Pyrolysis GC Research Articles

Molecular characterisation of the dissolved organic matter of wastewater effluents by MSSV pyrolysis GC–MS and search for source markers

Microscale sealed vessel pyrolysis (MSSVpy) was used to characterise the hydrophobic (HPO) and colloid (COL) fractions of dissolved organic matter (DOM) from the effluents (EFFs) of two waste water treatment plants (WWTPs) and several primary source waters (SWs). The EFFs showed a large range of anthropogenically sourced organics – including the metabolites of industrial chemicals (e.g., dioxanes, n- and sec-alkyl substituted benzenes and long chain alkyl phenols), pharmaceuticals (e.g., N- and S-heterocycles) and human waste (e.g., S- and N-organics, steranes/sterenes) – as well as high concentrations of alkyl aromatic and N-organic products (e.g., alkyl indoles, carbazoles and β-carbolines) attributed to the treatment biota. Some anthropogenic chemicals are potentially toxic at even trace levels, whilst the N-organics may be precursors for toxic N-disinfection by-products. Much lower concentrations of just a few of the anthropogenic and N-organic products were detected by more traditional flash pyrolysis (Flash-py) of the EFF samples, reflecting the higher sensitivity of MSSVpy to many chemical functionalities. Few of these products were detected in the corresponding MSSVpy analysis of the SWs, but these samples did show relatively high abundances of lignin (e.g., alkylphenols) and carbohydrate (e.g., furans) derived products. Their lower EFF abundances are consistent with efficient removal by the water treatment procedures applied. Conversely, the detection of the anthropogenics in the treated EFFs reflects their general resistance to treatment. Their occurrence in the HPO fractions isolated by XAD resin separation suggests a potential relationship with the structurally stable macromolecular fraction of the DOM.

Yields of Mine Fuel under the Heat Effect of Fire Flame when Methane Explosions

Abstract In order to study the mechanism of second-fire induced by methane explosions, the yields of several main fuels in mine were studied through doing some fast pyrolysis experiments. Use courier point fast pyrolysis system and GC to do this experiment. All experiment conditions fulfill methane explosions environment thoroughly. The experiment results show that the yields mainly include CH4, C2H4, C2H6, C3H6, C3H8, C4, C5, CO, CO2 etc. Where, CH4, C2H4, C3H6, C4, C5, CO, CO2 yields are larger than others. Only supporting wood has H2, and only PVC has HCl but others. And include some dangerous flammable gas such as CH4, CO, H2 etc. The model and influence factors show that temperature and heating rate have great influence on yields but pressure, especially temperature. All results show that methane explosions could produce some flammable gas which out of fuel, and could induce second fire.

Pyrolysis GC–MS as a rapid screening tool for determination of peat-forming plant composition in cores from ombrotrophic peat

Peat cores provide decadal to centennial records of climatic and environmental change, including evidence for human/environment interaction. Existing palaeoenvironmental proxies (macrofossils, pollen, humification, testate amoebae, lipid composition) require multiple laboratory preparation steps and may be subject to differential preservation that can limit production of a continuous time series. The potential for pyrolysis gas-chromatography–mass-spectrometry (Py–GC–MS) to be applied to bulk peat samples is investigated here. The only preparatory step required was freeze drying. Analysis of a range of important peat-forming plants demonstrates that Sphagnum moss species are unique in containing the pyrolysis product of sphagnum acid, 4-isopropenylphenol. In contrast, non- Sphagnum species are rich in lignin pyrolysis products, which are absent from Sphagnum. The presence of these pyrolysis markers is reflected in bulk peat composition and tested here using archives from Bolton Fell Moss and Butterburn Flow (UK), Kontolanrahka (Finland) and Bissendorfer Moor (Germany). A ratio between 4-isopropenylphenol and two lignin pyrolysis products is proposed as a proxy for total Sphagnum input to peat archives and shows potential for use as a rapid screening tool for characterising bulk peat composition before more intensive analysis.

