An evaluation of acid digestion methods for amniotic fluid phospholipids

Five methods of acid digestion of amniotic fluid phospholipids for inorganic phosphate release were evaluated at a temperature of 225 °C and a heating time of 30 min. The methods used the following digestants: (A (perchloric acid), B (perchloric acid containing molybdate), C (sulfuric acid, 30% hydrogen peroxide, 5% urea), D (sulfuric-perchloric acids), and E (sulfuric-perchloric acids with vanadium pentoxide). After digestion and dilution with water, a hydrogen ion concentration of about 2.5 mol/ liter was obtained that permitted the use of stannous chloride-hydrazine sulfate as the reducing agent for phosphate color development. Recoveries of the different amniotic fluid phospholipids and aqueous phosphate standards were quantitative for all methods. A comparative study with amniotic fluids showed similar results for all methods. Since all methods were found to be equivalent under the specified conditions described, the choice was dependent upon the user's preference.     

A semi-automated and manual method for determining the total phospholipid phosphorus in amniotic fluid

A rapid method for estimating the total phospholipid content of amniotic fluid has been described that requires 1 ml of sample. Perchloric acid containing a trace of molybdate is the acid digestant for inorganic phosphate release. After digestion at 225 °C for 30 min, dilution with water yields a solution with a hydrogen ion concentration of about 2.5 mol/liter that allows the use of stannous chloride-hydrazine sulfate as the reducing agent for phosphate color development. The color development and measurement may be carried out manually or with use of the AutoAnalyzer at an analysis rate of 40/hr. A coefficient of variation of about 7% and a standard deviation of 0.02 will be obtained with either the manual or semi-automated procedure.     

Determination of phosphatidylcholine in amniotic fluid

A relatively rapid method for measuring phosphatidylcholine (lecithin) quantitatively in amniotic fluid has been described that requires 1 ml or less of sample for fluids having a total phospholipid concentration greater than 25 mg/liter. Following extraction with chloroform-methanol, the solvent is passed through a calcium hydroxyphosphate column which removes the acidic phospholipids and allows passage of the phosphatidylcholine and sphingomyelin. Hydrolysis with periodate-sulfuric acid selectively releases inorganic phosphate from the phosphatidylcholine that is measured by reduction of the formed phosphomolybdate complex to the usual blue color. Various mixtures of phospholipids were carried through the entire procedure with excellent recoveries. Phosphatidylcholine added to an amniotic fluid pool was also quantitatively recovered, so that the method appeared completely suitable for routine clinical laboratory use.     

Kinetics of the chromic acid oxidation of glyoxylic and pyruvic acids

The reactions of glyoxylic and pyruvic acids by chromium (VI) have been studied in the presence of perchloric acid. Each reaction is first order with respect to chromium (VI), α-keto acid and hydrogen ion concentrations. The addition of sodium perchlorate to the reaction mixture had no effect on the rates but sodium chloride and sodium dihydrogen phosphate have retarding influences. Manganous ions increase the rate of reaction. The activation parameters are evaluated and tentative mechanisms for the oxidation reactions are discussed.     

重量法-电感耦合等离子体原子发射光谱法联用测定无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量

二氧化硅是无取向硅钢环保涂层液的核心成分,其含量直接影响硅钢涂层的固化工艺及涂层产品的磁性能。因此为保证涂覆过程的顺利进行,对涂层液中二氧化硅含量的检测是十分必要的。本方法采用样品中分别加入硝酸、双氧水及高氯酸,置于电热板上进行消解处理,处理后的样品经酸溶、过滤步骤,以重量法计算沉淀中二氧化硅的含量,采用电感耦合等离子体原子发射光谱（ICP-AES）仪测定滤液中可溶性硅含量,则样品中二氧化硅含量为重量法和电感耦合等离子体原子发射光谱法测定结果的合量。从而建立了重量法-电感耦合等离子体原子发射光谱法联用测定无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量的方法。讨论了样品前处理用消解酸及消解温度、滤液中可溶性硅及含量、ICP-AES仪器检测时的元素干扰。结果表明：按照本实验方法测定无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量,检测结果的相对标准偏差（RSD,n=12）在0.76%~1.08%之间,加标回收率在97.00%~104.0%之间。该方法可广泛应用于各检测部门对无取向硅钢磷酸盐体系环保涂层液中二氧化硅含量的监控。     

