Discrimination of constructed air samples using multivariate analysis of full scan membrane introduction mass spectrometry (MIMS) data.

RATIONALE: Volatile and semi-volatile organic compounds (S/VOCs) are important atmospheric pollutants affecting both human and environmental health. They are directly measured as an unresolved mixture using membrane introduction mass spectrometry (MIMS). We apply chemometric techniques to discriminate, classify, and apportion air samples from a variety of sources. METHODS: Full scan mass spectra of lab-constructed air samples were obtained using a polydimethylsiloxane membrane interface and an electron ionization ion trap mass spectrometer. Normalized full scan spectra were analyzed using principal component analysis (PCA), cluster analysis, and k-nearest neighbours (kNN) for sample discrimination and classification. Multivariate curve resolution (MCR) was used to extract pure component contributions. Similar techniques were applied to VOC mixtures sampled from different woodsmoke emissions and from the headspace above aqueous hydrocarbon solutions. RESULTS: PCA successfully discriminated 32 constructed VOC mixtures from nearly 300 air samples, with cluster analysis showing similar results. Further, kNN classification (k = 1) correctly classified all but one test set sample, and MCR successfully identified the pure compounds used to construct the VOC mixtures. Real-world samples resulting from the combustion of different wood species and those associated with water contaminated with different commercial hydrocarbon products were similarly discriminated by PCA. CONCLUSIONS: Chemometric techniques have been evaluated using full scan MIMS spectra with a series of VOC mixtures of known composition containing known compounds, and successfully applied to samples with known sources, but unknown molecular composition. These techniques have application to source identification and apportionment in real-world environmental samples impacted by atmospheric pollutants.

Characterization of a condensed-phase membrane introduction mass spectrometry (CP-MIMS) interface using a methanol acceptor phase coupled with electrospray ionization for the continuous on-line quantitation of polar, low-volatility analytes at trace levels in complex aqueous samples.

We report the development and application of a capillary hollow fibre membrane interface using methanol as an acceptor phase to deliver target analytes to an electrospray ionization source and a triple quadrupole mass spectrometer. Superior fluid handling systems lead to greater signal stability and membrane integrity for the continuous on-line monitoring of polar and charged analytes in complex aqueous samples with detection limits in the parts-per-trillion to parts-per-billion range. The system can be operated in either a continuous flow or a stopped acceptor flow mode - the latter giving rise to greater sensitivity. We report detection limits, enrichment factors and signal response times for selected analytes with polydimethylsiloxane and Nafion® polymer membrane interfaces. In addition, we demonstrate the use of this interface to detect pharmaceuticals and other contaminants in natural water and artificial urine. The improved sensitivity and analytical response times of our CP-MIMS system make it possible to continuously monitor dynamic chemical systems with temporal resolutions on the order of minutes. Presented is a comparison of the performance of CP-MIMS versus direct infusion electrospray ionization, demonstrating the potential advantages over direct infusion for trace analyte measurements in complex, high ionic strength samples. Furthermore, by continuously flowing a reaction mixture in a closed loop over the interface, we demonstrate the use of the system as an in situ reaction-monitoring platform for the chlorination of a model organic compound in aqueous solution.

Discrimination and geo-spatial mapping of atmospheric VOC sources using full scan direct mass spectral data collected from a moving vehicle.

Volatile and semi-volatile organic compounds (S/VOCs) are ubiquitous in the environment, come from a wide variety of anthropogenic and biogenic sources, and are important determinants of environmental and human health due to their impacts on air quality. They can be continuously measured by direct mass spectrometry techniques without chromatographic separation by membrane introduction mass spectrometry (MIMS) and proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS). We report the operation of these instruments in a moving vehicle, producing full scan mass spectral data to fingerprint ambient S/VOC mixtures with high temporal and spatial resolution. We describe two field campaigns in which chemometric techniques are applied to the full scan MIMS and PTR-ToF-MS data collected with a mobile mass spectrometry lab. Principal Component Analysis (PCA) has been successfully employed in a supervised analysis to discriminate VOC samples collected near known VOC sources including internal combustion engines, sawmill operations, composting facilities, and pulp mills. A Gaussian mixture model and a density-based spatial clustering of application with noise (DBSCAN) algorithm have been used to identify sample clusters within the full time series dataset collected and we present geospatial maps to visualize the distribution of VOC sources measured by PTR-ToF-MS.

The Use of MIMS-MS-MS in field locations as an on-line quantitative environmental monitoring technique for trace contaminants in air and water.

