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Opioids have become a serious public health concern over the last decade. These compounds are commonly found mixed, or cut, with safer compounds to make the opioids appear unadulterated while also enhancing the psychoactive effect on the user. Commercial benchtop and handheld IMS devices are capable of detection but published reduced ion mobility (K 0 ) values, used to identify the target analytes with IMS instrumentation, have shown variability. This lack of agreement, even for compounds used for calibration, is often due to the effects of drift tube temperature, drift gas water vapor levels and the use in-house built instrumentation rather than commercial equipment. Multiple reports exist on assessment of IMS reference standards but a single, consensus universal standard does not exist. Assessment of opioid cutting agents as internal standards is a worthwhile pursuit if precise and accurate K 0 values are obtained. The effects of drift gas water vapor content and drift tube temperature were used to evaluate the cutting agents. The K 0 values of papaverine, a representative opioid with a similar K 0 value to heroin and fentanyl, were calculated with respect to quinine and were in agreement with literature data. The use of quinine as an internal standard also improved precision relative to the instrument standard and shows promise in the application presented here., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier B.V.)

Secondary electrospray corona discharge ionization (SECDI) combines the principles of secondary electrospray ionization (SESI) and corona discharge (CD) to achieve higher sensitivity, which is demonstrated through the detection of 2,4,6-trinitrotoluene (TNT) and 2,6-dinitrotoluene (2,6-DNT) vapors using ion mobility spectrometry (IMS). Using SECDI, enhancements in the IMS signal for TNT and 2,6-DNT vapors at trace concentrations are as much as 2-26 times that observed with CD or SESI alone. The enhancement in sensitivity is hypothesized to result from an increase in ionization efficiency driven by a higher number of reactant ions associated with SECDI compared to either technique individually. The ability of SECDI to achieve higher sensitivity without the aid of dopant molecules demonstrates its merit as an alternative ionization technique., (Published by Elsevier B.V.)

The development of an online sampling method using programmable temperature vaporization gas chromatography with a mass spectrometer detector (PTV-GC/MS) for the analysis of trace pentaerythritol tetranitrate (PETN) vapor is presented. PETN degradation was minimized by optimizing the temperature and flow rates of the vapor sampling infrastructure. Validation of the online method was done using a previously published technique, vapor sampling with Tenax-TA thermal desorption tubes followed by analysis with a thermal desorption system coupled to a programmable temperature vaporization gas chromatograph with a micro-electron capture detector (TDS-PTV-GC/μECD). Trace PETN vapor was generated using state-of-the-art instrumentation known as the TESTbed, located at the US Naval Research Laboratory. For PETN vapor concentrations in the parts per trillion volume (ppt v ) range, quantitative results from the TDS-PTV-GC/μECD consistently showed concentrations approximately double that measured by the online PTV-GC/MS method, indicating that sample loss due to additional exposure to the vapor sampling infrastructure occurs when using online sampling. Further utilization of the online PTV-GC/MS system allowed for the quantitation/semi-quantitation of PETN vapor concentrations as low as 260 parts per quadrillion volume (ppq v ) with only 10 min of sampling time., (Published by Elsevier B.V.)

Silicon nanowire (SiNW) arrays are demonstrated as a suitable platform for the preconcentration of trace nitroaromatic compounds and subsequent desorption via Joule heating of the array. Arrays are fabricated from Si wafers containing an epitaxially grown layer of low conductivity intrinsic Si sandwiched between layers of high conductivity p-type Si. Passage of current through the nanowires results in nanowire temperatures in excess of 200 °C during heating of the arrays as verified by using the temperature-dependent shift of the Si Raman band at ˜520 cm -1 . Analyte vapor preconcentration and partial separation is achieved on the array at analyte concentrations nearly two orders-of-magnitude below saturated vapor concentrations at room temperature. The effects of desorption carrier gas flow rate and temperature on the ability to preconcentrate and resolve the analytes of interest are determined. 2,6-dinitrotoluene (2,6-DNT) and 2,4-dinitrotoluene (2,4-DNT) were detected at nominal vapor concentrations of 800 ppt v with a 1 min sample time (1.1 ng nominal mass load) and trinitrotoluene (TNT) was detected at a nominal vapor concentration of 65 ppt v with a 10 min sample time (1.1 ng nominal mass load)., (Published by Elsevier B.V.)

