Tin Capsules Research Articles

A study on the simultaneous determination of nitrogen content and 15N isotope abundance in plants using peak height intensities at m/z 28 and 29

A method for simultaneous determination of nitrogen content and 15N isotope abundance in plants was established by Elemental analysis-gas isotope ratio mass spectrometry. Taking poplar leaves and l-glutamic acid as standards, nitrogen content was determined using the standard curve established by weighted least squares regression between the mass of nitrogen element and the total peak height intensity at m/z 28 and 29. Then the 15N isotope abundance was calculated with the peak height intensity at m/z 28 and 29. Through the comparison of several sets of experiments, the impact of mass discrimination effect, tin capsule consumables, isotope memory effect, and the quality of nitrogen on the results were assessed. The results showed that with a weight of 1/x2, the standard curve has a coefficient of determination (R2) of 0.9996. Compared to the traditional Kjeldahl method, the measured nitrogen content deviated less than 0.2 %, and the standard deviation (SD) was less than 0.2 %. Compared to the sodium hypobromite method, the 15N isotopic abundances differed less than 0.2 atom%15N, and the SD was less than 0.2 atom% 15N. The established method offers the advantages of being fast, simple, accurate, and high throughput, providing a novel approach for the simultaneous determination of nitrogen content and 15N isotope abundance in plant samples.

Determination of Radiocarbon Content in Bio-Oil Samples by Mini Carbon Dating System in the Gliwice Radiocarbon and Mass Spectrometry Laboratory

Abstract The applications of isotopes are used by many European countries to investigate environmental changes. A compact modern accelerator mass spectrometry (AMS) system known as Mini Carbon Dating System (MICADAS) is used in Gliwice Radiocarbon and Mass Spectrometry Laboratory for determining the 14C content in different environmental samples including liquid fuels. For radiocarbon measurement using MICADAS, the liquid samples are accurately prepared using the tin capsules for liquids for combustion in elemental analyser (EA) and graphitisation in the AGE system. In this study, the determination of 14C content in three different bio-oil samples and one reference sample of 100% biomass was conducted. Bio-oil samples were prepared using tin capsules for liquids sealed in the second capsules for solids to avoid sample evaporation while the reference sample was prepared using the tin capsule for solids for combustion in EA and graphitisation in the AGE system. Based on the 14C measurement results, one of the bio-oils was not produced from the analysed reference biomass. Two others were determined as a mixture of bio- and fossil components, and based on 14C the bio-carbon content was calculated. For all samples, the 14C measurement showed reproducible and reliable results.

TESTING THE METHODS FOR DETERMINATION OF RADIOCARBON CONTENT IN LIQUID FUELS IN THE GLIWICE RADIOCARBON AND MASS SPECTROMETRY LABORATORY

ABSTRACTDetermining the biocomponents in liquid fuels using radiocarbon radioisotope (14C) dating requires sample preparation adaptations to the conditions of the Gliwice Radiocarbon and Mass Spectrometry Laboratory. Liquid scintillation counting (LSC), and accelerator mass spectrometry (AMS) were investigated using six samples, including one 14C-free fuel and modern hydrotreated vegetable oil (HVO). For AMS, samples were prepared using tin capsules for liquids for EA combustion and graphitization in an AGE system. For LSC, liquid fuels were prepared by mixing with purified preheated sand and a benzene synthesis line. Benzene resublimation was also tested. IRMS measurements were also conducted for benzene to account for isotopic fractionation. Sample background measurements using both methods showed good performances by both AMS and LSC without resublimation. Comparable results were also obtained for HVO.

Miau, a microbalance autosampler

Powder weighing is an essential but tedious activity in many branches of science. Here I describe a MIcrobalance AUtosampler (miau) that transfers solids in the sub-mg range to a microbalance. Miau is a pick-and-place machine which moves a gripper with dual function: 1) move tin capsules; 2) deliver powder from a container to tin capsules. In our laboratory we routinely use miau to prepare working standards for quality control of elemental and isotopic analyses. In a test, miau produced standards between 0.3 and 1.1 mg, which is a useful range in our laboratory. Failure to produce a weighed standard happened in 5% of the cases. A comparison with manual measurements demonstrated that obtained amounts for automated samples were as accurate and precise as manually prepared ones. Setup for daily use is simple, and the microbalance can be easily used alternately with or without miau. Miau is a low-cost device that can work with microbalances from many manufacturers, and can be readily adopted by many laboratories.

