Analysis of nitrogen-based explosives with desorption atmospheric pressure photoionization mass spectrometry.

RATIONALE: Fast methods that allow the in situ analysis of explosives from a variety of surfaces are needed in crime scene investigations and home-land security. Here, the feasibility of the ambient mass spectrometry technique desorption atmospheric pressure photoionization (DAPPI) in the analysis of the most common nitrogen-based explosives is studied. METHODS: DAPPI and desorption electrospray ionization (DESI) were compared in the direct analysis of trinitrotoluene (TNT), trinitrophenol (picric acid), octogen (HMX), cyclonite (RDX), pentaerythritol tetranitrate (PETN), and nitroglycerin (NG). The effect of different additives in DAPPI dopant and in DESI spray solvent on the ionization efficiency was tested, as well as the suitability of DAPPI to detect explosives from a variety of surfaces. RESULTS: The analytes showed ions only in negative ion mode. With negative DAPPI, TNT and picric acid formed deprotonated molecules with all dopant systems, while RDX, HMX, PETN and NG were ionized by adduct formation. The formation of adducts was enhanced by addition of chloroform, formic acid, acetic acid or nitric acid to the DAPPI dopant. DAPPI was more sensitive than DESI for TNT, while DESI was more sensitive for HMX and picric acid. CONCLUSIONS: DAPPI could become an important method for the direct analysis of nitroaromatics from a variety of surfaces. For compounds that are thermally labile, or that have very low vapor pressure, however, DESI is better suited.

Post-mortem analysis of lactate concentration in diabetics and metformin poisonings.

Lactate is produced in carbohydrate metabolism under anaerobic conditions. Lactic acidosis occurs when the production of lactate exceeds its removal. In post-mortem (PM) context, the lactic acidosis is difficult to interpret due to unknown pathophysiological factors prior to death and PM changes that may affect the lactate levels. We evaluated 1865 medico-legal autopsy cases where the quantitation of glucose, lactate, and ketone bodies was performed as a part of the cause of death (CoD) investigation. Lactate was shown to ascend in a logarithmic manner as the PM interval increased until a plateau was achieved approximately after 8-10 days PM, and the elevation was caused mainly by PM changes. The lactate level was higher than the mean in cases where the CoD was diabetes mellitus type 2 (DM2) or metformin poisoning. Although there was a correlation between metformin and lactate levels, our findings suggest the DM2 and its complications were the cause for elevated lactate levels rather than metformin, since the lactate levels were similar in DM2-associated deaths where no metformin was detected. Elevated lactate levels in PM samples rather referred to metabolic disturbances often caused by DM2. An assay to detect D-lactate in PM samples was described.

Atmospheric pressure photoionization-mass spectrometry and atmospheric pressure chemical ionization-mass spectrometry of neurotransmitters.

A group of five neurotransmitters with different properties was analyzed using atmospheric pressure photoionization (APPI) and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS). The sensitivity of the techniques for the analytes was tested in six solvents and in positive and negative ion modes. APPI was found to be superior in sensitivity for all the compounds in both positive and negative ion modes. In positive ion mode, water/methanol/formic acid was found to be the best solvent, whereas in negative ion mode, water/methanol/ammonium hydroxide performed best. Detection limits using APPI were between 2.5-250 fmol, depending on the compound. The sensitivity was best for the neurosteroids dehydroepiandrosterone and beta-estradiol, and acetylcholine (LOD 2.5-10 fmol).

Utilization of a multimembrane inlet and a cyclic sudden sampling introduction mode in membrane inlet mass spectrometry.

Sudden sampling introduction into a membrane inlet mass spectrometer (MIMS) considerably improves the selectivity of the membrane inlet and is therefore applicable even for compounds with low permeabilities through a silicone membrane. In this study the basics of cyclic non-steady-state sudden increase sample injection were studied using a three-membrane inlet and a portable sector double-focusing mass spectrometer. The operational parameters of the inlet system providing the most efficient enrichment of volatile organic compounds (VOCs) in air were defined. Simulation of the diffusion process following sudden sample introduction into the three-membrane inlet was also carried out. Experimental testing of the three-membrane inlet system with the cyclic sudden sample injection mode for benzene, toluene, styrene, and xylene in air was performed. The simulation and the experimental results demonstrated that, when this mode is used, the VOCs/nitrogen relative enrichment factor of samples introduced into the mass spectrometer equipped with a three-membrane inlet is increased by a factor of approximately 10(5) compared with a direct introduction method. This effect may be used to decrease detection limits of compounds obtained with mass spectrometry to decrease matrix flow through the inlet at the same detection limits.