羊水中痕量有机酸的气相色谱分析 Ⅰ.预分离方法的比较

本文研究了气相色谱分析羊水中痕量有机酸的各种预分离方法。对各种结构类型的标准有机酸水溶液进行回收实验以及实际的羊水样品分析表明,硅酸吸附法具有比较全面的优越性,是研究羊水中痕量有机酸较为理想的预分离方法。离子交换法对大多数有机酸也具有较高的回收率,但它的操作过程比较冗长。溶剂萃取法对柠檬酸、甘油酸等某些多元酸或羟基酸的回收不很理想,但对其它许多有机酸也可以取得较好的结果。所研究的方法均能分离除去羊水中大量的磷酸盐和硫酸盐,消除它们对有机酸气相色谱分析的干扰。     

土壤中铅的分析方法比对

对不同的样品消解方法及电感耦合等离子体质谱、电感耦合等离子体原子发射光谱、石墨炉原子吸收光谱法测定土壤中铅的测定结果进行比对。采用电热板、微波及水浴3种加热方式,选择硝酸、氢氟酸、双氧水、王水、高氯酸、盐酸的不同组合进行土壤样品消解,通过分析测定值的精密度和准确度,考察消解体系对电感耦合等离子体质谱、电感耦合等离子体发射光谱、石墨炉原子吸收光谱法测定结果的影响。结果表明采用电感耦合等离子体质谱法测定土壤中的铅,最适宜的消解体系是硝酸-氢氟酸-高氯酸(微波加热),采用电感耦合等离子体原子发射光谱法测定最适宜的消解体系是硝酸(电热板加热),采用石墨炉原子吸收光谱法测定最适宜的消解体系是硝酸-盐酸-高氯酸(微波加热)。电感耦合等离子体质谱法的精密度和准确度优于另外两种方法。     

Spectrophotometric determination of Irgafos 168 in polymers after different sample preparation procedures

Different sample preparation methods on the basis of the oxidation of Irgafos 168 (a phosphite ester used as a secondary antioxidant in polymers) to phosphate ion are presented for its determination in polymers. Different reagents such as perchloric acid and sodium hydroxide or heat were used to convert analyte to phosphate ions. In final step, a standard method (vanadomolybdophosphoric acid method) was used to determine the phosphate ions produced. The method is simple, reliable and relatively rapid. The repeatability was evaluated using a 20 mg·L⁻¹ solution of analyte and it is found that the relative standard deviation is less than 5% for all procedures. Accuracy of the method was tested by applying the spectrophotometric method along with gas chromatography to three commercial polymers. The results in all cases are in good agreement. In nine other polymers Irgafos 168 was not detected using both methods. The procedure in case of real samples (polyolefins) is: dissolution/precipitation of polymer, filtration, evaporation, dissolving residue in acetone and performing digestion procedures using HClO₄ or NaOH. In the case of the pyrolytic method, the polymer was burned in an electrical furnace at 500 °C and the residue was dissolved in HCl.     

Estimation of amniotic fluid phospholipids by high-performance liquid chromatography

We have developed a high-performance liquid chromatographic (HPLC) method for the analyses of surface-active amniotic fluid phospholipids, lecithin (L), sphingomyelin (S), phosphatidyl glycerol (PG), phosphatidyl inositol (PI), phosphatidyl ethanolamine (PE), and phosphatidyl serine (PS), which are important in the prediction of fetal lung maturity. The method incorporates an internal standard in the amniotic fluid extract, and utilizes a 10-microliter aliquot of a 2:1 chloroform-methanol extract of amniotic fluid injected onto a 5-micron DIOL or CN HPLC column, and a variable-wavelength detector set at 203 nm. Amniotic fluid phospholipid estimations were determined on 40 amniotic fluid samples by the HPLC method and by the routine thin-layer chromatographic (TLC) method. Good agreement was observed between the two methods for the L/S ratio, PG, and PI (rPG 0.94, rPI 0.95, rL/S 0.97). The advantages of the HPLC procedure include: Selective separation for PG, PI, PS, and PE, as well as L and S at the same time. The internal standard allows individual concentration of phospholipids to be estimated. The procedure is rapid: 16 min for a single assay compared with 50 min for the standard TLC procedure.     

