Interferences in the determination of total nitrogen in natural waters by photo-oxidation to nitrate-nitrite mixture

The method proposed by Armstrong, Williams and Strickland for the photo-oxidation of total nitrogen in sea-water to nitrate and nitrite has been studied in some detail, to extend its use to fresh and brackish waters, applying a more accurate method for the determination of the reaction products. Variables influencing the yield of nitrate and nitrite are irradiation time, pH and type of buffer, kind of nitrogen compound and its concentration, and the concentrations of oxygen, carbon dioxide, organic matter and salts, especially bromides, even at the low concentrations found in brackish waters. All these variables interact in a rather complicated way. Interferences from halides, organic matter and carbon dioxide are considerably reduced by ensuring that the pH is kept at 8.5-9 during the irradiation. Because pure solutions of many substances give quantitative yields (> or = 98%) in the pH-range 7-9 usually recommended, whereas others require lower pH for maximal oxidation, a method has been developed involving photo-oxidation first at pH 2.1 and then at pH 8.5-9. In the absence of interfering concentrations of halides the relative increase in yield by an initial irradiation at low pH is especially large (10-36%) for proteins, organic nitrogen in fresh waters, uric acid and urea. A comparison is made between determination of total nitrogen in some natural waters by using photo-oxidation and by a Kjeldahl method modified to give total nitrogen. By making use of the optimal conditions presented in this paper, a negative error of less than 8% is expected in the determination of total nitrogen in fresh waters. For saline waters the error will probably be larger, at least at a high ratio of organic to inorganic nitrogen.     

Chemometric approach to the optimisation of LC-FL and GC-MS methods for the determination of nitrite and nitrate in some biological,food and environmental samples

Gas chromatography–mass spectrometry (GC-MS) method and a liquid chromatography–fluorescence (LC-FL) detection method using experimental design and optimisation approach were improved for the quantitative determination of nitrite and nitrate in biological, food and environmental samples. The obtained recoveries of nitrite and nitrate ions from samples based on both GC-MS and LC-FL results ranged from 98.5% to 98.9% for nitrite and 97.9% to 98.4% for nitrate. The precision of these methods, as indicated by the relative standard deviations (RSDs), was within the range from 2.4% to 3.6% for nitrite and 2.5% to 3.8% for nitrate, respectively. The limits of detection of nitrite and nitrate ions from samples based on GC-MS and LC-FL results ranged from 0.01 to 0.14 ng L^?1 for nitrite and 0.02 to 0.71 ng L^?1 for nitrate, respectively. The optimised isolation procedure by central composite design was successfully applied to real samples. The results revealed that the proposed procedure combined with GC-MS and LC-FL techniques is more sensitive, reliable and selective compared to the other methods available for the precise determination of trace levels of nitrite and nitrate in biological, food and environmental samples.     

离子色谱不对称色谱峰的处理

介绍了通过微分处理分辨离子色谱中不对称峰的方法。实验将Ｆ＾－、Ｃｌ＾－、Ａｃ＾－、ＮＯ２＾－、ＮＯ３＾－、ＰｈＣＯＯ＾－、ＳＣＮ＾－、柠檬酸根、水杨酸根、山梨酸根和葡萄糖酸根等常见离子按一定比例配合混合液,对出现的不对称峰进行微分处理,得到的导数谱图可进行峰高定量,收到了较好的效果。     

Determination of low level nitrite and nitrate in biological, food and environmental samples by gas chromatography-mass spectrometry and liquid chromatography with fluorescence detection

Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography with fluorescence detection (LC-FL) methods have been proposed for the determination of low level nitrite and nitrate in biological, food and environmental samples. The methods include derivatization of aqueous nitrite with 2,3-diaminonaphthalene (DAN), enzymatic reduction of nitrate to nitrite, extraction with toluene and chromatographic analyses of highly fluorescent 2,3-naphthotriazole (NAT) derivative of nitrite by using GC-MS in selected-ion-monitoring (SIM) mode and LC-FL. Nitrite and nitrate ions in solid samples were extracted with 0.5 M aqueous NaOH by sonication. The recoveries of nitrite and nitrate ions based on GC-MS and LC-FL results were 98.40% and 98.10% and the precision of these methods, as indicated by the relative standard deviations (RSDs) were 1.00% for nitrite and 1.20% for nitrate, respectively. The limits of detection of the GC-MS in SIM mode and LC-FL methods based on S/N = 3 were 0.02 and 0.29 pg/ml for nitrite and 0.03 and 0.30 pg/ml for nitrate, respectively.     