Biological pretreatment of wheat straw by Phanerochaete chrysosporium supplemented with inorganic salts

Inorganic salts and tween 80 are known to induce the lignin degrading peroxidase expression of Phanerochaete chrysosporium in submerged culture. In this study, the wheat straw pretreatment supplemented with inorganic salts (salts group), tween 80 (plus) and no supplementation to the biomass (minus) were examined. Among the solid state fermentation groups, salts group resulted in a substantial degradation of wheat straw within one week, along with the highest lignin loss (25%) and ∼250% higher efficiency for the total sugar release through enzymatic hydrolysis. The results were correlated with pyrolysis GC-MS (Py-GC-MS), thermogravimetric (TG)/differential thermogravimetric (DTG) and X-ray diffraction (XRD). The results suggested that the supplementation of inorganic salts in the solid state fermentation of wheat straw significantly enhances the degradation rate of the biomass by P. chrysosporium which can be exploited as an alternative means to existing pretreatment technologies.

Characterization of organic particulates present in milk factory process waters used for reuse along with aerobically digested effluent wastewater

Wastewater from a dairy processor is being reused and recycled both within the plant and for irrigation. Flash pyrolysis GC-MS was used to examine nitrogen and phenol containing compounds (M.W.=35 to 450 g/mol) in the particulate fraction of the milk condensate, combined clean wastewater and aerobic bioreactor effluent. For comparison, the particulates were also prepared for standard GC-MS analyses using conventional solvent extraction methods. Compounds detected by pyrolysis GC-MS were found mostly in the bioreactor with the amino acid arginine (220 mg/kg) and the amino acid derivative 1-methyl-5-oxo-L-proline methyl ester (130 mg/kg) found at the highest concentrations. In comparison, sterols detected in the effluent were found at higher concentrations when using solvent extraction indicating some degradation with pyrolysis GC-MS. However, with few exceptions, particulates were generally found not to act as passive collectors capable of concentrating less water soluble chemicals.

Synthesis and thermal properties of spiro phosphorus compounds

Abstract Intumescent materials, 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecane-3,9-dioxideand 3,9-dichloro-2,4,8,10-tetraoxa-3,9-diphosphaspiro-[5,5]-undecane having the capacity to produce dehydratingagent, blowing agent, and undergo carbonization duringburning have been synthesized. The thermal behavior ofthe synthesized materials was investigated using differen-tial thermal analysis, thermal volatilization analysis, pro-grammed vacuum pyrolysis–mass spectrometry, flashpyrolysis–mass spectrometry and off-line pyrolysis–gaschromatography–mass spectrometry. The materials showexothermic degradation after 250 C. Monitoring therelease of hydrogen chloride and water, the blowing agentsfor the production of carbon foam, clearly indicated thesuperior performance of the pentavalent phosphorus com-pound over the trivalent phosphorus compound. The majorgaseous degradation products released during pyrolysisshowed the presence of sufficient quantities of severalalkyl-substituted benzenes and fused aromatics. Suitabledegradation mechanism has been proposed and discussedto explain the formation of various organics during thermaldegradation.Keywords Spiro phosphorus compounds Intumescence Thermal analysis Flash pyrolysis–mass spectrometry Off-line pyrolysis–GC–MSIntroductionIn the modern world, we the people live with flammableproducts such as chemicals, textile, upholstery, computers,mobile phones, etc. Flammability depends on the chemicalcomposition of the materials which generate huge amountof heat, subsequently release toxic corrosive gases oncombustion/pyrolysis [1]. Hence, it is necessary to developthermally stable products by modifying the chemicalstructure or to make the material thermally stable bycompounding it with flame retardants [2]. Usually, theincorporation of flame retardant additives or the develop-ment of flame retardant coating for flammable materials isa cost effective and easiest method for improved thermalstability.Flame retardant is a chemical substance, which inhibitsor retards physically or chemically the combustion processby releasing non-flammable products or altering the deg-radation path and allows more time for people to escapefrom the fire hazard [3, 4]. Halogenated flame retardantsremove reactive H and OH radicals, which are producedduring combustion. According to environment concerns theuse of halogenated flame retardant systems are restricted[5–7]. Inorganic metal hydroxides such as aluminumhydroxide, magnesium hydroxide, etc., are used to retardthe flammability, for effective achievement relatively highloadings are used and hence it alters the existing property[8]. Compounds having phosphorus can be effectively usedto impart flame retardancy. It traps the radicals formed in

