Unraveling the Marine Microplastic Cycle: The First Simultaneous Data Set for Air, Sea Surface Microlayer, and Underlying Water.

Microplastics (MP) including tire wear particles (TWP) are ubiquitous. However, their mass loads, transport, and vertical behavior in water bodies and overlying air are never studied simultaneously before. Particularly, the sea surface microlayer (SML), a ubiquitous, predominantly organic, and gelatinous film (<1 mm), is interesting since it may favor MP enrichment. In this study, a remote-controlled research catamaran simultaneously sampled air, SML, and underlying water (ULW) in Swedish fjords of variable anthropogenic impacts (urban, industrial, and rural) to fill these knowledge gaps in the marine-atmospheric MP cycle. Polymer clusters and TWP were identified and quantified with pyrolysis-gas chromatography-mass spectrometry. Air samples contained clusters of polyethylene terephthalate, polycarbonate, and polystyrene (max 50 ng MP m-3). In water samples (max. 10.8 µg MP L-1), mainly TWP and clusters of poly(methyl methacrylate) and polyethylene terephthalate occurred. Here, TWP prevailed in the SML, while the poly(methyl methacrylate) cluster dominated the ULW. However, no general MP enrichment was observed in the SML. Elevated anthropogenic influences in urban and industrial compared to the rural fjord areas were reflected by enhanced MP levels in these areas. Vertical MP movement behavior and distribution were not only linked to polymer characteristics but also to polymer sources and environmental conditions.

Determination of polyurethanes within microplastics in complex environmental samples by analytical pyrolysis.

Polyurethanes (PUR) are a group of polymers synthesized from different diisocyanate and polyol monomers resulting in a countless number of possible structures. However, the large market demand, and the variety of application fields justify the inclusion of PUR in microplastic (MP) investigation. This study aimed at providing comprehensive information on PUR within MP analysis by pyrolysis-gas chromatography-mass spectrometry to clarify whether (i) it is possible to make a reliable statement on the PUR content of environmental samples based on a few pyrolysis products and (ii) which restrictions are required in this context. PUR were managed as subclasses defined by the diisocyanates employed for polymer synthesis. Methylene diphenyl diisocyanate (MDI)- and toluene diisocyanate (TDI)-based PUR were selected as subclasses of greatest relevance. Different PUR were pyrolyzed directly and under thermochemolytic conditions with tetramethylammonium hydroxide (TMAH). Distinct pyrolytic indicators were identified. The study supported that the use of TMAH greatly reduced the interactions of pyrolytic MP analytes with the remaining organic matrix of environmental samples and the associated negative effects on analytical results. Improvements of chromatographic behavior of PUR was evidenced. Regressions (1-20 µg) showed good correlations and parallelism tests underlined that quantitation behavior of different MDI-PUR could be represented by the calibration of just one representative with sufficient accuracy, entailing a good estimation of the entire subclass if thermochemolysis were used. The method was exemplary applied to road dusts and spider webs sampled around a plastic processing plant to evaluate the environmental spread of PUR in an urban context. The environmental occurrence of MDI-PUR as MP was highly influenced by the proximity to a potential source, while TDI markers were not observed.

Microplastic Mass Concentrations and Distribution in German Bight Waters by Pyrolysis-Gas Chromatography-Mass Spectrometry/Thermochemolysis Reveal Potential Impact of Marine Coatings: Do Ships Leave Skid Marks?

In this first mass-related survey of microplastics (MPs, <1 mm) in the German Bight (North Sea, 2.5 m water depth), spatial load, temporal variations, and potential sources were examined. Relevant plastic types were detected using pyrolysis-gas chromatography-mass spectrometry/thermochemolysis (Py-GC/MS). This suitable method provides qualitative and trace-level polymer or polymer cluster-specific mass quantitative MP data. Neither MP concentration (2-1396 µg m-3) nor type distribution was homogeneous. Concentrations appeared to be substantially influenced by meteorological and oceanographic conditions. The coastal MP-type composition showed an overprint indicating a packaging waste-related signal. Considerably different compositions were observed in central and estuarine areas. Here, a close relation to marine (antifouling) coating particles, i.e., abrased chlorinated rubber-, acryl-styrene-, and epoxide binder-containing particles are hypothesized as the main MP source, indicating ship "skid marks". They represent a dominant, toxicologically relevant but underestimated marine-based MP share, inverting the widely cited 80% terrestrial- to 20% marine-based debris ratio for MPs. In consequence of the findings, polymer clusters attributed to the basic polymers polyethylene, polypropylene, polystyrene, poly(ethylene terephthalate), poly(vinyl chloride), poly(methyl methacrylate), and polycarbonate are proposed for Py-GC/MS MPs mass determination based on specific thermal decomposition products linked to related polymer structural units.

