Correction to: Monitoring Dose Response of Cyanide Antidote Dimethyl Trisulfide in Rabbits Using Diffuse Optical Spectroscopy.

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Rapid analysis of sulfur mustard oxide in plasma using gas chromatography-chemical ionization-mass spectrometry for diagnosis of sulfur mustard exposure.

Sulfur mustard (SM) is the most utilized chemical warfare agent in modern history and has caused more casualties than all other chemical weapons combined. SM still poses a threat to civilians globally because of existing stockpiles and ease of production. Exposure to SM causes irritation to the eyes and blistering of skin and respiratory tract. These clinical signs of exposure to SM can take 6-24 h to appear. Therefore, analyzing biomarkers of SM from biological specimens collected from suspected victims is necessary for diagnosis during this latent period. Here, we report a rapid, simple, and direct quantitative analytical method for an important and early SM biomarker, sulfur mustard oxide (SMO). The method includes addition of a stable isotope labeled internal standard, SMO extraction directly into dichloromethane (DCM), rapid drying and reconstitution of the extract, and direct analysis of SMO using gas chromatography-chemical ionization-mass spectrometry. The limit of detection of the method was 0.1 µM, with a linear range from 0.5 to 100 µM. Method selectivity, matrix effect, recovery, and short-term stability were also evaluated. Furthermore, the applicability of the method was tested by analyzing samples from inhalation exposure studies performed in swine. The method was able to detect SMO from 100% of the exposed swine (N = 9), with no interferences present in the plasma of the same swine prior to exposure. The method presented here is the first of its kind to allow for easy and rapid diagnosis of SM poisoning (sample analysis <15 min), especially important during the asymptomatic latency period.

Percent residual accuracy for quantifying goodness-of-fit of linear calibration curves.

Linear models for calibration curves are overwhelmingly created based on minimization of least squares error, with their goodness-of-fit (GOF) quantified using the square of the correlation coefficient (R2). Yet, R2 has well-known disadvantages when used to quantify GOF of calibration curves stemming from its calculation based on the absolute error of the signal (i.e., calculated vs. experimental). These disadvantages are exacerbated when using a geometric series of concentrations for calibration standards (e.g., 1, 2, 5, 10, etc.) and when calibration curves span 2-3 orders of magnitude, which is typical for modern analytical techniques. While there are multiple alternative GOF measures, R2 overwhelmingly persists in the field of Analytical Chemistry as the most reported measure of GOF. We evaluated R2, alternative GOF measures, and multiple quantitative bias parameters, along with residual analysis, for over 60 experimental calibration curves. R2 did a poor job of consistently and accurately quantifying the GOF over the entire calibration curve. This was especially true for situations where the low concentration calibrators were not accurately described by the calibration equation. While other GOF parameters, including the sum of the absolute percent error, mean absolute percent error, and quality coefficient, did a better job of describing GOF of calibration curves, each had significant theoretical and/or practical disadvantages. Therefore, we introduce a descriptive GOF parameter called Percent Residual Accuracy (%RA or PRA) which equally weights the accuracy of all calibrators into a single value, generally falling between 0% and 100%, with 100% representing a perfect fit and a "good" fit for calibration data producing a %RA of 90-100%. The %RA much more effectively described the GOF for the entire calibration range than R2, and it similarly quantified GOF as compared to the other GOF parameters tested. With the performance and practical advantages of %RA, we conclude that it is the most advantageous GOF parameter and that it should be reported as a standard GOF measure for calibration curves.

Monitoring Dose Response of Cyanide Antidote Dimethyl Trisulfide in Rabbits Using Diffuse Optical Spectroscopy.

INTRODUCTION: Cyanide (CN) poisoning is a serious chemical threat from accidental or intentional exposures. Current CN exposure treatments, including direct binding agents, methemoglobin donors, and sulfur donors, have several limitations. Dimethyl trisulfide (DMTS) is capable of reacting with CN to form the less toxic thiocyanate with high efficiency, even without the sulfurtransferase rhodanese. We investigated a soluble DMTS formulation with the potential to provide a continuous supply of substrate for CN detoxification which could be delivered via intramuscular (IM) injection in a mass casualty situation. We also used non-invasive technology, diffuse optical spectroscopy (DOS), to monitor physiologic changes associated with CN exposure and reversal. METHODS: Thirty-six New Zealand white rabbits were infused with a lethal dose of sodium cyanide solution (20 mg/60 ml normal saline). Animals were divided into three groups and treated with saline, low dose (20 mg), or high dose (150 mg) of DMTS intramuscularly. DOS continuously assessed changes in tissue hemoglobin concentrations and cytochrome c oxidase redox state status throughout the experiment. RESULTS: IM injection of DMTS increased the survival in lethal CN poisoning. DOS demonstrated that high-dose DMTS (150 mg) reversed the effects of CN exposure on cytochrome c oxidase, while low dose (20 mg) did not fully reverse effects, even in surviving animals. CONCLUSIONS: This study demonstrated potential efficacy for the novel approach of supplying substrate for non-rhodanese mediated sulfur transferase pathways for CN detoxification via intramuscular injection in a moderate size animal model and showed that DOS was useful for optimizing the DMTS treatment.

Determination of methyl isopropyl hydantoin from rat erythrocytes by gas-chromatography mass-spectrometry to determine methyl isocyanate dose following inhalation exposure.

