Short-term storability of volatile organic compounds in bag sampling systems under ambient conditions.

Although bag sampling is a common quantification tool for volatile organic compounds (VOCs), it can serve as a major source of experimental bias, when storing even over a short duration (<24 h). To learn more about the reliability of the bag sampling method, the temporal stability of 27 VOCs (classified into five groups (i.e., aldehydes, nonpolar aromatic hydrocarbons, aliphatic carboxylic acids, phenol and methylphenols, and miscellaneous odorants) is assessed using poly-ester aluminum (PEA) bags at five intervals over a day (0.17, 1, 2, 6, and 24 h). In terms of reproducibility (e.g., relative standard error [RSEt, %]), nonpolar aromatic hydrocarbons (BTXS) exhibit the highest consistency (e.g., average RSE <1.55%). Considerable loss of VOCs is observed in the preparation of gaseous standards from a liquid phase standard when assessed by gas/liquid (G/L) ratio. Further, VOCs with lower molecular weights (e.g., propionaldehyde: 77%-94.4%) and branched molecular structures (e.g., isovaleraldehyde: 67.2%-78.9%) tend to have high G/L ratio (e.g., relative to valeraldehyde: 55.1%-66%). The overall relative recovery (RR; %) values of VOCs indicate an exponential decrease over 24 h. BTXS maintain fairly good RR values (above 94.3% at all intervals), possibly due to the nonpolar structure with uniform distribution of π electrons. In contrast, indole and skatole show the least preservation after 24 h (e.g., RR4 values of 10.9% and 24.6%, respectively) due to their highly reactive characteristics. The storability of VOCs appears to be affected by a number of variables (e.g., molecular weight, presence of ethyl branch, and time: e.g., R2 > 0.9). The results of this study offer valuable guidelines for the accurate quantification of VOC levels in air.

Compositional changes at neighborhood and stand scales during recovery of a tropical lowland rainforest after shifting cultivation on Hainan Island, China.

Understanding compositional changes during secondary forest recovery is crucial for effective restoration efforts. While previous research has predominantly focused on shifts in species composition at the stand scale, this study delves into the recovery dynamics in three compositional aspects of location (neighbor distances), size (tree diameters), and species (tree species) at both stand and neighborhood scale. The investigation spans nine chronosequence plots within a tropical lowland rainforest ecosystem after shifting cultivation, including three each for young-secondary forests (18-30 years), old-secondary forests (60 years), and old-growth forests (without obvious human interference). The quantification of location, size, and species composition involved categorized neighbor distances (Near, Moderate, Far-distance), tree diameters (Small, Medium, Large-tree), and tree species (Pioneer, Intermediate, Climax-species) into three groups, respectively. Compositional changes at the stand scale (plot) were directly based on these groups, while at the neighborhood scale, assessment involved combination types of these groups within a neighborhood (comprising three adjacent trees). At the stand scale, neighbor distances shifted from Near to Moderate and Far, tree diameters transitioned from Small to Medium and Large, and tree species of Pioneer gave way to Climax. Meanwhile, at the neighborhood scale, there was a notable decline in the aggregations of Near-distance (N), Small-tree (S), and Pioneer-species (P), while the mixtures of Far and Moderate-distance (F-M), Large and Small-tree (L-S), and Climax and Intermediate-species (C-I) experienced a marked increase. The compositional change exhibited a recovery pattern, with the fastest recovery in neighbor distances, followed by tree diameters and tree species. Moreover, compositional recovery in tree diameters and tree species at the neighborhood scale generally lagged behind that at the stand scale. The study suggests that rapid restoration of secondary forest can be achieved by different targeted cutting according to the recovery stages, aimed at reduce the Pioneer-species, Small-tree and Near-distance in neighborhood. Our findings underscore that analyzing the compositional changes in three aspects at two scales not only provides a profound understanding of secondary forest recovery dynamics, but also offers valuable insights for guiding practices in the restoration of degraded forest ecosystems.

Proteomic investigation of protein adsorption to cerebral microdialysis membranes in surgically treated intracerebral hemorrhage patients - a pilot study.