Comparison of pyrolysis gas chromatography/mass spectrometry and hyperspectral FTIR imaging spectroscopy for the analysis of microplastics.

Analysis of microplastics (MP) in environmental samples is an emerging field, which is performed with various methods and instruments based either on spectroscopy or thermoanalytical methods. In general, both approaches result in two different types of data sets that are either mass or particle number related. Depending on detection limits of the respective method and instrumentation the derived polymer composition trends may vary. In this study, we compare the results of hyperspectral Fourier-transform infrared (FTIR) imaging analysis and pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) analysis performed on a set of environmental samples that differ in complexity and degree of microplastic contamination. The measurements were conducted consecutively, and on exactly the same sample. First, the samples were investigated with FTIR using aluminum oxide filters; subsequently, these were crushed, transferred to glass fiber filters, in pyrolysis cups, and measured via Py-GC/MS. After a general data harmonization step, the trends in MP contamination were thoroughly investigated with regard to the respective sample set and the derived polymer compositions. While the overall trends in MP contamination were very similar, differences were observed in the polymer compositions. Furthermore, polymer masses were empirically calculated from FTIR data and compared with the Py-GC/MS results. Here, a most plausible shape-related overestimation of the calculated polymer masses was observed in samples with larger particles and increased particle numbers. Taking into account the different measurement principles of both methods, all results were examined and discussed, and future needs for harmonization of intermethodological results were identified and highlighted. Graphical abstract.

Method development and validation for the quantification of organic acids in microbial samples using anionic exchange solid-phase extraction and gas chromatography-mass spectrometry.

Organic acids play a key role in central metabolic functions of organisms, are crucial for understanding regulatory processes and are ubiquitous inside the cell. Therefore, quantification of these compounds provides a valuable approach for studying dynamics of metabolic processes, in particular when the organism faces changing environmental conditions. However, the extraction and analysis of organic acids can be challenging and validated methods available in this field are limited. In this study, we developed a method for the extraction and quantification of organic acids from microbial samples based on solid-phase extraction on a strong anionic exchange cartridge and gas chromatographic-mass spectrometric analysis. Full method validation was conducted to determine quality parameters of the new method. Recoveries for 12 of the 15 aromatic and aliphatic acids were between 100 and 111% and detection limits between 3 and 272 ng/mL. The ranges for the regression coefficients and process standard deviations for these compound classes were 0.9874-0.9994 and 0.04-0.69 µg/mL, respectively. Limitations were encountered when targeting aliphatic acids with hydroxy, oxo or enol ester functions. Finally, we demonstrated the applicability of the method on cell extracts of the bacterium Escherichia coli and the dinoflagellate Prorocentrum minimum. Graphical abstract.

Comparison of µ-ATR-FTIR spectroscopy and py-GCMS as identification tools for microplastic particles and fibers isolated from river sediments.

In recent years, many studies on the analysis of microplastics (MP) in environmental samples have been published. These studies are hardly comparable due to different sampling, sample preparation, as well as identification and quantification techniques. Here, MP identification is one of the crucial pitfalls. Visual identification approaches using morphological criteria alone often lead to significant errors, being especially true for MP fibers. Reliable, chemical structure-based identification methods are indispensable. In this context, the frequently used vibrational spectroscopic techniques but also thermoanalytical methods are established. However, no critical comparison of these fundamentally different approaches has ever been carried out with regard to analyzing MP in environmental samples. In this blind study, we investigated 27 single MP particles and fibers of unknown material isolated from river sediments. Successively micro-attenuated total reflection Fourier transform infrared spectroscopy (µ-ATR-FTIR) and pyrolysis gas chromatography-mass spectrometry (py-GCMS) in combination with thermochemolysis were applied. Both methods differentiated between plastic vs. non-plastic in the same way in 26 cases, with 19 particles and fibers (22 after re-evaluation) identified as the same polymer type. To illustrate the different approaches and emphasize the complementarity of their information content, we exemplarily provide a detailed comparison of four particles and three fibers and a critical discussion of advantages and disadvantages of both methods.

