MS Measurements Research Articles

An azido coumarin-quinoline conjugated fluorogenic dye: Utilizing amide-iminol tautomerism for H2S detection in live MCF-7 cells.

Detection of H2S to analyze some diseases in living lives demands fast response, high selectivity and biocompatibility. Here we designed an azide containing coumarin attached with 8-aminoquinoline via amide backbone (ACAQ) fluorophore as the H2S sensing probe. Excellent response time of 6min, high sensitivity with the limit of detection (LOD) of 14.6nM and high selectivity with other possible interferences are revealed for ACAQ after characterized by spectroscopy, 1H NMR titration and LC-MS measurements. The sensing strategy is explained by amide-iminol tautomerism and azide reduction. In addition, the successful visualization measurement suggests the practicability of the probe ACAQ for H2S detection in live samples.

Lead-Doped Titanium-Oxo Clusters as Molecular Models of Perovskite-Type PbTiO3 and Electron-Transport Material in Solar Cells.

In this work we have successfully prepared two lead-doped titanium-oxo clusters with core structures that resemble isolated perovskite PbTiO3 species. In the obtained highly symmetric Pb8 Ti7 -oxo cluster, the central TiO6 octahedra are orthogonally extended to adjacent octahedra through corner-sharing and the eight dopant lead ions form a cubic arrangement, making it the first molecular model of perovskite PbTiO3 . Moreover, the clusters readily dissolved in chloroform and showed high solution stability, as confirmed by MALDI-TOF MS measurements. Based on such solution processability, they can be easily spin-coated to form homogeneous films, which were employed as electron-transport materials in perovskite solar cells to give an average power conversion efficiency of around 15 % and improved device stability. This newly developed bottom-up cluster assembly method provides an efficient approach to the construction of atomically precise models of perovskite metal oxides as well as potential molecular tools to extend their applications.

Fast and Highly Efficient Affinity Enrichment of Azide-A-DSBSO Cross-Linked Peptides.

Cross-linking mass spectrometry is an increasingly used, powerful technique to study protein–protein interactions or to provide structural information. Due to substochiometric reaction efficiencies, cross-linked peptides are usually low abundance. This results in challenging data evaluation and the need for an effective enrichment. Here we describe an improved, easy to implement, one-step method to enrich azide-tagged, acid-cleavable disuccinimidyl bis-sulfoxide (DSBSO) cross-linked peptides using dibenzocyclooctyne (DBCO) coupled Sepharose beads. We probed this method using recombinant Cas9 and E. coli ribosome. For Cas9, the number of detectable cross-links was increased from ∼100 before enrichment to 580 cross-links after enrichment. To mimic a cellular lysate, E. coli ribosome was spiked into a tryptic HEK background at a ratio of 1:2–1:100. The number of detectable unique cross-links was maintained high at ∼100. The estimated enrichment efficiency was improved by a factor of 4–5 (based on XL numbers) compared to enrichment via biotin and streptavidin. We were still able to detect cross-links from 0.25 μg cross-linked E. coli ribosomes in a background of 100 μg tryptic HEK peptides, indicating a high enrichment sensitivity. In contrast to conventional enrichment techniques, like SEC, the time needed for preparation and MS measurement is significantly reduced. This robust, fast, and selective enrichment method for azide-tagged linkers will contribute to mapping protein–protein interactions, investigating protein architectures in more depth, and helping to understand complex biological processes.

Effects of Tin in La-Sn-Codoped Zn(O,S) Photocatalyst to Strongly Cleave the Azo Bond in Azobenzene with in Situ Generated Hydrogen.

La-Sn-codoped Zn(O,S) catalysts were synthesized with different amounts (0%, 2.5%, 5%, and 10%) of Sn and a constant amount (10%) of La to improve the photocatalytic hydrogenation reaction (PHR) of azobenzene to aniline. The as-prepared catalysts were carefully characterized and tested for a hydrogenation reaction. The incorporation of Sn significantly enhanced the PHR activities since the incorporated Sn in the Zn(O,S) lattices could increase the conductivity of the catalysts to improve the charge transfer during the catalytic reaction as indicated with EIS measurement. Further measurement with a photoresponse of La-Sn-codoped Zn(O,S) catalysts also exhibited relatively higher intensities as compared to those of La-doped Zn(O,S) and Sn-doped Zn(O,S) catalysts. On the basis of the measurement results of EIS and transient photo current, the La-Sn-codoped Zn(O,S) with the best properties was further utilized for PHR to convert azobenzene to aniline. GC-MS measurement confirmed that 15 ppm azobenzene could be totally converted to aniline in only 60 min which was achieved with a catalyst that was prepared with 5%-Sn and 10%-La doping. The relatively short reaction time indicated that the as-prepared catalyst had a strong reduction capability able to cleave the strong bonding of N═N in azobenzene. The reaction kinetic of the N═N bond cleavage was elucidated based on solvation, adsorption, pinning, and photocatalytic hydrogenation processes on the catalyst surfaces.

