EXTRACTION DES ACIDES FULVIQUES D'UN HORIZON SPODIQUE PAR UNE RESINE ECHANGEUSE D'IONS DE TYPE H POSITIF

1971 ◽  
Vol 51 (2) ◽  
pp. 157-164
Author(s):  
G. HUBERT ◽  
A. GONZALEZ
Keyword(s):  
Organic Matter ◽  
Fulvic Acid ◽  
Freeze Drying ◽  
Gel Filtration ◽  
Fulvic Acids ◽  
Ash Content ◽  
Freeze Dried ◽  
Efficient Reagent

A resin in the H+ form (Dowex 50W-X8) was used to extract fulvic acids from a Spodic horizon. This resin has the following advantages in relation to the reagents normally used. It solubilizes organic matter while purifying it and without altering it by oxidation and hydrolysis. Furthermore, since the resin is eliminated completely from the extract, no contaminating ions remain. The soil was agitated in a mixture of water and resin. The extract obtained was filtered, centrifuged, purified by passage through a column of H+ resin and freeze-dried. The alternation of freeze-drying and resolubilization resulted in the coagulation of the silica which was removed by centrifugation. Acid organic matter with very low ash content (1%) was obtained. The fulvic acids extracted by resin and by Na-pyrophosphate were compared. Qualitatively they were practically the same, as evidenced by the similarity of the curves obtained by gel-filtration (Sephadex). Quantitatively the resin, however, was a more efficient reagent. Therefore, it is recommended for the extraction of fulvic acid and organo-mineral complexes.

HUMIC-FULVIC ACID RELATIONSHIPS IN ORGANIC SOILS AND HUMIFICATION OF THE ORGANIC MATTER IN THESE SOILS

1967 ◽  
Vol 47 (3) ◽  
pp. 245-250 ◽  
Author(s):  
M. Schnitzer
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Humic Acid ◽  
Fulvic Acid ◽  
Oxidative Degradation ◽  
Fulvic Acids ◽  
Organic Soil ◽  
Organic Soils ◽  
Salting Out ◽  
Naoh Solution

Twenty organic-soil samples of widely differing degrees of decomposition were extracted with 0.5 N NaOH solution under N2. Amounts of humic and of fulvic acids in the acidified extracts did not correlate significantly with pyrophosphate solubilities. This was thought to be due to interference in the separation scheme by relatively large amounts of ash constituents in the extracts. Since the "classical" fractionation of soil organic matter appears to involve essentially the "salting out" of higher molecular-weight humic from lower molecular-weight fulvic acids, an excessively high salt concentration during the separation should be avoided.To lower the concentration of inorganic constituents in the extracts, the samples were first pretreated with dilute HCl–HF solution and then extracted with 0.1 N NaOH rather than with 0.5 N NaOH. Under these conditions, amounts of fulvic acids in the acidified extracts showed a significant positive correlation (r = 0.52) with pyrophosphate solubilities of untreated extracts, whereas amounts of humic acids in the extracts exhibited a highly negative correlation (r = −0.57) with pyrophosphate solubilities. In the soils examined, increased humification was associated with increases in fulvic-acid but decreases in humic-acid concentrations.From the results of this and of earlier investigations done in this laboratory it appeared that the main mechanism governing humification in these soils was oxidative degradation, resulting ultimately in the formation of fulvic from humic acid.

scholarly journals Fluorescence Properties of the Air- and Freeze-Drying Treatment on Size-Fractioned Sediment Organic Matter

2021 ◽  
Vol 11 (17) ◽  
pp. 8220
Author(s):  
Cheng-Wen Chuang ◽  
Wei-Shiang Huang ◽  
Yung-Yu Liu ◽  
Chi-Ying Hsieh ◽  
Ting-Chien Chen
Keyword(s):  
Molecular Weight ◽  
Organic Matter ◽  
Organic Carbon ◽  
Freeze Drying ◽  
Biological Activities ◽  
Sediment Organic Matter ◽  
Bulk Solution ◽  
Similar Distribution ◽  
Organic Mixture ◽  
Freeze Dried