Phosphorus determination in biological materials

Summary An analysis scheme for the spectrophotometric determination of phosphorus as phosphate in biological materials has been worked out. The wet digestion of the sample was carried out in Kjeldahl flasks by a mixture of perchloric and nitric acids. The relative standard deviation (RSD) of the obtained results is not more than 1% for amounts up to 30 g. The method was applied to various biological materials.     

Determination of phosphorus in phosphazenes and phosphines

An improved technique for the determination of phosphorus in organic phosphazenes and phosphines is described. An acid digestion using a mixture of fuming nitric, sulphuric and perchloric acids converts the organically bound phosphorus into orthophosphate. The orthophosphate is precipitated as magnesium ammonium phosphate, which is ignited to magnesium pyrophosphate. With this technique phosphorus was determined in several compounds. The results establish both good accuracy and precision for the method.     

Submicro determination of cobalt, manganese or nickel in organometallic compounds

Methods for the determination of cobalt, manganese or nickel in samples of organometallic compounds weighing 30-100 mug have been developed. Spectrophotometric determination following digestion with nitric and sulphuric acids in a sealed tube is recommended, all results obtained from the analysis of standard compounds being within +/-0.4% absolute error. Digestion in an open tube with perchloric and sulphuric acids gives slightly low results for cobalt and nickel compounds and is inappropriate for manganese compounds.     

Determination of selenium in human tissues by atomic absorption spectrometry

A simple method is described for the determination of selenium in human tissues without the use of perchloric acid. Digestion with nitric and sulphuric acids is followed by hydride generation and atomic absorption spectrometry. Results for NBS bovine liver and IAEA horse kidney reference materials were in good agreement with assigned concentrations, as was also achieved with the perchloric acid digestion. Recovery of added selenium was >90%, and the relative standard deviation was 5.5% for within-batch and 6.9% for between-batch analyses. The values of selenium in heart tissue were 0.9–1.3 μg g^?1 dry weight.     

Improved scheme for the analysis of high-purity talc

An improved method is proposed for the determination of silica, magnesium oxide, R(2)O(3), ferric oxide, calcium oxide, and aluminium oxide in high-purity talc. In the method for silica and magnesium oxide, the sample is fused with sodium carbonate and the cooled melt is dissolved with perchloric acid in such a manner that it floats free from the crucible (in previous schemes for the analysis of talc there are frequently mechanical losses due to the difficulty of removing the magnesium silicate melt from the crucible). The solution is then evaporated to fumes of perchloric acid and the silica is filtered off and ignited. The magnesium oxide is determined in the filtrate by precipitation as magnesium ammonium phosphate and a correction is made for the calcium which is precipitated along with the magnesium ammonium phosphate. R(2)O(3) is determined after treatment of the sample with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Iron oxide and calcium oxide are determined by atomic absorption, after treatment with nitric and hydrofluoric acids and evaporation to fumes of perchloric acid. Al(2)O(3) is calculated by difference.     

Determination of the expiration date of chemical solutions

Thirty-five chemical solutions, acids, bases, complexing, argentometric, reducing, oxidising, salts and eluent mixtures, were studied continuously over a 7.5-month period. Twenty-seven remained reasonably stable and had acceptable expiration dates, which were equal to or more than 2 months longer than the established average deviation of ±2% relative to the initial value. Exceptions were made for potassium permanganate (0.1 M), perchloric acid (0.1 M) and disodium hydrogen phosphate (10%) solutions, as well as for HPLC eluent mixtures, which showed stability with expiration dates equal to stated values or shorter by 1 month. The eight chemical solutions presenting expiration dating higher than 6 months were hydrochloric acid (0.1 and 1 M), sulphuric acid (0.5 and 1.5 M), ethylenediamine tetraacetic acid (EDTA) (0.1 M), silver nitrate (0.1 M), ammonium thiocyanate (0.1 M) and iodine (0.1 M). The present data is a suitable guideline for the date of several chemical solutions routinely used in the analytical laboratories.     

