Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “NITROGEN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 307 records · Page 17Linked to original sources
PubMed1985

Nitrogen fixation specific regulatory genes of Klebsiella pneumoniae and Rhizobium meliloti share homology with the general nitrogen regulatory gene ntrC of K. pneumoniae.

We have determined the complete nucleotide sequences of three functionally related nitrogen assimilation regulatory genes from Klebsiella pneumoniae and Rhizobium meliloti. These genes are: 1) The K. pneumoniae general nitrogen assimilation regulatory gene ntrC (formerly called glnG), 2) the K. pneumoniae nif-specific regulatory gene nifA, and 3) an R. meliloti nif-specific regulatory gene that appears to be functionally analogous to the K. pneumoniae nifA gene. In addition to the DNA sequence data, gel-purified K. pneumoniae nifA protein was used to determine the amino acid composition of the nifA protein. The K. pneumoniae ntrC and nifA genes code for proteins of 52,259 and 53,319 d respectively. The R. meliloti nifA gene codes for a 59,968 d protein. A central region within each polypeptide, consisting of approximately 200 amino acids, is between 52% and 58% conserved among the three proteins. Neither the amino termini nor the carboxy termini show any conserved sequences. Together with data that shows that the three regulatory proteins activate promoters that share a common consensus sequence in the -10 (5'-TTGCA-3') and -23 (5'-CTGG-3') regions, the sequence data presented here suggest a common evolutionary origin for the three regulatory genes.

Amino Acid Sequence↗
PubMed2006

Ozone impairs autumnal resorption of nitrogen from birch (Betula pendula) leaves, causing an increase in whole-tree nitrogen loss through litter fall.

Saplings of one half-sib family of birch, Betula pendula Roth, were exposed to three ozone concentrations (non-filtered air (NF); non-filtered air + 10-20 nmol O(3) mol(-1) (NF+); non-filtered air + 40-60 nmol O(3) mol(-1) (NF++)) in open-top chambers during two growing seasons from 1997 to 1998. Shed leaves were collected regularly during both growing seasons and, in 1998, the dry mass (DM) and nitrogen (N) concentrations ([N]) of the shed leaves were measured to quantify the total amount of N lost through litter fall. Dry mass and [N] were also determined in mid-August for attached, mature and non-senescent leaves, in order to estimate autumnal leaf N resorption efficiency and proportional leaf DM decrease. Net photosynthetic capacity was measured during August and September 1998, in a population of leaves that emerged in mid-July. Photosynthesis declined with increasing leaf age in the NF++ treatment, whereas it remained high throughout the measurement period in the NF and NF+ treatments. In both years, leaves abscised prematurely in the NF++ treatment, whereas this effect was only significant in 1998 in the NF+ treatment. There was a strong linear relationship between proportional leaf shedding and daylight ozone exposure above a threshold of 40 nmol mol(-1) (daylight AOT40) during the growing season. The resorption of N was significantly impaired by ozone, and the smaller autumnal decrease in leaf DM in elevated ozone concentrations suggested that the bulk resorption of leaf DM was also inhibited. Nitrogen resorption efficiencies were 81, 73 and 63% and leaf mass decreases were 45, 36 and 30% in the NF, NF+ and NF++ treatments, respectively. Compared with the NF treatment, total N loss through litter fall was increased by 16 and 122% in the NF+ and NF++ treatments, respectively. We conclude that ozone impaired N resorption from birch leaves before abscission, causing a substantial increase in whole-tree N loss through litter fall.

Absorption↗
PubMed1995

Nitrogen dioxide production during mechanical ventilation with nitric oxide in adults. Effects of ventilator internal volume, air versus nitrogen dilution, minute ventilation, and inspired oxygen fraction.