Purge-and-membrane mass spectrometry, a screening method for analysis of VOCs from soil samples.

Purge-and-membrane mass spectrometry (PAM-MS) is a combination of dynamic headspace sampling and membrane extraction. A new and simple purge-and-membrane sampler is introduced and its basic testing results for the analysis of VOCs in soil samples are reported. Soil moisture had no effect on desorption times in the case of sand, but the desorption times increased when the content of organic matter in the soil sample (garden soil) increased. The longest desorption times were measured with dry garden soil samples. For both types of samples, minor differences in desorption peak areas were observed between 10 and 20% moisture. Detection limits of the VOCs varied in the range 2-150 microg/kg, depending on the soil type. Good linearity (correlation coefficient > 0.990) was observed in the range 0.5-50 mg/kg. Aging of the spiked soil samples had only a slight effect on desorption peak areas for samples stored at 5 degrees C up to two weeks, but after six months of storing, differences were observed between dry sand and moistened garden soil. In both cases, peak areas were diminished. On average, 46% of compounds could be desorbed from the aged sand and 86% from the aged garden soil. The modified vapor fortification method was used in preparing standard soil samples, which were analyzed by static headspace gas chromatography (HSGC) and PAM-MS. Some authentic soil samples were also analyzed using both of these techniques. Many of the vapor fortification samples and the authentic samples were also analyzed in another laboratory by HSGC. The agreement between the methods and the laboratories was generally good.

Optimization of capillary electrophoretic-electrospray ionization-mass spectrometric analysis of catecholamines.

The capillary electrophoretic-mass spectrometric analysis (CE-MS) of catecholamines was optimized with coaxial sheath flow interface and electrospray ionization (ESI). The parameters studied included the sheath liquid composition and its flow rate, separation conditions in ammonium acetate buffer together with the ESI and cone voltages as mass spectrometric parameters. In addition, the effect of ESI voltage on injection as well as the siphoning effect were considered. The optimized conditions were a sheath liquid composition of methanol-water (80:20 v/v) with 0.5% acetic acid, with a flow rate of 6 microL/min. The capillary electrophoretic separation parameters were optimized with 50 mM ammonium acetate buffer, pH 4.0, to +25 kV separation voltage together with a pressure of 0.1 psi. The most intensive signals were obtained with an ESI voltage of +4.0 kV and a cone voltage of +20 V. The nonactive ESI voltage during injection as well as avoidance of the siphoning effect increased the sensitivity of the MS detection considerably. The use of ammonium hydroxide as the CE capillary conditioning solution instead of sodium hydroxide did not affect the CE-MS performance, but allowed the conditioning of the capillary between analyses to be performed in the MS without contaminating the ion source.

Analysis of residual solvents in pharmaceuticals with purge-and-membrane mass spectrometry.

A method using purge-and-membrane mass spectrometry (PAM-MS) was developed for the analysis of residual solvents in pharmaceutical products. The method combines dynamic headspace and membrane inlet mass spectrometry. The limits of detection for the compounds studied, benzene, toluene, chloroform, 2-pentene and 2-methyl- and 3-methylpentane, were 0.05-0.1 mg/kg. In quantitative analysis the method showed good linearity (r(2) > 0.998) and acceptable within-day (RSD = 7.9-18%) and between-day (RSD = 6.8-10%) repeatability. The PAM-MS method combined with the custom-made Solver program was compared with a method using purge-and-trap gas chromatography/mass spectrometry (P&T-GC/MS) for identification of residual solvents from authentic samples. The results showed that PAM-MS/Solver provides reliable identification of the main volatile organic compounds (VOCs) in the pharmaceuticals, but VOCs with low concentrations (below 0.5 mg/kg) were better identified by P&T-GC/MS. Other advantages of the PAM-MS method were short analysis times and non-requirement for pre-treatment of samples.