Addition of two kerosene-based fuels to diesel–biodiesel fuel: Effect on combustion, performance and emissions characteristics of CI engine

This work investigates the effect of adding two kerosene-based fuels namely jet fuel (J100) and paraffinic solvent (P100) to diesel and diesel–biodiesel blends on performance, combustion characteristics and emissions of high-compression ratio (21.5) compression ignition (CI) engine. Engine experiments were conducted at a constant speed of 2000 rpm over the entire load span. Experiments were performed using a single cylinder, air-cooled, 4-stroke, direct injection CI engine. Three volume-based blending ratios including 5%, 10% and 15% of each additive were separately-blended with neat diesel and with B30 (70% diesel, 30% biodiesel). The two additives have a same number of carbon atoms C10−C13. FT-IR and GC–MS measurements showed that J100 has higher aromatic/less paraffinic contents than P100. Engine experiments revealed that for binary blends, adding 15% of J100 and P100 to diesel achieved maximum average reduction of 8.4% and 5.6% in brake specific fuel consumption (bsfc), respectively. Ternary blends kept running on bsfc close to this of diesel. For binary blends, stable performance of the engine was attained only with up to 10% addition of P100 or J100. For ternary blends, stable performance was achieved up to 10% and 15% of P100 and J100, respectively. Maximum reduction in NOx emissions of 38.7% was achieved for D95-P5. While B30-J15 achieved maximum reduction in CO emission of 50.3%. Using optimization maps, 10% and 15% of J100 were found as the optimum blending ratios for binary and ternary blends, respectively. These ratios achieve stable and economic performance with low NOx and CO emissions.

The FIREBIRD-II CubeSat mission: Focused investigations of relativistic electron burst intensity, range, and dynamics.

FIREBIRD-II is a National Science Foundation funded CubeSat mission designed to study the scale size and energy spectrum of relativistic electron microbursts. The mission consists of two identical 1.5 U CubeSats in a low earth polar orbit, each with two solid state detectors that differ only in the size of their geometric factors and fields of view. Having two spacecraft in close orbit allows the scale size of microbursts to be investigated through the intra-spacecraft separation when microbursts are observed simultaneously on each unit. Each detector returns high cadence (10 s of ms) measurements of the electron population from 200 keV to >1 MeV across six energy channels. The energy channels were selected to fill a gap in the observations of the Heavy Ion Large Telescope instrument on the Solar, Anomalous, and Magnetospheric Particle Explorer. FIREBIRD-II has been in orbit for 5 years and continues to return high quality data. After the first month in orbit, the spacecraft had separated beyond the expected scale size of microbursts, so the focus has shifted toward conjunctions with other magnetospheric missions. FIREBIRD-II has addressed all of its primary science objectives, and its long lifetime and focus on conjunctions has enabled additional science beyond the scope of the original mission. This paper presents a brief history of the FIREBIRD mission's science goals, followed by a description of the instrument and spacecraft. The data products are then discussed along with some caveats necessary for proper use of the data.

Interactions of indole alkaloids with myoglobin: A mass spectrometry based spectrometric and computational method.

