Trace level analysis of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its biodegradation intermediates in liquid media by solid-phase extraction and high-pressure liquid chromatography analysis

The use of solid-phase extraction for the analysis of liquid media containing low microg/L levels of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), mononitroso-RDX (MNX), dinitroso-RDX (DNX), and trinitroso-RDX (TNX) is examined. Aqueous samples (100 mL) consisting of water and a microbiological basal medium are spiked with known concentrations of RDX, MNX, DNX, and TNX. The compounds are extracted from the liquid media using a Porapak RDX cartridge and then eluted from the cartridge with 5 mL of acetonitrile. The eluent is concentrated to 1 mL before analysis by high-pressure liquid chromatography (HPLC). The method detection limits for RDX are 0.1 microg/L in water and 0.5 microg/L in the basal medium after a 100-fold concentration. For MNX, DNX, and TNX, the method detection limits are approximately 0.5 microg/L in water and approximately 1 microg/L in the basal medium after a 100-fold concentration. Interferences in the basal medium and a contaminant in the standard made quantitation for MNX and TNX, respectively, is less accurate below the 1 microg/L level. Solid-phase extraction of the liquid media gave good recoveries of nitramines and nitroso intermediates from a microbiological basal medium, allowing HPLC detection of RDX and the nitroso intermediates in the low microg/L (ppb) range.     

Extraction and analysis of trace amounts of cyclonite (RDX) and its nitroso-metabolites in animal liver tissue using gas chromatography with electron capture detection (GC-ECD)

An efficient extraction and cleanup technique, and an instrumental detection method suitable for determination of trace amounts of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and its nitroso-metabolites in animal liver tissue were developed and validated in this paper. The method includes the extraction of explosives from liver tissue samples using accelerated solvent extraction (ASE) followed by cleanup using florisil and styrene-divinyl benzene (SDB) cartridges to remove interfering naturally endogenous compounds. The instrumental analysis was conducted using a capillary column gas chromatograph coupled with an electron capture detector (GC-ECD). High recoveries (58.9-106.8%) of RDX, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX) were achieved at all concentrations studied. RDX, MNX, and TNX gave higher recoveries than DNX at all three tested concentrations (50, 250, 1250 ng/g). Overall recoveries of RDX, MNX, DNX, and TNX from 1 g beef liver samples containing 50, 250, and 1250 ng/g were 80.1, 82.8, 68.9, and 80.4%, respectively. The optimal injection port temperature range was 160-170 °C for analysis of RDX and its nitroso-metabolites. Higher or lower temperatures than 160-170 °C decreased signal amplitudes. RDX was unstable in the liver extraction matrix; as much as 50% of RDX was degraded 10 days after extraction if keeping the liver sample extracts at room temperature. Degradation of RDX to MNX, DNX, or TNX was not detected during the sample storage, extraction, or instrument analysis processes. Other optimized extraction and GC conditions are also discussed.     

Evaluating the bioavailability of explosive metabolites, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX), in soils using passive sampling devices

The uptake kinetics of two major RDX (hexahydro-1,3,5-trinitro-1,3,5-triazacyclohexane) metabolites, hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX), into passive sampling devices (PSDs), and the ability of PSDs to serve as surrogates for evaluating bioavailability of MNX and TNX were investigated in laboratory sand and two soil types. The results indicate that MNX and TNX absorption into PSDs was best fitted with a polynomial curve model: y = ax2 + bx + c (y: amount of MNX or TNX absorbed into PSD; x: incubation time of PSDs in soil), with an excellent correlation coefficient (>0.95) for each type of soil amended with 10 mg/kg MNX or TNX. TNX was more readily absorbed by PSDs than MNX. Soil conditions, especially organic matter content, affected MNX and TNX uptake into PSDs. A relatively good correlation between MNX and TNX uptake into PSDs and uptake into earthworms was obtained in two types of natural soils (a silt loam soil from Nebraska and a sandy loam soil from Texas) and laboratory sand. A linear relationship between PSD uptake and earthworm uptake was observed. The correlation coefficients (r2) were > or = 0.82 for all test soils spiked with MNX or TNX. Organic matter content is one soil factor that affected the ratio of MNX or TNX uptake into earthworms versus uptake into PSDs. These data indicate that C18 PSDs may be used as a surrogate for soil organisms such as earthworms and provide a simple and easy chemical test for assessing the bioavailability of contaminants in soils.     

