The Elemental Analyzer

The evaluation of metrological characteristics of the technique, perfonued with minerals of different composition, showed that technique developed for reliability and precision satisfies the requirements offered for quantitative determinations, category II. The detection limits are acceptable for solving the problems posed and amount to 0.1 - 0.4 wt. %, depending on the element analyzed. 

Many hollow cathode lamps are needed because each element, since it must be contained in the cathode, requires a different lamp. Some lamps, however, are multielement. The element analyzed must be contained in the cathode so that its line spectrum will be generated and absorbed by the same in the flame. 

In the method, a weighed portion of a sample of coke dried at 110°C (230°F) and crushed to pass a No. 200-mesh sieve, mixed with stearic acid, and then milled and compressed into a smooth pellet. The pellet is irradiated with an x-ray beam and the characteristic x-rays of the elements analyzed are excited, separated, and detected by the spectrometer. The measured x-ray intensities are converted to elemental concentration by using a cahbration equation derived from the analysis of the standard materials. The K spectral lines are used for aU the elements determined by this test method. This test method is also apphcable to the determination of additional elements provided that appropriate standards are available for use and comparison. 

In the other study. X-ray fluorescence spectroscopy was used to analyze trace element concentrations by observing dusts on 37 ram diameter cellulose acetate filters (20). Twenty-three elutriator and twenty-three area samples from 10 different bales of cotton were analyzed. The average fraction of total dust accounted for by the elements analyzed was 14.4% amd 7.6% for vertical elutriator and area samples, respectively. Although the variation in absolute quantity of atn element was high, the relative abundance of an element was consistent for measurements within a bale. Averaged over all the samples analyzed, calcium was the most abundant element detected (3.6%), followed by silicon (2.9%), potassium (2.7%), iron (1.1%), aluminum (1.1%), sulfur (1.0%), chlorine (0.8%) and phosphorous (0.6%). Other elements detected in smaller aunounts included titanium, manganese, nickel, copper, zinc, bromine, rubidium, strontium, barium, mercury amd lead. 

Table II shows, in some detail, the complexity and variability of the population involved in this study (laboratories analyzing archaeological materials) and of the reporting procedures. Even the elements analyzed by each laboratory are not completely clear. For example, laboratory 02 reported Cr in trace amounts (0.0001-0.001% ) in samples 1 and 2 but gave no report for sample 3 (the space is blank). Thus, we assume that they did not look for Cr in sample 3 although it seems equally likely that they looked for it and it was not present. The proper use of the term not detected, the consistent reporting of detection limits (done by few laboratories), and the choice of elements to be determined in archaeological bronzes are all open questions.

The metal balance for all the elements analyzed by mass spectrometry is good, but on the average shows a negative imbalance of 20%. Metals showing high imbalance, i.e., mercury, arsenic, and selenium, probably were in the gaseous state at the sample points. For example, a precipitator outlet sample of mercury showed a flow of 0.02 g min"1. At this sampling point the particulates are much cooler than the fly ash at the precipitator inlet. 

The sorbent and leaching characteristics of fly ash can be related to operating temperatures in the boiler and to coal ash compositions that provide low ash fusion temperatures. Boiler temperatures that favor the fusion of the ash and maintain the ash in the fused state reduce the amount of trace elements leached from the fly ash and improve the sorbent characteristics of the fly ash for removal of these elements from ash pond effluents. In addition, the leachable amounts of each of the elements analyzed in this study can be correlated with the fly ash particle area and with their bulk compositions in the original coal. No correlation could be identified between the sorbent characteristics of fly ashes and their particle size and bulk, major, minor and trace elemental compositions, with the exception of the carbon content. Only organic removals, as measured by COD from ash pond effluent could be correlated with the carbon content of the fly ash particles. 

Samples and standards were counted twice once 4-10 days and again 30-40 days after the irradiation. The elements analyzed in each count set are indicated in Table I. One of three high resolution Ce(Li) detectors coupled to 4996 channel pulse height analyzers was used to measure the y-rays emitted from the activated samples and standards. Automated data reduction included the calculation of the analytical un-... 

Table II. Approximate Visual Lower Limits of Determination for the Elements Analyzed by the Optical Emission Spectrographic Technique ...

The discovery of presolar grains in meteorites has, for the first time, enabled the precise chemical and isotopic analysis of interstellar material (e.g., Anders and Zinner, 1993 Chapter 1.02). The huge variations in the isotopic compositions of all the elements analyzed in presolar grains is in stark contrast to the basically uniform isotopic composition of solar system materials (see Figure 1). This uniformity would have required an effective isotopic homogenization of all the material in the solar nebula, i.e., gas and dust, during the early stages of the formation of the solar system. 

Several samples from Jonuta, of the Altar type of Fine Orange, have been analyzed by NAA at the Brookhaven National Laboratory and the results have been published. One sample is from a figurine named XCII by Goldstein (30), another is named sample 53 by Sayre et al. (34), and the last two are identified as samples 4 and 6 by SablofiF(43). The elements analyzed by both NAA and AAS were potassium, iron, chromium, manganese, and cobalt. The concentrations of these elements expressed as oxides, are given in Table III for all the samples analyzed by NAA and AAS. Again, recall that the concentrations of the elements analyzed by AAS do not represent absolute values they are only used for comparative purposes. 