Interactions of drug molecules and proteins play important roles in physiological and pathological processes in vivo. It is of significance to establish a reliable strategy for studying protein-drug ligand interactions and would be helpful for the design and screening of new drugs in pharmacological research. The interactions between four indole alkaloids (IAs) extracted from Ophiorrhiza japonica (O. japonica) and myoglobin (Mb) protein were investigated using a multi-spectrometric and computational method of native electrospray ionization mass spectrometry (native ESI-MS), hydrogen/deuterium exchange mass spectrometry (HDX-MS), circular dichroism (CD) and molecular docking (MD). The IA-bound Mb complexes were analyzed using native ESI-MS, with the obtained protein-to-ligand stoichiometry at 1:1, 1:2 and 1:3. Binding constants were measured according to the interpretation of MS spectra. MD complemented MS measurements, probing the binding sites and modes of the four IAs to Mb. Analyses involving CD and HDX-MS demonstrated that exposure to IAs could affect the conformation of Mb by decreasing the α-helix content and made Mb more susceptible to HDX at the backbone. A new MS-based integrated analysis method has been developed to successfully study the interactions of Mb and IAs extracted from O. japonica. The experimental and calculation results have good consistency, revealing all of the four IA molecules could bind to Mb to form 1:1, 1:2 and 1:3 Mb-IA complexes. The order of binding ability of these IAs to Mb was ophiorrhine B > compound C > ophiorrhine A > compound D. CD and HDX-MS results indicated that binding with IAs destabilizes Mb. HDX-MS analysis suggests that Mb becomes more susceptible to HDX, indicating that binding with IAs destabilizes the structure of Mb. In addition, the interaction with IAs affected the overall structure of Mb, ascribed to the decrease of α-helix content and less folding of the backbone.

R-Hexitronic acid, a new tetronic acid derivative isolated from a soil fungus FG9RK

A new tetronic acid derivative (1) together with terrestric acid (2), a known metabolite of Penicillium species, was isolated from the soil fungus, FG9RK following fermentation on solid rice medium. The structure of 1 was elucidated by one- and two-dimensional NMR and MS measurements. The absolute configuration of the oxygenated carbon in the side chain of 1 was identified as S by converting the compound into its Mosher ester whereas the absolute configuration of the lactone ring was deduced based on biogenetic considerations and comparison with 2.

DNA Binding, Molecular Docking and Antimicrobial Evaluation of Novel Azo Dye Ligand and Their Metal Complexes

In the present work, the synthesis of novel azo dye ligand 6-hydroxy-4-methyl-2-oxo-1-propyl-5-[(E)-1,3-thiazol-2-yldiazenyl]-1,2-dihydropyridine-3-carbonitrile (L) and its Cu(II), Co(II) and Ni(II) transition complexes were prepared. The newly formed compounds were characterized by elemental analysis, UV–Vis, FT-IR, 1H NMR, LC–MS, TGA and magnetic susceptibility measurement. The molar conductance indicates that all the metal complexes are non-electrolytic in nature Based on spectral data indicate square planar geometry was deduced for Cu(II) and Ni(II) complexes, Co(II) complex has tridentate chelation of ligand and produce an octahedral geometry around the metal ion. Additionally, the computational study has been performed using density functional theory (DFT) calculation was used to study the electronic structure of synthesized ligand and their complexes. The in vitro antimicrobial activity of the azo dye ligand and its complexes was tested against Gram +ve bacteria (Bacillus subtilis), Gram –ve bacteria (Escherichia coli), yeast (Candida albicans) and fungus (Aspergillus flavus). All the complexes showed enhanced biocidal activity compared to the free ligand. Moreover, azo dye ligand and its metal complexes have been studied for their antioxidant activity. The DNA-binding activity of metal complexes (1a–1c) was studied by electronic absorption spectroscopy and fluorescence spectroscopy. All the complexes bound to CT-DNA through an intercalation mode. Additionally, all the metal complexes act as good cleavage agents against the pBR322 DNA. The computer-aided molecular docking studies of metal complexes with the receptor of GlcN-6-P synthase showed that metal complexes are potent drugs for the target enzymes.

Development and Characterization of a Multimycotoxin Reference Material

Abstract Background: Matrix-matched reference materials (RMs) are critical for adequate quality assurance of extraction, digestion, separation, and/or detection processes for analytes of interest in foods and dietary supplements. The accurate determination of mycotoxins in foods is an international concern. While RMs for mycotoxins are available from a variety of RM producers, these mainly address a single mycotoxin or group of mycotoxins and therefore require the use of multiple RMs for multitarget methods. Objective: To address the increasing needs of laboratories moving toward LC-MS-based multimycotoxin analysis, the U.S. National Institute of Standards and Technology (NIST) collaborated with the U.S. Food and Drug Administration (FDA) to produce a naturally incurred RM for multiple mycotoxins in corn. Methods: Homogeneity of the RM has been assessed using a stratified random sampling of the final product based on mycotoxin mass fractions measured by the FDA and NIST. Multiple sample sizes were evaluated to maximize homogeneity in the obtained results. The mycotoxin levels in the final materials have been evaluated via interlaboratory comparison and isotope dilution LC–tandem MS measurements made at the FDA and NIST. The final value assignment combined results from these data sets. Conclusions: The study successfully developed a certified RM, SRM 1565 Mycotoxins in Corn, and a workflow for the future development of multimycotoxin RMs in different matrices.