Development of a pH titration method for the simultaneous determination of uranium,nitrate and free-acid in the feed solution of the sol-gel process of nuclear fuel fabrication

pH titration curves generated by slow addition of alkali to solutions containing varying concentrations of uranyl nitrate and nitric acid were studied using an autotitrator linked to a personal computer. A procedure with multiple choice of equations has been developed for the estimation of free acid, nitrate and uranium in pure uranyl nitrate solution by a single titration. The technique provides a simple single-step method with required accuracy and precision for the simultaneous estimation of the three quantities in the uranyl nitrate feed solution of the sol-gel process for making UO₃ microspheres. The relative standard deviations in the determination of uranium and nitrate were ±0.82% and ±1.52%, respectively, in 15 determinations.     

Utilization of flow injection with hydrazine reduction and photometric detection for the determination of nitrate in rain-water

The hydrazine reduction method for determination of nitrate at the parts per million level is adapted to flow injection sample processing of rain-water. Reagent composition and physical variables were evaluated and optimized. Forty samples per hour can be processed. A precision of better than 3% is possible in the range of 1.0–10.0 ppm nitrate. Results for nitrate obtained from 9 rain-water samples agreed favorably with those determined by ion chromatography.     

Spectrophotometric determination of mixtures of 2-, 3-, and 4-hydroxybenzaldehydes by flow injection analysis and uv/vis photodiode-array detection

A multivariate approach to the quantitative determination of 2-hydroxybenzaldehyde (salicylaldehyde), 3-hydroxybenzaldehyde, and 4-hydroxybenzaldehyde in their mixtures is described. The method is based on second order data generated in a flow injection analysis system with a pH gradient and photodiode-array detection. Each injection gave rise to an 89 (times) x 101 (wavelength) matrix, containing both the acidic and the basic characteristics of the sample injected. A least-squares algorithm based on Lambert-Beers law was used for the prediction of concentrations in unknown samples. No assumptions concerning the qualitative mixture composition of the hydroxybenzaldehydes were necessary to perform concentration predictions. The following four data types were used in the least-squares modelling: (1) unfolded raw data, (2) acidic spectra, (3) basic spectra, and (4) first spectral derivative of the raw data. The prediction errors obtained were comparable to literature results. A graphic method, based on the model residuals for detecting erroneous samples, was developed.     

Direct determination of U(VI) in TBP-kerosene extracts using first derivative ultraviolet spectroscopy

Summary The extractive first order derivative spectrophotometry is a selective method for the separation and determination of U(VI) using tri-n-butyl phosphate (TBP), which combines the roles of solvent and complexing agent. The complex is formed by extracting U(VI) from an aqueous 6M sodium nitrate solution at initial pH 3.0 into a 25% solution of TBP in kerosene. This extraction also separates U(VI) from many diverse ions that interfere. After extraction, the determination of uranium shows good accuracy and precision with relative standard deviation of 1.5% (n = 5) at 20 ppm using zero-order spectrum at l_max = 250 nm. Calibration curve was also found to obey Beer's law in the range of 10-100 ppm with 3.33 ppm detection limit. However, these accuracy and precision have been improved to give relative standard deviation of 0.7% (n = 5) at 20 ppm with a lower detection limit of 2.24 ppm using the first-derivative spectrum at l = 263 nm comparing to the normal one.     

Comparison of photodiode array,evaporative light scattering,and single-quadrupole mass spectrometric detection methods for the UPLC analysis of pyrolysis liquids

It is important to analyze pyrolysis liquids to evaluate the yield of valuable products as well as unfavorable by-products. This work focuses on choosing detectors for reversed-phase ultra high-performance liquid chromatography analysis of pyrolysis liquids. The linearity, sensitivity, precision, and recovery of photodiode array (PDA) detector, single-quadrupole mass spectrometer (MS), and evaporative light scattering (ELS) detector were compared for the quantitative determination of several typical compounds found in pyrolysis liquids. PDA and MS detectors were found to be suitable for the quantification of furans and phenol derivatives (furfural, vanillin, syringol), but sugars and their derivatives (glucose, xylose, levoglucosan) can be analyzed with MS or ELS detectors.     

