[Ion chromatography-pulsed amperometry method for determination of trace hydrogen sulfide in air].

Hydrogen sulfide (H2S) is a pervasive gaseous pollutant that emits the characteristic odor of rotten gas, even at low concentrations. It is generated during various industrial processes, including petroleum and natural gas refining, mining operations, wastewater treatment activities, and refuse disposal practices. According to statistics from the World Health Organization (WHO), over 70 occupations are exposed to H2S, rendering it a key monitoring factor in occupational disease detection. Although H2S has legitimate uses in the chemical, medical, and other fields, prolonged exposure to this gas can cause severe damage to the respiratory and central nervous systems, as well as other organs in the human body. Moreover, the substantial release of H2S into the environment can lead to significant pollution. This noxious substance has the potential to impair soil, water, and air quality, while disrupting the equilibrium of the surrounding ecosystems. Therefore, sulfide has become one of the most commonly measured substances for environmental monitoring worldwide. Achieving the stable enrichment and accurate detection of low-level H2S is of great significance. Common methods for detecting this gas include spectrophotometry, chemical analysis, gas chromatography, rapid field detection, and ion chromatography. Although these methods provide relatively reliable results, they suffer from limitations such as high detection cost, low recovery, lack of environmental friendliness, and imprecise quantification of low-concentration H2S. Furthermore, the sampling processes involved in these methods are complex and require specialized equipment and electrical devices. Additionally, approximately 20% of the sulfides in a sample are lost after 2 h in a conventional alkaline sodium hydroxide solution, causing difficulties in preservation and detection. In this study, an accurate, efficient, and cost-saving method based on ion chromatography-pulse amperometry was developed for H2S determination. A conventional IonPac AS7 (250 mm×4 mm) anion-exchange column was employed, and a new eluent based on sodium hydroxide and sodium oxalate was used to replace the original sodium hydroxide-sodium acetate eluent. The main factors influencing the separation and detection performance of the proposed method, including the pulse amperage detection potential parameters and integration time, as well as the type and content of additives in the stabilizing solution, were optimized. The results showed that the proposed method had a good linear relationship between 10 and 3000 µg/L, with correlation coefficients (r2) of up to 0.999. The limits of detection (S/N=3) and quantification (S/N=10) were 1.53 and 5.10 µg/L, respectively. The relative standard deviations (RSDs) of the peak area and retention time of sulfides were less than 0.2% (n=6). The new method exhibited excellent stability, with up to 90% reduction in reagent costs. Compared with conventional ion chromatography-pulse amperometry, this method is more suitable for detecting low concentrations of sulfides in actual samples. Sulfides in a 250 mmol/L sodium hydroxide-0.8% (mass fraction) ethylenediaminetetraacetic acid disodium salt solution were effectively maintained for over 10 h. The new stabilizer significantly improved the reliability of both large-scale and long-term detection. The recovery of the proposed method was investigated by combining the system with a badge-type passive sampler. This sampling method requires no power devices; it is inexpensive, simple to operate, and can realize long-term sampling without the need for skilled personnel. Moreover, it can overcome the influence of short-term changes in pollutant concentration. The sampling results have high reference value for large-scale intervention-less pollutant monitoring in ultraclean rooms, museum counters, and other places. The results demonstrated that the recovery of the proposed method was greater than 95% for the blank sample and 80% for the sample plus standard solution. Finally, the newly established method was applied to determine H2S levels in air samples collected via passive sampling at school garbage stations. The measured results did not exceed the national limit.

[Determination of electrosynthesized urea products by igh performance liquid chromatography based n porous graphitic carbon column].

Urea is a simple organic compound that is widely used in both the industry and daily life. Compared with conventional methods, the preparation of urea by electrochemical synthesis is more environmentally friendly and sustainable. However, after the reaction, low amounts of urea and high concentrations of inorganic ions, including [Formula: see text] concentration was achieved without interference. Thus, the developed method can be applied for the detection of trace urea and other related ions in urea-containing electrolyte products.

[Determination of inorganic anions and gluconate by two-dimensional ion chromatography].

A new two-dimensional ion chromatography method was developed to parallelly analyze two different types of samples with the application of valve switching technology-suppressed conductivity and pulsed amperometric analysis system, for concurrent determination of chloride, nitrite, sulfate, nitrate four inorganic anions and gluconate. The first dimensional chromatography was using Ionpac AG18+Ionpac AS18 anion analysis columns with a suppressed conductivity detector for the separation and detection of Cl-, NO2-, SO4(2-) and NO3-. Respectively, the elution was 5 and 20 mmol/L NaOH at an isocratic flow rate of 1.0 mL/min and sample injection volume of 25 µL. The second dimensional chromatography was utilizing two guard columns, CarboPac PA1 and CarboPac PA20, with 90 mmol/L NaOH solution for the isocratic eluent of 0.8 mL/min. Gluconate was enriched by an AG15 column and switched into the pulsed amperometric detector. The results showed that: each inorganic anion in 0. 1-5.0 mg/L and gluconate in 0.085 6-4.282 5 mg/L had a good linear relationship (R2 ≥ 0.994 5). The RSDs of the peak areas were between 1.05%-1.94%. The limits of detection were 0.61-2.17 µg/L for the anions and 24.24 µg/L for the gluconate. The recoveries were between 90.3% - 102.8%. The two detection modes parallelly have good separation efficiency, detection accuracy and the precision of the separation and are suitable for the analysis of complex samples.

Determination of tricarboxylic acid cycle acids and other related substances in cultured mammalian cells by gradient ion-exchange chromatography with suppressed conductivity detection.

