ethanediol,propanediol and formamide

The He(I) photoelectron spectra of gaseous and liquid ethane-1,2-diol, propane-1,3-diol and formamide have been measured in a new instrument with a Bessel box analyser. Both phases were studied at ambient temperature or a little above with a resolution of 0.1 eV. A simple method of calibration is described. The addition of NaI to formamide (0.3 M) does not result in the appearance of the characteristic peaks of I^? in the spectrum but it causes the appearance of bands characteristic of water in the gas-phase spectrum.     

Surface Study of Polymers by Static Secondary Ion Mass Spectrometry Using a Magnetic-Sector Mass Spectrometer

Results from static SIMS analysis of six thermoplastic polymers — polytetrafluoroethylene (PTFE), polyethylene (PE), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), polystyrene (PS) and polycarbonate (PC) — using a magnetic-sector SIMS instrument and O₂⁺ primary beam are presented. For PTFE as a representative sample, the charging effect is reduced only with a metal grid when analyzing positive secondary ions. When negative secondary ions are analyzed, excessive charges are self-compensated with a normal-incidence electron gun. Positive-ion spectra collected agree with spectra obtained using either a quadrupole or time-of-flight SIMS instrument and noble-gas ion beams. The agreement is objectively demonstrated by means of the capability to compare spectra in the NIST/EPA/MSDC mass spectral database. The merits of the use of high-mass resolution, of which magnetic-sector SIMS is inherently capable, to provide analytical information about the molecular species native to the sample are demonstrated in distinguishing three ambiguous peaks with nominal mass ratios m/z = 27, 39 and 59 from PMMA.     

A strategy for metabolite identification using triple-quadrupole mass spectrometry with enhanced resolution and accurate mass capability

Using a single platform of a triple-quadrupole mass spectrometer equipped with enhanced resolution and accurate mass capabilities, a strategy for metabolite identification of a drug in a biological matrix has been demonstrated. The strategy is based on first screening for metabolites via neutral loss and precursor ion scan schemes, devised as the result of the product ion spectrum of a matrix-free standard of the drug. The accurate masses of the precursor ions identified via the two scan schemes plus the precursor ions of structurally likely metabolites are then determined by enhanced resolution, accurate mass (AM) selected ion monitoring (SIM). The identities of the metabolites are further established by determining the accurate masses of the product ions via enhanced resolution AM selected reaction monitoring (SRM). The feasibility of the strategy was demonstrated using a liver microsome incubation sample of nefazodone, an antidepressant drug. The neutral loss and precursor ion screening runs were able to identify most of the metabolites of nefazodone. The subsequent SIM and SRM experiments gave mass accuracy of better than +/-0.003 u for the masses of the precursor and product ions of nefazodone and all the metabolites. The ability to perform metabolite screening by using the scan features followed by accurate mass determinations on the same instrument is an attractive feature of using a triple-quadrupole mass spectrometer with enhanced resolution and accurate mass capability.     

Measurement of unimolecular decay in peptides of masses greater than 1200 units by a reflecting time-of-flight mass spectrometer

Daughter ions from decomposition of [M + H]+ parent ions have been observed in a time-of-flight mass spectrometer fitted with an ion mirror. Unit mass resolution is obtained for parent ions of masses up to several thousand u when the mirror voltage is set at a value determined by the usual velocity-focusing criterion for parent ions. Under this condition the daughter-ion resolution in the low-mass range suffers. Considerable improvement is obtained when the daughter-ion spectrum is examined in several segments, with the mirror voltage optimized for each segment. The daughter-ion spectrum from decay of metastable [M + H]+ parent ions in Substance P is measured using this technique. Reasons are suggested for differences between the spectrum obtained and a spectrum for the same compound recently obtained using a tandem double-focusing instrument.     