BACKGROUND: Inhaled nitric oxide (NO) may be useful in the treatment of adult respiratory distress syndrome and other diseases characterized by pulmonary hypertension and hypoxemia. NO is rapidly converted to nitrogen dioxide (NO2) in oxygen (O2) environments. We hypothesized that in patients whose lungs are mechanically ventilated and in those with a long residence time for NO in the lungs, a clinically important [NO2] may be present. We therefore determined the rate constants for NO conversion in adult mechanical ventilators and in a test lung simulating prolonged intrapulmonary residence of NO. METHODS: NO (800 ppm) was blended with nitrogen (N2), delivered to the high-pressure air inlet of a Puritan-Bennett 7200ae or Siemens Servo 900C ventilator, and used to ventilate a test lung. The ventilator settings were varied: minute ventilation (VE) from 5 to 25 l/min, inspired O2 fraction (FIO2) from 0.24 to 0.87, and [NO] from 10 to 80 ppm. The experiment was then repeated with air instead of N2 as the dilution gas. The effect of pulmonary residence time on NO2 production was examined at test lung volumes of 0.5-4.0 l, VE of 5-25 l/min, FIO2 of 0.24-0.87, and [NO] of 10-80 ppm. The inspiratory gas mixture was sampled 20 cm from the Y-piece and from within the test lung. NO and NO2 were measured by chemiluminescence. The rate constant (k) for the conversion of NO to NO2 was determined from the relation 1/[NO]t-1/[NO]o = k x [O2] x t, where t = residence time. RESULTS: No NO2 was detected during any trial with VE 20 or 25 l/min. With N2 dilution and the Puritan-Bennett 7200ae, NO2 (< or = 1 ppm) was detected only at a VE of 5 l/min with an FIO2 of 0.87 and [NO] > or = 70 ppm. In contrast, [NO2] values were greater with the Servo 900C ventilator than with the Puritan-Bennett 7200ae at similar settings. When NO was diluted with air, clinically important [NO2] values were measured with both ventilators at high [NO] and FIO2. Rate constants were 1.46 x 10(-9) ppm-2.min-1 when NO was mixed with N2, 1.17 x 10(-8) ppm-2.min-1 when NO was blended with air, and 1.44 x 10(-9) ppm-2.min-1 in the test lung. CONCLUSIONS: [NO2] increased with increased FIO2 and [NO], decreased VE, blending with air, and increased lung volumes. Higher [NO2] was produced with the Servo 900C ventilator than the Puritan-Bennett 7200ae because of the greater residence time. With long intrapulmonary residence times for NO, there is a potential for NO2 production within the lungs. The rate constants determined can be used to estimate [NO2] in adult mechanical ventilation systems.

Adult↗
PubMed1989

Validity of urinary urea nitrogen as a measure of total urinary nitrogen in adult patients requiring parenteral nutrition.

The validity of the urinary urea nitrogen (UUN) estimate of total urinary nitrogen (TUN) was tested in patients who required iv nutrition. UUN and TUN were determined in 120 urine collections from ten preoperative, 13 postoperative, and 11 stressed patients. The relationship between TUN and UUN was examined by linear regression, and analysis of covariance was used on log-transformed data to assess differences between the patient groups. Although there was a close relationship between UUN and TUN for the preoperative patients (r2 = .94, total range of differences = 3.85 g N), this was not as accurate in postoperative and stressed patients (r2 = .69 and .76, respectively, total range of differences = 16.8 and 10.7 g N, respectively). There was no significant difference between the slopes of the regression lines for the relationship between UUN and TUN for three groups (f = 1.1, df = 2114, p less than .3), but the intercepts of the regression lines differed between the preoperative and stressed patient groups (t = 3.47, v = 114, p less than .001). The relationship between TUN and UUN for the whole group was improved by the inclusion of the independent variables of both the patient's clinical state and the urinary creatinine excretion. Arm muscle circumference, which is an estimate of muscle mass, may replace creatinine excretion with little loss in prediction accuracy.

