Data acquisition dilution

Light-up, ion lens tuning, mass calibration, optimization of data acquisition parameters, determination of Cd in water by isotope dilution... 

The success of ratioing techniques is entirely dependent upon the proper choice of an internal standard or ratio reference. Certainly, another isotope of the same element under study is the best choice indeed, it has been shown that lead signals temporally varying with 17% RSD can be radioed to yield 1.9% RSD, with this limitation imposed by the data acquisition system. In some cases, such as the monoisotopic elements or expense considerations, isotopic dilution may not be attractive and thus alternative elements must be utilized for ratioing. Here, it was found that improvements in precision were greatly dependent upon the choice of internal standard, with best results obtained for elements of close mass and ionization energy. 

In experiments with either dilute samples or insensitive nuclei (such as l3C), one pulse usually does not give a sufficiently high S/N to allow the determination of the component frequencies and intensities accurately. The S/N can be improved by repeating the pulse-data acquisition sequence, then... 

Demonstration of linear response enables the use of single point calibration techniques, which can offer considerable cost savings regarding the number of calibration materials that must be maintained and the time it takes to calibrate the on-line analyzer. A 2000 ppmw standard was made with 7.88 g of pure dibutyl sulfide diluted in 1 L of toluene. This standard was further diluted sequentially 1 1 nine times until the expected sulfur concentration in the sample was down to 3.91 mg/kg. Each of these 10 samples were injected multiple times in a 6000 series analyzer that was set for a 2500 ppmw full scale range and calibrated with the 2000 ppmw sample (see Figs. 8 and 9). Data from the results of the 16.13 ppmw sample were lost due to a data acquisition problem. The data, shown in Table 3, indicate a % RSD of better than 1 % in the sulfur range 62-2000 mg/kg. At lower sulfur levels of 4-31 mg/kg, the %RSD is 11-2 %. 

The reaction equipment is operated by means of a data acquisition and control program. The reactor is of stainless steel 316, with 9 mm internal diameter. It is provided with a fixed bed of catalyst diluted with alumina as inert and operates in isothermal regime. The reaction products are analysed by gas chromatography (Hewlett Packard 6890) by means of detectors based on thermal conductivity (TCD) and flame ionization (FID). The separation of products is carried out by means of a system made up of three eolumns 1) HP-1 semicapillary column for splitting the sample into two fi actions a) volatile hydrocarbon components (C4.) and polar components (ethanol, water and diethyl ether) b) remaining products (C5+). 2) SUPEL-Q Plot semicapillary column for individually separating out both volatile components and polar components, which will be subsequently analysed by TCD and FID. 3) PONA capillary column for separation of Cs+ hydrocarbons, which will be analysed by FID. 

Specifically, data was presented describing moisture desorption and intermediate temperature air oxidation of a powdered sub-bituminous coal. In comparison to its companion method, PA-IR, DRIFT spectroscopy would appear to be the technique of choice for the study of such reaction processes involving powdered samples since the temperature and environment of the sample are more conveniently controlled. Also PA-IR in general requires longer data acquisition times than DRIFT to produce a similar quality S/N ratio (34), No effort has been made in this report to treat in any way the quantitative aspects which most surely at some point must be considered. Most quantitative work involving DR spectra has utilized the Kubelka-Munk Equation to mathematically treat the data. This Equation seems to apply mainly to species in highly reflecting matrices at low dilution. Therefore, it remains to be determined what treatment may be required for DR spectral data obtained from neat materials such as coal. 

Figure 8.26. Apparatus for melt DCC crystallization, using air as a coolant. A = Reservoir B = Data acquisition system C = Thermostatic baths and circulators D = Particle analysis sensor E = Dilution tank F= Temperature recorder G = Crystallizer H= Flowmeter I = Refrigerator J = Temperature programming controller K Heat exchanger. After Kim and Mersmann, 1997)...

Duplicate samples are placed on the column, the sample solution is diluted by a factor of 3 and duplicate samples are again placed on the column. This procedure is repeated, increasing the detector sensitivity setting where necessary until the height of the eluted peak is commensurate with the noise level. If the detector has no data acquisition and processing facilities, then the peaks from the chart recorder can be used. The width of each peak at 0.607 of the peak height is measured and the peak volume can be calculated from the chart speed and the mobile-phase flow rate. Now,... 

Calibration of peak position for accurate mass determination can be performed internally or externally to minimize systematic errors. Internal calibration can be conducted when compounds with known molecular weight (called calibration compounds or calibrants) are mixed with the sample prior to the introduction into the ion source. This calibration can be performed, for example, by adding the calibrant to the liquid-phase sample while diluting it prior to analysis. The best result is achieved when multiple calibration signals are used to interpolate the m/z of ions within the range of interest. In proteomics, a tryptic digest of albumin from horse heart is typically used as the calibrant because it covers a wide m/z range (e.g., m/z 800-3000) that is ideal for mass calibration of low- to medium-sized peptides. In external calibration, the calibrants are analyzed before the analysis of real samples. The peaks of the calibrants are used to create and set the calibration equation in the data acquisition software. This method provides less mass accuracy because the instrument condition may still vary between the calibration and analyses of real samples. However, external calibrations save time and calibration compounds, and such methods also make analyses of analytes free from interferences caused by calibrants. 

A method is distinctly different from a standard operating procedure (SOP). An SOP is the document that details the exact operating procedures that were derived from the method and are oflen laboratory specific. An SOP will define sample size/weight and preparation, diltient and dilution volumes, standard curve concentrations, flow rates, detector/data acquisition settings, etc. In essence, the SOP is the master document used in the quality assurance/control laboratory. 

In dilute solutions the problem may be attacked by light scattering. X-ray scattering, or hydrodynamic measurements. In solution, the acquisition of experimental data is relatively easy, but the interpretation presents formidable problems which have not yet been solved completely satisfactorily. The main trouble arises from the fact that models are required to interpret data on dilute solutions, and it is difficult to assess how applicable the models are to molecularly dispersed species. Very often dubious assumptions are introduced which tend to render the results meaningless. Our first task, therefore, shall be to examine a variety of hydrodynamic experiments and see to what extent the data from such experiments can be interpreted in terms of size and shape. We shall not discuss scattering measurements here, except to mention that they too involve difficulties of the same kind in the interpretation of the data. 

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