Typical trace vapor analysis involves sorbent trapping, followed by desorption and chromatographic separation. This communication describes a method for streamlining this process by combining sorbent sampling/preconcentration with partial separation achieved through temperature-programmed thermal desorption. A novel sorbent trap was formulated in which tubular glass liners for a programmable-temperature gas chromatograph inlet were coated with a sol-gel based polymer stationary phase synthesized from methyltrimethoxysilane precursor and installed into the inlet, which was directly connected to a mass-selective detector by a fused silica capillary transfer line. This method is shown to achieve partial separation of two nitroaromatic vapors in a total 3-5min analysis time, which represents a tenfold improvement in speed in terms of the overall cycle time compared to an analogous conventional vapor analysis method. Both analytes proved to have a high dynamic range and loading capacity, with nitrobenzene achieving both high and low sampling extremes (0.32ng-4μg sampling concentration) with only a slight compromise in peak broadening. The multivariate curve resolution by alternating least squares algorithm (MCR-ALS) was shown to successfully resolve the overlapped elution profiles of the two nitroaromatic test vapors examined in this study., (Published by Elsevier B.V.)

An analytical method for establishing calibration curves for the quantitation of pentaerythriol tetranitrate (PETN) from sorbent-filled thermal desorption tubes by gas chromatography with electron capture detection (TDS-GC-ECD) was developed. As PETN has been demonstrated to thermally degrade under typical GC instrument conditions, peaks corresponding to both PETN degradants and molecular PETN are observed. The retention time corresponding to intact PETN was verified by high-resolution mass spectrometry with a flowing atmospheric pressure afterglow (FAPA) ionization source, which enabled soft ionization of intact PETN eluting the GC and subsequent accurate-mass identification. The GC separation parameters were transferred to a conventional GC-ECD instrument where analytical method-induced PETN degradation was further characterized and minimized. A method calibration curve was established by direct liquid deposition of PETN standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Two local, linear relationships between detector response and PETN concentration were observed, with a total dynamic range of 0.25-25ng., (Published by Elsevier B.V.)

Two methods for quantitation of triacetone triperoxide (TATP) vapor using a programmable temperature vaporization (PTV) inlet coupled to a gas chromatography/mass spectrometer (GC/MS) have been demonstrated. The dynamic headspace of bulk TATP was mixed with clean humid air to produce a TATP vapor stream. Sampling via a heated transfer line to a PTV inlet with a Tenax-TA™ filled liner allowed for direct injection of the vapor stream to a GC/MS for vapor quantitation. TATP was extracted from the vapor stream and subsequently desorbed from the PTV liner for splitless injection on the GC column. Calibration curves were prepared using solution standards with a standard split/splitless GC inlet for quantitation of the TATP vapor. Alternatively, vapor was sampled onto a Tenax-TA™ sample tube and placed into a thermal desorption system. In this instance, vapor was desorbed from the tube and subsequently trapped on a liquid nitrogen cooled PTV inlet. Calibration curves for this method were prepared from direct liquid injection of standards onto samples tube with the caveat that a vacuum is applied to the tube during deposition to ensure that the volatile TATP penetrates into the tube. Vapor concentration measurements, as determined by either GC/MS analysis or mass gravimetry of the bulk TATP, were statistically indistinguishable. Different approaches to broaden the TATP vapor dynamic range, including diluent air flow, sample chamber temperature, sample vial orifice size, and sample size are discussed. Vapor concentrations between 50 and 5400ngL(-1) are reported, with stable vapor generation observed for as long as 60 consecutive hours., (Published by Elsevier B.V.)

A simple method for establishing calibration curves with sorbent-filled thermal desorption tubes has been demonstrated for nitroaromatic and nitramine vapor samples using a thermal desorption system with a cooled inlet system (TDS-CIS), which was coupled to a gas chromatograph (GC) with an electron capture detector (ECD). The method relies upon the direct liquid deposition of standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Linear calibration results and ideal system conditions for the TDS-CIS-GC-ECD were established for mixtures containing both cyclotrimethylenetrinitramine, a.k.a. RDX, and 2,4,6-trinitrotoluene (TNT). Because of the chemical characteristics of RDX, a higher TDS-CIS flow rate relative to the optimized approach for TNT was required for efficient RDX desorption. Simultaneous quantitation of TNT and RDX using the direct liquid deposition method with optimized instrumentation parameters for RDX were compared to results from a standard split/splitless GC inlet and a CIS., (Published by Elsevier B.V.)