Simultaneous Trace Identification and Quantification of Common Types of Microplastics in Environmental Samples by Pyrolysis-Gas Chromatography-Mass Spectrometry.

The content of microplastics (MP) in the environment is constantly growing. Since the environmental relevance, particularly bioavailability, rises with decreasing particle size, the knowledge of the MP proportion in habitats and organisms is of gaining importance. The reliable recognition of MP particles is limited and underlies substantial uncertainties. Therefore spectroscopic methods are necessary to ensure the plastic nature of isolated particles, determine the polymer type and obtain particle count related quantitative data. In this study Curie-Point pyrolysis-gas chromatography-mass spectrometry combined with thermochemolysis is shown to be an excellent analytical tool to simultaneously identify and optionally quantify MP in environmental samples on a polymer specific mass related trace level. The method is independent of any mechanical preselection or particle appearance. For this purpose polymer characteristic pyrolysis products and their indicative fragment ions were used to analyze eight common types of plastics. Further aspects of calibration, recoveries, and potential matrix effects are discussed. The method is exemplarily applied on selected fish samples after an enzymatic-chemically pretreatment. This new approach with mass-related results is complementary to established FT-IR and Raman methods providing particle counts of individual polymer particles.

Occurrence and backtracking of microplastic mass loads including tire wear particles in northern Atlantic air.

Few studies report the occurrence of microplastics (MP), including tire wear particles (TWP) in the marine atmosphere, and little data is available regarding their size or sources. Here we present active air sampling devices (low- and high-volume samplers) for the evaluation of composition and MP mass loads in the marine atmosphere. Air was sampled during a research cruise along the Norwegian coast up to Bear Island. Samples were analyzed with pyrolysis-gas chromatography-mass spectrometry, generating a mass-based data set for MP in the marine atmosphere. Here we show the ubiquity of MP, even in remote Arctic areas with concentrations up to 37.5 ng m-3. Cluster of polyethylene terephthalate (max. 1.5 ng m-3) were universally present. TWP (max. 35 ng m-3) and cluster of polystyrene, polypropylene, and polyurethane (max. 1.1 ng m-3) were also detected. Atmospheric transport and dispersion models, suggested the introduction of MP into the marine atmosphere equally from sea- and land-based emissions, transforming the ocean from a sink into a source for MP.

Plastic in the air?! - Spider webs as spatial and temporal mirror for microplastics including tire wear particles in urban air.

Studies concerning quantities of microplastics (MP) including tire wear particles (TWP) contamination in air samples are scarce. Spider webs have been suggested as a cheap and easily accessible biomonitor particularly for inorganic contaminates. Here, we emphasize the potential of spider webs to gain insights in the spatial and temporal trends of MP in urban air. The samples, collected in a mid-sized German city, were processed with Fentons reagent and measured using pyrolysis-gas chromatography-mass spectrometry for specific, polymer related indicator compounds. All samples contained TWP and other MP. The latter are detected and quantified as pyrolysis products of a polymer backbone. The results were expressed as clusters (prefix "C"). Determined polymer contaminations ranged from 11.4 µg/mg to 108 µg/mg spider web sample. The dominant polymer was C-PET (Ø 36.0% of total MP) derived most likely from textile fibers. Additionally, there was evidence for traffic-related contaminations. In particular car tire tread (Ø 40.8% of total MP) and ⁎C-PVC (Ø 12.0% of total MP) were found, with the latter presumably originating from paint used for road markings. Truck tire tread, C-PE, C-PP, C-PS, C-PMMA, and C-PC were also frequently found, but in much lower abundance (Ø <6.4% of total MP). Differences in contamination levels could be plausibly related to the sampling locations.

30 years trends of microplastic pollution: Mass-quantitative analysis of archived mussel samples from the North and Baltic Seas.