The use of glyoxal and glyoxylic acid to determine N- and N,N-alkyl-substituted hydrazines by liquid chromatography

Using chromatography and spectrophotometry, it has been shown that the reaction of 1,1-dimethylhydrazine (UDMH), methylhydrazine (MH), and 2-hydroxyethylhydrazine (HEH) with excess of glyoxal (Gl) and glyoxylic acid (GlA) in aqueous solutions yields corresponding monohydrazones as single derivatization products. The derivatization reaction occurs in a quantitative yield for 20 min at 25 or 40°C for Gl and GlA, respectively (pH 3.5). The electronic absorption spectra of the derivatives have maxima in the range of 275–305 nm. The conditions for the simultaneous determination of hydrazines in waters by reversed-phase HPLC coupled with UV detection in aqueous solutions with preliminary derivatization are proposed. The derivatives are separated on a Zorbax SB-C18 (150 × 4.6 mm) column with a mobile phase of 20 mM phosphate buffer solution (pH 3.5) and 2–5% acetonitrile. The detection limits are 0.25–0.5 or 0.4–0.7 μg/L for the derivative of Gl and GlA, respectively.     

Matrix elimination ion chromatography method for the determination of trace levels of anionic impurities in high purity cesium iodide

In the present study an ion chromatographic method based on matrix elimination has been developed for the determination of anionic impurities in high purity cesium iodide crystals. The presence of impurities has a detrimental effect on the characteristics of detectors based on cesium iodide crystals. In particular, oxygen-containing anions inhibit the resolving power of scintillators and decrease the optical absorption. The quantitative determination of anions (fluoride, chloride, bromide, nitrate, phosphate, and sulphate) simultaneously in the high-purity cesium iodide crystals has not been carried out before. The large concentration of iodide poses a challenge in the determination of anions (especially phosphate and sulphate); hence, matrix elimination is accomplished by adopting a sample pretreatment technique. The method is validated for linearity, accuracy, and precision. The limit of detection for different anions is in the range of 0.3-3 μg/g, and the relative standard deviation is in the range of 4-6% for the overall method.     

基于多肽标记物分析的肉制品掺伪定量检测技术

该文开发了一种基于多肽标记物分析的肉制品掺伪检测技术,可同时进行定性和定量分析。样品经蛋白质提取和胰蛋白酶消化后,采用高分辨质谱(HRMS)和生物信息学工具,寻找牛、鸡、鸭、猪和羊5种肉类的特异性热稳定多肽标记物。在多反应监测(MRM)模式下,通过高效液相色谱-串联四极杆质谱(HPLC-QQQ-MS)对这些标记物进一步验证。使用由两种不同质量分数的肉类混合物(0%~100%)建立定量校准曲线,测定低限可达1%。采用该方法对市售的实际样品进行测试,验证结果表明该方法是一种可靠、有效的肉制品鉴定手段,可同时用于生肉和熟肉掺伪的定量检测。     

Controlled potential lodometric determination of nitrate after reduction to nitrite by coppered cadmium

A controlled-potential coulometric iodometric method previously developed for the accurate determination of small amounts of nitrite has been extended for the determination of nitrate after its reduction on a coppered cadmium reductor. The conditions for quantitative reduction have been investigated with respect to type of reductor and pH. Nitrate-nitrogen in the range 0.01-100 mug ml may be determined with high accuracy in less than 10 min, including the reduction step. The method has been applied with good results to a large variety of samples such as meat products, juices and waste waters.     

Analysis of saponins in raw and steamed Panax notoginseng using high-performance liquid chromatography with diode array detection

A reversed-phase high-performance liquid chromatography-diode array detection method was developed and validated for the simultaneous determination of six saponins (notoginsenoside R1, ginsenosides Rg1, Re, Rb1, Rc, Rd) in raw and steamed Panax notoginseng. Linearity (r2 > 0.9988), intra- and inter-day precision (RSD < 4%), limit of detection (0.008-0.013 mg/ml), limit of quantification (0.027-0.042 mg/ml) of the saponins were determined. The method was successfully applied to 11 pairs of raw and steamed P. notoginseng products. Three products showed discrepancies between theirlabelled claims (raw or steamed) and the results of analysis. This new, simple and reliable method could be used in the quality control of raw and steamed P. notoginseng.     