A Review of Synthetic Polymer Characterization by Pyrolysis–GC–MS

Pyrolysis–GC with mass spectrometry detection (Py–GC–MSD) study of the thermal degradation products of synthetic polymers is reviewed. Due to the high heating speed, accurate temperature reproducibility and a wide temperature range, Py–GC–MSD has been applied successfully for polymer characterization. Introduction of samples using the pyrolysis carrier gas through the split injection port, followed by sub-ambient cryofocusing of the pyrolysis products, has shown to give reproducible chromatograms (pyrograms). One of the advantages of this method is that all compositions of the polymers and additives can be investigated without any pretreatment, providing important compositional and structural information in a simple way. The method is a convenient method for compositional analysis of complex polymer materials. The aim of this review is to describe the kinds of applications for which Py–GC–MSD has been found to be suitable; to present guidelines for method optimization; to survey innovations that have recently been developed or are currently being researched; to point to problems in our understanding of the pyrograms; and to suggest areas in which research efforts might be most effective in realizing the full potential of this technique.

Microscopic structure features changes of rice straw treated by boiled acid solution

This study focuses on the determination of structure change of surface area, morphology, crystallinity and pyrolysis characteristics of cellulosic feedstock treated by hot acid solution. The microscopic structure change of acid-treated samples was examined by using BET, SEM/EDX, XRD and pyrolysis–GC–MS under reasonable condition. Results showed that both surface area and pore volume of treated sample were conspicuous increased partial due to dissolution of silica and organic polar-components. Morphological change of plant cell wall surface was viewed as damage such as exfoliation, cave and fracture appeared on epidermis, vascular bundles. The crystallinity index of residual cellulose microcrystalline was widely enhanced because amorphous hemicellulose was removed off while crystalline was changeless. Under hot acid solution reaction, amorphous hemicellulose was hydrolyzed and leaving larger perfect cellulose thus increasing of crystalline size. Those available cellulose was obvious exposed after acid treatment and gave intensive characteristic peak on pyrogram analyzed by pyrolysis–GC–MS.

On the occasion of Professor Werner Engewald’s 70th birthday

In this issue of Analytical and Bioanalytical Chemistry you will find a tribute to Professor Emeritus Werner Engewald on the occasion of his 70th birthday. I got to know Werner Engewald when I was a student at the University of Leipzig attending my first lectures on separation science. He has been a mentor and advisor ever since and it is my great honor and pleasure to start this issue with a few reflections on his work and vitae. Werner was born in Glauchau, a small town in Saxony, Germany, in August 1937. He studied chemistry at the University of Leipzig from 1957 to 1962 and obtained his Ph.D. in 1968. In the same year, he attended an international symposium on chromatography in Berlin, and I believe it was back then that he discovered his passion for the separation sciences. After postdoctoral studies in 1971 under A.V. Kislev at the Moscow State University he returned to Leipzig and obtained his habilitation in 1978. In 1979 he was appointed assistant professor in analytical chemistry, and later became a full professor. His scientific interests cover a broad range, including structure–retention relationships in gas chromatography, chromatographic multicomponent analysis, environmental trace analysis, and various sample preparation techniques. He is also interested in hyphenated techniques, such as GC–MS and GC–AED, adsorptive enrichment in combination with thermal desorption, pyrolysis GC, and more recently LC–MS techniques. Werner has mentored more than 35 Ph.D. students, and he is still in contact with many of them. He has published over 200 articles, reviews, and book chapters. Besides the challenging task of running a research group, Werner has always set time aside for professional activities such as serving as departmental head. Werner is also an active member of the separation science working group in the analytical chemistry division of the German Chemical Society; he has served as chairman of the working group and is still a board member of the analytical chemistry division of the German Chemical Society. Over the years he has participated on the editorial boards of several journals, including Fresenius’ Journal of Analytical Chemistry, and reviewed countless manuscripts. In cooperation with the German Chemical Society, he has organized many well-known training courses in gas Anal Bioanal Chem (2007) 388:1631–1632 DOI 10.1007/s00216-007-1380-2

