[Determination of acetylacetone in workplace air by solvent desorption-gas chromatography].

Objective: To establish a method for the determination of acetylacetone in the air of workplace by gas chromatography. Methods: In August 2020, acetylacetone in the air of workplace was collected by silica gel tube, eluted with methanol, separated and detected by gas chromatography with flame ionization detector. The detection limit and precision of the method were also analyzed. Results: The linear range of acetylacetone was 1.95-1950.60 µg/ml with the regression equation of y=0.815x-3.667, and the correlation coefficient was 0.99993. The limit of detection of the method was 0.18 µg/ml and the minimum detection concentration was 0.12 mg/m(3) (collected sample volume was 1.50 L). The within-run precisions were 1.08%-4.11% and the between-run precisions were 1.98%-2.80%. The desorption rates were 99.68%-100.45%. The sealed samples could be kept at least 15 days at room temperature without significant loss. Conclusion: The solvent desorption-gas chromatography method for the determination of acetylacetone has good precision, high sensitivity and simple operation, and is suitable for the determination of acetylacetone in the air of the workplace.

[Research and development of an air sampling tube for chlorobenzene compounds and its supporting determination method].

Objective: To establish a GDH-3 air sample tube for simultaneous determination of twelve kinds of chlorobenzene compounds (CBs) in workplace air by gas chromatography. And to established a matching determination method. Methods: In October 2020, the vapor and aerosol CBs in workplace air were collected by GDH-3 air sampling tube, and desorption and elution with 3.00 ml toluene for 15 min, then the solution separated by DB-23 capillary column, and finally detected with microcell electron capture detector. Results: The quantitative determination ranges of twelve isomers of CBs were 0.71×10(-3)-2000.00 mg/L, with the correlative coefficients were 0.99967-0.99998. The minimum detectable concentrations were 0.04-112.63 µg/m(3), and the minimum quantification concentrations were 0.14-375.42 µg/m(3) (15.00 L sample, 3.00 ml sample solution) . The average elution efficiencies were 96.00%-104.00%. The within-run relative standard deviations (RSDs) were 2.54%-6.12%, and the between-run RSDs were 3.85%-7.87%. Sealed samples could be stable at room temperature for at least 15 days. Conclusion: GDH-3 air sample tube can be used for simultaneous determination of twelve kinds of CBs in workplace air by gas chromatography. The established supporting measurement method meets the measurement requirements of the occupational health standard detection method, and the it's suitable for the simultaneous determination of 12 kinds of CBS in the air.

[The method of determination for butyronitrile and isobutyronitrile in the air of workplace by dissolved desorption-gas chromatography].

Objective: To establish a method for the determination of butyronitrile and isobutyronitrile in the air of workplace by gas chromatography. Methods: In March 2020, butyronitrile and isobutyronitrile in the air of workplace was collected by silica gel, eluted with methanol, separated and determined by gas chromatogram with flame ionization detector, the characteristics of determination of nitrile and isobutyronitrile by gas chromatography were analyzed. Results: The limit of detection for butyronitrile and isobutyronitrile was 0.33 µg/ml. The linear range of butyronitrile determined by this method was 1.60-1600.00 µg/ml, y=2.295x-3.480, and the coefficient correlation was 0.99998, and the minimum detection concentration was 0.22 mg/m(3) (collected sample volume was 1.50 L) . The within-run precisions were 2.43%-4.12%, the between-run precisions were 1.72%-3.70%, and the desorption rates were 93.26%-98.41%. The linear range of isobutyronitrile determined by this method was 1.52-1520.00 µg/ml, y=2.208x-0.102, and the coefficient correlation was 0.99998, and the minimum detection concentration was 0.22 mg/m(3) (collected sample volume was 1.50 L) . The within-run precisions were 2.52%-3.22%, the between-run precisions were 1.20%-3.82%, and the desorption rates were 96.85%-102.50%. The sealed samples could be stored at least 10 days at room temperature without significant loss. Conclusion: The method has the advantages of good precision, high sensitivity and simple operation. It is suitable for the simultaneous determination of butyronitrile and isobutyronitrile in the air of workplace.