Overall, more even distribution patterns of inorganic elements may be characteristic of elements associated with organic components and more pronounced or irregular patterns with elements related to concentrations of detrital and authigenic minerals. Distribution patterns are listed in Table III for the elements analyzed in this study. The distribution of elements in the seams may show characteristics of more than one pattern and are noted accordingly in Table III. Zubovic and others (10) described distribution patterns similar to ours for Ti, V, Cr, Co, Cu, Y and La in several North Dakota lignites. 

One sample of Wyoming fly ash (WYO-FA) from the Northern Great Plains Coal Province was subjected to leaching. Mn, Pb, Zn and Cu were detected in very minor amounts (<0.15 mg/1). The initial leachate solution had an Fe concentration of 6.2 mg/1, with no Fe being detected in later samples. Of the elements analyzed, the major constituents in the leachate were Ca, Na and K. 

Elemental Analysis (C, H, N, O S) helps us understand the actual extent of grafting. From the synthesis details (Table 5.1) we get the percentage grafting. Now from percentage grafting and from the known elemental composition of the polysaccharide and that of the graft polymer, we can calculate the theoretical elemental composition, which we can simply compare with that actually obtained from the elemental analyzer. 

Once the methodology for trace element determination in petroleum products by ICP-MS was validated, it was applied to several crude oils (supplied by Petrobris) and their fractions originating from a Brazilian petroleum basin. In order to prove the reliability of analytical results obtained after oil fractionation, total mass balance (TMB) was calculated for each element measured. Table 3 shows an example of crude oil and its fractions analyzed by ICP-MS. TMB results were in the range of 90-110 % for most of the elements analyzed. In order to confirm the repeatability of oil fractionation and analysis, each sample (oil + fractions) was analyzed three... 

Two elemental analyzer systems have been developed, the "Continuous On-line Nuclear Assay of Coal", CONAC, (Science Application, Inc., Palo Alto, CA) and "The Elemental Analyzer" (MDH Industries, Inc., Monrovia, CA). Both of these units are based upon the measurement of prompt gamma rays that are emitted from a nucleus following the capture of a neutron. This technique is commonly known as prompt neutron activation analysis, PNAA. 

It is apparent that the spectrophotometric procedures are rather time consuming since several multiple extractions must be performed in order to minimize interferences. Atomic absorption spectroscopy has enjoyed wide popularity in recent years as a trace metal analysis tool. This is due to a number of factors including high sensitivity, selectivity, and ease of sample preparation. With biological fluids, often no sample preparation at all is required, depending on the element analyzed, its concentration and the sample matrix. Because of its advantages, this technique will be treated in some detail. 

In the direct-determination procedure, carbonate carbon is first removed from the sediment subsample by treatment with dilute (3N) hydrochloric or phosphoric acid, washing and drying the carbonate-free residue, and then measuring the carbon content of the residue with an elemental analyzer. An alternative direct-determination procedure employs acid vapors to remove inorganic carbon (Yamamuro Kayanne, 1995). A related procedure employs direct reaction with HCl that is added to the sediment sample while it is in the tin boat that is used in the elemental analyzer. After reaction for 24 hours, the acid is evaporated prior to carbon analysis. Yet another alternative direct-determination method involves measuring the amount of CO2 released from carbonate-free sediment subsamples during off-line oxidation of the residual carbon in preparation for carbon isotope analysis. Off-line preparation lines for isotopic analyses can be manometrically calibrated to yield this measurement. Regardless of the procedure, TOC concentrations of lake sediments are usually expressed on a whole-sediment basis. 

The sensitivity of NAA for a particular element depends on the irradiation parameters (i.e., neutron flux, irradiation, and decay times), measurement conditions (i.e., measurement time, detector efficiency), nuclear parameters of the elements being measured (i.e., isotope abundance, neutron cross-section, half-life, and y-ray abundance). The accuracy of an individual NAA determination usually ranges from 10 to 10 ° grams per gram of sample. Accuracy of a NAA determination is usually between 2% and 10% of the reported value, depending on the element analyzed and its concentration in the sample. 

This is practically similar to that of emission flame photometry. An important point of difference is the need to have a radiation source. It is practically impossible to isolate a particular resonance wavelength from a continuous source by using a prism or a diffraction grating or both simultaneously. This problem was solved with the development of hollow-cathode discharge lamps. Such lamps produce monochromatic radiation characteristic of the element analyzed. In these lamps the cathode is a hollow tube which is lined by the element in question. The lamp will thus emit monoehromatic radiation characteristic of the emission spectrum of the element Involved. Such lamps have now become commercially available for a long range of elements. In less sophisticated instruments, a continuous discharge lamp with double monochromators is used. 

An electron microprobe measures the X-rays produced from the incidence of a beam of electrons on a material. The wavelengths of the X-rays are characteristic of each element, and the intensities of the X-rays depend on the quantity of the element. The technique is accurate to 1 %-3%, with the allowable mass of the element analyzed in the sample ranging from to 10 g [73]. 

The elemental analyzer measures the C, H and N content of biomass upon its combustion at 925°C in a pure oxygen environment by monitoring the volatile compounds (C in CO2, N in N2, H in H2O). The results are reproducible but largely dependent on the growth conditions the solid residue of combustion is ash and contains oxides and salts. Mass fractions of biomass can be expressed as ... 

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