Determination of nitrate in environmental water samples by conversion into nitrophenols and solid phase extraction−spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry

Conversion of nitrate into a nitro-phenol derivative by reaction with 2-methylphenol or 2,6-dimethylphenol allowed at least 100-fold enrichment of the derivative on Lichrolut EN polymeric cartridge, and it is stable for up to 1 month on the cartridge. The derivative could be eluted with ammonia-methanol mixture. This reaction for nitrate determination has permitted a choice of final measurement by UV-Vis spectrophotometry, liquid chromatography or gas chromatography-mass spectrometry when the limits of detection were 10, 6 and 3 μg l⁻¹, respectively, and the calibration range 20 μg to 10 mg l⁻¹ nitrate. The method has been validated by spiking natural water samples, when the recovery of nitrate was 98.5-108.4% (relative standard deviation 2.5-6.1%).     

Development and validation of three stability-indicating methods for determination of bisacodyl in pure form and pharmaceutical preparations

Three new, simple, sensitive, and accurate stability-indicating methods were developed for quantitative determination of bisacodyl in the presence of its degradation products, monoacetyl bisacodyl (I) and desacetyl bisacodyl (II), in enteric coated tablets, suppositories, and raw material. The first is a spectrodensitometric method in which the drug is separated from I and II on silica gel plates using chloroform-acetone (9 + 1, v/v) as the mobile phase with ultraviolet detection of the separated bands at 223 nm over a concentration range of 0.2-1.4 microg/band for bisacodyl with mean recovery 100.35 +/- 1.923%. The second method is fourth derivative D4 spectrophotometry, which allows determination of bisacodyl in the presence of its degradation products in raw material at 223 nm using acetonitrile as the solvent with adherence to Beer's law over the concentration range 2-18 microg/mL with mean recovery 99.77+/-1.056%. In the third method, the spectrophotometric data of bisacodyl, I, and II using absolute ethanol as solvent were processed by 3 chemometric techniques: classical least-squares, principal component regression, and partial least-squares. A training set consisting of 15 mixtures containing different ratios of bisacodyl, I, and II was used for construction of the 3 models. A validation set consisting of 6 mixtures was used to validate the prediction ability of the suggested models. The 3 chemometric methods were applicable over a concentration range between 2-14microg/mL for bisacodyl with mean recovery of 99.97+/-0.865, 100.01 +/- 0.749, and 99.97 +/- 0.616% for the 3 models, respectively. The proposed methods were checked using laboratory-prepared mixtures and were successfully applied to the analysis of raw material and pharmaceutical formulations containing bisacodyl, except for the second method that applies only for raw material. The validity of the suggested procedures was further assessed by applying the standard addition technique; the recoveries obtained were in accordance with those given by the reference method.     

Development and Validation of HPLC,TLC and Derivative Spectrophotometric Methods for the Analysis of Ezetimibe in the Presence of Alkaline Induced Degradation Products

Reversed phase‐high performance liquid chromatography (RP‐HPLC), thin layer chromatography (TLC) densitometry and first derivative spectrophotometry (1D) techniques are developed and validated as a stability‐indicating assay of ezetimibe in the presence of alkaline induced degradation products. RP‐HPLC method involves an isocratic elution on a Phenomenex Luna 5μ C₁₈ column using acetonitrile: water: glacial acetic acid (50:50:0.1 v/v/v) as a mobile phase at a flow rate of 1.5 mL/min. and a UV detector at 235 nm. TLC densitometric method is based on the difference in Rf‐values between the intact drug and its degradation products on aluminum‐packed silica gel 60 F₂₅₄ TLC plates as stationary phase with isopropanol: ammonia 33% (9:1 v/v) as a developing mobile phase. On the fluorescent plates, the spots were located by fluorescence quenching and the densitometric analysis was carried out at 250 nm. Derivative spectrophotometry, the zero‐crossing method, ezetimibe was determined using first derivative at 261 nm in the presence of its degradation products. Calibration graphs of the three suggested methods are linear in the concentration ranges 1–10 mcg/mL, 0.1–1 mg/mL and 1–16 mcg/mL with a mean percentage accuracy of 99.05 ± 0.54%, 99.46 ± 0.63% and 99.24 ± 0.82% of bulk powder, respectively. The three proposed methods were successfully applied for the determination of ezetimibe in raw material and pharmaceutical dosage form; the results were statistically analyzed and compared with those obtained by the reported method. Validation parameters were determined for linearity, accuracy and precision; selectivity and robustness and were assessed by applying the standard addition technique.     

