Determination of ethylene by field asymmetric ion mobility spectrometry

The determination of ethylene with a field asymmetric ion mobility spectrometer, which can easily be constructed in-house, is described. The device makes use of a Krypton lamp for ionization. A rectangular pulse of 500 V(pp)at 1 MHz was employed as separation waveform in the drift tube rather than the commonly used less efficient bisinusoidal waveform. The calibration curve for the range from 670 ppb((V/V))to 67 ppm((V/V))was found to be highly linear with a correlation coefficient of r = 0.9999. The limit of detection was determined as 200 ppb((V/V)). The reproducibility was 4% (relative standard deviation). The device was found to be suitable for the determination of ethylene given off by fruit; 6 types of climacteric fruit were tested, namely apples, bananas, kiwi fruit, nectarines, pears and plums

Determination of Binary Gas Mixtures by Measuring the Resonance Frequency in a Piezoelectric Tube

The composition of gas mixtures may be determined via changes of the speed of sound. As this affects the resonance frequency of the gas inside a tube, indirect measurements through a frequency analysis are also possible. It is demonstrated that this may be carried out with unprecedented simplicity by the novel employment of a piezoelectric tube which serves at the same time as a resonance tube and as transducer into the electronic domain. Experiments were run using a simple diecast aluminum box as the measuring cell, inside which the piezoelectric tube made from lead zirconium titanate with 30-mm length and 5.35-mm inner diameter was suspended. A small loudspeaker placed into the cell served for excitation of the resonance. Peak frequencies between 3910 and 14,590 Hz (for pure CO2 and He, respectively) were obtained. Two component mixtures of O2/N2, CO2/N2, and He/N2 at various composition were tested. A linear frequency change from 4790 to 5100 Hz was observed when going from pure O2 to pure N2

Contactless conductivity detection for analytical techniques: Developments from 2016 to 2018

The publications concerning capacitively coupled contactless conductivity detection for the 2-year period from mid-2016 to mid-2018 are covered in this update to the earlier reviews of the series. Relatively few reports on fundamental investigations or new designs have appeared in the literature in this time interval, but the development of new applications with the detection method has continued strongly. Most often, contactless conductivity measurements have been employed for the detection of inorganic or small organic ions in conventional capillary electrophoresis, less often in microchip electrophoresis. A number of other uses, such as detection in chromatography or the gauging of bubbles in streams have also been reported

Determination of tobramycin in eye drops with an open-source hardware ion mobility spectrometer

The analysis of tobramycin was demonstrated successfully as an example for electrospray ionization on an open-source hardware ion mobility spectrometer. This instrument was assembled inexpensively in-house, and required only very few purpose-made components. The quantitative determination of tobramycin required 20 s for a reading. The calibration curve for the range from 50 to 200 μM was found to be linear with a correlation coefficient of r = 0.9994. A good reproducibility was obtained (3% relative standard deviation) and the limit of detection was determined as 8 μM. As the concentration of the active ingredient in the eye drops (ophthalmic solutions) is too high for the sensitivity of the instrument, the samples had to be diluted appropriately

Background conductivity independent counter flow preconcentration method for capillary electrophoresis

A preconcentration method for anions is presented, which relies on a trap created by applying an electric field against a hydrodynamic flow of the sample. The trapping zone is created in front of a cation exchange membrane that allows the isolation of the electrode and thus prevents any interference by electrolysis products. Preconcentration factors of up to 20 were demonstrated for nitrate and formate as model analyte ions and were linearly related to the sample volume passed through the trap. A discrimination between the ions was found possible by adjustment of the hydrodynamic flow velocity. The method was also found to be suitable for the preconcentration of an anion (nitrate at 100 mu M) in presence of a second anion at a very high concentration (50 mM formate). The detection limits for the four anions chloride, nitrate, perchlorate, and formate could be lowered from 4, 4.3, 4.2, and 7.2 mu M obtained without trapping respectively to 127, 142, 139, and 451 nM with trapping

Ambient ionization source based on a dielectric barrier discharge for direct testing of pharmaceuticals using ion mobility spectrometry

The instrument is based on a miniature plasma source mounted at an oblique angle close to the injection gate of the ion mobility spectrometer. The plasma torch consists of two 5 mm wide external cylindrical electrodes, 10 mm apart, which are placed coaxially around a fused silica tube (1.5 mm i.d. and 3.0 mm o.d.). A small helium plasma is created by applying a alternating voltage of 8 kV at 28 kHz and employed for the direct desorption and ionization of solid or liquid samples, which are placed on an electrically isolated support. The separation section of the ion mobility spectrometer has a drift tube of 10 cm length and an applied high voltage of 4 kV. The instrument was built in-house at low cost and can easily be duplicated. Its usefulness was demonstrated by the rapid identification of five different pharmaceutical drugs, namely acetaminophen, loratadine, norfloxacin, tadalafil, thiamine as well as caffeine in ground coffee beans

Low-cost electronic circuitry for photoacoustic gas sensing

The circuitry comprises a sine wave generator based on direct digital synthesis, a laser diode driver module, a band-pass frequency filter, a synchronous detector with phase adjustment circuitry and a low pass filter to form an analog lock-in amplifier, and an analog-to-digital converter. A 32-bit ARM microcontroller programmed with the open source Mecrisp dialect of the Forth interpreter language is used to set the frequency, and read the data from the analog-to-digital converter. The circuitry is tethered via a serial interface to a personal computer. A graphical user interface written in Phython allows easy interaction with the microcontroller by sending the appropriate Forth commands. The data acquired is visualized and stored on the personal computer for further processing. The circuitry is easy to build as it is based on through-hole devices, except for two necessary surface mount items, which, however, still can be soldered with a fine tipped soldering iron. The performance of the circuitry was demonstrated by the photoacoustic detection of NO2 using a laser diode with a wavelength of 450 nm

Deaf Children’s Science Content Learning in Direct Instruction versus Interpreted Instruction

This research study compared learning of 6-9th grade deaf students under two modes of educational delivery – interpreted vs. direct instruction using science lessons. Nineteen deaf students participated in the study in which they were taught six science lessons in American Sign Language. In one condition, the lessons were taught by a hearing teacher in English and were translated in ASL via a professional and certified interpreter. In the second condition, the lessons were taught to the students in ASL by a deaf teacher. All students saw three lessons delivered via an interpreter and three different lessons in direct ASL; the order of delivery of each presentation was counter balanced between the two groups of students. Following the instruction, each group was tested on the science lecture materials with six comprehension questions. Results indicated that deaf students who received direct instruction in ASL from the deaf teacher scored higher on content knowledge

High voltage pulser for ion shutters in ion mobility spectrometry based on an optocoupler

A novel high voltage pulser for an ion shutter used in drift-tube ion-mobility spectrometers is described. The simple design suitable for the in-house construction of these spectrometers relies on a special optocoupler to isolate the triggering circuitry from the high voltage at the ion shutter. The device was tested with an electrospray-ionization ion-mobility device with a 10 cm drift tube operated at 4 kV into which a standard test mixture of four tetraalkylamines was injected with a negative going gating pulse of about 50 V on top of 4 kV. A fall time of 15.7 µs and a rise time of 2.0 µs were determined for the pulse, which was adequate for the required injection pulse width of 450 µs. Resolving powers between 61 and 81 were determined for the four quaternary amines, which were found to be comparable to the performance obtained with a previously reported pulser circuitry of a different design used as a reference