Determination of traces of molybdenum in foods by electrothermal atomic absorption spectrometry

Low levels of molybdenum in different food samples were determined by atomic absorption spectrometry with electrothermal atomization after destruction of organic matter using four different methods, involving dry ashing at 600°C, wet digestion with heating with nitric/sulphuric and nitric/sulphuric/perchloric acid mixtures or direct extraction with dilute hydrochloric acid. In all cases the working conditions, reproducibility, precision and accuracy were investigated. The dry ashing method was generally the optimum destruction method.     

High pressure liquid chromatography of standard and amniotic fluid phospholipids

A method for the HPLC separation of phosphatidylglycerol (PG), phosphatidylinositol (PI), phosphatidylcholine (PC), and sphingomyelin (SPH) was achieved using five in-series columns packed with LiChrosorb, Partisil, and μ-Porasil adsorbents, a solvent mixture of chloroform/methanol/ammonium hydroxide (50 : 36 : 6.7, by volume), and a Pye LCM2 Moving Wire (FID) detector. The same phospholipid mixture was also separated using four μ-Porasil columns with the same eluent and detector. The latter conditions were found to be suitable for the analysis of phospholipids obtained after centrifuging, extraction, and precipitation of surface-active lipid components of patient amniotic fluid collected at amniocentesis section. The lecithin/sphingomyelin (L/S) ratios, determined by the HPLC method, correlated well with those determined by the TLC technique in four normal pregnancies, whereas results of shake tests did not correlate too well with L/S ratios determined by the above two chromatographic methods. Besides the lecithin/sphingomyelin ratio, the present method was able to supply additional information: the concentrations of phosphatidylglycerol and phosphatidylinositol, for prediction of fetal lung maturity, and the palmitic acid content of amniotic fluid phosphatidylcholine.     

Decomposition of vegetables for determination of Zn,Cd, Pb and Cu by stripping voltammetry

A simple and accurate digestion method using nitric acid, perchloric acid and hydrogen peroxide has been developed for use in trace analysis for heavy metals in vegetables by differential pulse anodic stripping voltammetry. The recovery of the metals from the samples is lower if the hydrogen peroxide is omitted from the digestion mixture. Standard reference materials have been analysed satisfactorily by this method.     

电感耦合等离子体原子发射光谱法测定植物中钾、钠、钙和镁

采用硝酸–高氯酸湿法消解或硝酸–双氧水微波消解植物样品,以电感耦合等离子体原子发射光谱法同时测定样品溶液中钾、钠、钙和镁含量。用该法测定灌木枝叶和茶叶标准样品,测定值均在标准值范围内,测定结果的相对标准偏差为0.45%~4.05%(n=8)。钾、钠、钙、镁的加标回收率分别为94.4%~107.6%,92.6%~107.9%,93.7%~105.4%,92.9%~107.2%。该方法操作简便,测量精密度和准确度完全满足植物中钾、钠、钙和镁含量的测定要求。     

A rapid method for the determination of organic nitrogen and phosphorus based on a single perchloric acid digestion

Results of nitrogen determinations obtained by perchloric acid digestion of organic matter under reflux were found to be equivalent to those obtained by the conventional sulfuric acid Kjeldahl method. A rapid determination of nitrogen and phosphorus was thus possible after a single perchloric acid digestion. Nitrogen was determined by nesslerization and phosphorus by a conventional molybdenum blue technique. The method devised was found satisfactory for a great variety of natural products and pure organic compounds, including materials containing all kinds of tertiary nitrogen.