Mapping carbon and nitrogen isotopic composition of fingernails to demonstrate a rural-urban nutrition transition in the Center-West, Northeast, and Amazon regions of Brazil.

The main objective of this study is to investigate diet patterns among rural and urban populations of the Center-West, Northeast, and Amazon regions of Brazil through the carbon and nitrogen isotopic composition of fingernails, recognizing that the extent of market integration is a key driver of food consumption. In the Center-West, Northeast, and Amazon regions of Brazil, fingernails were sampled in clusters encompassing a major city, town, and rural village. A total of 2,133 fingernails were analyzed. Fingernails were clipped by donors using fingernail clippers. In the laboratory, samples were cleaned then weighed in small tin capsules before being isotopically analyzed for carbon and nitrogen. The overall mean δ13 C and δ15 N were -19.7 ± 2.8‰ and 10.6 ± 1.1‰, respectively. In the more remote villages, where access to food markets is more challenging, lower δ13 C prevails, suggesting that Brazilian staple foods (rice, beans, and farinha) still dominate. In areas with easier access to food markets, δ13 C values were higher, suggesting a change to a diet based on C4 plants, typical of a Brazilian supermarket diet. The variability among inhabitants in the same location expressed by a significant inverse correlation between δ13 C and δ15 N fingernail values suggested that "market integration" does not affect everyone equally in each community. The nutrition transition has not yet reached some remote villages in these regions of Brazil or that the nutrition transition has not yet reached all residents of these remote villages. On the other hand, in several villages there is a considerable adherence to the supermarket diet or that some residents of these villages are already favoring processed food.

Tracing the Geographical Origin of Roasted and Green Coffee Using Isotope Fingerprints.

Background: Coffee is one of the most popular beverages worldwide, sourced from different geographical regions. To ensure that coffee beans come from labelled locations, laboratories need an analytical solution that can discriminate geographical origin. Coffee beans have a fingerprint, a unique chemical signature that allows them to be identified: Isotope fingerprints of carbon, nitrogen, sulfur, hydrogen, and oxygen have been reliably used for origin claim verification. Objective: Show that hydrogen and oxygen isotope fingerprints from green and roasted coffee beans can determine the origin of coffee beans. Methods: The coffee beans were initially ground to as fine as possible a powder using a cryo-mill. Following, samples were weighed into tin capsules and introduced to the Thermo Scientific EA IsoLink™ IRMS System via the Thermo Scientific MAS Plus autosampler, where they were pyrolyzed at 1450°C, and converted to H₂ and CO for analysis. Results: The hydrogen and oxygen isotope fingerprints of the coffee beans show that they can be clearly differentiated at the continent scale. Conclusions: It is evident that measuring the isotope fingerprint of coffee beans helps support legislation on food integrity and labelling (EC Reg. No. 1169/2011) and product geographical indication/origin (EC Reg. No. 510/2006), therefore protecting consumers and brands. The origin of a coffee bean can be determined using their hydrogen and oxygen isotope fingerprints. Highlights: Hydrogen and oxygen isotope fingerprints can help determine the origin of coffee beans, allowing the label claim to be verified.

Do artificial structures affect the feed of Patella caerulea limpets?

Do artificial structures affect the feed of Patella caerulea limpets?

A closer look into the nitrogen blank in elemental analyser/isotope ratio mass spectrometry measurements.

One important limitation for the precise measurement of minute amounts of nitrogen (N) in solid samples by elemental analyser/isotope ratio mass spectrometry (EA/IRMS) is the accurate determination of the analyser blank value. This study was performed to identify different sources, amounts and isotopic composition of N blanks in EA/IRMS in order to identify measures for minimising the effect of the N blank on N isotopic data quality. Different types of autosamplers, with and without zero-blank functionality, were tested by analysing different amounts of substances of varying isotopic composition by EA/IRMS. Using zero-blank autosamplers reduces the atmospheric N2 blank from 60nmol to between 4 and 5nmol depending on the autosampler type. This blank is derived from atmospheric N2 leaking into the elemental analyser, trapped in the sample tin capsules or contained in the oxygen added for combustion. Another source of blank is the reaction tube. As the sources of the blank differ, the isotopic composition of the blank is very variable. In addition, cross-contamination from previous samples may contribute up to 3.3nmol N. For precise measurements of minute amounts of N in solid samples, reduction of the N blank is the most promising strategy. Correcting for the remaining N blank is only meaningful if the sample isotopic composition is very different from that of the N blank, because the precise determination of the isotopic composition of the N blank is not possible.