An ion-exchange chromatography method was established for simultaneously analyzing the tricarboxylic acid (TCA) cycle acids and other related substances in cultured mammalian cells, including citrate, cis-aconitate, isocitrate, alpha-ketoglutarate, succinate, malate, fumarate, oxaloacetate, trans-aconitate, phosphate, lactate and pyruvate. A Dionex 600 ion chromatograph with an ion suppressor and a conductivity detector, and an IonPac AS11-HC analytical column were employed. An NaOH gradient elution containing 13.5% methanol contributed to sufficient separation of target substances. The stability of carboxylic acids was investigated and oxaloacetate was found to be extremely unstable especially at pH 3. TCA cycle acids and other related substances in Chinese hamster ovary (CHO) cells were separated completely, and lactate, malate, phosphate, citrate and cis-aconitate were quantified due to their higher concentrations. In the quantification of the five substances, detection limits (S/N=3) ranged from 0.12 to 0.48 microM, the correlation coefficients from 0.9982 to 1.0000 in their linear ranges of concentration, and the recoveries from 87 to 95%. The metabolic status of CHO cells was analyzed on the basis of the intracellular concentrations of TCA cycle acids.

Characterization of mercury concentrations in snow and potential sources, Shanghai, China.

This work focused on quantifying the total mercury (HgT) and major ion concentrations in snow samples to understand the importance of this pathway and sources of Hg deposited in Shanghai, China. Rare snow event samples were collected at 26 sites within the city of Shanghai on February 18, 2006, January 27, 2008 and January 20, 2011. The sites were distributed among four main functional area types (i.e., industrial impacted, residential impacted, traffic impacted sites and sites in the city center). Concentrations of HgT and major soluble ions, and pH values were determined for each site. Mean HgT concentrations for all sites were 78±52 ng L(-1), 277±184 ng L(-1), 189±123 ng L(-1) in 2006, 2008 and 2011, respectively. Values were higher in Shanghai than observed in other cities including Beijing which has a smaller population and is less industrial. Principle component analysis (PCA) indicated that secondary aerosols (SO4(2-), NO3(-) and NH4(+)), and biomass combustion (K(+), CH3COO(-), and HCOO(-)) were best related to mercury concentrations in the snow in 2008 and 2011. Although HYSPLIT back trajectory modeling indicated air mass transport from areas with significant coal combustion, results indicate that anthropogenic pollution from within Shanghai was the predominant source of Hg in snow.

[Determination of trace anions in atmosphere absorption solution by ion chromatography with the application of online sample neutralization, column concentration and online standard addition].

A novel ion chromatographic method was developed to directly determine trace anion (Cl(-), NO2(-), NO3(-), SO4(2-)) in atmosphere absorption solution with incorporation of large volume injection, online sample neutralization, column concentration and online standard addition. After comparing the results in different valve switching times and the chromatograms using different online neutralizing columns, the optimum experimental conditions were established. The application of Inguard H online neutralizing column and Carbonate Removal Device (CRD 200) eliminated the matrices OH(-) and carbonate. The improvement of the anion detection limit could be achieved by using large volume injection. The results showed that the detection limits of Cl(-), NO2(-), NO3(-) and SO4(2-) were 17.5, 171, 34.7, and 42.4 ng/L, respectively. Online standard addition replaced the preparation of trace anion standard solution and avoided the low recovery of NO2(-). The method has the characteristics of automatic operation, good repeatability and high efficiency, and can be applied to the detection of ultra trace anions which are hard to be determined in common ion chromatography.

[Determination of glyphosate in heart blood of corpse by ion chromatography].

A method for the determination of glyphosate in human blood by ion chromatography was established. The protein in heart blood from a corpse was precipitated with acetonitrile. The large molecules and Cl(-) in the supernatant were removed by a Dionex OnGuard II RP column and a Dionex OnGuard II Ag column, respectively. The filtrate was separated on an IonPac AS-19 column with KOH solution as eluent produced online by an eluent generator (EG). A suppressor with external water mode and a conductivity detector for the detection were used. The linear range of this method was 10 - 100 mg/L with a correlation coefficient (r2) of 0.9999. The limits of detection (LOD, S/N = 3) and quantification (LOQ, S/N = 10) of glyphosate in blood were 0.12 mg/L and 0.39 mg/L, respectively. The recoveries ranged between 95.2% -109.1% with the relative standard deviations (RSDs, n = 5) of 1.2% - 3.7%. The glyphosate content in a heart blood sample from a corpse in an actual case was 508 mg/L detected by this method. This method is simple, sensitive, accurate, and can rapidly provided reliable clues and evidences for glyphosate poisoning cases. This method can meet the needs of public security work.

[Determination of six anthraquinone compounds in soil by parallel type dual gradient high performance liquid chromatography].

A high performance liquid chromatography (HPLC) was established for the determination of six anthraquinone compounds, 1,8-dinitroanthraquinone, 1,5-dinitroanthraquinone, 1-aminoanthraquinone, anthraquinone, naphthalene, 1,4,5,8-tetrachlorodibenzo anthraquinone, in polluted soil of residential construction. In this method, by using an Ultimate dual gradient liquid chromatograph (DGLC), designing a set of parallel dual system and accepting two same Dikma Diamonsil C18 columns (150 mm x 4.6 mm, 5 microm) to cross-analysis, 41.46% of the analysis time can be saved. By using assisted ultrasonication to the extraction of the six substances in the samples with 50 mL N,N-dimethyl-formamide/1,4-dioxane/methanol (5/20/25, v/ v/v), the average recoveries of the six analytes spiked in nine blank soil samples were 82.7% - 101% with the relative standard deviations (RSDs) of 1.8% - 3.2% and the limits of detection were 0.007 - 0.054 mg/kg, which can reach the limited requirement of the local standard in Beijing of DB11/T811-2011. With the advantages of accessibility, high sensitivity and good reproducibility, this method can be used in the determination of anthraquinone compounds in soil.