Persulfate Digestion Research Articles

Nitrate and organic N analyses with second-derivative spectroscopy

Simple and reliable procedures have been developed for analyses of N03-, total N, and organic N in freshwaters. NO,is determined by second-derivative UV spectroscopy. Total N and organic N are determined based on secondderivative analyses of NO,following persulfate digestion. Resolution of organic N determinations was increased by using ion-exchange resins to remove NO,from samples with high concentrations of N03prior to persulfate oxidation of the organic N. Although numerous methods have been developed for the determination of N in aqueous samples, there is continued need for simple and reliable procedures for both inorganic and organic N analyses. The most widely accepted methods for N03analysis include Cd reduction and ion chromatography (Am. Public Health Assoc. 1989). Both methods have been adapted for automated analysis and, with proper consideration of potential interferences, both are accurate and precise. Ion chromatography has the advantage of also measuring several additional anions in a single aliquot of samAcknowledgments This work was supported in part by the Iowa State Water Resour. Res. Inst., the Iowa DNR, the U.S. EPA, and Wetlands Res. Inc., Chicago, Illinois. We thank Iowa State University staff and researchers for their contributions to this research. Automated Cd reduction analyses were performed by the Analytical Services Laboratory (Iowa State Univ. Eng. Res. Inst.) and by the U.S. EPA ERL, Duluth, Minnesota. ple. Ion chromatography and Cd reduction, however, are relatively complicated and expensive. Samples must normally be filtered to remove suspended matter before analysis, and in the case of Cd reduction, sample color, metal ions, and phosphate are potential interferences (Olson 1980). The principal methods for organic N determination are based on conversion of organic N to NH,+ or N03and subsequent analysis of these inorganic forms. Separate analysis of ambient inorganic N allows organic N levels to be calculated by difference. For freshwater samples, conversion of organic N to inorganic forms is most commonly based on either Kjeldahl digestion (U.S. EPA 1979; Am. Public Health Assoc. 1989), photo-oxidation (Armstrong et al. 1966), or persulfate digestion (Koroleff 1976; D’Elia et al. 1977; Solorzano and Sharp 1980). Photo-oxidation requires more specialized equipment and may be ineffective for some compounds (Henriksen 1970). Kjeldahl digestion is a complicated and expensive procedure and may be unsuitable for systems receiving high inorganic N loads. High concentrations of N03severely interfere with standard Kjeldahl N determinations (Schlueter 1977; U.S. EPA 1979; Am. Public Health Assoc. 1989). N03--N concentrations 10-20 times greater than those of organic N result in >90% inhibition of Kjeldahl N determinations (Schlue-

Measurement of total dissolved phosphorus in small volumes of iron rich interstitial water

It is shown that sorption of orthophosphate to iron compounds, formed during persulfate digestion, can cause a significant underestimation of total dissolved phosphorus in interstitial waters rich in iron and poor in phosphorus. Labelling the samples with carrier free32PO4 before digestion allows to correct for these losses.

Automated determination of total phosphorus in aqueous samples

The determination of total phosphorus in an automated microbatch analyzer system is described. The procedure combines persulfate digestion of the sample and colorimetric detection of orthophosphate by the ascorbic acid reduction of phosphomolybdate in a single processing chamber. Approximately 9 min are required per sample; ∼ 1.7 ml of sample and 0.17 ml of total reagent are consumed. The limit of detection is ⩽10 μg/1. phosphorus. The method is tolerant of variations in salinity of the sample. Good agreements with ASTM procedures are shown for a variety of test compounds, lake water, wastewater and urine samples.

Algal use of sedimentary phosphorus from an Amazon floodplain lake: Implications for total phosphorus analysis in turbid waters

Chemical forms of P and their availabilities to Selenastrum capricornutum were measured in sediments collected from Lago Calado, an Amazon floodplain lake. Postbioassay analysis confirmed that Selenastrum used ∼60– 70% of the P in the NaOH‐extracted fraction during a 9‐d incubation. No evidence for algal use of Ca‐bound P or organic P was found. Methodological comparisons revealed that persulfate digestion may not adequately recover algal‐available particulate P in waters high in inorganic turbidity. An average of 26% of the agal‐available P in Amazon River water was in particulate form.