An optimized method for stable isotope analysis of tree rings by extracting cellulose directly from cross-sectional laths

Stable isotopes in tree-ring α-cellulose are valued as environmental proxies and their use is steadily increasing; however, preparation of α-cellulose is a bottleneck in isotope analysis. Recent methodological breakthrough for extracting tree-ring α-cellulose directly from tree-ring cross-sectional laths drastically increased the throughput of tree-ring isotope data. In this paper, we evaluate our recently designed “cross-section” method. This method employs polytetrafluoroethylene (PTFE) cases, enabling direct extraction of α-cellulose from 1-mm thick tree-ring laths, in combination with fixation sheets to prevent disintegration of freeze-dried α-cellulose laths. Perforated PTFE cases are easily producible at an affordable cost. They are made of commonly available lab consumables in catalogs and do not require specially made PTFE parts. Freeze-dried α-cellulose laths preserved distinct anatomical structure, enabling precise separation at the tree-ring boundaries. Once separated from a lath, tree-ring α-cellulose can be weighed directly into silver or tin capsules for analysis. We checked chemical purity of α-cellulose prepared by the cross-section method from five tree species (larch, pine, spruce, beech, and oak). Residual lignin and hemicellulose contents were quantitatively assessed by Fourier transform infrared spectrometry and gas chromatography. The average chemical purity of α-cellulose laths from the five species was 94.5%, similar to the chemical purity of α-cellulose prepared with the standard Jayme-Wise method. Both oxygen and carbon isotope values of α-cellulose prepared by the cross-section method also closely matched those prepared by the standard method. We conclude that, by overhauling the method of α-cellulose preparation for tree-ring isotope analysis, we increased throughput of tree-ring oxygen and carbon isotope data without sacrificing sample purity.

Evidence for Proteomic and Metabolic Adaptations Associated with Alterations of Seed Yield and Quality in Sulfur-limited Brassica napus L

In Brassica napus, seed yield and quality are related to sulfate availability, but the seed metabolic changes in response to sulfate limitation remain largely unknown. To address this question, proteomics and biochemical studies were carried out on mature seeds obtained from plants grown under low sulfate applied at the bolting (LS32), early flowering (LS53), or start of pod filling (LS70) stage. The protein quality of all low-sulfate seeds was reduced and associated with a reduction of S-rich seed storage protein accumulation (as Cruciferin Cru4) and an increase of S-poor seed storage protein (as Cruciferin BnC1). This compensation allowed the protein content to be maintained in LS70 and LS53 seeds but was not sufficient to maintain the protein content in LS32 seeds. The lipid content and quality of LS53 and LS32 seeds were also affected, and these effects were primarily associated with a reduction of C18-derivative accumulation. Proteomics changes related to lipid storage, carbohydrate metabolism, and energy (reduction of caleosins, phosphoglycerate kinase, malate synthase, ATP-synthase β-subunit, and thiazole biosynthetic enzyme THI1 and accumulation of β-glucosidase and citrate synthase) provide insights into processes that may contribute to decreased oil content and altered lipid composition (in favor of long-chain fatty acids in LS53 and LS32 seeds). These data indicate that metabolic changes associated with S limitation responses affect seed storage protein composition and lipid quality. Proteins involved in plant stress response, such as dehydroascorbate reductase and Cu/Zn-superoxide dismutase, were also accumulated in LS53 and LS32 seeds, and this might be a consequence of reduced glutathione content under low S availability. LS32 treatment also resulted in (i) reduced germination vigor, as evidenced by lower germination indexes, (ii) reduced seed germination capacity, related to a lower seed viability, and (iii) a strong decrease of glyoxysomal malate synthase, which is essential for the use of fatty acids during seedling establishment.