Sediment humic substance (SHS) is a highly heterogeneous and complex organic mixture with a broad molecular weight range. It is the significant component that associates distribution, transport, and biotoxicity of pollutants in a river environment. Air- and freeze-drying sediment pre-treatment may cause different biological activity and may result in different chemical quantities and sediment organic matter. This study collected sediments that received livestock wastewater discharge. The sediments were air- (AD) and freeze-dried (FD). The dried sediment organic matter was extracted with an alkaline solution and separated into three size-fractioned SHS samples. Size-fractioning is an effective method used to differentiate materials, on a molecular level. The bulk solution (<0.45 μm) was designated as BHS, and size-fractioned solutions were identified as LHS (<1 kDa), MHS (1–10 kDa), and HHS (10 kDa-0.45 μm). The AD SHS had a lower dissolved organic carbon (DOC) concentration than the FD SHS for the bulk and individual size-fractioned SHS, but the AD and FD SHS had a similar distribution of organic carbon in the size-fractioned SHS. The AD SHS had higher aromaticity (SUVA254) and an extent of humification (HIX) than the FD SHS. In addition, the high molecular weight SHS (HHS) had a higher SUVA254 but lower HIX than the MHS and LHS. The HHS had significantly lower fulvic acid but had higher humic acid-like substances than the MHS and LHS. This is possibly the reason the LHS had a higher humification degree but lower aromaticity than HHS. The size-fractioned SHS and optical indicators distinguished the difference between the chemical properties when air- or freeze-dried, due to the different degree of biological activities.

scholarly journals Pengaruh Metode Pengeringan Simplisia Daun Ubi Jalar Ungu (Ipomoea batatas (L.) Lamk) Varietas Antin 3 Terhadap Kadar Abu Ekstrak

2019 ◽  
Vol 4 (1) ◽  
pp. 11-14
Author(s):  
Damaranie Dipahayu ◽  
Djamilah Arifiyana
Keyword(s):  
Ipomoea Batatas ◽  
Freeze Drying ◽  
Leaf Extract ◽  
Ash Content ◽  
Raw Material ◽  
Drying Method ◽  
Freeze Dried

ABSTRAKEkstrak daun ubi jalar ungu ( Ipomoea batatas (L.) Lamk Varietas Antin 3 mengandung flavonoid yang dapat digunakan sebagai bahan baku sediaan tabir surya. Sediaan tabir surya penting untuk digunakan karena dapat melindungi kulit dari paparan radiasi sinar UV A dan UV B dari sinar matahari yang dapat merusak kulit dan memicu terjadinya penuaan dini pada kulit. Agar dapat menjadi bahan baku yang terukur efektifitas dan keamanannya maka diperlukan standarisasi ekstrak, salah satunya standarisasi non spesifik kadar abu. Penelitian ini dilakukan untuk membandingkan kadar abu ekstrak daun yang dikeringkan secara freeze drying dan oven, karena keduanya terbukti mengandung kadar flavonoid yang berbeda. Hasil penelitian ini menunjukkan bahwa pada ekstrak daun Antin 3 yang dikeringkan secara freeze drying suhu -45 0C selama 48 jam dan oven suhu 400C selama 24 jam memiliki kadar abu total adalah 6.9 % dan 7.3 % sedangkan kadar abu tidak larut asam adalah1.6 % dan 0.9 %.Kata kunci: Ekstrak daun Antin 3, freeze drying, oven, kadar abu total, kadar abu tidak larut asam ABSTRACTEthanolic extract of purple sweetpotatoes (Ipomoea batatas (L.) Lamk Antin 3 variety contain flavonoids. Flavonoids has sunscreen effectivity. Antin 3 extract need to be standardized, in order to be a raw material ofsunscreen. Nonspecific standardization can measures the effectiveness and safety of the extract. Sunscreen can protect the skin harmfull effect of UV A and UV B radiation from sunlight. The study aims to provide data the effect of Antin 3 leaf drying method dried freeze (-45 0C) during 48 hours and oven (40 0C) during 24 hours on its ash content. This study finds that freeze dried Antin 3 leaf have total ash content and insoluable acid ash content respectively is 6.9 % and 7.3 %, while oven Antin 3 leaf respectively is 1.6 % and 0.9 %.Keywords: Antin 3 leaf extract, freeze dried, oven, total ash content, insoluable acid ash content.