Development and validation of liquid chromatographic and ultraviolet derivative spectrophotometric methods for determination of epinastine hydrochloride in coated tablets

High-performance liquid chromatographic (LC) and ultraviolet derivative spectrophotometric (UVD) methods were developed and validated for the quantitative determination of epinastine hydrochloride in coated tablets. LC was performed on a reversed-phase RP-18 column with a mobile phase composed of 0.3% triethylamine (pH adjusted to 4.0 with 10% orthophosphoric acid)-methanol (60 + 40, v/v). The first-order derivative method was performed at 243.8 nm using HCI and methanol as the solvent. The methods were validated according to U.S. Pharmacopoeia and International Conference on Harmonization guidelines. The statistical analysis by Student's t-test showed no significant difference between the results obtained by the 2 methods. The proposed methods were found to be simple, rapid, precise, accurate, robust, and sensitive, allowing perfect interchange. The LC and UVD methods can be used in the routine quantitative determination of the epinastine hydrochloride in coated tablets.     

Simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in peanuts and their derivative products by ultra-high-performance liquid chromatography-tandem mass spectrometry

A reliable ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method for simultaneous determination of aflatoxins B1, B2, G1, G2, M1 and M2 in peanuts and their derivative products was developed. The sample was extracted by 84% of acetonitrile aqueous solution and the extract was purified by a reliable solid phase extraction-based clean-up method. Then, the analytes were separated on Acquity UPLC HSS T3 column (100 mm × 2.1 mm, 1.8 μm particle size), and eluted with a mobile phase consisting of (A) water containing 0.1% formic acid and (B) acetonitrile/methanol (50/50, v/v). The separated compounds were detected with a Waters Micromass Quattro Ultima Pt tandem quadrupole mass spectrometer operating in positive electro-spray ionization using multiple reaction monitoring mode. The established method was extensively validated by determining the linearity (R² ≥ 0.9990), average recovery (74.7-86.8%) and precision (relative standard deviation ≤ 10.9%). It was shown to be a suitable method for simultaneous determination of the six aflatoxins in peanuts and their derivative products. Finally, a total of 73 samples randomly collected from different areas in Zhejiang province were screened for aflatoxins with the proposed method. The results showed that 31 samples of peanut butter, 14 samples of fresh peanut and 5 samples of musty peanut were contaminated with aflatoxins. Meanwhile, this was the first report on aflatoxins M1 and M2, which were found in unprocessed peanuts and their derivative products.     

Measurement of insulin sensitivity indices using 13C-glucose and gas chromatography/combustion/isotope ratio mass spectrometry

Important aspects of glucose metabolism can be quantified by using the minimal model of glucose kinetics to interpret the results of intravenous glucose tolerance tests. The power of this methodology can be greatly increased by the addition of stable isotopically labelled tracer to the glucose bolus dose. This allows the separation of glucose disposal from endogenous glucose production and also increases the precision of the estimates of the physiological parameters measured. Until now the tracer of choice has been deuteriated glucose and the analytical technique has been gas chromatography/mass spectrometry (GC/MS). The consequence of this choice is that nearly 2 g of labelled material are needed and this makes the test expensive. We have investigated the use of (13)C-labelled glucose as the tracer in combination with gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) as the analytical technique. This methodology offers superior analytical precision when compared with the conventional method and so the amount of tracer used, and hence the cost, can be reduced considerably. Healthy non-obese male volunteers were recruited for a standard intravenous glucose tolerance test (IVGTT) protocol but 6,6-(2)H-glucose and 1-(13)C-glucose were administered simultaneously. Tracer/tracee ratios were derived from isotope ratio measurements of plasma glucose using both GC/MS and GC/C/IRMS. The results of these determinations indicated that the two tracers behaved identically under the test protocol. The combination of these results with plasma glucose and insulin concentration data allowed determination of the minimal model parameters S*g and S*i. The parameter relating to insulin-assisted glucose disposal, S*i, was found to be the same in the two techniques, but this was not the case for the non-insulin-dependent parameter S*g.