Spectrometer performance tests

The proton lineshape test uses chloroform in deuteroacetone typically at concentrations of 3% at or below 400 MHz, and 1% at or above 500 MHz. Older instruments and/or probes of lower sensitivity or observations via outer decoupler coils , may require 10% at 200 MHz and 3% at 500 MHz to prevent noise interfering with measurements close to the baseline. A single scan is collected and the data recorded under conditions of high digital resolution (acquisition time of 16 s ensuring the FID has decayed to zero) and processed without window functions. Don t be tempted to make measurements at the height of the satellites themselves unless these are confirmed by measurement to be 0.55%. Since these arise from protons bound to C, which relax faster than those of the parent line, they may be relatively enhanced should full equilibrium not be established after previous pulses. The test results for a 400 MHz instrument is shown in Fig. 3.66. The traditional test for proton resolution which dates back to the CW era (o-dichlorobenzene in deuteroacetone) is becoming less used nowadays, certainly by instrument manufacturers, and seems destined to pass into NMR history. 

Lineshape and resolution tests on other nuclei follow a similar procedure to that above. Not all nuclei available with a given probe need be tested and typically only tests for inner and outer coil observations on multinuclear probes are required. This means the second test will often involve carbon-13 for which two samples are in widespread use the ASTM (American Society for Testing and Materials) test sample (40% p-dioxane in deuterobenzene also used for the sensitivity test) or 80% benzene in deuteroacetone. In either case on-resonance continuous-wave (CW) decoupling of protons should be used as this provides improved results for a single resonance relative to broadband decoupling. Rather long (30-40 s) acquisition times will be required for a well shimmed system. 

15n 90% formamide in de-DMSO Use inverse gated decoupling to suppress negative NOE 

A great disadvantage of NMR spectroscopy relative to many other analytical techniques is the intrinsically low sensitivity from which it suffers. This, of course, is greatly outweighed by its numerous benefits, yet is still one of the more likely causes of experiment failure and so deserves serious attention instrumental approaches to enhancing NMR sensitivity are described in Section 3.4.2. The term sensitivity strictly defines a minimum amount of material that is detectable under defined conditions and so represents the limit of 

The peak-to-peak measurement must include all noise bands within the defined frequency window but is somewhat susceptible to what one might call operator optimism in the exclusion of spikes or glitches . Computational methods for determining noise have the advantage of removing such operator bias, and it is consistency of approach that is important for performance monitoring. 

Use broadband proton decoupling No decoupling, CsDs used for measurement No decoupling No decoupling 

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Testing of the spectrometer performance requires a variety of test samples, usually provided by the... 

The technical specifications identified and described by most of the manufacturers of absorption photometers for medical use include wavelength accuracy, spectral half-width of spectral radiation flux at the detector, photometric accuracy, percentage of wavelength integrated, false radiation, and photometric short-time repeatability. As discussed previously [2], the Instrumental Performance Validation Procedures, issued by serious manufacturers of analytical instruments, indicate the methods and the reference materials required to test and to maintain optimum spectrometer performance in daily routine analysis. 

Even in those cases where an aiialysis is qualitative, quantitative measures are employed in the processes associated with signal acquisition, data extraction, and data processing. The comparison of, say, a sample s infrared spectrum with a set of standard spectra contained in a pre-recorded database involves some quantitative measure of similarity in order to find and identify the best match. Differences in spectrometer performance, sample preparation methods, and the variability in sample composition due to impurities will all serve to make an exact match extremely unlikely. In quantitative analysis the variability in results may be even more evident. Within-laboratory tests amongst staff and inter-laboratory round-robin exercises often demonstrate the far from perfect nature of practical quantitative analysis. These experiments serve to confirm the need for analysts to appreciate the source of observed differences and to understand how such errors can be treated to obtain meaningful conclusions from the analysis. 