Isolation of the humin fraction from soil: preliminary comments

2020 ◽  
Author(s):  
Jerzy Weber ◽  
Elżbieta Jamroz ◽  
Andrzej Kocowicz ◽  
Magdalena Debicka ◽  
Aleksandra Ukalska-Jaruga ◽  
...  
Keyword(s):  
Organic Matter ◽  
Humic Substances ◽  
Soil Analysis ◽  
Mineral Soil ◽  
Ash Content ◽  
Optimal Time ◽  
Distilled Water ◽  
Science Center ◽  
Freeze Dried ◽  
Humin Fraction

&lt;p&gt;The organic matter is the most important component of soil material, which determines most soil properties. Among humic substances, humin fraction has been the least studied to date, although it usually constitutes over half of their composition. This is probably due to the fact, that humin fraction has highly hydrophobic properties and is insoluble at all pH values, which makes its isolation much more difficult, compared to humic (HA) and fulvic (FA) acid fractions. In addition, humin fraction forms very stable humic-clay complexes with mineral part of the soil (Stevenson 1994), which cannot be destructed during humic substances extraction. According to the literature, the methods of humin fraction isolation can be divided into two main groups: (1) extraction by different organic solvents, and (2) isolation by extraction of HA and FA followed by digestion of mineral soil components. Nevertheless, each of these methods has different limitations.&lt;/p&gt;&lt;p&gt;We investigated some modifications of the latter method, obtaining humin fraction from eight mollic horizons of Chernozems and Phaeozems, which differed in their physico-chemical properties.&lt;/p&gt;&lt;p&gt;The first step was to separate HA and FA according to IHSS method described by Swift (1996), however we adopted different shaking procedure. To asses differences, each supernatant obtained was analyzed for the carbon content concentration, which corresponded to HA and FA extracted.&lt;/p&gt;&lt;p&gt;HA and FA free residue was then digested to reduce the content of mineral components. We used several digestion with 10% HF/HCl , as higher concentrations of HF can result in structural alteration of the organic compounds (Hayes et al. 2017). To find the optimal time of the procedure, the ash content was determined following each digestion stage. After the HF/HCl treatment, the residue was rinsed with 10% HCl to eliminate secondary minerals. The residue was washed with distilled water until the neutral pH, then transferred to dialysis membranes and dialyzed with distilled water until a negative Cl&lt;sup&gt;&amp;#8722;&lt;/sup&gt; test with AgNO&lt;sub&gt;3&lt;/sub&gt;. Afterwards the humin fraction was freeze dried.&amp;#160;&lt;/p&gt;&lt;p&gt;Finally, obtained humin fraction contained various ash content, ranged from 6 to 30%, depending on the soil. The conducted test indicated that: (1) the concentration of carbon in supernatant considerably increased as shaking time was extended to 20 hours, and (2) longer than 4 weeks digestion with HF/HCl did not affect the reduction of the ash content of the humin fraction obtained.&amp;#160;&amp;#160; &amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Literature&lt;/p&gt;&lt;p&gt;Hayes M.H.B., Mylotte R., Swift R.S. 2017. Humin: Its Composition and Importance in Soil Organic Matter. In: Sparks D.L. (ed) Advances in Agronomy, Vol. 143, Academic Press, Burlington, 47&amp;#8211;138.&lt;/p&gt;&lt;p&gt;Stevenson F.J. 1994. Humus Chemistry; Genesis, Composition, Reaction. 2nd ed. John Wiley &amp; Sons., New York.&lt;/p&gt;&lt;p&gt;Swift R.S. 1996. Organic matter characterization. In: Sparks, D.L., et al. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods - Soil Science Society of America, Book Series no 5,&amp;#160; 1011-1069.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Acknowledgements&lt;/p&gt;&lt;p&gt;This work was supported by the National Science Center (NCN) Poland (project No 2018/31/B/ST10/00677 &amp;#8220;Chemical and spectroscopic properties of soil humin fraction in relation to their mutual interaction with pesticides&quot;).&lt;/p&gt;

NITROGEN DISTRIBUTION IN ILLUVIAL ORGANIC MATTER

1967 ◽  
Vol 47 (2) ◽  
pp. 111-116 ◽  
Author(s):  
F. J. Sowden ◽  
M. Schnitzer
Keyword(s):  
Amino Acids ◽  
Organic Matter ◽  
Fulvic Acid ◽  
Fulvic Acids ◽  
Organic N ◽  
Insoluble Residue ◽  
Amino Sugars ◽  
Humic And Fulvic Acids ◽  
Organic C ◽  
Soil Amino Acids