Membrane introduction mass spectrometry (MIMS) is emerging as an important technique for on-line, real-time environmental monitoring. Because MIMS interfaces are simple and robust, they are ideally suited for operation in MS instrumentation used for in-field applications. We report the use of an on-line permeation tube to continuously infuse an isotopically labeled internal standard for continuous quantitative determinations in atmospheric and aqueous samples without the need for off-line calibration. This approach also provides important information on the operational performance of the analytical system during multi-day deployments. We report measured signal stability during on-line deployments in air and water of 7% based on variation of the internal standard response and have used this technique to quantify BTEX (benzene, toluene, ethylbenzenes, and xylenes), pinenes, naphthalene and 2-methoxyphenol (guaiacol) in urban air plumes at parts-per-billion by volume levels. Presented are several recent applications of MIMS-MS-MS for on-line environmental monitoring in atmospheric and aqueous environmental samples demonstrating laboratory, remote and mobile deployments. We also present the use of a thermally assisted MIMS interface for the direct measurement of polyaromatic hydrocarbons, alkylphenols, and other SVOCs in the low ppb range in aqueous environmental samples and discuss improvements in both the sensitivity and response times for selected SVOCs. The work presented in this paper represents significant improvements in field deployable mass spectrometric techniques, which can be applied to direct on-site analytical measurements of VOC and SVOCs in environmental samples.

Analyzing the red-shift characteristics of azulenic, naphthyl, other ring-fused and retinyl pigment analogs of bacteriorhodopsin.

Prompted by the near infrared-absorbing properties of some of the azulenic bacteriorhodopsin (bR) analogs, we have analyzed their absorption characteristics along with 11 new related ring-fused analogs and the corresponding Schiff bases (SB) and protonated Schiff bases (PSB). The following three factors are believed to contribute to the total red shift of each of the pigment analogs (sigma RS): perturbation of the basic chromophore (SB shift, delta SB), protonation of the SB (PSB shift, PSBS) and protein perturbation (the opsin shift, OS). For each factor, effects of structural modifications were examined. For the red-shifted pigments, percent OS has been suggested as an alternate way of measuring protein perturbation. Computer-simulated chromophores provided evidence against any explanation involving altered shapes of the binding pocket as a major cause for absorption differences. Implications of the current bR results on preparation of further red-shifted bR and possible application to visual pigment analogs are discussed.

Retinal detachment after cataract extraction in myopic eyes.

PURPOSE: To determine the incidence of retinal detachment (RD) after cataract extraction in people 40 years of age or older with axial myopia (i.e., axial length > or = 25.5 mm). SETTING: Fifteen Danish eye clinics. METHODS: Two hundred forty-five eyes had cataract extraction performed at 15 eye clinics; 237 eyes had extracapsular cataract extraction (ECCE) and 8 eyes, intracapsular cataract extraction (ICCE). Postoperative data were reported by the practicing ophthalmologists. Mean follow-up was 27 months (range 14 to 32 months). RESULTS: Five RDs occurred in the 245 eyes (2.0%). Excluding the ICCE cases and the two cases of combined cornea transplantation and ECCE, RD occurred in 4 of the 235 eyes that had ECCE (1.7%). The incidence after ECCE with posterior chamber lens implantation was 1.4%. Complete postoperative status was reported on 158 eyes. Forty-eight eyes (30.4%) had a neodymium:YAG capsulotomy and 3 (6.0%) developed an RD 1, 3.5, and 21 months after the capsulotomy. CONCLUSION: The RD incidence after ECCE with posterior chamber lens implantation was low but higher than that in unselected populations. The incidence increased after laser capsulotomy.

[Indications for the use of differential ventilation and selective positive end-expiratory pressure]. / Indikationer for anvendelse af differentiel ventilation og selektivt positivt sluteksspiratorisk tryk.

In some cases of unilateral or bilateral severe lung disease, there is serious hypoxia despite a high level of oxygen in the inspiratory gas mixture. Disturbances in the ventilation/perfusion ratio (V/Q) is a major contributing factor to the hypoxia seen in acute lung disease. The use of positive end expiratory pressure (PEEP) has in some cases been shown to make this V/Q mismatch even worse, and the use of high levels of PEEP is known to increase the risk of barotrauma and to reduce cardiac output. In this article, a method is described which makes it possible to ventilate each lung separately in proportion to its expected perfusion (differential lung ventilation), with or without the use of PEEP to one or both lungs (selective PEEP). Because of a more uniform V/Q the oxygenation in unilateral as well as in bilateral lung disease is improved. The risk of barotrauma as well as the impact on cardiac output is reduced. The patient has to be intubated with a double lumen endotracheal catheter. The gas is delivered by two ventilators synchronized by a master-slave cable. This method can also be used in the operating room, when surgical procedures have to take place in the lateral position, in order to counteract V/Q mismatch and hypoxia.

[Primary care and transportation of patients with neural trauma]. / Primaer behandling og transport af den neurotraumatiserede patient.

It is well-known that it is difficult for the inexperienced doctor to estimate the need for treatment regarding patients with acute brain trauma. Brain ischaemia developing after a brain trauma (secondary cerebral ischaemia) is known to severely worsen the prognosis of the patient. This article gives a review of the most important pathophysiological changes occurring during the acute phase of severe brain trauma. The principles of prevention and management of cerebral ischaemia after brain trauma and during transportation of the patient are discussed.

VER in intraocular hypertension. Short communication.