This section is primarily intended for those who need to set-up experiments or those who have new hardware to install for which new calibrations are required. As with any analytical instrumentation, correct calibrations are required for optimal and reproducible instrument performance. All the experiments encountered in this book are critically dependent on the application of rf and gradient pulses of precise amplitude, shape and duration and the calibrations described below are therefore fundamental to the correct execution of these sequences. Periodic checking of these calibrations, along with the performance tests described in the following section, also provides an indication of the overall health of the spectrometer. 

For the determination of the sugar sequence of these saponins, an early prototype of a new ion trap mass spectrometer was tested. With this instrument, it has been possible to perform not only an MS/MS experiment, but a multiple stage MS/MS experiment (MS"). In MS ", it was possible to isolate and excite only one ion of interest and thus, to decrease the amount of consecutive reactions [10]. For example on the pentaglycosylated saponin 4, six stages of MS/MS were performed (MS ). The sugar sequence information was obtained by successive decomposition of the main ion, as shown in Fig. 6. 

Table 1 American Society for Testing and Materiais (ASTM) standards reiating to spectrometry and spectrometer performance... 

Mass Spectrometer—The suitability of the mass spectrometer to bie used with this method of analysis shall be proven by performance tests described herein. 

In gas chromatography/mass spectrometry (GC/MS), the effluent from a gas chromatograph is passed into a mass spectrometer and a mass spectrum is taken every few milliseconds. Thus gas chromatography is used to separate a mixture, and mass spectrometry used to analyze it. GC/MS is a very powerful analytical technique. One of its more visible applications involves the testing of athletes for steroids, stimulants, and other performance-enhancing drugs. These drugs are converted in the body to derivatives called metabolites, which are then excreted in the... 

Michael Story is retired from Thermo Electron Corporation. He was involved in the research, design, and commercialization of mass spectrometers for 37 years, and is a cofounder of the Finnigan Corporation. He was a member of previous NRC committees on commercial aviation security (1988-1993) and chaired the Panel on Test Protocol and Performance Criteria. 

As the anapole interaction is the candidate which directly breaks parity conservation in electromagnetic interaction [1], it is very desirable to test whether the anapole moment could couple to the p decay or not. This experiment can be performed by solid state detectors as well asby a magnetic spectrometer. There are also other choices for the crystal samples [3] and p sources. Since the anapole moment has the same intrinsic structure as for Majorana neutrinos, its coupling is valid to both p decay and p+ decay. 

Temperature consistency between measurements performed on different spectrometers is particularly critical for accurate interpretation of the data (see Refs. [19, 20] for post-acquisition temperature consistency tests). However, temperature control and equalization are also important for the combined analysis of T1, T2, and NOE data measured on the same spectrometer, because of the possible temperature differences between these measurements. Fig. 12.1 illustrates the sensitivity of relaxation parameters to temperature variations. Accurate measurement of protein dynamics requires that all experiments be done at the same temperature. To improve temperature consistency between Tlr T2, and... 

The analytical performance of four modes of LC-MS, multiple MS (MS"), and tandem MS operation (APCI and ESI with positive and negative ionizations) has been compared for two mass spectrometers, a triple-quadrupole and an ion-trap instrument.With 15 flavonoids as test compounds, the use of APCI in the negative-ion mode gave the best response, with the signal intensities and the mass-spectral characteristics not differing significantly between the two instruments. Under optimum conditions, full-scan limits of detection of... 

ASTM E 1421-94, Standard Practice for Describing and Measuring Performance of Fourier Transform Infrared (FT-IR) Spectrometers Level Zero and Level One Tests, 1994. 

System suitability allows the determination of system performance by analysis of a defined solution prior to running the analytical batch. System suitability should test the entire analytical system, chromatographic performance as well as the sensitivity of the mass spectrometer for the compounds of interest. Some LC-MS SOPs reference analytical methods as the source of operating details for a given analysis. This works particularly well for quantitative analysis, where analytical methods include critical details on instrument parameters and special calibrations that might be required for a particular analyte. Thus, system suitability testing provides the daily [3] checking of the system. 

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