Serendipitous Discovery of PSR J1431-6328 as a Highly Polarized Point Source with the Australian SKA Pathfinder

Abstract We identified a highly polarized, steep-spectrum radio source in a deep image with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope at 888 MHz. After considering and rejecting a stellar origin for this source, we discovered a new millisecond pulsar (MSP) using observations from the Parkes radio telescope. This pulsar has period 2.77 ms and dispersion measure 228.27 pc cm−3. Although this pulsar does not yet appear to be particularly remarkable, its short spin period, wide profile, and high dispersion measure make it relatively hard to discover through traditional blind periodicity searches. Over the course of several weeks we see changes in the barycentric period of this pulsar that are consistent with orbital motion in a binary system, but the properties of any binary need to be confirmed by further observations. While even a deep ASKAP survey may not identify large numbers of new MSPs compared with the existing population, it would be competitive with existing all-sky surveys and could discover interesting new MSPs at high Galactic latitude without the need for computationally expensive all-sky periodicity searches.

A mass spectrometric stochastic dynamic diffusion approach to selective quantitative and 3D structural analyses of native cyclodextrins by electrospray ionization and atmospheric pressure chemical ionization methods

The paper addressed shortcoming with highly precise and selective 3D structural analysis of native cyclodextrins in mixture using ions observable at low m/z–region by ESI– and APCI–mass spectrometry. Because of, the quantitative and structural analyses of CDs, in general, are vexed by a set of complications. The study outlines our own stochastic dynamic approaches to the latter issues based on new model relations, quantifing the measurable MS outcome intensity. They introduce the so–called stochastic dynamic mass spectrometric diffusion “DSD” parameter, exhibiting high accuracy, precision, sensitivity and selectivity, respectively. It is linearly connected with the so–called quantum chemical diffusion parameter “DQC” according to Arrhenius’s theory. The most important upshot is that statistical parameters r = 0.99639–0.99981 has been obtained correlating between DSD and DQC parameters. Therefore, we determine high accurately 3D molecular and electronic structures of analytes by mass spectrometry. Fragment peaks at m/z 313, 279, 272, 252, 231, 214, 198, 171, 158 and 141 are examined. Mixtures of CDs and monomeric and acyclic oligomer carbohydrates glucose (1), sucrose (2), raffinose (3), melezitose (4) and cellotriose (5) are also studied. Our method is able to account precisely for the effect of the temperature under ESI– and APCI–MS conditions, as well. Correlative analysess between DSD parameters of ESI– and APCI–MS measurements under different temperatures is also shown. Chemometric tests are used. Another important results and conclusions, among others, to draw from this research are: (i) excellent linear correlation between DSD and DQC parameters of r = 0.99636 is found looking at common ions at m/z 141, 158 and 171, belonging to 2-formyl-3,4-dihydroxy-pyranylium, 4,5,6-trihydroxy-6H-pyran-2-carbaldehyde and 3,4,5-trihydroxy-6-oxo-6H-pyran-2-ylmethylidyne-oxonium ions. Thus, we distinguish precisely between the last structure and 3-formyl-4,5-dihydroxy-2,7-dioxa-8-oxonia-bicyclo[4.2.0]octa-1(8),3,5-triene cation. In the case of ion at m/z 141 subtle electronic effects are distinguished between the mentioned structure and the charged 3,4-dihydroxy-6H-pyran-2-carbaldehyde one. The method determines precisely very similar structurally poly–OH–substituted derivatives. Because of, (ii) absolute reproducibility (r = 1) of DSD parameters of ESI–MS spectra is obtained studying the shown in point (i) MS peaks of β-CD between jth and jth numbers of experiments. The statistical equation is DiSD = (0.51 ± 3.1.10−5) × DjSD; (iii) the APCI– and ESI–MS provide identical results studying common MS ions of CDs and the correlation between DAPCISD and DESISD parameters excludes from error, due to, experiment; and (iv) The correlation between theory and experiment accounting for the factor temperature within our model equations shows r = 0.9828 looking at the MS peaks at m/z 313 280, 279, 274 and 252, respectively. The effect of the temperature under both ESI– and APCI–MS conditions on the 3D molecular and electronic structures of CDs is precisely studied, respectively.