Organic matter (O.M.) was extracted with 0.5 N NaOH under N2, from samples of the Bh horizon of a Podzol soil. The NaOH-soluble O.M. from one sample was partitioned into "classical" humic and fulvic acids. The O.M. extracted from other samples was passed over an H-resin and purified fulvic acid" was prepared from the eluate. The O.M. retained on the resin was eluted with base. After hydrolysis a sample of the original soil the NaOH-insoluble residue and the various O.M. preparations were analyzed for amino acids, amino sugars and ammonia.Eighty percent of the amino acids in the original soil were accounted for in the NaOH-insoluble residue plus the purified fulvic acid and the NH4OH eluate. Most of the soil amino acids were recovered in the NaOH-insoluble residue plus classical humic plus classical fulvic acid fractions. Qualitatively, the amino acid distribution in all fractions was similar to the distribution or amino acids in an "average" protein. Amounts of amino sugars were small consisting of two-thirds glucosamine and one-third galactosamine. Recoveries of amino sugars were low, possibly due to the effect of alkali.Slightly more than 50% of the soil-N was accounted for as amino acids plus NH3 plus amino sugars. The behavior of the fraction on the exchange resin suggested that the organic C- organic N-system extracted from the soil was not uniform, and that at least portions of the ammo acids and amino sugars were either adsorbed on or physically mixed with organic matter.

scholarly journals PENGARUH KONSENTRASI SUKROSA SEBAGAI CRYOPROTECTANT TERHADAP KARAKTERISTIK SIFAT KIMIA YOGHURT SINBIOTIK KERING BEKU

2020 ◽  
Vol 5 (2) ◽  
pp. 81
Author(s):  
Yunita Yunita ◽  
Agustina Intan Niken Tari ◽  
Afriyanti Afriyanti
Keyword(s):  
Lactic Acid ◽  
Lactic Acid Bacteria ◽  
Water Content ◽  
Freeze Drying ◽  
Ash Content ◽  
Lactobacillus Bulgaricus ◽  
Total Acid ◽  
Freeze Dried ◽  
Acid Titration ◽  
Range Test

ABSTRAKYoghurt sinbiotik merupakan susu fermentasi oleh Bakteri Asam Lakat (BAL) spesies Lactobacillus bulgaricus dan Streptococcus thermophillus, dan Lactobacillus plantarum Dad 13 sebagai probiotik dengan penambahan ubi jalar ungu sebagai prebotik. Yoghurt sinbiotik diproses dengan pengeringan beku. Pada proses pengeringan beku ditambahkan Cryoprotectant untuk mencegah kerusakan membran sel bakteri pada yoghurt.  Cryoprotectant berfungsi sebagai pelindung sel bakteri asam laktat selama pembekuan. Tujuan penelitian adalah mengetahui pengaruh konsentrasi Cryoprotectant sukrosa terhadap sifat kimia yoghurt sinbiotik kering beku. Penelitian ini menggunakan Rancangan Acak Lengkap dengan satu variasi yaitu konsentrasi Croprotectant (0%, 2,5%, 5%, 7,5%). Data yang diperoleh dianalisis statistic menggunakan Analysis Of Variance (ANOVA) dengan tingkat signifikan 5% dan jika terdapat perbedaan yang nyata antar perlakuan maka dilanjutkan dengan uji Duncan’s Multiple Range Test (DMRT). Parameter pengamatan yang digunakan untuk menganalisis yoghurt sinbiotik kering beku meliputi kadar air, kadar abu, total asam titrasi, dan pH. Hasil penelitian menunjukkan bahwa konsentrasi Cryoprotectant tidak berpengaruh nyata terhadap kadar air, dan pH yoghurt sinbiotik kering beku, namun berpengaruh nyata terhadap kadar abu dan total asam titrasi. Pengaruh konsentrasi sukrosa sebagai Cryoprotectant diperoleh hasil terbaik pada konsentrasi 5% mempunyai kadar air 5,633%, kadar abu 4,900%, total asam titrasi 8,8167%, dan pH 3.867.ABSTRACTSynbiotic yogurt is fermented milk by Lactic Acid Bacteria (LAB) species Lactobacillus bulgaricus and Streptococcus thermophillus, and Lactobacillus plantarum Dad 13 as probiotics with the addition of purple sweet potatoes as prebotics. Synbiotic yogurt is processed by freeze drying. In the freeze drying process Cryoprotectant is added to prevent damage to bacterial cell membranes in yogurt. Cryoprotectant functions as a protective cell for lactic acid bacteria during freezing. The purpose of this study was to determine the effect of sucrose cryoprotectant concentrations on the chemical properties of freeze dried sinbiotic yogurt. This study uses a Completely Randomized Design with one variation, namely the concentration of Croprotectant (0%, 2.5%, 5%, 7.5%). The data obtained were statistically analyzed using Analysis Of Variance (ANOVA) with a significant level of 5% and if there were significant differences between treatments then continued with the Duncan's Multiple Range Test (DMRT). Observation parameters used to analyze freeze dried synbiotic yogurt include water content, total titration acid, ash content, and pH. The results showed that the concentration of Cryoprotectant had no significant effect on water content, and the pH of freeze dried synbiotic yogurt, but had a significant effect on ash content and total acid titration. Effect of sucrose concentration as Cryoprotectant obtained the best results at a concentration of 5% having a moisture content of 5.633%, ash content of 4.900%, total acid titration of 8.8167%, and pH of 3,867.Keywords: Synbiotic Yogurt, Purple Sweet Potato, Cryoprotectant