Extraction and determination of trace amounts of energetic compounds in blood by gas chromatography with electron capture detection (GC/ECD)

This paper describes an efficient and sensitive method for determining five energetic compounds at trace levels (ng/mL) in blood by gas chromatography with electron capture detection (GC/ECD). For seven test concentrations (1-1250 ng/mL), the average recoveries (%) were 104 ± 16, 108 ± 22, 105 ± 14, 100 ± 22 and 108 ± 16 for hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX), hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX), hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX), hexahydro-1,3,5-trinitro-1,3,5-triazacyclohexane (RDX) and 2,4,6-trinitrotoluene (TNT) (n = 84), respectively. Analysis of DNX and RDX produced lower precision than other energetic compounds. Acetonitrile extracts of blood samples should be analyzed immediately as the test compounds can transform into unknown compounds, which lowered the recovery by 0-45% within 10 days at room temperature (∼20 °C). Maintaining sample extracts at 4 °C decreased loss of test compounds. The method described herein was validated by different analysis teams on different days. Two-way ANOVA indicated that there was no significant difference between analysis teams or days of analysis. The method was successfully employed in the analysis of blood samples from a mouse dosing study involving TNX and RDX.     

Enhanced extraction of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the presence of sodium dodecyl sulphate and its application to environmental samples

A method for enhanced extraction of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from environmental samples is developed with the assistance of sodium dodecyl sulphate (SDS) surfactant. In this study, the concentration of SDS surfactant and other analytical parameters are optimized on a high-performance liquid chromatography-UV system. An isocratic flow of 1.0 mL/min with mobile phase acetonitrile-water; 70:30 (v/v) at 230 nm wavelength on a reverse-phase amide column is used for baseline separation of explosives and making calibration curves. The amount of recovered explosives from spiked soil and water samples are calculated. The limits of detection obtained for HMX and RDX standards are 1.5 and 3.8 ppb (S/N=3), respectively, which are much better than obtained by the Environmental Protection Agency method 8330. The recoveries are found to be enhanced by 1.7 and 1.6-fold with SDS solution as compared to water for HMX and RDX, respectively, from soil samples.     

HPLC Approach to Evaluate the Degree of Coverage of Polymer-Coated Hexahydro-1,3,5-trinitro-1,3,5-triazine

An efficient and reliable technique to evaluate the degree of coverage of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was described. The method was based on a quantitative analysis of RDX leakage carried out with a high performance of liquid chromatography (HPLC). For this study, replicated analyses were performed on coated samples prepared by different kinds of coating materials and methods. The efficiency of characterization by using both HPLC and scanning electron microscope was compared. To note, the evaluation through former technique is more on macroscopic perspective rather than morphological observation of sample. Meanwhile, the HPLC method also provided characterization results that were in good agreement with morphology observation. A noteworthy advantage of this original technique is that the evaluation of coating quality of melt-cast explosives can be carried out under similar conditions. The experimental data were provided for deep understanding of the soluble behavior of coated RDX and its possible applications in practical problems.

     

Micellar extraction and high performance liquid chromatography-ultra violet determination of some explosives in water samples

An analytical method based on the cloud point extraction combined with high performance liquid chromatography is used for the extraction, separation and determination of four explosives; octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT) and pentaerythritol tetranitrate (PETN). These compounds are extracted by using of Triton X-114 and cetyl-trimethyl ammonium bromide (CTAB). After extraction, the samples were analyzed using a HPLC-UV system. The parameters affecting extraction efficiency (such as Triton X-114 and CTAB concentrations, amount of Na₂SO₄, temperature, incubation and centrifuge times) were evaluated and optimized. Under the optimum conditions, the preconcentration factor was 40 and the improvement factors of 34, 29, 61 and 42 with detection limits of 0.09, 0.14, 0.08 and 0.40 (μg L⁻¹) were obtained for HMX, RDX, TNT and PETN, respectively. The proposed method was successfully applied to the determination of these compounds in water samples and showed recovery percentages of 97-102% with RSD values of 2.13-4.92%.     