Simultaneous determination of total nitrogen and total phosphorus in freshwater samples using persulfate digestion

The accuracy and precision of total nitrogen (T‐N) and total phosphorus (T‐P) determinations in freshwater samples by the simultaneous digestion method using an oxidizing reagent solution of NaOH‐K2S2O8 were assessed. Detection limits based on the blank test of nitrogen and phosphorus were 0.02 mgN/1 and 0.001 mgP/1, respectively. This simultaneous digestion method gave not only a high recovery and reproducibility over a wide range of various nitrogen and/or phosphorus compounds of known nitrogen and phosphorus compositions, but also high recoveries of nitrogen and phosphorus from standard reference materials, such as orchard leaves, pond sediment and chlorella. No significant difference was found between the determinations of T‐N and T‐P in freshwater samples by this method and those determined by the standard methods of T‐N and T‐P, respectively. This method should be useful for the routine analysis of T‐N and T‐P in freshwater samples containing particulate material and samples of low T‐N and/or T‐P co...

Comparison of Methods for the Preparation of Sewage Sludge Samples Prior to the Spectrophotometric Determination of Phosphorus

Abstract Three procedures for the preparation of sewage sludge samples prior to the colorimetric determination of phosphorus as “molybdenum blue” were evaluated. Using samples of the US EPA's municipal digested sludge as a reference material, sulfuric acid/ammonium persulfate digestion, muffle furnace ignition followed by extraction of the ash with hydrochloric acid, and direct extraction of the sewage sludge with sodium bicarbonate solution were compared in terms of phosphorus recovery as determined by colorimetric measurements. On the basisof phosphorus recovery, the samples prepared by muffle furnace ignition/hydrochloric acid extraction of the ash showed the best accuracy and precision. This procedure was also superior in terms of the time and effort expended in the preparation of the sewage sludge samples.

Determination of total nitrogen in sediments and plants using persulfate digestion. An evaluation and comparison with the Kjeldahl procedure

Accuracy and precision of the persulfate and Kjeldahl determinations of total nitrogen in solid samples were assessed with certified standards, plant material and river sediments. Accuracy determined with the certified reference materials was within an acceptable range to assure quality control for routine laboratory analyses. In addition, results obtained by examining plant samples indicated that TPN and TKN were not significantly different. Precision for analyses of all samples was high; however a direct comparison of plant material indicated that TPN (RSD = 5.3%) was more precise than TKN (RSD = 8.4%). TPN is a reasonable alternative to the standard TKN procedure for analysis of sediment and plant materials. The TPN method would increase the feasibility of conducting replicate analyses and would result in increased quality control.

Evaluation of a persulfate digestion method for particulate nitrogen and phosphorus

A persulfate digestion method for particulate nitrogen and phosphorus in aufwuchs suspensions was tested on two types of dried materials (orchard leaves and aufwuchs) and samples from a freshwater microcosm. Recoveries ranged from 80–100% depending on the reference material composition, and coefficients of variation were from 1.3–26.8% for nitrogen and 0.3–9.3% for phosphorus. The ease of the persulfate method is an advantage over the Kjeldahl procedure and in addition, the method appears to be well suited for analysis of particulate nitrogen and phosphorus in freshwater aufwuchs communities.

A comparison of a persulfate digestion and the Kjeldahl procedure for determination of total nitrogen in freshwater samples

Precision and accuracy of the persulfate and Kjeldahl determinations of total nitrogen were assessed on 20 standards of known nitrogen concentrations and samples collected from a variety of aquatic habitats. The persulfate method was more precise than the Kjeldahl method for both sets of samples; accuracy and recovery of nitrogen from the samples were the same. Persulfate determinations should find wide application in laboratories analyzing freshwater samples for total nitrogen.