On the interaction between 5-hydroxytryptamine and N-acetylneuraminic acid under aqueous conditions

1985 ◽  
Vol 63 (7) ◽  
pp. 757-763 ◽  
Author(s):  
Leslie R. Berry ◽  
Frank V. Puzzuoli ◽  
Mark W. C. Hatton
Keyword(s):  
Freeze Drying ◽  
Gel Filtration ◽  
Fluorescence Emission ◽  
Equimolar Amount ◽  
Resonance Spectroscopy ◽  
Chemical Analyses ◽  
Acetylneuraminic Acid ◽  
Freeze Dried ◽  
Aqueous Conditions ◽  
Comparison Measurements

A complex designated 5-HT–NeuAc was formed between 5-hydroxytryptamine (5-HT) and N-acetylneuraminic acid (NeuAc) under aqueous conditions. Complex formation was encouraged by exposure to light (3000–3800 Å; 1 Å = 0.1 nm) and freeze-drying and the freeze-dried complex was isolated by gel filtration chromatography. Although stable to rechromatography on Bio-Gel P-2 if H2O was the eluent, 5-HT–NeuAc dissociated into the free components when placed in 0.1 M NaCl. Chemical analyses of the isolated complex showed that an equimolar amount of 5-HT and NeuAc was present and that all group functions were intact; these data suggested that the association between 5-HT and NeuAc was noncovalent. Spectrophotometric measurements demonstrated a small increase (approximately 12%) in extinction coefficient (275 nm) and a large increase (340- to 440-fold) in fluorescence emission (340 nm) compared with 5-HT alone. Data obtained from 1H nuclear magnetic resonance spectroscopy (250 MHz) of 5-HT and NeuAc standards compared closely to published reports. In comparison, measurements made with 5-HT-NeuAc showed that all 5-HT protons were slightly deshielded; of the NeuAc protons, slight deshielding of H8 and significant shielding of H3eq, H3ax, and H6 was observed. From these observations, a model describing the association between 5-HT and NeuAc is proposed.

scholarly journals Effect of freeze drying on qualities of fresh cow milk and soy cheeses

2020 ◽  
Vol 45 (3) ◽  
pp. 1-14
Author(s):  
Tosin Paul ◽  
Bolanle Adejumo ◽  
Nnaemeka Nwakuba ◽  
Augustine Igbozulike
Keyword(s):  
Freeze Drying ◽  
Ash Content ◽  
Cow Milk ◽  
Soy Milk ◽  
Standard Methods ◽  
Microbial Counts ◽  
Freeze Dried ◽  
Sodium Magnesium ◽  
Sensory Qualities ◽  
Bacteria And Fungi