δ13C values and phytanic acid diastereomer ratios: combined evaluation of two markers suggested for authentication of organic milk and dairy products

Authentication of organic milk by suitable markers is currently attracting more and more interests in food control. In this study, we aimed to compare the efficiency of the markers stable carbon isotope ratio (δ13C value) with the SRR/RRR phytanic acid diastereomer ratio (SRR/RRR) of milk fat for distinguishing different feeding systems. For stable carbon isotope ratio analysis by elemental analysis–isotope ratio mass spectrometry (EA-IRMS), we first developed a simple sample preparation method based on milk fat extracts allowed to evaporate the solvent in tin capsules for liquid samples. The δ13C values and reproducibility measured with this alternative sample pre-treatment method excellently matched those obtained with the current standard method. Applied to milk samples, the results of the EA-IRMS analysis were linked to the SRR/RRR, and both markers allowed to distinguish milk from cows fed with hay (δ13C value > −28.0 ‰, SRR/RRR <1.5) from feed used in conventional milk production which contained maize silage (C4-plants) (p < 0.001). Milk fat of organic retail cheese samples was also highly depleted in 13C (δ13C value −30.0 ‰ ± 1.1), and the SRR/RRR was low (<1.5). However, seven cheese samples showed inconsistent δ13C values and SRR/RRR, most likely due to the feeding of grass silage. Both parameters (δ13C values and SRR/RRR), together with the phytanic acid content of milk fat, also allowed distinguishing between the feeding of high amounts of pasture, hay, and/or grass silage.

“Do it yourself” reference materials for δ 13C determinations by isotope ratio mass spectrometry

A method is described to prepare inexpensive organic reference materials for routine stable isotope work. The method blends isotope-enriched and isotope-depleted materials to match closely international measurement standards. Examples are presented showing how (13)C-enriched and (13)C-depleted glucose were blended to match the isotopic compositions of the international carbon isotope standards, NBS 19 and L-SVEC. Preparation of the blended standards was straightforward, and the prepared solutions proved easy to dispense into tin capsules and easy to combust in a conventional isotope analysis system. The blended materials allow a laboratory to perform a two-point calibration for isotopic composition on a daily basis, with the use of an international reference material recommended for routine quality assurance. The blending method can be applied widely to make isotope standards for other elements and compounds.

On-line Radiocarbon Measurements of Small Samples Using Elemental Analyzer and MICADAS Gas Ion Source

An on-line measurement system was installed at the MICADAS in Zurich, using an elemental analyzer (EA) as a combustion unit to enable direct radiocarbon measurement of samples containing carbon in the range of 5–100 μg possible with minimum effort. The samples are combusted in small capsules and the gaseous combustion products are separated by the EA. The carbon dioxide leaving the EA in a high helium flow is concentrated on a small external trap containing X13 zeolite adsorber material. This new concept, avoiding a cryogenic trapping for the enrichment step, allows the construction of a very compact system able to work even with the smallest samples. Concentrated on the external trap, the carbon dioxide is flushed into the gas-tight syringe of our gas inlet system using a low helium stream. The gas mixture is measured with the MICADAS gas ion source. Several different sample capsules were analyzed to minimize the major blank contribution coming from the sample vessel. The best results were achieved with 25-μL tin capsules, which contained only 0.34 ± 0.13 μg carbon at 65 pMC. This work describes the development of the on-line system and the protocol for measurement runs. Results are presented for on-line measurements of reference materials and a comparison is performed with typical dating samples measured previously as graphite targets. Finally, relevance and limitations of on-line measurements are discussed.

Using Total Material Requirement to Reduce the Global Environmental Burden

SummaryTotal material requirement (TMR), a measure of all of the material input required by a national economy, is sometimes criticized for failing to link material flows within an economy and their global environmental impacts. This article presents a three‐step method for bridging this gap. The method shows how to (1) analyze TMR accounts to identify potentially environmentally relevant flows (PERF), that is, material flows with potential environmental impacts abroad; (2) assess the socioenvironmental impacts of the identified PERF; and (3) determine the main economic activities underlying these PERF. Using this method we are able to add an environmental dimension to TMR accounts and to make the connection between economic activities and their socioenvironmental impacts worldwide. This methodology has been applied to the Basque Country (BC) region (Spain). An in‐depth analysis of the trends in the TMR of the BC shows that tin imports associated with tin capsule production account for around 7% of the TMR. These high figures are due to the substantial hidden flows (HF) of tin imports, which is an indicator of potential environmental impacts abroad. We find that tin extraction and concentration involve several social and environmental impacts such as waste generation, soil, water, and air pollution affecting biodiversity and human health, and child labor. These impacts are located in Indonesia, China, Peru, Bolivia, Brazil, Malaysia, and Thailand.