Application of high resolution-ICP-MS (sector field-ICP-MS) to the fast and sensitive quality control of process chemicals in semiconductor manufacturing

For fast routine analysis of process chemicals used in semiconductor technology such as tetramethylammonium hydroxide (TMAH), ammonium fluoride/hydrofluoric acid mixtures, phosphoric, sulphuric or peroxodisulphuric acid (PDSA) low blanks are the paramount requirement for reliable sector field ICP-MS ultratrace analysis. When solutions containing a high amount of dissolved solids e.g. seawater samples have been analysed before, a thorough cleaning procedure and an adapted element menu is essential to lower the instrument blanks where possible or to achieve sufficient limits of detection (LoD) even at high blank levels. Due to its improved transmission and its ability to resolve spectral interferences inductively coupled plasma-sector field mass spectrometry is capable of detecting 1 ng/g of all metal impurities even K, Ca, and Fe in every matrix used for semiconductor production. LoDs range from < 1 to 30 pg/mL in diluted chemicals corresponding to 5 to 800 pg/mL in the original. This work describes the experiences with instrument cleaning and maintenance, sample preparation and introduction. The interface region between torch and lenses was seen to be the main source of blanks for elements such as Na. All sample manipulation has to be carried out under clean room conditions. The use of an inert sample introduction system (ISIS), platinum cones and at least medium resolution for elements between 24 and 80 amu creates a very robust method. High efficiency sample introduction systems such as USN and MCN have been studied alternatively.     

High-resolution photoelectron spectroscopy through deconvolution

A new iterative deconvolution algorithm for the development of very high resolution Hc(I)-excited photoelectron spectra of gases is presented. The algorithm accepts as input a medium-resolution spectrum and an instrument function obtained by scanning intrinsically narrow line (e.g. the Ar²P_3/2 line) under conditions identical to those used to acquire the medium resolution spectrum. The deconvolved partial spectrum of an O₂H₂O mixture is presented as a test case prior to presentation of results for three nitrogen lines. For comparison purposes directly obtained high-resolution spectra of the nitrogen lines are included. The shapes of the nitrogen lines are discussed within the framework of a one-center expansion theory of photoionization. The conditions under which deconvolution can be profitably applied are briefly discussed and an attempt is made to establish the deconvolution (contrary to still popular belief) is not in any way equivalent to curve fitting.     

Characterization of laser-induced plasma in a vacuum using laser ablation mass spectrometry and laser-induced breakdown spectrometry

An analytical system for simultaneously monitoring laser-ablation mass spectra and laser-induced breakdown spectra for solid sample has been developed. The performance of the developed system is evaluated by measuring characteristics of laser-induced plasma such as lifetime of ions inside the plasma and laser power dependence of mass resolution for solid samples. Adopted samples are gadolinium plate, gadolinium coated on stainless steel plate, and one of the NIST standard samples, C-1248 (Ni–Cu alloy). The threshold laser energy in obtaining mass spectrum was dependent on the type of sample characteristics in the order of a few MW/cm², while a few hundred MW/cm² was necessary in order to observe emission signal. When laser energy was increased enough to produce emission signal, mass resolution of the time-of-flight mass spectrum was severely deteriorated. The lifetime of the continuum ion signal was estimated 200 and 250 ns for Gd plate and C-1248, respectively, by monitoring emission signals, while the lifetime of ions near sample surface was estimated as 400 ns and 430 ns for Gd plate and C-1248, respectively. The deterioration of mass resolution can be understood as originating from the space charge effect in high plasma density in a given space and different velocity distribution of ions inside the plasma, while longer lifetime of ions near sample surface can be understood as originating from speed of ion ejection near the sample surface. The details of the characteristics of laser-induced plasma are discussed and optimum experimental conditions for simultaneous monitoring are suggested.     