[Application of a new solid adsorbent tube for the determination of three kinds of epoxy eompounds in air].

Objective: To develop a new solid sorbent tube for simultaneously capturing ethylene oxide (EO) , propylene oxide (PO) and epichlorohydrin (ECH) in air, and establish a complete set of method. Methods: In June 2018, EO, PO and ECH in air were captured by the new solid sorbent tube filled with carbon aerogel adsorbent, desorbed with solution of 5% (V/V) methanol-methylene chloride, separated through capillary chromatographic column, and then analyzed by gas chromatography-flame ionization detector. Results: The linear ranges of EO, PO and ECH were 0.24-960.00, 0.60-2384.00 and 0.12-472.40 mg/L respectively, and the related coefficients were between 0.99995-0.99997. The relative standard deviations (RSD) within the group were 1.66%-4.09%, 1.36%-4.43%, and 1.99%-5.65%, respectively, and the RSD between the group were 2.69%-4.95%, 2.77%-5.30%, and 3.27%-6.67%, respectively. The average desorption efficiencies were 88.25%-94.50%, 98.17%-98.60%, and 97.79%-101.04%, respectively. The samples could be stored at 4 ℃ refrigerator for at least 27 days. Conclusion: The newly developed solid sorbent tube filled with carbon aerogel adsorbent and its complete set of gas chromatography method could be used for sampling and quantitative detection of EO, PO and ECH in workplace air.

[Simultaneous determination of four kinds methyl acrylate compounds in workplace air].

Objective: To develop a solvent desorption-gas chromatography method for simultaneous determination of methyl methacrylate (MMA) , ethyl methacrylate (EMA) , n-propyl methacrylate (PMA) and butyl methacrylate (BMA) in workplace air. Methods: MMA, EMA, PMA and BMA in workplace air were captured by charcoal tubes and desorbed with carbon disulfide, separated through capillary chromatographic column, and then analyzed by gas chromatography-flame ionization detector. Results: The linear ranges of MMA, EMA, PMA and BMA were 0-8 305.00 mg/L, 0-9 080.50 mg/L, 0-8 899.00 mg/L and 0-8 371.00 mg/L respectively, and the related coefficients were between 0.999 96-0.999 98. The relative standard deviations (RSD) within the group were 0.56%-1.71%, 0.45%-1.65%, 0.51%-1.49% and 0.45%-1.50% respectively, and the RSD between the group were 1.14%-2.79%, 0.79%-2.13%, 0.93%-2.30% and 1.09%-2.84% respectively. The average desorption efficiencies were 95.76%-99.58%, 97.82%-102.28%, 98.55%-102.28%and 98.70%-102.40% respectively. The minimum quantification concentrations were 0.12 mg/m(3), 0.10 mg/m(3), 0.07 mg/m(3) and 0.07 mg/m(3) respectively (3.00 L sample) . The samples could be stored at room temperature for at least 7 days. Conclusion: This method could be used for monitoring of MMA, EMA, PMA and BMA in workplace air.

[Study on determination of ethylal in workplace air by gas chromatography].

Objective: A solvent desorption-gas chromatography method for determination of ethylal in workplace air has been established. Methods: Ethylal in workplace air was collected by activated carbon tube and desorbed with carbon disulfide, and the desorption solutions were analysed by capillary column GC with FID detector. Results: The method presented a good linearity in the range of 0.87~34 800.00 mg/L of ethylal in the standard solution, with the correlation coefficient being r=0.999 7. The limit of detection and the limit of quantification of this method were respectively 0.20 mg/L and 0.80 mg/L, and the minimum detectable concentration and the minimum quantification concentration of this method were respectively 0.17 mg/m(3) and 0.60 mg/m(3) per 1.50 L of air.The within-run precision of the method was 2.93%-6.20%, and the between-run precision 3.67%-6.44%. The desorption efficiency between 94.22%-97.27%. Ethylal in activated carbon tube could be kept at least 7 days at room temperature without significant loss. Conclusion: The method could be used for determination of ethylal in workplace air.

[Determination of glycidyl methacrylate in the air of workplace captured adsorbent tube by gas chromatography].