BACKGROUND: Cerebral microdialysis (CMD) is a minimally invasive technique for sampling the interstitial fluid in human brain tissue. CMD allows monitoring the metabolic state of tissue, as well as sampling macromolecules such as proteins and peptides. Recovery of proteins or peptides can be hampered by their adsorption to the CMD membrane as has been previously shown in-vitro, however, protein adsorption to CMD membranes has not been characterized following implantation in human brain tissue. METHODS: In this paper, we describe the pattern of proteins adsorbed to CMD membranes compared to that of the microdialysate and of cerebrospinal fluid (CSF). We retrieved CMD membranes from three surgically treated intracerebral hemorrhage (ICH) patients, and analyzed protein adsorption to the membranes using two-dimensional gel electrophoresis (2-DE) in combination with nano-liquid mass spectrometry. We compared the proteome profile of three compartments; the CMD membrane, the microdialysate and ventricular CSF collected at time of CMD removal. RESULTS: We found unique protein patterns in the molecular weight range of 10-35 kDa for each of the three compartments. CONCLUSION: This study highlights the importance of analyzing the membranes in addition to the microdialysate when using CMD to sample proteins for biomarker investigation.

Insights into the storage stability of ammonia in polyester aluminum bags.

A list of gaseous odorants such as ammonia (and hydrogen sulfide) are generally collected using rigid containers or flexible bags for quantitative analysis. The aim of this investigation was to assess the stability of polyester aluminum bags used for gaseous ammonia sampling and storage. To this end, ammonia standards were prepared at two concentration levels of low (7.8 ppm) and high concentrations (39 ppm) and stored in the polyester ammonia bags for durations of 0, 1, 2, 4, and 6 days. These samples were then analyzed at each interval by an impinger-based indophenol method utilizing a spectrophotometer. At each pre-set period, three different mass loadings of ammonia samples were collected from the storage bag to obtain response factors (RF) for comparison between different elapsed times set for the storage. Subsequently, the relative recovery values for each interval were computed by dividing the RF for each sampling day by that of the 0th day. The relative recovery values for low and high concentration standards decreased with increasing storage time as 82.9% (day 1) to 36% (day 6) and 89.9% (day 1) to 59.7% (day 6), respectively. As such, the potentially superior recovery of ammonia from polyester aluminum bags was demonstrated (e.g., relative to other storage options introduced previously) to support its practical merit as storage media.

Is TBX agar a suitable medium for monitoring Escherichia coli in bathing water using the membrane filtration method?

The use of a suitable method for the enumeration of indicator microorganisms is of crucial importance for reliable monitoring and assessment of the quality of bathing waters. Among other characteristics, the method should be selective enough and ensure acceptable relative recovery of target microorganisms. This study presents the basic parameters, relative recovery and categorical performance characteristics of Tryptone Bile X-glucuronide (TBX) agar for Escherichia coli (E. coli) enumeration in bathing water samples using the membrane filtration method.The results of the relative recovery study, in which TBX agar was compared against temperature-modified ISO 9308-1:2014, showed that in order to achieve a satisfactory relative recovery of E. coli with TBX agar at 44 ± 0.5 °C, the resuscitation period on a non-selective medium (Minerals Modified Glutamate Agar, MMGA) at 36 ± 2 °C is crucial. Incubation on a double-layer MMGA/TBX medium with a 6-h resuscitation period and alternating incubation on single-layer MMGA and TBX agar with a 4-h resuscitation period resulted in acceptable and very similar relative recovery. The achieved performance characteristics of the tested medium, double-layer MMGA/TBX agar, are acceptable. The selectivity was matrix-dependent and was 60.6% for inland and 69.9% for coastal waters. No significant effect of the resuscitation period on selectivity was recorded. Finally, the results showed that when the resuscitation period on a non-selective medium is included, TBX agar is a suitable medium for E. coli enumeration in bathing water samples using the membrane filtration method and that its use, theoretically, would not have negative effects on the assessment of bathing water quality.

Validation of a simple liquid chromatography coupled to tandem mass spectrometry method for the simultaneous determination of tacrolimus, sirolimus, everolimus and cyclosporin A in dried matrix on paper discs.

INTRODUCTION: Due to its high specificity and sensitivity, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is the gold standard method for immunosuppressant quantification in therapeutic drug monitoring. In this context, dried blood spots (DBS) have become a promising strategy as a sample collection procedure. Although the advantages of DBS over venipuncture are well known, this approach has limitations that strongly influence the acceptance of analytical results. Among them, the most important is hematocrit (Ht). The easiest way of overcoming this problem is by analyzing complete spots. In this strategy, called dried matrix on paper discs (DMPD), blood is volumetrically applied on pre-punched discs. OBJECTIVES: To validate an LC-MS/MS method for the quantification of tacrolimus, sirolimus, everolimus and cyclosporin A using DMPD. METHODS: The procedure was validated according to international guidelines using a commercial kit. The following performance parameters were evaluated: selectivity, carryover, linearity, accuracy, precision, lower limit of quantitation, relative recovery, commutability and stability. In addition, a method comparison study was performed to evaluate the clinical influence of Ht on the results. RESULTS: All performance parameters were within acceptance criteria and, hence, it was determined that the validated method is fit for the intended purpose. Likewise, calculated bias values on medical decision levels showed that there was no clinical influence of Ht on the results. CONCLUSION: Unlike other similar methodologies that have been published, here, a simple method has been fully validated. This is the first LC-MS/MS methodology adapting a commercial kit to use DMPD as a sampling strategy.