Microplastics (MP) are ubiquitous throughout the environment as a result of an ongoing, increasing, but also lavish use, of plastics over time and its inherent persistence. In contrast, there are almost no data that allow drawing conclusions about the evolution of plastic pollution in the environment over the past decades. This study investigates the MP load in blue mussels from the North and Baltic Sea archived by the German Environmental Specimen Bank in a time series covering almost 30 years. Samples were enzymatically and chemically oxidative digested for MP extraction and subsequent analyzed mass-quantitatively for nine common polymer clusters by pyrolysis gas chromatography-mass spectrometry. Seven polymer clusters were detected in mussel tissue. Summed MP levels were at ppm levels (<20 µg/g mussel, dry weight). North Sea samples reflected a gradual increase from the 1980s/90s to the 2000s whereas those from Baltic Sea showed consistently higher, rather constant MP levels similar to the North Sea site later than 2000. Polymer composition of both sites stood out by cluster (C) of C-PVC and C-PET at both sites. Mussels from Baltic Sea site had larger C-PE and C-PP proportions. Opposed polymer- and site-specific trends indicated both regional and trans-regional MP sources for different polymer clusters. The MP composition of mussels showed strong similarities with adjacent sediment and water samples. The study introduces a relevant dataset addressing the temporal development of MP pollution. It emphasizes a high indicative potential of environmental MP composition/loads received by mussels but raises the necessity on adequate control materials accompany such kind of studies.

Microplastics in two German wastewater treatment plants: Year-long effluent analysis with FTIR and Py-GC/MS.

Microplastics (MP) have been recorded in various environments around the globe. For a better understanding of distribution patterns and for providing a basis for risk assessments, detailed data on MP concentrations and polymer compositions are required. This study investigated the effluents of two German wastewater treatment plants (WWTP) monthly over one year, in order to better understand their temporal input of MP into the receiving river systems. MP item data down to 11 µm were obtained by means of Fourier Transform Infrared (FTIR) spectroscopy under the application of an improved polymer database. Complementary mass data were obtained by pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) (for one WWTP). Both FTIR and Py-GC/MS analysis revealed a homogeneous polymer composition over the year, with a general dominance of polyolefins. Elevated MP item and mass concentrations (maximum: 3 × 104 items m-3 and 3.8 × 103 µg m-3) were observed during winter months and were accompanied by either heavy rainfall (increased discharge and total organic carbon) or elevated turbidity values. These observations emphasize the need for the assessment of background parameters in future MP monitoring studies. By providing monthly data over one year on MP items and masses in WWTP effluents, this study helps enhancing the understanding of temporal MP dynamics and can act as a valuable reference point for future assessments.

Car and truck tire wear particles in complex environmental samples - A quantitative comparison with "traditional" microplastic polymer mass loads.

Tire wear particles (TWP) are assumed to be the most dominant source of environmental microplastics (MP). Besides rubber components around 60% of tires are additives such as filling material and various chemicals added for vulcanization. The inevitably released TWP in daily traffic are therefore considered a threat to the ecosystem. Nevertheless, published studies on MP mass loads often exclude elastomers. Data concerning composition and concentrations of TWP compared to prominent "traditional" MP polymers, such as polyethylene, polypropylene, poly(ethylene terephthalate) and poly(vinyl chloride), are missing. Identification and quantification of TWP was implemented in an existing pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) method for MP determination. An approach to differentiate between car and truck tire wear and to quantify their respective mass loads is presented. Complex environmental samples such as road dust, fresh water and marine sediments, blue mussels, and marine salts were partly retrospectively analyzed using Py-GC/MS. The results showed ratios of car to truck tire wear up to 16 to 1 and underline the dominance of car compared to truck tire wear mass loads in all analyzed samples. Even though some retrospective data sets might be affected by suboptimal density separation conditions (NaBr, ρ = 1.5 g/cm3), TWP concentrations in road dust clearly exceeded those of "traditional" MP (Ø 5 g TWP vs 0.3 g MP per kg road dust (dry weight). Samples included in this study, which were archived further away from TWP sources such as roads, reflected decreasing TWP concentrations (Ø 24 µg TWP vs. 107 µg MP per kg sediment (dry weight); Ø 126 µg TWP vs. 378 µg MP per kg marine salt) or were no longer present (blue mussels), while "traditional" polymers were still ubiquitously distributed.

Microplastic extraction from sediments established? - A critical evaluation from a trace recovery experiment with a custom-made density separator.