Methyl isocyanate (MIC) is an important precursor for industrial synthesis, but it is highly toxic. MIC causes irritation and damage to the eyes, respiratory tract, and skin. While current treatment is limited to supportive care and counteracting symptoms, promising countermeasures are being evaluated. Our work focuses on understanding the inhalation toxicity of MIC to develop effective therapeutic interventions. However, in-vivo inhalation exposure studies are limited by challenges in estimating the actual respiratory dose, due to animal-to-animal variability in breathing rate, depth, etc. Therefore, a method was developed to estimate the inhaled MIC dose based on analysis of an N-terminal valine hemoglobin adduct. The method features a simple sample preparation scheme, including rapid isolation of hemoglobin, hydrolysis of the hemoglobin adduct with immediate conversion to methyl isopropyl hydantoin (MIH), rapid liquid-liquid extraction, and gas-chromatography mass-spectrometry analysis. The method produced a limit of detection of 0.05 mg MIH/kg RBC precipitate with a dynamic range from 0.05-25 mg MIH/kg. The precision, as measured by percent relative standard deviation, was <8.5%, and the accuracy was within 8% of the nominal concentration. The method was used to evaluate a potential correlation between MIH and MIC internal dose and proved promising. If successful, this method may be used to quantify the true internal dose of MIC from inhalation studies to help determine the effectiveness of MIC therapeutics.

ICE Concentration Linked with Extractive Stirrer (ICECLES).

Trace and ultra-trace analysis can be difficult to achieve, especially for polar, more volatile, and/or thermally unstable analytes. A novel technique, coined ICE Concentration Linked with Extractive Stirrer (ICECLES), may help address this problem. The implementation of ICECLES described here combines stir bar sorptive extraction (SBSE) with freeze concentration (FC), where an aqueous solution is frozen during SBSE in order to concentrate analytes into a polydimethylsiloxane (PDMS) coated stir bar. Five test probe molecules with a range of log Kows (2-butanol, benzyl alcohol, benzaldehyde, dimethyl trisulfide and bromobenzene) were prepared from aqueous solutions using ICECLES. Thermal desorption gas-chromatography mass-spectrometry was then used to quantify these analytes. Parameters affecting the performance of ICECLES (e.g., freeze rate) were evaluated, with extraction at lower speeds resulting in higher extraction efficiencies, whereas the freeze rate and initial analyte concentration only had a minor effect. ICECLES produced much higher extraction efficiencies than SBSE alone, with signal enhancements of up to 474× SBSE. ICECLES also provided excellent reproducibility and lower LODs than SBSE for all compounds tested. ICECLES performed well when used to analyze multiple triazine pesticides and breakdown products in environmental surface waters. Overall, the ICECLES technique was excellent at preparing aqueous samples for trace analysis and shows promise as a novel analytical sample preparation technology.

Determination of dimethyl trisulfide in rabbit blood using stir bar sorptive extraction gas chromatography-mass spectrometry.

Cyanide poisoning by accidental or intentional exposure poses a severe health risk. The current Food and Drug Administration approved antidotes for cyanide poisoning can be effective, but each suffers from specific major limitations concerning large effective dosage, delayed onset of action, or dependence on enzymes generally confined to specific organs. Dimethyl trisulfide (DMTS), a sulfur donor that detoxifies cyanide by converting it into thiocyanate (a relatively nontoxic cyanide metabolite), is a promising next generation cyanide antidote. Although a validated analytical method to analyze DMTS from any matrix is not currently available, one will be vital for the approval of DMTS as a therapeutic agent against cyanide poisoning. Hence, a stir bar sorptive extraction (SBSE) gas chromatography - mass spectrometry (GC-MS) method was developed and validated for the analysis of DMTS from rabbit whole blood. Following acid denaturation of blood, DMTS was extracted into a polydimethylsiloxane-coated stir bar. The DMTS was then thermally desorbed from the stir bar and analyzed by GC-MS. The limit of detection of DMTS using this method was 0.06µM with dynamic range from 0.5-100µM. For quality control standards, the precision, as measured by percent relative standard deviation, was below 10%, and the accuracy was within 15% of the nominal concentration. The method described here will allow further investigations of DMTS as a promising antidote for cyanide poisoning.

Simultaneous high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) analysis of cyanide and thiocyanate from swine plasma.

An analytical procedure for the simultaneous determination of cyanide and thiocyanate in swine plasma was developed and validated. Cyanide and thiocyanate were simultaneously analyzed by high-performance liquid chromatography tandem mass spectrometry in negative ionization mode after rapid and simple sample preparation. Isotopically labeled internal standards, Na(13)C(15)N and NaS(13)C(15)N, were mixed with swine plasma (spiked and nonspiked), proteins were precipitated with acetone, the samples were centrifuged, and the supernatant was removed and dried. The dried samples were reconstituted in 10 mM ammonium formate. Cyanide was reacted with naphthalene-2,3-dicarboxaldehyde and taurine to form N-substituted 1-cyano[f]benzoisoindole, while thiocyanate was chemically modified with monobromobimane to form an SCN-bimane product. The method produced dynamic ranges of 0.1-50 and 0.2-50 µM for cyanide and thiocyanate, respectively, with limits of detection of 10 nM for cyanide and 50 nM for thiocyanate. For quality control standards, the precision, as measured by percent relative standard deviation, was below 8 %, and the accuracy was within ±10 % of the nominal concentration. Following validation, the analytical procedure successfully detected cyanide and thiocyanate simultaneously from the plasma of cyanide-exposed swine.