Drug combinations and impact of experimental conditions on relative recovery in in vitro microdialysis investigations.

The need for pharmacokinetic knowledge about antibiotics directly at the site of infection, typically the interstitial space fluid (ISF) of tissues, is gaining acceptance for effective and safe treatment. One option to acquire such data is the microdialysis technique employing a catheter with a semipermeable membrane inserted directly in the ISF. A prerequisite is catheter calibration, e.g. via retrodialysis, yielding a conversion factor from measured to true ISF concentrations, termed relative recovery. This value can be influenced by various factors. The present investigation assessed the impact of three of them on relative recovery using seven drugs: (I) drug combinations/order, (II) air in the microdialysis system, (III) flow rate changes inherent when using common in vivo microdialysis pumps. All experiments were performed in a standardised in vitro microdialysis system. (I) Relative recovery of single antibiotics (linezolid, meropenem, cefazolin, metronidazole, tigecycline) was determined in microdialysis and retrodialysis settings and compared with values using either antibiotic or antibiotic+analgesic (acetaminophen and metamizole) combinations or single drugs with reversed microdialysis order. For assessing these factors for lower relative recovery values (as in in vivo), these were mimicked by increasing the flow rate for linezolid. (II) For the impact of air, linezolid relative recovery of freshly carbonated solutions was compared to degassed ones in microdialysis and retrodialysis settings. For each condition in (I) and (II), summary statistics of relative recovery were calculated and for the impact of the factors a linear mixed-effect model developed. (III) From samples taken during an automatic flush sequence (15 µL/min) of an in vivo pump and afterwards switching to the flow rate of 1 and 2 µL/min for 120 min, the time necessary for relative recovery to reach equilibrium was determined. (I) High relative recovery values (flow rate 2 µL/min: ≥84%; flow rate 5 µL/min: ≥65%) were observed for all investigated single drugs. Intra- and intercatheter variability ranged from 0.3%-11% and 3%-25%, respectively. Based on these values and on the statistical model, the impact of drug combination versus single drug as well as of reversed order was small with changes in relative recovery of smaller equal 9%. (II) Compared to degassed solutions, relative recovery in carbonated solutions was 23% and 19% lower (relative reduction) in the microdialysis and retrodialysis setting, respectively, with increased intercatheter variability (up to 37%). (III) As expected, relative recovery increased after the flush sequence and was constant 10-15 min after the switch to the typical 1 and 2 µL/min flow rate. Given the intercatheter variability, combinations and the order of drugs showed minor but clinically negligible impact on relative recovery. In contrast, air in the microdialysis catheter/system caused falsely low and inconsistent relative recovery values and must be avoided when performing a trial. Also changes in flow rate at the end of pump flush sequence impacted relative recovery. Hence, a sufficient equilibration time of 10-15 min prior to sampling should be implemented in sampling protocols. In vitro microdialysis presents a highly valuable complementary platform to clinical microdialysis studies impacting the design, sampling schedule and data analysis of such trials to gain knowledge of target-site pharmacokinetics for contributing to better informed decisions in the individual patient/special populations in future.

An Approach for Measuring the Sorptive Behavior of Odorants Using a Multifunction Thermal Desorber Unit: Preliminary Tests on Reduced Sulfur Compounds.

In this study, the sorptive behavior of reduced sulfur compounds (RSC) was investigated using a combination of thermal desorber (TD) unit and gas chromatography (GC). To examine the sorptive properties of RSC on textile materials, two types of experiments were conducted under experimental conditions favorable for sorptive processes. In all the experiments, gaseous standards of hydrogen sulfide, methanethiol, dimethyl sulfide, and dimethyl disulfide were supplied to initiate the adsorption processes on textile pieces. The textile pieces were then forced to release those adsorbed RSC under a fixed condition. It was found that the extent of adsorption, if evaluated quantitatively, occurred at approximately 1/1000 to 1/100 of the level of RSC standards supplied originally to induce adsorption. It also indicated that RSC adsorption was affected very sensitively by the initial exposure durations to induce RSC adsorption with an exponential decrease in relative recovery (RR) values with increasing exposure time. The relative sorptive patterns, when compared between different RSCs, were affected most sensitively by such factors as molecular weight and/or physical contact conditions.