By now, microplastics are present in every environmental compartment of which sediments are considered one major sink. As a result, several approaches for their enrichment from sediments have been established in microplastic analysis. At the same time, the smaller microplastics gained increasing attention regarding their ecotoxicological relevance. A customized sediment separator was evaluated with trace amounts of small microplastic particles (150-300 µm) of the nine most common polymers. Separation was performed with sodium bromide (ρ = 1.5 g cm-3). The experimental recovery comprises pristine as well as incubated polymers to include early biofouling effects. Polymer quantification was achieved exclusively using pyrolysis-gas chromatography-mass spectrometry. The results reflected an overall mean recovery of 65%. Interestingly, the observed behaviour seems to be density related. While polymers of higher densities revealed higher average extraction efficiencies (74-97%), those of less dense polymers are reduced and span between 34 and 65%. These observations hypothesize possible polarity related surface interactions as a relevant factor for microplastic particle extraction. In contrast, the density of the separation fluid seemed to be of subordinate relevance, if small microplastic particles were extracted in trace amounts. Early biofouling enhanced recoveries of some polar polymers, whereas the effect on apolar polymers was even negative in some cases. In a comparative synopsis with other published density separation approaches, a limited number of comparable experimental setups concerning particle size, polymer density range and polymer concentration were revealed. Nonetheless, some related experiments point to similar density/polarity driven extraction behaviour. In conclusion, the presented study suggests a re-evaluation of current separation approaches for extraction of low number/mass concentrations of small microplastics from sediments to enable a more comprehensive insight into factors that influence surface properties for microplastics extraction. Concurrently, it raises the question of how an ideal environment relevant recovery experiment can be designed.

Critical Assessment of Analytical Methods for the Harmonized and Cost-Efficient Analysis of Microplastics.

Microplastics are of major concerns for society and is currently in the focus of legislators and administrations. A small number of measures to reduce or remove primary sources of microplastics to the environment are currently coming into effect. At the moment, they have not yet tackled important topics such as food safety. However, recent developments such as the 2018 bill in California are requesting the analysis of microplastics in drinking water by standardized operational protocols. Administrations and analytical labs are facing an emerging field of methods for sampling, extraction, and analysis of microplastics, which complicate the establishment of standardized operational protocols. In this review, the state of the currently applied identification and quantification tools for microplastics are evaluated providing a harmonized guideline for future standardized operational protocols to cover these types of bills. The main focus is on the naked eye detection, general optical microscopy, the application of dye staining, flow cytometry, Fourier transform infrared spectroscopy (FT-Ir) and microscopy, Raman spectroscopy and microscopy, thermal degradation by pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) as well as thermo-extraction and desorption gas chromatography-mass spectrometry (TED-GC-MS). Additional techniques are highlighted as well as the combined application of the analytical techniques suggested. An outlook is given on the emerging aspect of nanoplastic analysis. In all cases, the methods were screened for limitations, field work abilities and, if possible, estimated costs and summarized into a recommendation for a workflow covering the demands of society, legislation, and administration in cost efficient but still detailed manner.

Effects of microplastic particles and leaching additive on the life history and morphology of Daphnia magna.

Plastic waste is continuously introduced not only into marine, but also freshwater environments, where it fragments into microplastics. Organisms may be affected by the particles themselves due to ingestion and indirectly via incorporated additives such as plasticizers, since these substances have the ability to leach out of the polymer matrix. Although it has been indicated that the likelihood of additives leaching out into the gut lumen of organisms exposed to microplastics is low, studies distinguishing between the effects of the synthetic polymer itself and incorporated additives of the same polymer are scarce. Since this is obligatory for risk assessment, we analyzed the chronic effects of flexible polyvinylchloride (PVC), a widely used polymer, containing the plasticizer diisononylphthalate (DiNP) on morphology and life history of the freshwater crustacean Daphnia magna and compared these effects with the effects of rigid PVC, lacking DiNP, as well as a glass bead control. After up to 31 days of exposure, rigid PVC and glass beads did not affect body length and relative tail spine length of D. magna, whereas flexible PVC led to an increased body length and a reduced number of offspring. None of the treatments increased the mortality significantly. We were able to show that 2.67µg/L DiNP leached out of the flexible PVC into the surrounding medium using GC-MS. Yet, we were not able to measure leachate inside the gut lumen of D. magna. The effects emerged towards the end of the experiment, due to the time dependent process of leaching. Therefore, the results highlight the relevance of long-term chronic exposure experiments, especially as leaching of additives takes time. Further, our study shows the importance to distinguish between microplastics containing leachable additives and the raw polymer in ecotoxicological testing.

Ontogenetic resource utilization and migration reconstruction with δ13C values of essential amino acids in the Cynoscion acoupa otolith.