A technique to facilitate diffusions for nitrogen‐isotope analysis by direct combustion

A technique was developed that permits the use of boric acid‐indicator solution in carrying out diffusions for inorganic 15N analysis of soil extracts by direct combustion, so as to eliminate the need for a separate quantitative determination. In this technique, the titrated sample is acidified with 2.5 M KHSO4 and subsequently treated with methanol to remove H3BO3 The NH+4‐N is dissolved in 1 mL of deionized water, concentrated after transfer to a microcentrifuge tube, and freeze‐dried in a tin capsule. Isotope‐ratio analyses were accurate to within 5% when diffusions were performed on 100 to 1000 μg of NH+4‐N (0.2–10 atom % 15N), whereas errors of 8 to 17% occurred with 25 to 50 μg of labeled N, even after correction for isotopic dilution by atmospheric NH3 The technique described permits 15N analysis of any form of N that can be recovered by H3BO3 diffusion of soil, soil extracts, soil hydrolysates, Kjeldahl digests, water, or wastewater.

Technical Note: Measuring Moisture Content of Small Seeds

An accurate determination of moisture content in hydrated or partially hydrated seeds is fundamental to understanding early physiological processes in seeds, and the associated environmental interactions that affect seedling vigor, establishment, and survival. One difficulty encountered while measuring the moisture content of imbibed seeds is that water evaporates from the seed during weighing. This is particularly significant for small seeds because they have a large surface area to volume ratio. We developed a procedure using a standard tin capsule and microbalance which was simple, inexpensive, facilitated precise measurement of moisture in hydrated seeds, and provided reliable results with a minimal amount of seeds. The method is recommended as a means for increasing the accuracy of seed weight and seed moisture measurements.

Features of determination of the oxygen and nitrogen contents in aluminum nitride and oxide powders by the method of reduction extraction

To a great degree an improvement in the properties of aluminum nitride-base ceramics is related to an increase in purity of the raw material, particularly to a reduction in the quantity of oxygen, the impurity most strongly influencing the thermal conductivity and mechanical and other properties of the material. In addition, methods of determination of the oxygen content in nitrides, as in other aluminum compounds, are very inadequate. For these purposes the method of reduction extraction of oxygen by carbon in the form of carbon monoxide, which is distinguished by high sensitivity and rapidity, is normally recommended [1]. However, for aluminum compounds this method has poor reproducibility and accuracy and also low reliability of the results. This is the result of difficulty in reduction of aluminum oxide by carbon, formation of A10 gaseous suboxide not recorded by this method, intense dissociation of aluminum nitride during the analysis, and the fact that the particles of the unreacting substance are carried off by the liberated nitrogen from the reaction zone. In order to eliminate these processes in analysis of oxygen in the nitride and other aluminum compounds, the authors of [1] recommend that platinum or tin capsules with the weighed portion be dropped into a graphite crucible with a platinum bath heated to 2700 K. It is clear that, for largescale analyses, the necessity of which is the result of the wider use of aluminum nitride ceramics, such recommendations are inapplicable. Reference has been made to the possibility of determination of nitrogen in refractory nitrides [2] and in mixture of aluminum and vanadium nitrides [3], and of oxygen in mixtures of aluminum and calcium oxides [4] with use of the TN314, TC-136, and RO-316 instruments (Leco, USA) but the conditions of the analyses are not described. In order to establish the possibility of determination of the oxygen content in aluminum nitride and other aluminum compounds in this work, the temperature and time relationships of extraction of oxygen from aluminum nitride and oxide and mixtures of them under different conditions, including in the presence of a molten nickel---copper mixture and with sealing of the opening of the graphite crucible with a partially fused metal stopper, were studied. The method of the experiment consisted of measurement of the temperature and time relationships of the degree of extraction of oxygen and nitrogen (share of extracted gas in relation to its total content in %) from aluminum oxide and nitride and also of proportioned mixtures of them in pulsed heating of the substances being analyzed in a graphite crucible in a flow of helium. The design of the instrument for pulsed reduction extraction with chromatographic separation of the gases and recording with a detector based on thermal conductivity, the dimensions of the graphite crucibles, and the basic stages of preparation of the samples and conducting the analysis, are similar to those described in [5, 6]. The investigations were made in the 500-4300 K range and one heating pulse for a 5--30 mg sample lasted 3--30 sec. The LKhM-80 chromatograph (model No. 2) was operated with a column thermostat temperature of 333 K, a thermal conductivity detector thermostat temperature of 383 K, a thermal conductivity detector current of 120 mA, and helium consumptions through the measuring column of 1.5" 10 -4 and through the comparison column of 3" 10 -5 m3/min. With the use of the metal bath 1--4 mg of carbonyl nickel powder was added to the graphite crucible together with the sample before analysis. The crucible was covered with well-matched copper plugs (diameter 3 mm, weight about 0.35 g). In turning on of heating a portion of the copper plug adjoining the water-cooled electrode of the pulse furnace remains infused while the opposite portion fuses earlier than interaction of the plug with the graphite starts. The copper--nickel alloy wets the graphite well, and with the help of capillary forces closes the lack of tightness close to the plug, envelops the sample, and covers the inner surface of the crucible, decreasing the gas permeability of its walls. In this way carrying away of the dispersed particles of the sample by the liberated gas is prevented. Powder substances with known oxygen (standard specimens of No. 471, R21 iron powder, tungsten and erbium oxides) and nitrogen (S41b and $44b standard specimens, and also titanium nitride powders, the quantity of nitrogen in which was determined by the Kjeldahl method) were used for calibration of the instrument. The nitrogen content in the aluminum nitride powders was determined by the same method.