Williamsia serinedens sp. nov., isolated from an oil-contaminated soil

The taxonomic status of a bacterium designated strain IMMIB SR-4(T) isolated from an oil-contaminated soil sample was characterized by using a polyphasic approach. Chemotaxonomic investigations revealed the presence of cell-wall chemotype IV, short-chain mycolic acids that co-migrated with those extracted from members of the genus Williamsia and that on pyrolysis GC produce C(16 : 0) and C(18 : 0) fatty acids, and dihydrogenated menaquinone with nine isoprene units as the predominant menaquinone. The generic assignment was confirmed by 16S rRNA gene sequence analysis. Comparative analysis of the 16S rRNA gene sequence showed that strain IMMIB SR-4(T) formed a distinct phyletic line within the genus Williamsia, displaying sequence similarities of 95.5-98.1 % with the type strains of recognized Williamsia species. Strain IMMIB SR-4(T) was distinguished from the type strains of recognized species of the genus Williamsia based on a set of phenotypic features. The genotypic and phenotypic data indicated that strain IMMIB SR-4(T) represents a novel species of the genus Williamsia, for which the name Williamsia serinedens sp. nov. is proposed. The type strain is IMMIB SR-4(T) (=DSM 45037(T)=CCUG 53151(T)).

Thermal Degradation Analysis of Amino Acids in Fingerprint Residue by Pyrolysis GC–MS to Develop New Latent Fingerprint Developing Reagents*

Conventional development of latent fingerprints is compromised when the prints are decomposed by extreme temperatures, such as those encountered when a weapon cartridge is fired, an improvised explosive device is detonated, and/or in arson cases. Understanding how these extreme temperatures alter the chemical and physical properties of latent fingerprint residue could aid in the discovery of a reagent that could effectively develop these decomposed fingerprints. To mimic scenarios where fingerprints may be exposed to high heat conditions, standards of the five most abundant amino acids in fingerprint residue as well as extracted fingerprint residue were pyrolized under controlled conditions. Compounds identified as pyrolytic decomposition products were 3,6-dimethylpiperazine-2,5-dione (from alanine), maleimide, and 2,5-furandione (from aspartic acid). The pyrograms and selected ion traces show these products to hold promise as indicators of decomposed fingerprint residues and, therefore, may serve as good candidate substrates for a developing reagent.

Catalytic charring–volatilization competition in organoclay nanocomposites

The thermal behaviour of organoclays, and especially their organic treatment, is an important issue in polymer nanocomposite preparation and their fire retardant properties. The thermal behaviour of the organomodifier is strongly affected by the different composition parameters of the clays. Thus the thermal degradation, in inert and in oxidative atmosphere, of natural montmorillonite and synthetic fluorohectorite both exchanged with polar and non-polar organomodifiers was studied using a combined thermogravimetry/Fourier transform infrared and a flash pyrolysis GC–MS system. Decomposition and charring mechanisms of the organic molecules in the clays are proposed for each kind of clay and a relationship between the composition of the clays and the kinetics of the decomposition reactions is found. Furthermore, it is shown that the charring–volatilization competition on heating organoclays in the presence of oxygen depends on the structure of the clay, the confined or unconfined position of the organic molecules and their polarity.

Universal and discriminative detection using a miniaturized pulsed discharge detector in comprehensive two‐dimensional GC

A miniaturized pulsed discharge detector (Mini-PDD) has been successfully demonstrated for comprehensive 2-D GC (GC x GC) analysis of pyrolysis gasoline and the pyrolysis GC x GC analysis of a polyethylene copolymer. The detector cell volume of the Mini-PDD is reduced to 25% of the Valco plug-in PDD D-3. An n-C11 peak width at base is 96 ms for the Mini-PDD, about 23% larger than a peak width of 78 ms detected by a flame ionization detector (FID). The Mini-PDD has sufficient response time for most GC x GC applications. When Mini-PDD is operated in helium photoionization mode (Mini He-PDD), it is a universal detector for both inorganic and organic compounds. This is especially useful when detection of water is needed in GC x GC applications. When krypton is doped in the helium discharge gas (Mini Kr-PDD), it can suppress signals of compounds having higher ionization potentials and enhance relative signal intensities of aromatic compounds. The determination of aliphatic to aromatic hydrocarbon ratios is essential to the operation of petroleum crackers. Comparison of the signal from two modes of the Mini-PDD is a simple and fast way to verify the location of aromatics in comprehensive 2-D gas chromatograms.