GC-MS measurement of spermidine and putrescine in serum of elderly subjects: intriguing association between spermidine and homoarginine.

Gas chromatography-mass spectrometry (GC-MS) methods were developed, validated and used to measure serum spermidine (SPD) and putrescine (PUT) in 9 seropositive Helicobacter pylori (Hp +) and 18 seronegative Helicobacter pylori (Hp -) subjects (31-105years). Homoarginine (hArg) was also measured by GC-MS. There were no statistical differences (unpaired t test) between the Hp + and Hp - subjects with respect to the serum concentrations of SPD (67.6 ± 40.3 vs. 93.7 ± 37.7nM, P = 0.109), PUT (220 ± 139 vs. 236 ± 85nM, P = 0.708) and hArg (1.60 ± 0.64µM vs. 1.83 ± 0.74µM, P = 0.554). Serum SPD and hArg concentrations correlated with each other (r = 0.426, P = 0.026, n = 27). The PUT/SPD molar ratio correlated inversely with the hArg concentration (r = - 0.406, P = 0.034, n = 27) and proteinic citrulline (r = - 0.487, P = 0.01, n = 27). These results suggest that SPD and PUT synthesis is associated with hArg formation and protein citrullination in healthy elderly subjects. The mechanisms underlying these associations and their significance remain to be elucidated.

A Practical Gait Feedback Method Based on Wearable Inertial Sensors for a Drop Foot Assistance Device

To maximise the efficiency of gait interventions, gait phase and joint kinematics are important for closing the system loop of adaptive robotic control. However, few studies have applied an inertial sensor system including both gait phase detection and joint kinematic measurement. Many algorithms for joint measurement require careful alignment of the inertial measurement unit (IMU) to the body segment. In this paper, we propose a practical gait feedback method, which provides sufficient feedback without requiring precise alignment of the IMUs. The method incorporates a two-layer model to realise simultaneous gait stance and swing phase detection and ankle joint angle measurement. Recognition of gait phases is performed by a high-level probabilistic method using angular rate from the sensor attached to the shank while the ankle angle is calculated using a data fusion algorithm based on the complementary filter and sensor-to-segment calibration. The online performance of the algorithm was experimentally validated when 10 able-bodied participants walked on the treadmill with three different speeds. The outputs were compared to the ones measured by an optical motion analysis system. The results showed that the IMU-based algorithm achieved a good accuracy of the gait phase recognition (above 95%) with a short delay response below 20 ms and accurate angle measurements with root mean square errors below 3.5° compared to the optical reference. It demonstrates that our method can be used to provide gait feedback for the correction of drop foot.

CBCT Segmentation in Volumetric Measurements of MS Using Different Soft Wares: A Validity and Reliability Study

CBCT Segmentation in Volumetric Measurements of MS Using Different Soft Wares: A Validity and Reliability Study

Ionic liquid assisted synthesis of snowflake ZnO for detection of NOx and sensing mechanism

Ionic liquid [Bmim][BF4] is used as a templating agent to synthesize ZnO with snowflake morphology by hydrothermal method. Different calcination temperatures make snowflake ZnO retain different content of ionic liquid residual which results in different gas response. The mesoporous ZnO material obtained after calcination at 650 °C shows the best gas response to NOx. The sensor not only has excellent gas selectivity, but also exhibits an optimal response to NOx (S = 73.4) at 170 °C with a response range of 0.05 ∼ 10 ppm. In addition, the sensor has good repeatability and long-term stability and also exhibits good moisture resistance at different humidity levels which may be attributed to an appropriate amount of residual ionic liquid after high temperature calcination. The reaction mechanism of the sensor to NOx is also discussed in detail based on XPS analysis, GC–MS measurement and DFT calculations.