Activation analysis with standards containing two or more active nuclides A computerized method of calculation involving decay and gamma spectral resolution

The resolution of the gamma spectra of activities induced in materials by fast neutron, charged particle and gamma photon activation is complicated by the fact that many elements produce more than one active nuclide in significant amounts. Direct resolution by least-squares fitting of the spectra of standards is only possible in these circumstances if the standard and sample spectra are obtained at the same time after irradiation, as the shapes of the standard spectra change with time. An alternative to the practical collection of spectra in this way is the correction of the standard spectra to the mid-time of counting of a sample spectrum. This may be achieved by recording spectra for a standard at different times and resolving the decay curves obtained for each channel on the basis of the half-lives of the component nuclides, which may be decay-independent or related or both. From the component nuclide count-rates in each channel at some arbitrary time, the standard spectrum at the time of counting of the sample can be generated and then used in a conventional least squares-fit of the sample spectrum. A FORTRAN IV program has been written to carry out this type of calculation on an IBM 360 65 computer. The feasibility of using this method is demonstrated by its application to activation analyses involving standards containing decay-related and independent nuclides.     

High‐resolution peak analysis in TOF SIMS data

High mass resolution time‐of‐flight secondary ion mass spectrometry (TOF SIMS) can provide a wealth of chemical information about a sample, but the analysis of such data is complicated by detector dead‐time effects that lead to systematic shifts in peak shapes, positions, and intensities. We introduce a new maximum‐likelihood analysis that incorporates the detector behavior in the likelihood function, such that a parametric spectrum model can be fit directly to as‐measured data. In numerical testing, this approach is shown to be the most precise and lowest‐bias option when compared with both weighted and unweighted least‐squares fitting of data corrected for dead‐time effects. Unweighted least‐squares analysis is the next best, while weighted least‐squares suffers from significant bias when the number of pulses used is small. We also provide best‐case estimates of the achievable precision in fitting TOF SIMS peak positions and intensities and investigate the biases introduced by ignoring background intensity and by fitting to just the intense part of a peak. We apply the maximum‐likelihood method to fit two experimental data sets: a positive‐ion spectrum from a multilayer MoS₂ sample and a positive‐ion spectrum from a TiZrNi bulk metallic glass sample. The precision of extracted isotope masses and relative abundances obtained is close to the best‐case predictions from the numerical simulations despite the use of inexact peak shape functions and other approximations. Implications for instrument calibration, incorporation of prior information about the sample, and extension of this approach to the analysis of imaging data are also discussed.     

Design and performance of a plasma-source mass spectrograph

A plasma-source, simultaneously detecting, Mattauch-Herzog mass spectrograph for multi-element analysis was developed. Simultaneous detection should improve throughput, precision, and sensitivity over those instruments that use quadrupole or sector mass spectrometers. The new instrument is compact (approximately 80 cm in length) and is designed to detect a complete atomic mass spectrum in two mass windows that straddle but avoid argon. The design and some figures of merit are presented. With a dc glow discharge source, a precision of 0. 5% determined from eight consecutive 10-s images was obtained for Cu isotope ratios in Naval Brass B. With the same sample, nickel and lead were detected at limits of 8 and 1 ppm. Measured Mg isotope ratios with an inductively coupled plasma source were within 4% of the expected values. The resolution at full width at half maximum is currently limited to approximately 60, in part because of poor peak shape. The origin of this peak shape has been determined to lie within the array detector and possibly results from its interaction with the fringing magnetic fields produced by the second sector.     

Tandem mass spectrometric accurate mass performance of time-of-flight and Fourier transform ion cyclotron resonance mass spectrometry: a case study with pyridine derivatives