On-line sample preconcentration is an essential tool in the development of microfluidic-based separation platforms. In order to become more competitive with traditional separation techniques, the community must continue to develop newer and more novel methods to improve detection limits, remove unwanted sample matrix components that disrupt separation performance, and enrich/purify analytes for other chip-based actions. Our goal in this review is to familiarize the reader with many of the options available for on-chip concentration enhancement with a focus on those manuscripts that, in our assessment, best describe the fundamental principles that govern those enhancements. Sections discussing both electrophoretic and nonelectrophoretic modes of preconcentration are included with a focus on device design and mechanisms of preconcentration. This review is not meant to be a comprehensive collection of every available example, but our hope is that by learning how on-line sample concentration techniques are being applied today, the reader will be inspired to apply these techniques to further enhance their own programs., (Published by Elsevier B.V.)

The use of thermal desorption systems for the analysis of trace vapors typically requires establishing a calibration curve from vapors generated with a permeation tube. The slow equilibration time of permeation tubes causes such an approach to become laborious when covering a wide dynamic range. Furthermore, many analytes of interest, such as explosives, are not available as permeation tubes. A method for easily and effectively establishing calibration curves for explosive vapor samples via direct deposition of standard solutions on thermal desorption tubes was investigated. The various components of the thermal desorption system were compared to a standard split/splitless inlet. Calibration curves using the direct liquid deposition method with a thermal desorption unit coupled to a cryo-focusing inlet were compared to a standard split/splitless inlet, and a statistical difference was observed but does not eliminate or deter the use of the direct liquid deposition method for obtaining quantitative results for explosive vapors., (Published by Elsevier B.V.)

Practical considerations for the injection and separation of nitroaromatic explosives in seawater sample matrices are discussed. The use of high surfactant concentrations and long electrokinetic injections allows for improved detection limits. Sensitivity was enhanced by two mechanisms, improved stacking at the detector-side of the sample plug and desorption of analyte from the capillary wall by surfactant-containing BGE from the inlet side of the sample plug. Calculated limits of detection (S/N=3) for analytes prepared in pure seawater were 70-800 ppb with injection times varying from 5 to 100 s., (Published by Elsevier B.V.)

There is much interest in developing methods amenable to amplifying nucleic acids by the polymerase chain reaction (PCR) in small volumes in microfabricated devices. The use of infrared-mediated temperature control to accurately thermocycle microliter volumes in microchips fabricated from polyimide is demonstrated. Amplification of a 500-base-pair fragment of lambda-phage DNA was achieved in a 1.7-microl chamber containing a thermocouple that allowed for accurate control of temperature. While previous work showed that Taq polymerase was inactivated when in direct contact with the thermocouple, this was circumvented with the polyimide chip by the addition of polyethylene glycol as a buffer additive. This, consequently, allowed for adequate amounts of PCR product to be observed after only 15 cycles, with a total time for amplification of 240 s., (Copyright 2001 Academic Press.)

Transferrin sialoforms with fewer than three sialic acid residues (carbohydrate deficient transferrin; CDT) have been implicated as a marker of certain liver pathologies. Transferrin sialoforms in human sera from alcoholic and non-alcoholic patients was analyzed by capillary electrophoresis (CE) using diaminobutane (DAB) to dynamically-coat the capillary wall to minimize protein-wall interactions. Using a DAB concentration of 3 mM, transferrin sialoforms were adequately resolved to allow for direct detection of CDT without extensive treatment of the sera. Serum immunoglobulins, which migrated close to the CDT region, were removed via subtraction with protein A, enhancing the detection of CDT. The reproducibility of sialoform separation in dynamically-coated capillaries was found to be acceptable with run-to-run relative standard deviation values of 0.15% for a sample on a given day and 0.29+/-0.06% for four samples day-to-day. These results suggest that dynamic-coating approaches may provide a simple alternative to the use of covalently-coated capillaries for the CE separation of complex samples.