Adult↗
PubMed2001

Nitrogen Loss Estimation Worksheet (NLEW): an agricultural nitrogen loading reduction tracking tool.

The Neuse River Basin in North Carolina was regulated in 1998, requiring that all pollution sources (point and nonpoint) reduce nitrogen (N) loading into the Neuse Estuary by 30%. Point source N reductions have already been reduced by approximately 35%. The diffuse nature of nonpoint source pollution, and its spatial and temporal variability, makes it a more difficult problem to treat. Agriculture is believed to contribute over 50% of the total N load to the river. In order to reduce these N inputs, best management practices (BMPs) are necessary to control the delivery of N from agricultural activities to water resources and to prevent impacts to the physical and biological integrity of surface and ground water. To provide greater flexibility to the agricultural community beyond standard BMPs (nutrient management, riparian buffers, and water-control structures), an agricultural N accounting tool, called Nitrogen Loss Estimation Worksheet (NLEW), was developed to track N reductions due to BMP implementation. NLEW uses a modified N-balance equation that accounts for some N inputs as well as N reductions from nutrient management and other BMPs. It works at both the field- and county-level scales. The tool has been used by counties to determine different N reduction strategies to achieve the 30% targeted reduction.

Agriculture↗
PubMed2001

Nitrogen interactions with phosphorus and potassium for optimum crop yield, nitrogen use effectiveness, and environmental stewardship.

The development of best management practices (BMPs) for optimum nitrogen (N) use by crops contributes to farm profitability, increased food and fiber production, and best stewardship of the environment and its resources. Such BMPs are both site- and crop-specific. Optimum N use by plants is influenced not only by climate and certain soil characteristics, but also by management practices such as tillage, time and method of N application, or positive interactions with nutrients and supporting cropping practices. Phosphorus (P) and potassium (K) are two of the nutrients essential for effective use of N by plants. Nitrogen interactions with P and/or K help to improve root system development, dry matter production, and other plant functions regulating crop yield and quality.

Agriculture↗
PubMed1969

Nitrogen metabolism of Lemna minor. I. Growth, nitrogen sources and amino acid inhibition.

Lemna minor grown in sterile culture on a minerals-sucrose medium can utilize as nitrogen source, in order of increasing growth rate: ammonia, nitrate, a mixture of glutamic and aspartic acids plus arginine, or a balanced mixture of amino acids (hydrolyzed casein). Maximum growth is found with nitrate plus hydrolyzed casein. Many synthetic mixtures of amino acids are unable to support growth. Many single amino acids are inhibitory, and when added (at 2 mm or less) to cultures, growing in the presence of nitrate, cause a decrease in growth rate or even death of the plants (e.g. with alanine, valine, methionine or leucine). Some of these inhibitory effects are also found when the amino acid is added to cultures growing on ammonia or hydrolyzed casein. Arginine was the only amino acid of those tested which gave a marked stimulation of growth when added to cultures growing with inorganic nitrogen. The rapid rate of growth, sterile nature of tissue, decreased biological variation of samples containing many plants and ability to utilize different culture media make this an attractive organism for studies on higher plant metabolism.

Amino Acids↗
PubMed2001

Nitrogen-regulated group 2 sigma factor from Synechocystis sp. strain PCC 6803 involved in survival under nitrogen stress.

The expression of sll1689, an open reading frame from the cyanobacterium Synechocystis sp. strain PCC 6803 putatively encoding a member of the sigma(70) family of sigma factors, appears to be regulated by the nitrogen control transcription factor NtcA. Disruption of sll1689 had no noticeable effect on exponential growth, identifying its product as a member of the group 2, nonessential class of sigma(70)-like sigma factors; however, this disruption decreased the viability of the cells after long periods of nitrogen starvation. We have named this gene rpoD2-V. The expression of glnN, encoding a type III glutamine synthetase, was impaired in strains bearing an inactivated copy of the rpoD2-V gene.