With the increasing anthropogenic impacts on fish habitats, it has become more important to understand which primary resources sustain fish populations. This resource utilization can differ between fish life stages, and individuals can migrate between habitats in search of resources. Such lifetime information is difficult to obtain due to the large spatial and temporal scales of fish behavior. The otolith organic matrix has the potential to indicate this resource utilization and migration with δ13C values of essential amino acids (EAAs), which are a direct indication of the primary producers. In a proof-of-concept study, we selected the Acoupa weakfish, Cynoscion acoupa, as a model fish species with distinct ontogenetic migration patterns. While it inhabits the Brazilian mangrove estuaries during juvenile stages, it moves to the coastal shelf as an adult. Thus, we expected that lifetime resource utilization and migration would be reflected in δ13CEAA patterns and baseline values in C. acoupa otoliths. By analyzing the C. acoupa otolith edges across a size range of 12-119 cm, we found that baseline δ13CEAA values increased with size, which indicated an estuarine to coastal shelf distribution. This trend is highly correlated with inorganic δ13C values. The δ13CEAA patterns showed that estuarine algae rather than mangrove-derived resources supported the juvenile C. acoupa populations. Around the juvenile size of 40 cm, resource utilization overlapped with those of adults and mean baseline δ13CEAA values increased. This trend was confirmed by comparing otolith core and edges, although with some individuals potentially migrating over longer distances than others. Hence, δ13CEAA patterns and baseline values in otoliths have great potential to reconstruct ontogenetic shifts in resource use and habitats. The insight could aid in predictions on how environmental changes affect fish populations by identifying the controlling factors at the base of the food web.

Qualitative impact of salinity, UV radiation and turbulence on leaching of organic plastic additives from four common plastics - A lab experiment.

Four common consumer plastic samples (polyethylene, polystyrene, polyethylene terephthalate, polyvinylchloride) were studied to investigate the impact of physical parameters such as turbulence, salinity and UV irradiance on leaching behavior of selected plastic components. Polymers were exposed to two different salinities (i.e. 0 and 35 g/kg), UV radiation and turbulence. Additives (e.g. bisphenol A, phthalates, citrates, and Irgafos® 168 phosphate) and oligomers were detected in initial plastics and aqueous extracts. Identification and quantification was performed by GC-FID/MS. Bisphenol A and citrate based additives are leached easier compared to phthalates. The print highly contributed to the chemical burden of the analyzed polyethylene bag. The study underlines a positive relationship between turbulence and magnitude of leaching. Salinity had a minor impact that differs for each analyte. Global annual release of additives from assessed plastics into marine environments is estimated to be between 35 and 917 tons, of which most are derived from plasticized polyvinylchloride.

Alkylated phenol series in lacustrine black shales from the Nördlinger Ries, southern Germany.

Several series of alkylated phenols were detected for the first time in the extractable bitumens of organic matter-rich sediments from the Nördlinger Ries (southern Germany). Most abundant and significant constituents comprise those with n-octadecyl, n-eicosanyl, phytanyl, and iso-pentadecyl and anteiso-pentadecyl substituents. The structures of these compounds are suggested from mass spectrometric and retention time data and coinjection with synthetic standards. Diagenetic alteration of phenolic algal lipids is suggested as a possible way to the formation of these compounds in the Nördlinger Ries sediments.

Cardiac glycosides from Yellow Oleander (Thevetia peruviana) seeds.

Thevetia cardiac glycosides can lead to intoxication, thus they are important indicators for forensic and pharmacologic surveys. Six thevetia cardiac glycosides, including two with unknown structures, were isolated from the seeds of the Yellow Oleander (Thevetia peruviana (Pers.) K. Shum., Apocynaceae). LC-ESI⁺-MS(/MS) analysis under high-resolution conditions used as a qualitative survey of the primary glycosides did not lead to fragmentation of the aglycones. Acid hydrolysis of the polar and non-volatile thevetia glycosides under severe conditions yielded the aglycones of the thevetia glycosides and made them amenable to GC-MS analysis. Comparison of mass spectral fragmentation patterns of the aglycones, as well as high-resolution mass spectrometric and NMR data of four of the primary thevetia glycosides including the two unknowns, revealed the structures of the complete set of six thevetia glycosides. The identified compounds are termed thevetin C and acetylthevetin C and differ by an 18,20-oxido-20,22-dihydro functionality from thevetin B and acetylthevetin B, respectively. The absence of an unsaturated lactone ring renders the glycosides cardio-inactive. The procedures developed in this study and the sets of analytical data obtained will be useful for screening and structure assessment of other, particularly polar, cardiac glycosides.