Objective: To develop a new solid sorbent tube for capturing glycidyl methacrylate (GMA) in workplace air, and establish a complete set of method. Methods: GMA in workplace air was captured by the new solid sorbent tube filled with carbon aerogel adsorbent, desorbed with solution of 50% (V/V) dimethylformamide-carbon disulfide, separated through capillary chromatographic column, and then analyzed by gas chromatography-flame ionization detector. Results: The linear range of GMA was 0.38-604.80 mg/L, and the related coefficient was 0.999 82. The within-run and the between-run precision were 1.11%-2.80% and 2.53%-4.84% respectively. The average desorption efficiency was 93.20%-94.97%. The minimum quantification concentration and The minimum quantification concentration were 0.02 and 0.07 mg/m(3) respectively (3.00 L sample) . Samples could be stored for at least 8 days at room temperature. Conclusion: The newly developed solid sorbent tube and its complete set of gas chromatography method is simple, and has high sensitivity and precision, so it can be used for sampling and quantitative detection of GMA in workplace air.

[Determination of hippuric acid and methylhippuric acid in urine by high performance liquid chromatography after extracted with acetonitrile].

OBJECTIVE: To establish pretreatment conditions of hippuric acid (HA)and methyl-hippuric acid (MHA)in urine and HPLC conditions. METHODS: HA and MHA in urine were extracted with acetonitrile under acid condition and determinated by HPLC-DAD. The operating conditions by HPLC were C18 column (150 mm× 4.6 mm, 5 µm), methanol-0.2% acetic acid (contained 6.5 mmol/L potassium dihydrogen phosphate)(25∶75, V/V) as mobile phase,1 ml/min as flow rate and wavelength was at 254 nm. RESULTS: The standard curves for HA, 2-MHA and 3-MHA(4-MHA)showed good linearity between 9.91~2 974.20 µg/ml(r=0.999 98), 1.91~573.60 µg/ml (r=0.999 84)and 2.00~598.65 µg/ml (r=0.999 85), respectively. The mean recoveries were 96.38%~98.01%, 83.17%~94.05 %, 103.22%~104.45%, respectively. The within-run precision were 0.50%~1.20%, 0.51%~1.59%, 0.49%~0.95%, respectively, and the between-run precision were 1.70%~3.20%, 1.30%~2.67%, 0.86%~2.74%, respectively. The detection limit of HA, 2-MHA and 3-MHA(4-MHA)were 0.18 µg/ml, 0.46 µg/ml and 0.12 µg/ml, and the low determination concentrations of the method were 0.36 µg/ml, 0.92 µg/ml and 0.24 µg/ml(1 ml urine). The urine can be kept 15 days at 4 ℃ refrigerator without significantly loss. CONCLUSION: This method with simply pretreatment conforms to the relevant requirements of guide for establishing occupational health standards-part 5: determination methods of chemicals in biological materials. It can be used to detect HA and MHA in urine for occupational population exposure to toluene and xylene.

[Determination of volatile organic compounds in air by portable gas chromatography-mass spectroscopy].

Objective: To investigate the method of portable gas chromatography-mass spectroscopy (GC-MS) for the determination of common volatile organic compounds in air. Methods: The static volumetric method was used, with highly purified nitrogen gas as the diluents gas, to prepare the mixed standard gas of common volatile organic compounds with various mass concentrations. A portable GC-MS handheld probe was used for sampling and measurement, retention time and characteristic ion were used for qualitative analysis, and the full-scan mode was used for quantitative analysis. Results: The correlation coefficient of 12 volatile organic compounds determined by this method was higher than 0.999. The minimum detection mass concentration was 0.02~0.12 mg/m3, and the minimum quantitative mass concentration was 0.07~0.40 mg/m3. The relative standard deviation of precision was 4.10%~12.50%; the relative deviation of acetone, benzene, methylbenzene, and dimethylbenzene was-13.56% , 9.03% , -10.82% , and 8.67% , respectively. Conclusion: Portable GC-MS method can be used for the qualitative analysis and quantification of volatile organic compounds in occupational hazard factors and provide technical supports for identification of occupational hazard factors.