Adaptation, Biological↗
PubMed1992

Effects of nitrogen fertilization and maturity of bromegrass on nitrogen and amino acid utilization by cows.

Four nonlactating Holstein cows (593 kg) with ruminal cannulas were fed bromegrass hay that was fertilized with 0 or 89 kg of N/ha and harvested in the late-boot or full-head stage of maturity. Total tract apparent digestibility of N was less for full-head than for late-boot bromegrass (48 vs 64%; P less than .01) and was greater for N-fertilized than for unfertilized bromegrass (60 vs 52%, P less than .01). True N digestibility was greater (P less than .01) by cows fed late-boot hay than by those fed full-head bromegrass (85 vs 81%). Maturity did not affect N retention. Nitrogen fertilization increased N retained, both grams per day (70 vs 20; P less than .01) and as a percentage of N intake (P less than .01). Nitrogen and amino acid disappearance kinetics were determined in situ. Rate constants for N disappearance within rapidly and slowly degraded pools were not different among treatments, but because late-boot had a larger proportion of N in the rapidly degraded pool, overall disappearance rate for N was faster (P less than .05) for late-boot than for full-head bromegrass (12.0 vs 7.1 %/h). Treatment effects observed for individual amino acids were similar to those found for N. Both composition and kinetic data were needed to explain differences in N digestion and balance. Distribution of N within the forage had profound effects on the N economy of the cows.

Amino Acids↗
PubMed1998

Nitrogen utilization in pigs fed diets with soybean and rapeseed products leading to different ileal endogenous nitrogen losses.

Nitrogen (N) balance was determined in 36 pigs (BW 24 to 30 kg) fed diets inducing different ileal endogenous N losses (ENL). We tested the hypothesis that enhanced ENL may be indicative of a higher recycling of endogenous proteins that will induce a greater urinary N loss and a lower efficiency of the dietary N utilization for retention. The cornstarch-based diets contained either soy concentrate (SC), soybean meal (SBM), a mixture of toasted and untoasted soybean meal (mSBM), dehulled-toasted rapeseed cake (RC1), non-dehulled-toasted rapeseed cake (RC2), or dehulled-untoasted rapeseed cake (RC3). The diets were balanced for their content of apparent ileal digestible (ID) CP (108 g/kg feed) and apparent ID of Lys, Thr, Met+Cys, Trp, and Ile. Feeding level was 2.7 times ME for maintenance per kilogram BWx75 and restricted to 88% of the requirements for ID Lys as the first-limiting amino acid. During a 5-d period, urine and feces were collected daily in metabolism cages. Compared with the SC diet (low ENL), the diets with SBM (medium ENL) and mSBM (high ENL) resulted in a greater (P < .05) urinary N excretion. Nitrogen retention tended to be less (P = .08) in pigs fed diets that caused greater ENL. The utilization of ID N for retention in pigs fed the mSBM diet was lower (P < .05) than for those fed the SC diet. There were no differences in urinary N excretion, N retention, and the utilization of ID N for retention in pigs fed the rapeseed diets of different fiber contents (hulls as the NDF source). We concluded that, at similar intakes of the first-limiting ID amino acid, N retention in pigs fed soybeans tended to be reduced by greater ENL as induced by antinutritional factors (e.g., trypsin inhibitors). Rapeseed hulls, as the predominant fiber source, do not affect N retention and the utilization of ID N for retention.

Amino Acids↗
PubMed2006

Effect of various levels of imbalance between energy and nitrogen release in the rumen on microbial protein synthesis and nitrogen metabolism in growing double-muscled Belgian Blue bulls fed a corn silage-based diet.