Trisubstituted 1,3,5-triazines. 2. Synthesis of 1,3,5-triazines from 2,4,6-tris[di(tert-butoxycarbonyl)methylene]hexahydro-1,3,5-triazine

A study was carried out on electrophilic addition and hydrolytic dissociation of 2,4,6-tris[di(tert-butoxycarbonyl)methylene]hexahydro-1,3,5-triazine. Chloro, bromo, and methyl derivatives of tris[di(tert-butoxycarbonyl)methyl]-1,3,5-triazine were synthesized for the first time as well as 2,4,6-tris-(tert-butoxycarbonylmethyl)-1,3,5-triazine. For Communication 1, see ref. [1]. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow and Institute of Chemical Physics, Russian Academy of Sciences at Chernogolovka, 142432 Chernogolovka, Moscow Oblast. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1404–1407, October, 1998.     

Solid phase microextraction-high performance liquid chromatographic determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in the presence of sodium dodecyl sulfate surfactant

A simple and sensitive method has been developed using preconcentration technique solid phase microextraction (SPME) and analytical technique HPLC-UV for the determination of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) from the environmental samples. Aqueous solution of anionic surfactant SDS was used for the extraction of both nitramine high explosives, viz., HMX and RDX from soil samples which were subsequently sorbed on SPME fiber. The static desorption was carried out in the desorption chamber of the SPME-HPLC interface in the presence of mobile phase ACN/methanol/water (30:35:35) and the subsequent chromatographic analysis at a flow rate of 0.5 mL/min and detection at 230 nm. For this purpose, a C(18), 5 microm RP analytical column was used as a separation medium in this method. Several parameters relating to SPME, e.g., adsorption/desorption time, concentration of salt, stirring rate, etc., were optimized. The method was linear over the range of 20-400 ng/mL for HMX and RDX standards in the presence of surfactant in aqueous phase, respectively. The correlation coefficient (R(2)) for HMX and RDX are 0.9998 and 0.9982, respectively. With SPME, the detection limits (S/N = 3) in ng/mL are 0.05 and 0.1 for HMX and RDX, respectively in the presence of the SDS surfactant. The developed method has been applied successfully to the analysis of real environmental samples like bore well water, river water, and ground alluvial soil.     

Cyclodextrin-assisted capillary electrophoresis for determination of the cyclic nitramine explosives RDX,HMX and CL-20 comparison with high-performance liquid chromatography

A sulfobutyl ether-beta-cyclodextrin-assisted electrokinetic chromatographic method was developed to rapidly resolve and detect the cyclic nitramine explosives 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane (CL-20), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and their related degradation intermediates in environmental samples. Development of the electrophoretic method required the measurement of the aqueous solubility of CL-20 which was determined to be 3.59 +/- 0.74 mg/l at 25 degrees C (95% confidence interval, n=3). The performance of the method was then compared to results obtained from existing high-performance liquid chromatography methods including US Environmental Protection Agency method 8330.     

Nitromethyl derivatives of 1,3,5-triazine. Synthesis and properties

The destructive nitration of 2,4,6-tris[di(carboxy)methylene]hexahydro-1,3,5-triazine and its esters has been investigated. A first representative of the nitromethyl derivatives of 1,3,5-triazine, viz. 2,4,6-tris(nitromethyl)-1,3,5-triazine, has been synthesized.Deceased.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences, Chernogolovka 142432. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1254–1259, September, 1997.     