Sulfur dioxide relaxes rat aorta by endothelium-dependent and -independent mechanisms.

This study aimed to investigate the vasoactivity of sulfur dioxide (SO2), a novel gas identified from vascular tissue, in rat thoracic aorta. The thoracic aorta was isolated, cut into rings, and mounted in organ-bath chambers. After equilibrium, the rings were gradually stretched to a resting tension. Isometric tension was recorded under the treatments with vasoconstrictors, SO2 derivatives, and various drugs as pharmacological interventions. In endothelium-intact aortic rings constricted by 1 microM phenylephrine (PE), SO2 derivatives (0.5-8 mM) caused a dose-dependent relaxation. Endothelium removal and a NOS inhibitor L-NAME reduced the relaxation to low doses of SO2 derivatives, but not that to relatively high doses (>or=2 mM). In endothelium-denuded rings, SO2 derivatives attenuated vasoconstriction induced by high K+ (60 mM) or CaCl2 (0.01-10 mM). The relaxation to SO2 derivatives in PE-constricted rings without endothelium was significantly inhibited by blockers of ATP-sensitive K+(KATP) and Ca2+-activated K+ (KCa) channels, but not by those of voltage-dependent K+ channels, Na+- K+-ATPase or Na+-Ca2+ exchanger. SO2 relaxed vessel tone via endothelium-dependent mechanisms associated with NOS activation, and via endothelium-independent mechanisms dependent on the inhibition of voltage-gated Ca2+ channels, and the opening of KATP and KCa channels.

Effect of ketamine on presympathetic neurons in rostral ventrolateral medulla of rats.

AIM: To study the effects of ketamine on central sympathetic and cardiovascular regulation. METHODS: The experiment was performed on 25 urethane anaesthetized, artificially ventilated adult rats. A total of 32 presympathetic neurons in the rostral ventrolateral medulla (RVLM) were electrophysiologically identified, which had properties of both barosensitivity and projection to the spinal cord. Responses of these neurons to intravenously administrated ketamine (a non competitive N-methyl-D aspartate receptor antagonist) were observed. RESULTS: Intravenous injection of ketamine (3, 6, 12 mg/kg body weight) increased the firing rate and blocked the barosensitivity of presympathetic neurons in the RVLM in a dose dependent manner. CONCLUSION: Ketamine could affect the sympathetic outflow by blocking tonic baroreceptor inhibition of the presympathetic neurons in the RVLM.

[Effects of corticosterone on the activity of the neurons in the rostral ventrolateral medulla of rats].

Spontaneous discharges of the rostral ventrolateral medulla (RVLM) neurons were extracellularly recorded by multi-barrelled microelectrodes in urethane-anesthetized rats. A total of 145 neurons were recorded: 33 were cardiovascular, 31 were nociceptive modulating, and 81 were unknown functional. The cardiovascular neurons were electrophysiologically identified through activating baroreceptor reflex by electrical stimulation of the aortic nerve and by intravenous injection of phenylephrine. Of the 33 cardiovascular neurons, 25 (76%) increased in firing rate after iontophoretical application of corticosterone sulfate (CORT), and 8 (24%) failed to respond. Of the 31 nociceptive modulating neurons excited by noxious stimulation, the firing rate decreased in 19 (64%), increased in 2 (6%), and did not respond in 10 (30%) after iontophoresis of CORT. Of the remaining 81 unknown functional neurons, 32 (40%) were excited, 5 (6%) inhibited, and 44 (54%) were not affected by CORT. These results demonstrate that CORT may modulate the activities of the neurons in RVLM through fast non-genomical effect, suggesting that the mechanism of the fast actions of CORT may play an important role in integration of the cardiovascular, nociceptive modulating activity under some conditions such as stress.

NMDA receptor mechanism involved in arterial baroreflex.