The effect of freeze drying on the qualities of fresh cow milk and soy milk cheeses was investigated, with a view to preserve and present them in a more stable and portable form. The cow milk cheese and soy milk cheese used were freshly prepared with dimension of 2 x 3 cm and 0.2 cm thickness. The cow milk and soy cheese were divided into 6 portions of 100 g each. The initial properties of the cheeses samples been determined using a portion of 100 g each, the remaining 500 g were freeze dried. The nutritional, microbial and sensory qualities of the freeze dried cheeses were determined using standard methods. Results showed that freshly prepared cow milk cheese contains 54.02% moisture, 20.34% protein, 6.40% ash, 18.11% fat and 4.25% carbohydrate, 3.52mg/100g sodium, 7.02mg/100g potassium, 5.22mg/100g magnesium, 6.32mg/100g iron, 11.12mg/100g calcium, 3x103 cfu/g bacteria and 2.54 x 106 cfu/g fungi whereas freshly prepared soy cheese contains 50.89% moisture, 22.05% protein, 6.31% Ash, 19.02% fat and 4.06% carbohydrate, 3.52mg/100g sodium, 7.04mg/100g potassium, 5.14mg/100g magnesium, 6.20mg/100g iron, 10.76mg/100g calcium, 2.76x103 cfu/g bacteria and 2.60 x 106 cfu/g fungi. The moisture and fat contents of the freeze dried cow milk and soybean milk decreased significantly (P < 0.05) from 54.02% to 4.28%, 18.11% to 4.05% and 50.89% to 4.19%, 19.02% to 4.30% respectively. Freeze drying significantly decreased the bacteria and fungi contents of fresh cheeses; it decreased from 3x103 cfu/g to 2.72 x 103 cfu/g, 2.54 x 106 cfu/g to 2.35 x 106 cfu/g, and 2.76 x 103 cfu/g to 2.54 x 103 cfu/g, 2.60 x 106 cfu/g to 2.38 x 106 cfu/g for cow milk and soy milk cheese respectively. The carbohydrate, protein, ash content, calcium, sodium, magnesium, taste, appearance, flavour, acceptability of the cow milk cheeses increased significantly (P < 0.05) when freeze dried. Decreases in moisture content, fat and microbial counts of cheeses would enhance its stability and shelf life if properly packaged.

scholarly journals Molecular fractionation of a soil fulvic acid (FA) and competitive sorption of trace metals (Cu, Zn, Cd, Pb) in hematite–solution systems: effect of the FA-to-mineral ratio

RSC Advances ◽  
2017 ◽  
Vol 7 (68) ◽  
pp. 43090-43103 ◽  
Author(s):  
Guillaume Fleury ◽  
Mirella Del Nero ◽  
Remi Barillon
Keyword(s):  
Organic Matter ◽  
Trace Metals ◽  
Fulvic Acid ◽  
Fulvic Acids ◽  
Competitive Sorption ◽  
Mineral Solution ◽  
Molecular Fractionation ◽  
Micro Pollutants

Understanding of the interactions occurring between fulvic acids (FAs) and trace metals in mineral–solution systems is a major issue for cycles of organic matter and micro-pollutants in surface media.

Scanning Electron Microscopy-cuticular Lesions on the Roundworm Ascaris Suum

1970 ◽  
Vol 28 ◽  
pp. 114-115
Author(s):  
P. A. Madden ◽  
W. R. Anderson
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Freeze Drying ◽  
Room Temperature ◽  
Secondary Electron ◽  
Distilled Water ◽  
Freeze Dried ◽  
Silver Paint ◽  
To Come ◽  
Scanning Electron

The intestinal roundworm of swine is pinkish in color and about the diameter of a lead pencil. Adult worms, taken from parasitized swine, frequently were observed with macroscopic lesions on their cuticule. Those possessing such lesions were rinsed in distilled water, and cylindrical segments of the affected areas were removed. Some of the segments were fixed in buffered formalin before freeze-drying; others were freeze-dried immediately. Initially, specimens were quenched in liquid freon followed by immersion in liquid nitrogen. They were then placed in ampuoles in a freezer at −45C and sublimated by vacuum until dry. After the specimens appeared dry, the freezer was allowed to come to room temperature slowly while the vacuum was maintained. The dried specimens were attached to metal pegs with conductive silver paint and placed in a vacuum evaporator on a rotating tilting stage. They were then coated by evaporating an alloy of 20% palladium and 80% gold to a thickness of approximately 300 A°. The specimens were examined by secondary electron emmission in a scanning electron microscope.

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