The interpretation of mass spectra is a key process during compound identification, and the combination of tandem mass spectrometry (MS/MS) with high-accuracy mass measurements may deliver crucial information on the identity of a compound. Obtaining accurate mass data of fragment ions in MS/MS reveals the particular problem of mass calibration when a lockmass, which is frequently used to obtain accurate masses in MS, is absent. An alternative technique is to recalibrate the MS/MS spectrum using a reference MS/MS spectrum acquired under the same conditions. We have tested and validated this approach using a hybrid quadrupole/orthogonal acceleration reflectron-type time-of-flight (TOF) mass spectrometer. The results were compared with those obtained under similar conditions on a Fourier transform ion cyclotron resonance (FT-ICR) instrument. We found that the mass accuracy observed with such an "external" recalibration on the TOF instrument in MS/MS is identical to what can be obtained on a similar instrument operating in one-dimensional MS mode using the lockmass technique. However, mass accuracy in both cases is one order of magnitude inferior to that obtained using FTMS, and also inferior to that observed using sector field MS when operated at comparable resolution. Nevertheless, for small (<200 Da) molecules, this mass accuracy was still sufficient to have the "true" elemental composition identified as the first hit in about 70% of all cases. It was possible to elucidate the fragmentation mechanism of eight azaheterocycles containing a pyridine moiety, where the accurate mass data from the TOF instrument allowed distinction between two alternative fragmentation pathways.     

Combined chemical and topographic imaging at atmospheric pressure via microprobe laser desorption/ionization mass spectrometry–atomic force microscopy

The operational characteristics and imaging performance are described for a new instrument comprising an atomic force microscope coupled with a pulsed laser and a linear ion trap mass spectrometer. The operating mode of the atomic force microscope is used to produce topographic surface images having sub‐micrometer spatial and height resolution. Spatially resolved mass spectra of ions, produced from the same surface via microprobe‐mode laser desorption/ionization at atmospheric pressure, are also used to create a 100 × 100 µm chemical image. The effective spatial resolution of the image (～2 µm) was constrained by the limit of detection (estimated to be 10⁹–10¹⁰ molecules) rather than by the diameter of the focused laser spot or the step size of the sample stage. The instrument has the potential to be particularly useful for surface analysis scenarios in which chemical analysis of targeted topographic features is desired; consequently, it should have extensive application in a number of scientific areas. Because the number density of desorbed neutral species in laser desorption/ionization is known to be orders‐of‐magnitude greater than that of ions, it is expected that improvements in imaging performance can be realized by implementation of post‐ionization methods. Published in 2009 by John Wiley & Sons, Ltd.     

Automated instrumentation for multidimensional preparative scale GC (PSGC)

Summary An automated instrument for preparative scale separations is described. The instrumental system, which does not include the general use of temperature programmed operation allows for the application of multidimensional techniques of carrier gas flow switching such as heart cutting, backflushing etc. in order to optimize the resolution within selected cuts taken from a preseparation, to enrich trace components or to shorten separation times at still sufficient sample capacity of the entire system. Typical applications of the instrument are discussed. Presented at the 15th International Symposium on Chromatography, Nürnberg, October 1984     

Scanning microprobe matrix-assisted laser desorption ionization (SMALDI) mass spectrometry: instrumentation for sub-micrometer resolved LDI and MALDI surface analysis

A new instrument and method is described for laterally resolved mass spectrometric surface analysis. Fields of application are in both the life sciences and the material sciences. The instrument provides for imaging of the distribution of selected sample components from natural and artificial surfaces. Samples are either analyzed by laser desorption ionization (LDI) time-of-flight mass spectrometry or, after preparation with a suitable matrix, by matrix-assisted laser desorption ionization (MALDI) mass spectrometry. Areas of 100 x 100 microm are scanned with minimal increments of 0.25 microm, and between 10,000 and 160,000 mass spectra are acquired per image within 3 to 50 min (scan rate up to 50 pixels per s). The effective lateral resolution is in the range of 0.6 to 1.5 microm depending on sample properties, preparation methods and laser wavelength. Optical investigation of the same sample area by UV confocal scanning laser microscopy was found to be very attractive in combination with scanning MALDI mass analysis because pixel-identical images can be created with both techniques providing for a strong increase in analytical information. This article describes the method and instrumentation, including first applicational examples in elemental analysis, imaging of pine tree roots, and investigation of MALDI sample morphology in biomolecular analysis.