Seven double-muscled Belgian Blue bulls (initial BW: 341 +/- 21 kg) with cannulas in the rumen and proximal duodenum were used in an incomplete replicated Latin square. The study examined the effect of imbalance between energy and N in the rumen on microbial protein synthesis and N metabolism by giving the same diet according to 3 different feeding patterns. The feed ingredients of the diet were separated into 2 groups supplying the same amount of fermentable OM (FOM) but characterized by different levels of ruminally degradable N (RDN). The first group primarily provided energy for the ruminal microbes (12.5 g of RDN/kg of FOM), whereas the second provided greater N (33.3 g of RDN/kg of FOM). These 2 groups were fed to the bulls in different combinations with the aim of creating 3 levels of imbalance (0, 20, and 40 g/ kg of DM) between energy and N supplies in the rumen. Imbalance was measured by the variation of the degradable protein balance (OEB value in the Dutch system) of the diet between the 2 meals each a day. Diurnal variations in ruminal NH3-N concentrations and plasma urea concentrations were greatly influenced by the feeding patterns of the diet. Introduction of imbalance affected neither microbial N flow at the duodenum (P = 0.97) nor efficiency of growth (P = 0.54). The feeding patterns of the diet had no negative impact on NDF degradation in the rumen (P = 0.33). Nitrogen retention was not affected by imbalance (P = 0.74) and reached 49.7, 52.0, and 51.3 g/d, respectively for 0, 20, and 40 g of OEB/kg of DM imbalance. It seems that introduction of an imbalance between energy and N supplies for the ruminal microbes by altering the feeding pattern of the same diet does not negatively influence the microbial activity in the rumen nor N retention of the animal. Nitrogen recycling in the rumen plays a major role in regulating the amount of ruminally available N and allows a continuous synchronization of N and energy-yielding substrates for the microorganisms in the rumen. Therefore, imbalance between dietary energy and N created over a 24-h interval was not detrimental to rumen microbial growth for the animal as long as the level of imbalance did not exceed 40 g of OEB/kg of DM. Thus, these feeding patterns of the diet can be used under practical feeding conditions with minimal impact on the performance of ruminant animals for meat production.

Animal Nutritional Physiological Phenomena↗
PubMed1987

Nitrogen metabolism in crossbred steers with varying levels of Brahman using a nitrogen depletion-repletion regimen.

Nine N metabolism trials were conducted in a N-depletion-repletion regimen using five breed crosses of steers with 0, 25 or 50% Brahman. Three steers from each breed cross (avg initial wt 239 kg) were standardized for 3 wk on an 18% protein diet and depleted for 5 wk on a 7.5% protein diet and then repleted for 4 wk on the 18% protein diet. Nitrogen balance and blood and urinary N metabolites were monitored to determine changes in metabolic status due to changes in dietary N intake. Reduced N intake during the depletion period almost completely inhibited fiber digestion (P less than .01), while ruminal ammonia concentration fell from an average concentration of 156 during standardization to 22 mg/liter (P less than .01) during depletion. Organic matter digestion was depressed (P less than .05) due to the reduced fiber digestion. Absolute amounts of intake, fecal, urinary, absorbed and retained N were severely depressed during depletion. Apparent digestibility of N was reduced from an average of 68% during standardization to 42% (P less than .05) during depletion, but truly digested N was not affected. Nitrogen retained, as a percentage of intake, or absorbed was reduced only during the first week of depletion. Urea N comprised the major identified urinary fraction during standardization and repletion, whereas creatinine was the major fraction during depletion. Brahman-cross steers excreted more urinary N (P less than .1) and retained less N (P less than .13) during repletion than Angus X Hereford steers. Creatinine excretion was also higher (P less than .01) during depletion for Brahman-cross steers. Blood urea and albumin N concentrations were higher (P less than .05) during both depletion and repletion among Brahman crosses. These experiments suggest that blood measurements were more sensitive than N balance to changes in dietary N state and that faster recharge of blood N measurements in Brahman cattle may help mitigate adverse effects of N depletion stress.

Animals↗
PubMed2002

Evaluation of models to estimate urinary nitrogen and expected milk urea nitrogen.