Determination of nitrogen in UN, PuN and (U,Pu)N by oxidation in circulating oxygen and gas chromatographic measurement of the combustion gases

A simple and accurate method for the determination of nitrogen in uranium- and plutonium-bearing materials was developed. The loss of nitrogen by oxidation of the sample before analysis was prevented by pulverizing, weighing and packing the sample into a tin capsule in a glove-box with a high-purity argon atmosphere. Nitrogen was determined by oxidizing the nitrides in the tin capsule in circulating oxygen at 850 °C and analysing the combustion gases by gas chromatography with thermal conductivity detection. The relative standard deviation was about 0.7% and the time required to analyse one sample was about 10 min for successive analyses. Skilled techniques for glove-box work are not necessary. The method is applicable not only to the analysis of research samples but also to the quality control of nitride fuel production lines.

Vacuum fusion determination of oxygen in gadolinium, terbium metal and iron-terbium alloy

The extraction conditions for the accurate determination of oxygen in gadolinium, terbium and iron-terbium alloy using vacuum fusion analysis were studied. The influence of the gettering effect, the analyzing temperature and the weight ratio of the bath metal to the sample were investigated. Oxygen values of gadolinium and terbium were measured by the graphite crucible, the graphite capsule, the tin bath, the iron-tin bath and the platinum-tin bath techniques in the temperature range of 1500–2100 °C using vacuum fusion analysis. These oxygen values were compared with those obtained by inert gas fusion analysis. In inert gas fusion analysis, the samples were analyzed with iron and tin in a tin capsule, and the samples with platinum in a tin capsule were analyzed in a graphite capsule enclosing with carbon powder. Oxygen values of both metal samples in the graphite capsule at 2000 °C, with an iron-tin bath at 1850 °C and a platinum-tin bath at 2000 °C in vacuum fusion analysis, were respectively in good agreement within their errors; the oxygen values of gadolinium were also in good agreement with that from inert gas fusion analysis in the iron-tin bath, but those of terbium were not in agreement. This agreement for gadolinium guarantees the reliability of the conditions for the accurate determination, and the difference of oxygen values for terbium suggests a need for further consideration on the conditions of the inert gas fusion analysis.

Improved combustion techniques for the microdetermination of nitrogen in organic compounds with an automatic analyzer

Routine analysis with the Coleman nitrogen analyzer, over the past 2 years, has led to various modifications in the procedure. It was found that compounds containing certain structures, such as 1,2,4-triazoles, pyridine rings, etc., often gave low results, while others containing long aliphatic chains gave high results. In many cases premature degradation of the sample, regardless of the melting point, has appeared to be the main problem. Cooling of the sample before and during the preheat period has eliminated this difficulty. The most effective catalyst found has been a mixture of silver oxide, manganese dioxide, vanadium pentoxide, and cobaltic oxide. This is placed on the sample which is weighed in a tin capsule. The use of tin capsules has proved to be more effective than aluminum boats with amine hydrochlorides and aliphatic chains. A modified post-treatment tube packing, with silver on aluminum oxide (alumina) between the copper oxide and copper, is used to effectively remove halogens and sulfur which quickly poison the copper packing. The modifications described have improved the reliability and accuracy of the instrument without increasing the time of a determination. The absolute deviation for standards was ±0.05% nitrogen, and for unknown compounds, ±0.14% nitrogen.