Use of ultraviolet spectrophotometric determination of nitrate for the determination of total nitrogen in environmental water samples using alkaline persulfate digestion

Use of ultraviolet spectrophotometric determination of nitrate for the determination of total nitrogen in environmental water samples using alkaline persulfate digestion

INFLOW-OUTFLOW OF NUTRIENTS AND SEDIMENT FOR A FLOOD- AND A SPRINKLER-IRRIGATED WATERSHED IN ALBERTA

Nutrients and sediment were monitored in irrigation supply and in the drainage waters associated with a flood- and a sprinkler-irrigated watershed. NO3-N concentrations in runoff from the flood-irrigated farm ranged from 1.38 mg/liter in 1975 to 1.60 mg/liter in 1976. Rapid transformations in a drain channel reduced these by 90% after the water travelled 2.5 km in the drain. P concentrations were also reduced in the runoff water in the drain channel. At the basin outlets, the concentrations were only marginally higher than in the supply water. NO3-N discharged at the basin outlet represented 0.5 kg/ha/yr for flood-irrigated land and 0.7 kg/ha/yr for sprinkler-irrigated land. Corresponding total-P exports computed from the persulfate digestion method were 0.2 and 0.3 kg/ha/hr. Exports represented about 1.5% of fertilizer-applied N and 1.0% of the applied P in each basin. Sprinkler irrigation resulted in a net inflow of suspended sediment whereas on flood irrigation, sediment inflow and outflow were about equal. Total-P concentrations by the perchloric digestion method were about twice as high as those determined by the persulfate method, confirming that the persulfate method does not remove all the P adsorbed to sediment.

Determination of total nitrogen in aqueous samples using persulfate digestion1

Determination of total nitrogen in aqueous samples after potassium persulfate digestion compared favorably in both precision and nitrogen recovery with determinations obtained using Kjeldahl digestion.

Simplified Kjeldahl nitrogen determination for seawater by a semiautomated persulfate digestion method.

Simplified Kjeldahl nitrogen determination for seawater by a semiautomated persulfate digestion method.

A semiautomated procedure for the determination of phosphorus in water, waste waters and particulates

Improved procedures for the determination of total dissolved phosphorus (TDP), particulate phosphorus (PP) and dissolved inorganic orthophosphate (DP) are described. Organic particulate material is solubilized in 5 n NaOH, and phosphorus compounds are oxidized and mineralized to orthophosphate by persulfate digestion. DP is determined by an improved automated molybdenum blue procedure that does not require sample pH adjustment or a correction for silicate interference in the 0–50 mg Si 1 −1 range. The use of 36-position digestion racks allows 32 TDP or PP samples to be digested in ca. 1 and 4 h respectively. Detection limits in μg of phosphorus 1 −1 are DP, 2; TDP, 5; and PP. 1. Waste water samples were analyzed for TDP and PP by the nitric acid-sulfuric acid procedure and by the proposed method. There was no significant difference between the two sets of data (P > 0.45).

Comparison of Methods for the Determination of Total Phosphorus in Waters Containing Particulate Material

AbstractPerchloric acid digestion compared favorably with Na2CO3 fusion for the determination of total P in a range of waters containing varying concentrations of both P and particulate material. The recovery of particulate P by persulfate digestion tended to decrease with increasing particulate material concentration in both natural unfiltered samples and in filtered samples to which particulate material was added. Recovery of added soil particulate P by persulfate digestion also decreased with increasing particle size. Low recovery of P by persulfate digestion was caused by the incomplete extraction of P occluded within oxides and hydrous oxides of iron. Between 58 and 86% of the P not recovered by persulfate digestion was in the inorganic form. Persulfate digestion is not recommended for the determination of total P in waters containing particulate inorganic materials of soil origin. Perchloric acid digestion is considered to be a more suitable method for such samples.

Determination of particulate phosphorus by alkaline persulfate digestion.

Determination of particulate phosphorus by alkaline persulfate digestion.