The significance of kinetic parameters and structural markers in source rock asphaltenes, reservoir asphaltenes and related source rock kerogens, the Duvernay Formation (WCSB)

Asphaltenes from reservoir oils, source rock bitumen and the kerogen of related source rocks of the Duvernay Formation (WCSB) have been studied in order to compare their petroleum generation characteristics. Open system bulk petroleum pyrolysis for bulk kinetic evaluation and geological extrapolation and pyrolysis GC experiments for petroleum compositional characterisation were applied in order to evaluate the reliability of petroleum asphaltenes in source rock evaluation studies in which a potential source rock sample is not available. Kinetic parameters and resulting geological extrapolations of petroleum formation calculated on immature source rock kerogens and asphaltenes fit exactly to corresponding parameters measured on asphaltenes precipitated on low mature oils. In contrast molecular characteristics such as aromaticity and the amount of alkylated thiophenes reveal highest values in source rock asphaltenes, while oil asphaltenes demonstrate lowest aromaticity. Source rock kerogens seem to represent an intermediate between both types of asphaltenes at low levels of maturity. Interestingly the molecular ratios observed in products formed from oil asphaltenes fit exactly to those observed in natural oils and support the application of petroleum asphaltenes to predict petroleum formation and especially petroleum compositional characteristics.

Influence of particle size on the analytical and chemical properties of two energy crops

Two energy crops (switchgrass and reed canary grass) have been processed using ball mills and divided into two size fractions (<90 μm and 90–600 μm) and analysed using an array of analytical techniques including proximate and ultimate analysis, metal analysis, calorific value determination, and plant component analysis (cellulose, lignin and hemicellulose contents). The results indicate that smaller particles of the two grasses have a significantly higher concentration of inorganic matter and moisture content than larger particles. In contrast the larger size fractions had a higher carbon content, and lower nitrogen content, with a resulting higher calorific value. The volatile content was also higher in the larger size fraction. The composition of the organic content varied between the two size fractions, most noticeable was the difference in cellulose concentration which was approximately 50% higher in the >90 μm sample. Two laboratory scale techniques, thermogravimetric analysis (TGA) and pyrolysis–GC–MS (py–GC–MS), were used to study the significance of these differences in thermal conversion. In py–GC–MS of reed canary grass, and switchgrass to a lesser extent, the amounts of cellulose and lignin decomposition products were higher for the larger particle size fraction. The differences in cellulose contents were also apparent from the TGA studies, where different mass losses were seen in the cellulose decomposition region of the two size fractions. From the results of these two techniques it was concluded that the differences in ash, and therefore catalytic metal contents, between the two size fractions, resulted in lower pyrolysis temperatures, lower char combustion temperatures, and higher yields of catalytic pyrolysis decomposition products for the smaller size fractions. The implications of the results are discussed in terms of the bio-oil quality in fast pyrolysis and the predicted behaviour of the ash in combustion. It is suggested that pre-treatment by milling is one route that might be used routinely as a feedstock quality improvement strategy in integrated biomass conversion processes.

Structural features of lignite humic acid in light of NMR and thermal degradation experiments

Structural composition of a lignite humic acid (HA) fraction was studied by means of solid-state 13C NMR, different solution-state 1H NMR pulse techniques and thermally assisted hydrolysis–methylation with TMAH and TMAAc followed-up with pyrolysis–GC–MS experiments. The results verified that certain aliphatic compounds have their special tasks in the complicated structural network of lignite HA material, and aprotic solvents with strong electron-donor powers are needed to release the tightly bound certain aliphatics from the macromolecular network for obtaining a fully dissolved HA solution. The occurrence of the relatively large content of different carboxylic acids as their free-acid forms was surprising. The structural interpretations performed by special 1H NMR pulse techniques verified the complexity of aliphatic moieties, the presence of hydroaromatic carbons, residual lignin derivatives, the abundance of aliphatic and aromatic carboxylic acids, and the ability of aliphatics to form intermolecular bridges between aromatic building blocks.

Pyrolysis GC–MS and THM-GC–MS studies of a black coating from Little Lost River Cave, Idaho

A black, shiny coating overlies rock paintings in Little Lost River Cave No. 1, located in southeastern Idaho. If this coating is the result of human activity within the cave – a condensate from cooking fires, for example – then a radiocarbon date on the coating would provide a minimum age for the underlying paintings. The work reported here was undertaken to test the assumption that the coating has an anthropogenic origin. Using pyrolysis-gas chromatography–mass spectrometry (py-GC–MS) and thermally assisted hydrolysis-methylation-GC–MS, we have compared samples of the black coating from Idaho to humic acid, an experimental cooking residue, and amberat from packrats. The results show that the coating is not amberat, but bears the most similarity to humic acid, which would indicate a geologic origin for the coating. The age of the coating, then, is not likely related to the age of the paintings.