Milk urea nitrogen (MUN) has been introduced as a means to estimate urinary nitrogen (N) excretion and protein status of dairy cattle. For Holstein cows, the amount of urinary N excreted (g/d) was originally reported to be 12.54 x MUN (mg/dl), but recently urinary N (g/d) was reported to equal 17.64 x MUN (mg/dl). The objectives of the present study were to evaluate models to predict urinary N and expected MUN, by using older and newer data sets, and to quantify changes that may have occurred in MUN measurements over time. Two data sets were used for model evaluation. Data set 1 was from the spring of 1998 and data set 2 was from the spring of 1999. Similar cows and diets were used in both studies. By using data set 1, the newer model underestimated MUN by an average of 3.8 mg/dl, whereas the older model was accurate. By using data set 2, the older model overestimated MUN by 4.8 mg/ dl, but the newer model was accurate. In the period between the two studies, the MUN measured appeared to decrease by an average of 4.0 mg/dl. By using current wet chemistry methods to analyze for MUN, urinary N (mg/dl) can be predicted as 0.026 x MUN (mg/dl) x body weight (kg). Because of changes in methodology that occurred in the fall of 1998, target MUN concentrations have decreased to 8.5 to 11.5 mg/dl for most dairy herds compared with previous target concentrations of 12 to 16 mg/dl.

Animals↗
PubMed1975

Nitrogen metabolism in bears: urea metabolism in summer starvation and in winter sleep and role of urinary bladder in water and nitrogen conservation.

Three bears were studied under conditions of (1) no food but access to water for 2 weeks and (2) no food or water for 3 weeks. During starvation in summer, the bears could not inhibit the net production of urea but used lean body mass; when denied access to water as well, the bears became dehydrated and azotemic. Urea was continuously formed and degraded in the winter. Arginase activity in liver increased in winter sleep; hepatic steatosis and inflammatory reactions were also noted. The urinary bladder readsorbed labeled urea and D20 in winter; the rate of absorption of urea was equal to the rate of excretion of it into the bladder. The ability to preserve lean body mass during winter sleep apparently is a special mechanism associated with the induction of winter sleep. Bears cannot duplicate this feat during summertime starvation. In winter sleep, urea is formed and degraded but the nitrogen produced is conserved in some manner that maintains the total nitrogen pool constant. The urinary bladder plays a central role in maintaining the state of winter sleep by absorbing water and solute at a rate equal to their entry into the urinary bladder.

Animals↗
PubMed1975

Metabolic effects of antisickling amounts of nitrogen and nor-nitrogen mustard on rabbit and human erythrocytes.

Nitrogen mustard (NH2) and Nor-nitrogen mustard (Nor-HN2) both inhibit the polymerization of deoxyhemoglobin S in solution and in intact erythrocytes. Metabolic studies were undertaken to determine the feasability of an extracorporeal treatment with these or related agents. Glucose utilization, hexose monophosphate shunt activity, methemoglobin reduction, and incubation with acetylphenylhydrazine for Heinz body formation were performed, as well as specific assays for hexokinase, pyruvate kinase, glucose-6-phosphate dehydrogenase, glutathione reductase, ATP, reduced glutathione (GSH), and survival of autologous mustard-treated cells in rabbits. HN2 was found to enter red cells rapidly and bind to intracellular contents. Metabolic studies revealed no significant inhibition or alteration of function by Nor-HN2 at 10 mg/ml of whole blood. Rabbit red cell survival was also normal. HN2, however, inhibited glutathione reductase and blocked the free sulfhydryl group of GSH by forming serveral addition products of alkylated GSH. Heinz body test with acetylphenylhydrazine became positive in HN2-treated cells, and rabbit red cell survival was shortened considerably in the concentration range used to inhibit sickling. Ascorbic acid stimulation of the hexose shunt pathway was inhibited by HN2, but methylene blue stimulation remained unaffected. 14-C-HN2 remains bound to red cells in vivo, and the disappearance of radioactivity is similar to that found with 14-C-DFP (disopropylfluorophosphate). Oxygen affinity of both HN2 and Nor-HN2 treated human red cells remains virtually the same as that found in control samples. It is concluded that Nor-HN2 may be a suitable agent for an extracorporeal therapy, and that each mustard needs to be evaluated individually for its antisickling effects and its suitability for extracorporeal use.