Determination of mono- and sesquiterpenes in water samples by membrane inlet mass spectrometry and static headspace gas chromatography.

A membrane inlet mass spectrometric (MIMS) method is presented and compared with a static headspace gas chromatographic method (HSGC) for the determination of terpenes in water. The MIMS method provides a very simple and fast analysis of terpenes in water, detection limits being relatively low, from 0.2 mug l(-1) for monoterpenes to 2 mug l(-1) for geraniol. The analysis of terpenes by the HSGC (equipped with flame ionization detector, FID) method is more time-consuming and the detection limits (2 mug l(-1) for monoterpenes to 100 mug l(-1) for geraniol) are higher than with MIMS. However, the HSGC method has the advantage of determining individual mono- and sesquiterpene compounds, whereas MIMS provides only separation of different classes of terpenes. Both methods were applied to the analysis of mono- and sesquiterpenes in several condensation water samples of pulp and paper mills.

Determination of phenolic compounds in water using membrane inlet mass spectrometry.

Two membrane inlet mass spectrometric (MIMS) methods for determining phenolic compounds in water are described and compared, namely direct analysis and analysis after acetylation of the phenolic compounds. Direct analysis of phenolic compounds in water is a very simple and rapid method and detection limits are relatively low (from 30 mug 1(-1) for phenol to 1000 mug 1(-1) for 4-nitrophenol). Analysis of phenolic compounds after aqueous acetylation is also a very simple and rapid method, and the detection limits are even two orders of magnitude lower than in the direct analysis. For example the detection limit of phenol acetate is 0.5 mug 1(-1) and that of 4-nitrophenol is 10 mug 1(-1). The acetylation method was also tested in the analysis of phenolic compounds from contaminated surface water samples.

Comparison of different methods for the determination of volatile organic compounds in water samples.

The aim of this work was to compare the characteristics of three methods, membrane inlet mass spectrometry (MIMS), purge-and-trap gas chromatography-mass spectrometry (P&T) and static headspace gas chromatography (HSGC), for the determination of volatile organic compounds in water samples as used in routine analysis. The characteristics examined included linear dynamic ranges, detection limits of selected environmentally hazardous volatile organic compounds (e.g. toluene, benzene and trichloroethene) in water, required analysis time and reproducibility of the analytical methods. The MIMS and P&T methods had the lowest detection limits for all the tested compounds, ranging from 0.1 to 5 mug 1(-1). Linear dynamic ranges using the MIMS method were about four orders of magnitude and using the P&T method about two orders of magnitude. Detection limits of the HSGC method were 10-100 times higher than those of the other two methods, but the linear dynamic ranges were larger, even up to six orders of magnitude. The analysis time per sample was shortest for the MIMS method, from 5 to 10 min, and ranged around from 35 to 45 min for the HSGC and P&T methods. The reproducibilities of the methods were of the same order of magnitude, in the range of 1-13%. Agreement between the analytical results obtained for spiked samples and for environmental water samples by the three different methods was very good.

Quantitative Determination of Semivolatile Organic Compounds in Solution Using Trap-and-Release Membrane Inlet Mass Spectrometry.

This paper discusses the use of trap-and-release membrane inlet mass spectrometry (T&R-MIMS) for the quantitative determination of semivolatile organic compounds in real samples. We found that the T&R-MIMS technique is particular sensitive to relatively polar, semivolatile organic compounds. For example, the detection limits for the acids acetylsalicylic acid and phenoxyacetic acid were lowered by a factor of 100 as compared with those possible with standard MIMS, and caffeine was detectable only with the T&R-MIMS method. The detection limits were in the parts-per-billion range, and the dynamic range was 3 orders of magnitude. As a practical example of the application of the T&R-MIMS technique, we used it for the quantitative analysis of caffeine in ground coffee and tea leaves. Good agreement between T&R-MIMS and HPLC determinations was found, and the reproducibility of the whole analytical system for caffeine determination (extraction procedure and T&R-MIMS determination) was within 10% as relative standard deviation. However, for coffee, a large background from the essential oils prevented low-level work, such as the determination of residual caffeine in decaffeinated coffee. Obviously, the analysis of many complex matrixes will require the use of tandem mass spectrometry.