Recovery rates of combination antibiotic therapy using in vitro microdialysis simulating in vivo conditions.

Microdialysis is a technique used to measure the unbound antibiotic concentration in the interstitial spaces, the target site of action. In vitro recovery studies are essential to calibrating the microdialysis system for in vivo studies. The effect of a combination of antibiotics on recovery into microdialysate requires investigation. In vitro microdialysis recovery studies were conducted on a combination of vancomycin and tobramycin, in a simulated in vivo model. Comparison was made between recoveries for three different concentrations and three different perfusate flow rates. The overall relative recovery for vancomycin was lower than that of tobramycin. For tobramycin, a concentration of 20µg/mL and flow rate of 1.0µL/min had the best recovery. A concentration of 5.0µg/mL and flow rate of 1.0µL/min yielded maximal recovery for vancomycin. Large molecular size and higher protein binding resulted in lower relative recoveries for vancomycin. Perfusate flow rates and drug concentrations affected the relative recovery when a combination of vancomycin and tobramycin was tested. Low perfusate flow rates were associated with higher recovery rates. For combination antibiotic measurement which includes agents that are highly protein bound, in vitro studies performed prior to in vivo studies may ensure the reliable measurement of unbound concentrations.

A Review on Microdialysis Calibration Methods: the Theory and Current Related Efforts.

Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

Brain microdialysis as a tool to explore the ionic profile of the brain extracellular space in neurocritical patients: a methodological approach and feasibility study.

Our aim is to determine whether the ionic concentration in brain microdialysate enables calculations of the actual Na(+), K(+), and Cl(-) concentrations in vitro and whether this method can be applied to determine the ionic concentrations in the brain extracellular fluid. We designed an experiment using CMA-71 probes (M Dialysis, Stockholm, Sweden) and the standard conditions used in a clinical setting. Nine CMA-71 probes were inserted in different matrices and perfused with mock cerebrospinal fluid containing 3% albumin at the standard infusion rate used in the clinical setting (0.3 µL/min). Microvials were replaced every 12 h, and the ionic concentrations, both in the dialysate and the matrix, were analyzed. For each ion, scatter plots were built, with [Na(+)], [K(+)], and [Cl(-)] in the dialysate as the predictor variables and the matrix concentrations as the outcome variables. A linear regression model allowed us to calculate the true ionic concentrations in the matrix. To demonstrate the feasibility of the method, we present the calculated ionic profile of one patient with a malignant infarction and a second with a severe traumatic brain injury. Our results confirm that the ionic concentration in microdialysate can be used to calculate the true concentrations of ions in a matrix and the actual concentrations in the extracellular fluid. Microdialysis offers the unique possibility of monitoring the dynamic changes of ions in the brain over time and opens a new avenue to explore the brain's ionic profile, its changes in brain edema, and how this profile can be modified with different therapies.

Membrane assisted micro-solid phase extraction of pharmaceuticals with amino and urea-grafted silica gel.

Individual polar sorbents with surface-displayed amino groups (APS) and non-nucleophilic urea-groups (UPS), were prepared by chemical modification of granular silica gel with bifunctional silane coupling reagents. In this preliminary study, they were separately employed for micro-solid phase extraction (µ-SPE) of the quarternary salt of Amitriptyline (Ami), Carbamazepine (Cbz), Ketoprofen (Ket) and Diclofenac (Dfn) from aqueous samples in conjunction with high performance liquid chromatography. The resulting enrichment factors for both APS and UPS are comparable and exceeded those of µ-SPE involving commercial C18-silica gel sorbents. The presence of highly polar, but non-basic and non-nucleophilic surfaces on UPS prompted the development of a UPS-based µ-SPE method. Good linear correlation was found over a concentration range of 0-50 µg L(-1) with limits of detection ranging from 0.66 to 2.36 µg L(-1)). Limits of quantification between 1.61 and 7.88 µg L(-1) were obtained. HPLC analyses indicated that relative recoveries of 123% for Ami, 65.6% for Cbz, 71.2% for Ket and 66.5% for Dfn were obtained during µ-SPE of spiked (10 µg L(-1)) environmental water samples with percentage relative standard deviations (%RSD) of between 2.1% and 12.6%.