Detection of the cyclic nitramine explosives hexahydro-1,3,5-trinitro- 1,3,5-triazine (RDX) and octahydro- 1,3,5,7-tetranitro- 1,3,5,7-tetrazine (HMX) and their degradation products in soil environments

The cyclic nitramine explosives hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazine (HMX) were examined in field and microcosm soil samples to determine their patterns of degradation and environmental fates. A number of analytical techniques, including solid-phase microextraction with on-fiber derivatization, gas chromatography-mass spectrometry, gas chromatography with electron-capture detection, liquid chromatography-mass spectrometry, and micellar electrokinetic chromatography were required for the analyses. Two different classes of intermediates were detected, both of which lead ultimately to the formation of nitrous oxide (N2O) and carbon dioxide (CO2). The first class was identified as the nitroso derivatives formed by the sequential reduction of -NO2 functional groups. The second class of intermediates, which was favored at higher humidities and in the presence of anaerobic sludge amendments, consisted of ring cleavage products including bis-(hydroxymethyl)-nitramine and methylenedinitramine. Rye-grass (Lolium perenne) present in field samples was found to extract and accumulate HMX from soil without further degradation. In all cases (excepting the plant samples), the indigenous microbes or amended domestic anaerobic sludge consortia degraded the cyclic nitramine explosives eventually to produce N2O and CO2.     

3,4-Dialkoxybenzoyl substituted derivatives of hexahydro-1,3,5-triazine with hexagonal columnar mesophases

The synthesis of a homologous series of amidic derivatives of azacyclic compounds, i.e. 3,4-dialkoxybenzoyl ('two chain') N',N',N'-substituted hexahydro-1,3,5-triazines with alkoxy chains-OCnH2n+1 having n = 5, 6, 8-14 and 16 carbon atoms, and of one corresponding amine derivative, i.e. 1,3,5-tris(3,4-didecyloxybenzyl)hexahydro-1,3,5-triazine, is described. The thermal behaviour of the compounds is characterized by means of polarizing microscopy and differential scanning calorimetry. The amide with n = 6 is a monotropic liquid crystalline material, whereas the amides with n = 8-14 and 16 exhibit enantiotropic mesomorphism. The amine derivative with n = 10 is not a thermotropic liquid crystalline compound. The optical textures of the mesogenic compounds are spherulitic. X-ray diffraction measurements for the amides with n = 8, 10, 12, 13 and 16 show evidence of a hexagonal columnar structure (Colh) in the mesophase. The lattice constants of the mesophase are compared with the values from CPK models.     

Trace analysis of explosives in soil: pressurized fluid extraction and gas and liquid chromatography-mass spectrometry

Soil samples are collected from the former Open Burn/Open Detonation Unit, Makua Military Reservation, on the island of Oahu, Hawaii. The soil is the Helemano series. The soil samples are fortified with eight explosives for development of the analytical method. These analytes are 2-amino-4,6-dinitrotoluene; 1,3-dinitrobenzene; 2,4-dinitrotoluene (DNT); hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX); nitrobenzene (NB); octogen; 1,3,5-trinitrobenzene; and 2,4,6-trinitrotoluene. The analytes are recovered with pressurized fluid extraction and measured with liquid chromatography (LC), LC-mass spectrometry (MS), and gas chromatography-MS. Average recoveries of the seven analytes, except for NB, range from 67% to 110% from freshly fortified samples. The procedure fails to extract NB in soil. The average recoveries decrease from 67-110% to 41-81% as the soil is aged for 1 day to 6 months after fortification of the soil with the seven explosives. The field samples are analyzed for the presence of explosives, of which DNT and RDX are indeed detected. The results obtained with this procedure agree well with those obtained by an independent laboratory following the standard U.S. Environmental Protection Agency (EPA) method SW-846 8330. Compared with the EPA method, this new method provides MS confirmation of the analytes, and the extraction requires approximately 15 min, rather than 18 h by the EPA method.     