Transient and steady state VER's before and after artificial IOP elevation were recorded from 16 eyes (9 persons) with untreated intraocular hypertension observed for several years without signs of functional loss or optic disc changes. Four eyes (two patients) demonstrated a pathological transient VER amplitude drop after pressure increase. One eye with an ophthalmoscopically atypical disc presented a grossly deformed transient VER at the habitual pressure level; the fellow eye was lost from trauma. Another eye presented an abnormal VER pattern and showed as yet normal function and ophthalmoscopy, the fellow eye had developed open angle glaucoma and showed identical VER changes. The prognostic and diagnostic implications are briefly discussed.

Intramuscular rabbit anesthesia ketamine hydrochloride and mebumalnatrium (NFN). A safe and easy combination.

For the attainment of deep anesthesia in rabbits, a combination of ketamine hydrochloride (Ketalar) and mebumalnatrium (NFN) (Nembutal), administered intramuscularly, was evaluated. The anesthetic effect was satisfactory and no deaths or side effects were recorded.

DC recording of the human corneofundal potential.

The limitation of an AC technique for the amplification and display of the indirectly recorded human corneofundal potential (CFP)is discussed. A Mingograph M34 with EMT 12 B preamplifiers (Siemens) has been tested with regard to a DC recording of the CFP. With the same purpose the electrical characteristics of two electrode types--a Kaiser lead alloy electrode and a Beckman silver-silver chloride cupped electrode--were examined and a suitable preparation of the skin contact area indicated. Finally the base line stability was evaluated and a comparative study of AC and DC recordings of the CFP presented and subjected to statistical anaylsis.

Normal values in clinical electrooculography. II. Analysis of potential and time parameters and their relation to other variables.

The following EOG potential and time parameters from 72 normal subjects were analysed: base value B, dark trough D, light peak L, light induced potential rise L-D, interval between beginning of dark adaptation and occurrence of dark through d and interval between dark trough and light peak l. Their relations to sex, age pupillary diameter, degree of iris pigmentation, refractive error, axial length, corneal curvature and diameter, ocular protrusion and interpupillary distance were assessed. Right eye and left eye samples of the EOG parameters were congruent, although individual differences were sometimes appreciable. The levels of B and D were higher in the female half of the sample. A positive correlation existed between age and D level. L-D was negatively correlated to the degree of refractive error and positively correlated to the ocular protrusion. A positive correlation was found between d and the four potential parameters, and there was a positive correlation between age and l. Practical consequences of the statistical analysis relating to the interpretation of such EOG data are discussed.

Normal values in clinical electrooculography. 1. Material, method, methodological investigations and distribution of the potential and time parameters.

For the evaluation of normal EOG potential and time parameters a case series (142 eyes) is presented. An EOG technique aiming at the largest possible amplitude between the dark trough and the light peak is described. It is shown that the light-induced response following a 20 min period of adaptation to a very low degree of illumination (about 1/10 lx, allowing a rough orientation on the displayed trace) does not differ from that produced after 20 min of total darkness. Also, the independence of the pupillary area for the light-induced response is demonstrated, which means that the light stimulus employed (2500-4000 lx) is supramaximal. Furthermore, the good quality of the gaze fixation in the actual test situation with respect to the recording of equidistant saccades is proven. A DC amplification of the signal is used, which secures independency of inter- and intra-individual differences in the saccadic velocity and makes possible accurate measurements of deflections disfigured by correcting movements. The following EOG parameters are recorded: A base value after 10 min of preadaptation with the light stimulus, the dark trough and the light peak potentials. Also the periods between the beginning of the dark adaptation and the dark trough and between the dark trough and the light peak are noted. The frequency distribution and the general level of the various parameters are discussed in the light of comparable figures of previous publications.

Normal values in clinical electrooculography. V. Variability within and between eyes.

Three EOG's (DC amplified 30-degree saccades, slightly modified Arden schedule) were recorded at weekly intervals from each of 16 normal human eyes (eight subjects). The light induced potential rise of the dark-adapted eye, the Arden ratio and the Gliem ratio entered into the analysis of intra- and inter-eye variation. The 95% confidence intervals for the mean parameter values of each eye were: +/- 59 muV (mean = 415 muV) for the light induced potential rise, +/- 22 (mean = 260) for the Arden ratio and +/- 10 (mean = 92) for the Gliem ratio. The intra-eye variability was compared to earlier studies of the day-to-day variation of the ERG by means of a dimensionless index; no substantial differences were found. Highly significant differences in the EOG parameter levels existed between the subjects, whereas the variation between right eye and left eye means in the individual subjects was ise respects. The primarily qualitative nature of the EOG in the present version is emphasized by the present results.

Normal values in clinical electrooculography. III. Numerical evaluation of two dimensionless EOG parameters.

The distribution of the Arden ratio (A) and another dimensionless EOG quantity (G) devised by Gliem (1971) in a sample of normal human subjects are presented. The minimum, median and maximum values for A are 148--241--449 and for G 34-88-167. A demonstrates a smaller degree of dispersion than G, the latter resembling in this respect the EOG potential parameters of the same sample. The average accumulation of errors due to inaccurate assessment of the included potential figures is almost equal in the functions of A and G. Divergencies between the figures from the present and earlier investigations are discussed together with the general advantage of dimensionless EOG parameters. It is concluded that the present investigation has not demonstrated the need to replace or supplement the Arden ratio by the Gliem quantity.