AIM: To study the roles of N-methyl-D-aspartate (NMDA) receptors in arterial baroreflex. METHODS: Experiments were performed in 17 urethane-anaesthetized male Sprague-Dawly rats. Twenty-seven rostral ventrolateral medulla (RVLM) neurons were electrophysiologically identified as putative presympathetic neurons. Responses of these neurons to baroreflex activation were used as an index to observe the effects of 3-(2-carboxypiperazin-4-yl) propyl-1-phosphonic acid (CPP) microinjected (0.1 microL, 50 mmol.L-1) into the nucleus tractus solitarii (NTS) or the caudal ventrolateral medulla (CVLM) ipsilaterally. RESULTS: In the NTS, CPP eliminated or attenuated the inhibition of these neurons induced by aortic nerve stimulation, but the inhibition induced by elevation of arterial pressure was not eliminated and the cardiac cycle-related rhythm of spontaneous discharge still existed. Whereas in the CVLM, CPP eliminated not only the inhibition of these neurons induced by aortic nerve stimulation, but the inhibition induced by blood pressure elevation and the cardiac cycle-related rhythm of spontaneous discharge disappeared. CONCLUSION: NMDA mechanism is importantly involved in the mechanism of baroreflex both in the NTS and in the CVLM; the barosensitive neurons in the NTS project to ipsilateral CVLM.

[Effect of acetylcholine on the discharge of presympathetic neurons of the rostral ventrolateral medulla of rats].

Effect of acetylcholine (ACh) on presympathetic neurons of the rostral ventrolateral medulla (RVLM) was studied by extracellular recording technique and microiontophoresis in urethane-anaesthetized rats. Spontaneous discharges of 35 presympathetic neurons of RVLM were recorded. All the neurons showed increased discharge by microiontophoresis of ACh dose- dependently with the increase of iontophoretic current. In 22 units microiontophoresis of atropine decreased the baseline discharge rate and completely blocked the excitatory effect of ACh on these neurons, while in the remaining 7 and 6 neurons microiontophoresis of d-tubocurarine (d-TC) and hexamethonium (C(6)) respectively had no effect and did not block the action of ACh. The above finding suggests that presympathetic neurons of RVLM receive a tonic excitatory cholinergic input mediated by M receptors.

Pre-sympathetic neurones in the rostral ventrolateral medulla of the rat: electrophysiology, morphology and relationship to adjacent neuronal groups.

The activity of preganglionic sympathetic neurones largely depends on synaptic excitation from antecedent reticulospinal neurones located in the rostral ventrolateral medulla (RVLM). Our study, conducted in anaesthetized rats, showed that all RVLM pre-sympathetic neurones display a substantial synaptic noise and their action potentials are usually preceded by fast EPSPs. No evidence was found for presence of gradual depolarizations (autodepolarizations) between individual spikes. Therefore our results are consistent with the "network" hypothesis for the generation of sympathetic vasomotor tone. Axons of some pre-sympathetic neurones intracellularly labelled with Neurobiotin or Lucifer Yellow had collaterals arborizing in several medullary regions. Thus these neurones have synaptic inputs not only to preganglionic sympathetic neurones, but also to other, yet unidentified cells in the brainstem. Finally, our results show that anatomically adjacent RVLM pre-sympathetic and Bötzinger respiratory neurones from two functionally distinct neuronal subpopulations, and that some pre-sympathetic neurones have an adrenergic phenotype.

Criteria for intracellular identification of pre-sympathetic neurons in the rostral ventrolateral medulla in the rat.

Previous studies revealed that a relatively small group of reticulospinal neurons located in the rostral ventrolateral medulla (RVLM) plays a key role in the generation of resting vasomotor tone and in reflex control of arterial blood pressure. These medullary pre-sympathetic neurons have been extensively studied with extracellular microelectrodes, but so far few attempts have been made to examine their intracellular properties in vivo. This report, based on intracellular recordings from 8 RVLM pre-sympathetic neurons in anaesthetised rats, sets out criteria for intracellular identification of such neurons. We propose that two features are sufficient to classify RVLM neurons as pre-sympathetic during intracellular recording: inhibitory response to stimulation of the aortic depressor nerve with short bursts of pulses applied at low frequency; and antidromic stimulation from the upper thoracic segments. Cardiac oscillations in the membrane potential or responses during large changes in blood pressure can be due to movement artefact, and are therefore not reliable as a means of demonstrating baroreceptor input. Further intracellular studies of these neurons will undoubtedly result in further progress in understanding their function.