Animals↗
PubMed1975

Metabolic changes in newborn infants following surgical operations. I. Blood levels of glucose, plasma free fatty acids, alpha-amino nitrogen, plasma amino acid ratio and urea nitrogen.

In 29 newborn infants subjected to surgery for congenital anomalies, the blood glucose, free fatty acid (FFA), amino acid, alpha-amino nitrogen and blood urea levels were observed from the first to the seventh postoperative days. The blood glucose level showed moderate changes in the postoperative period, while FFA decreased significantly. The combined concentration of non-essential amino acids (glycine + glutamine + serine + taurine) and that of essential amino acids (leucine + isoleucine + valine + methionine), their quotient (Whitehead's ratio), as well as the alpha-amino nitrogen level indicated dynamic changes in the postoperative period. The gradual return of blood urea to the preoperative level is explained by the diminished breakdown and the improved excretory function of the kidney following surgical procedures.

Amino Acids↗
PubMedDate not supplied

Determination of nitrogen- and phosphorus-containing pesticide residues in vegetables by gas chromatography with nitrogen-phosphorus and flame photometric detection after gel permeation chromatography and a two-step minicolumn cleanup.

An efficient and reliable multiresidue method for determining pesticide residues in a large number of vegetable samples was studied. First, the important target compounds for monitoring, 52 nitrogen- and/or phosphorus-containing pesticides, were selected. The sample was extracted with acetonitrile, and the separated acetonitrile layer was cleaned up by a salting-out step. The acetonitrile extract was purified by gel permeation chromatography that divided the pesticide eluate into 2 fractions; the pesticide fractions were respectively purified by a 2-step minicolumn cleanup in which the second pesticide fraction was loaded on a silica-gel minicolumn. After a Florisil minicolumn was inserted on the silica-gel minicolumn, the first pesticide fraction was loaded on the tandem minicolumn, which was eluted with acetone-petroleum ether (3 + 7). The combined eluate was subjected to dual-column gas chromatography (GC) with nitrogen-phosphorus and flame photometric detection. By application of the optimum cleanup conditions to the 52 pesticides selected, good resolution and low breakdown levels of the pesticides during GC were maintained. Recoveries of the 52 pesticides from fortified cabbage, lettuce, spring onion, and spinach ranged from 72 to 108% with relative standard deviations of 2-17%, except for the recoveries of methamidophos and chlorothalonil. The detection limits of the pesticides were satisfactory (0.001-0.009 mg/kg) for monitoring pesticide residues in vegetables.

Chromatography, Gas↗
PubMed2003

[Ammonia volatilization loss of nitrogen fertilizer from rice field and wet deposition of atmospheric nitrogen in rice growing season].

Plot and field experiments showed that the NH3 volatilization loss from rice field reached its maximum in 1-3 days after N-fertilization, which was affected by the local climate conditions (e.g., sun illumination, temperature, humidity, wind speed, and rainfall), fertilization time, and ammonium concentration in surface water of the rice field. The wet deposition of atmospheric nitrogen was correlated with the application rate of N fertilizer and the rainfall. The amount of nitrogen brought into soil or surface water by the wet deposition in rice growing season reached 7.5 kg.hm-2. The percent of NH4(+)-N in the wet deposition was about 39.8%-73.2%, with an average of 55.5%. There was a significant correlation of total ammonia volatilization loss with the average concentration of NH4(+)-N in wet deposition and total amount of wet deposition in rice growing season.

Ammonia↗