The structure of 2,4,6-tris[di(tert-butoxycarbonyl)methylidene]-hexahydro-1,3,5-triazine

The structure of 2,4,6-tris[di(tert-butoxycarbonyl)methylidene]hexahydro-1,3,5-triazine was studied by quantum chemistry, NMR and IR spectroscopy, and X-ray diffraction. This compound exists exclusively in the hexahydro-1,3,5-triazine form both in solution and in the solid phase, although due to the loss of the aromatization energy, this structure should be less stable than a 1,3,5-triazine structure. The formation of strong intramolecular hydrogen bonds confirmed by NMR and IR spectroscopy and X-ray diffraction data may be a main reason for stabilization of the hexahydro-1,3,5-triazine isomer. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1022–1026, June, 2006.     

High-pressure vibrational spectroscopy of energetic materials: hexahydro-1,3,5-trinitro-1,3,5-triazine

Vibrational spectroscopy has been used to investigate the room-temperature high-pressure phases of the energetic material hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The pressure-induced alterations in the spectral profiles were studied in a compression sequence to 30.2 GPa using Raman spectroscopy and to 26.6 GPa using far-infrared spectroscopy. At pressures near 4.0 GPa, several changes become immediately apparent in the Raman spectrum, such as large frequency shifts, mode splittings, and intensity changes, which are associated with a phase transition from alpha-RDX to gamma-RDX. Our study extends the kinetic stability of gamma-RDX to pressures near 18.0 GPa. Evidence for a new phase was found at pressures between 17.8 and 18.8 GPa and is based on the appearance of new vibrational bands and associated changes in intensity patterns. The new phase has vibrational characteristics that are similar to those of beta-RDX, suggesting the two polymorphs share a related crystal structure.     

CARS probe of RDX decomposition

Coherent anti-Stokes Raman scattering (CARS) was used to probe RDX (hexahydro-1,3,5-trinitro-s-triazine) in a carbohydrate matrix burning unconfined in air. Several spectral regions were scanned in an attempt to document the transient species of the RDX combustion for use in determining decomposition mechanisms.     

Square-wave cathodic stripping voltammetric analysis of RDX using mercury-film plated glassy carbon electrode

A mercury film (MF) is prepared by an electrochemical deposition on a glassy carbon electrode (GCE), and employed for an analysis of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) using square-wave stripping voltammetry (SWSV). RDX was deposited at -0.15 V (vs. Ag/AgCl) for 120 s, then reduced at -0.7 V on the MF coated GCE(MFGCE). Optimal experimental conditions were searched and reported for the analysis. Two linear concentration ranges were observed: one in a lower RDX concentration range of 0.2-10 mg l(-1) and the other in a higher RDX concentration range of 10.0-100.0 mg l(-1) with a 120 s of pre-concentration time. At RDX concentrations of 2 and 8 mg l(-1), the relative standard deviations in measured concentrations (n=16) were 9.79 and 0.49%, respectively. The detection limit found to be 0.12 mg l(-1) with the 120 s accumulation time. The method was applied to determine RDX in several soil samples that yielded a relative error of 1% in the concentrations.     

Temperature-dependent far-infrared spectra of single crystals of high explosives using terahertz time-domain spectroscopy

Survey spectra of single-crystal HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and PETN (pentaerythritol tetranitrate) were acquired in the region from 10 to 80 cm(-1) using terahertz time-domain spectroscopy. The spectra were taken at temperatures ranging from 8.4 to 300 K. Generally, the spectra show multiple absorption peaks in the range 50-80 cm(-1), with PETN (110) showing strong absorption features at room temperature. RDX (210) is the most notable in the region 10-40 cm(-1), showing multiple spectral features, while HMX (010) shows a very broad absorption at 47.8 cm(-1) with a fwhm of 37.3 cm(-1). Future plans include polarization-dependent investigations for multiple crystallographic orientations over an increased spectral range and higher-level theoretical calculations.     

Charge-transfer exciton trapping at vacancies in molecular crystals: photoconductivity quenching,optical damage and detonation

Calculations are presented that show that vacancies can trap charge-transfer (CT) states in anthracene, acetanilide and hexahydro-1,3,5-trinintro-1,3,5-triazine (RDX). Such trapping provides a mechanism for photoconductivity quenching by geminate recombination, and for optical damage and detonation by concentrating optical or mechanical energy stored in CT states.