Chelation behavior of N′-(4-(dimethylamino)benzylidene)-2-oxo-2H-chromene-3-carbohydrazide towards Cd(П), Zn(П), Ni(П), Hg(П), Cu(П) and Co(П) metal ions in presence of SiO2

A series of Cd(П), Zn(П), Ni(П), Hg(П), Cu(П) and Co(П) complexes with N′-(4-(dimethylamino)benzylidene)-2-oxo-2H-chromene-3-carbohydrazide (HAL) were synthesized in presence of SiO2 as a catalyst that consumed time of the reaction and produced high yield. The building formula of prepared compounds was verified by using various performances like (IR, UV-Visible, 1HNMR, SEM, XRD, ESR, MS, thermal analysis, elemental analysis & magnetic measurements). The optimized structure of all prepared compounds was proved by applying DFT theory. Also, MIC and the colorimetric assay for isolated solid compounds were tested.

Analysis of sesquiterpene hydrocarbons in grape berry exocarp (Vitis vinifera L.) using in vivo-labeling and comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS).

Sesquiterpenes are structurally diverse, potent flavoring substances that significantly influence the aroma profile of grapes (Vitis vinifera L.) at the time of physiological ripening. To investigate these natural compounds, freshly harvested, ripe berries of the red wine variety Lemberger (Vitis vinifera subsp. vinifera L.) were analyzed using comprehensive two-dimensional gas chromatography (GC×GC) coupled to a time-of-flight mass spectrometer (TOF–MS) after headspace-solid phase microextraction (HS-SPME). The identification of structurally complex natural compounds, such as sesquiterpenes from fruits and vegetables, is often reported as “tentative”, as authentic standards are not commercially available for most of the analytes. For this reason, feeding experiments (in vivo labeling) were carried out using the stable isotope-labeled precursors [5,5-2H2]-1-deoxy-ᴅ-xylulose (d2-DOX) and [6,6,6-2H3]-(±)-mevalonolactone (d3-MVL) to clearly identify the volatiles. Based on the recorded mass spectra of the unlabeled and deuterated compounds, mechanisms for sesquiterpene formation in V. vinifera could be proposed and already known pathways could be confirmed or disproved. For example, the HS-SPME–GC×GC–TOF–MS measurements of fed sample material showed that the tricyclic sesquiterpene hydrocarbons α-copaene, β-copaene, α-cubebene, β-cubebene and the bicyclic δ-cadinene were biosynthesized via (S)-(−)-germacrene D rather than via (R)-(+)-germacrene D as intermediate.

Mechanistic Insight into Synergistic Catalysis of Olefin Hydrogenation by a Hetero-Dinuclear RuII–CoII Complex with Adjacent Reaction Sites

We have designed and synthesized a hetero-dinuclear RuII-CoII complex with a dinucleating ligand inspired by hetero-dinuclear active sites of metalloenzymes. A synergistic effect between the adjacent RuII and CoII sites has been confirmed in catalytic olefin hydrogenation by the complex, exhibiting a much higher turnover number than those of mononuclear RuII or CoII complexes as the components. A RuII-hydrido species was detected by 1H NMR and electrospray ionization (ESI)-time-of-flight (TOF)-MS measurements as an intermediate to react with olefins, and CoII-bound methanol was suggested to act as a proton source.

Underground transfer of carbonised organic residues to lithics during preliminary fire experiments: implications for archaeology

Using fire experiments, we investigate claims that black organic residues on lithics found in Stone Age sites are markers for heat treatment of rocks in the embers of aboveground wood fires. We buried sedges overlain with lithics and bone to replicate plant bedding sometimes found in archaeological sites. Small fires were lit over the material buried under a mixture of coarse- and medium-grained sand. Black carbonised residues formed on several lithics that were in direct contact with buried sedges that burned below the fire. FTIR, Raman and preliminary GC–MS measurements were made on dried and burnt sedge, burnt bone, and on a prominent black residue that formed on one quartz piece that had been in contact with buried fresh sedge when it was heated. Importantly, we were able to confirm the spontaneous and accidental transfer of organic compounds to lithics buried and heated underground in the presence of plant material. This means that carbonised organic residues are not useful markers for determining whether heat treatment of rocks took place above or below ground. Our preliminary experiments imply that further work should be done to investigate the causes of the residues formed on lithics underground.