Williamsia deligens sp. nov., isolated from human blood

The taxonomic status of two bacterial strains isolated from human blood was characterized using a polyphasic approach. Chemotaxonomic investigations revealed the presence of cell-wall chemotype IV, short-chain mycolic acids that co-migrated with those extracted from members of the genus Williamsia and that produce C(16 : 0) and C(18 : 0) fatty acids on pyrolysis GC, and dihydrogenated menaquinone with nine isoprene units as the predominant isoprenologue. The generic assignment was confirmed by 16S rRNA gene sequencing. Comparative analysis of the 16S rRNA gene sequence showed that these isolates constitute a distinct phyletic line within the genus Williamsia, displaying 96.2 and 97.2 % sequence similarities to Williamsia muralis and Williamsia maris, respectively. The two isolates could be distinguished from the type strains of the latter species on the basis of several phenotypic traits. The genotypic and phenotypic data show that the strains merit classification as a novel species of Williamsia, for which the name Williamsia deligens sp. nov. is proposed, with type strain IMMIB RIV-956T (= DSM 44902T = CCUG 50873T).

Coordination complexes of functionalized pyrazines with metal ions: reagents for the controlled release of flavourant molecules at elevated temperatures

The potential for stabilization of volatile flavourant molecules such as functionalized pyrazines by coordination to metal ions, and the application of the resultant coordination complexes as controlled release agents at elevated temperatures were explored. New complexes containing the flavourant molecules 2,3,5-trimethylpyrazine (TMP), 2-ethyl-3-methylpyrazine (EMP) and 2-acetylpyrazine (ACP) with copper(II) and copper(I) salts were prepared and structurally characterized. Representative examples of known copper(II) and calcium(II) complexes containing pyrazine carboxylic acids were also prepared. The complexes were examined by thermal analysis techniques and demonstrated, by a combination of thermogravimetric (TGA) and pyrolysis GC–MS analyses, to act as convenient reagents for the release of the parent pyrazine at elevated temperatures. Thus, pyrolysis GC–MS revealed that the complex [Cu3Cl3(EMP)2]n cleanly releases EMP in 96.5% selectivity at 200 °C. Of particular significance is that the calcium complex [Ca(3-aminopyrazine-2-carboxylate)2·H2O], under ramped pyrolysis conditions, was shown to undergo decarboxylation prior to the release of 2-aminopyrazine (AMP), as essentially the only volatile component, in the temperature range 600–800 °C. This finding provides a precedent for the application of complexes of pyrazinecarboxylate salts with metal ions (of which an almost infinite number of combinations is potentially available) as controlled release agents of the parent pyrazine molecule at elevated temperatures, suitable for exploitation by the foodstuffs, flavour and fragrance industries. Copyright © 2006 John Wiley & Sons, Ltd.

La Medusa by Caravaggio: characterisation of the painting technique and evaluation of the state of conservation

The oil painting “La Medusa” executed by Caravaggio at the end of the XVI century on a wooden shield, was investigated by integrated physical–chemical and analytical methodologies in order to obtain scientific data capable of elucidating the state of conservation and the painting technique. Optical (OM) and electronic (SEM-EDS) microscopy, micro-FT-IR spectroscopy, gas chromatography–mass spectrometry (GC–MS) and pyrolysis GC–MS were applied on two microfragments and some organic samples obtained by solvent extraction using the swab cleaning technique. The obtained results indicated that Caravaggio probably reused an old shield as a previous gypsum preparation layer has been detected under the original painting layers. He used white lead, natural earths, verdigris and lead–tin yellow type I mixed with drying oils to paint. The considerable amount of amorphous particles of copper chlorides found in the green pigment verdigris suggests that it could have been produced according to the ancient recipe of verde salsum described by Theophilus. Mordant gilding has been identified on the upper part of the shield that can be related to an abandoned experiment to give the painting a mirror-like reflecting effect. Three different varnishes layers have been detected above the painted surface. The original and restoration varnishes have been identified and they contain a mixture of drying oil, mastic and turpentine and some beeswax. Cleaning tests, performed with different organic solvents, suggest the use of isopropyl alcohol as cleaning agent because it is less efficient in comparison to others solvents; thus it ensures a careful and controlled removal of the varnishes.