Filterable reactive phosphorus

Maher, W. and L. Woo. 1998. Procedures for the storage and digestion of natural waters for the determination of filterable reactive phosphorus, total filterable phosphorus and total phosphorus. Anal. Chim. Acta 375 5 -7. 

We noted earlier that mass spectrometry had not been used to any extent in speciation studies of organic phosphorus in natural environments. Here we define phosphorus speciation as the determination of actual molecular formulas and structures of molecules containing phosphorus, and not the more commonly accepted, broad classes of phosphorus such as filterable reactive phosphorus, total filterable phosphorus, filterable organic phosphorus, etc. While a few studies have focused on particular classes of organic phosphorus, such as the inositol phosphates, we are not aware of any attempt to broadly speciate... 

Enzymes that cleave phosphate from certain organic molecules may not be produced principally to satisfy a phosphorus limitation (Bjorkman and Karl, 1994). For example, the enzyme 5 -nucleotidase recognizes the C-N group of DNA and RNA, yet it has been shown to release significant amounts of phosphate (Benitez-Nelson and Buesseler, 1999). Benitez-Nelson and Bues-seler (1999) found rapid rates of turnover for filterable reactive phosphorus and filterable... 

Fig. 16.1. Seasonal variation of carbon-to-phosphorus ratio in organic material collected in a sediment trap at 20 m depth in Lake Sempach, Switzerland (upper panel) and seasonal variation in filterable reactive phosphorus (FRP) concentration observed at 10 m depth in Lake Sempach (lower panel). The carbon-to-phosphorus ratio is significantly higher than the Redfield ratio of 106 1 (dashed line) during periods of low filterable reactive phosphorus. Reproduced from Hupfer etal. (1995) with permission from Birkhauser Verlag.

Figure 8.2 shows the commonly analyzed fractions of phosphorus that can be determined depending on which sample pretreatment procedure is employed. Of these fractions, total phosphorus (TP) and filterable reactive phosphorus (FRP) are perhaps the most... 

Preliminary sample treatment often involves filtration, which helps to "arbitrarily" separate the particulate and the dissolved phases. Filtration is required to obtain filterable reactive and total filterable reactive phosphorus and is highly recommended at site just... 

However, the nature of the filtrate is ultimately dependent on the nature of the membrane used, the conditions under which the filtration is performed, and the nature of the sample itself, and for these reasons, the use of the terms soluble and dissolved reactive phosphorus is misleading. A less ambiguous nomenclature would be the use of the term filterable reactive phosphorus membrane pore size ( xm)), e.g., FRF (0.2) where a 0.2 xm filter was used. 

Transport of contaminants by surface runoff is illustrated in the experimental results of Turner et al. (2004), which deal with the colloid-mediated transfer of phosphorus (P) from a calcareous agricultural land to watercourses. Colloidal molybdate-reactive phosphorus (MRP) was identified by ultrafiltration associated with particles between l am and Inm in diameter. Colloidal P compounds can constitute a substantial component of the filterable MRP in soil solution and include primary and secondary P minerals, P occluded or adsorbed on or within mineral or organic particles, and biocolloids (Kretzschmar et al. 1999). 

For many scientists involved in the analysis of phosphorus in water, sediment and soil, the only available techniques depend on the colorimetric determination of molybdate-reactive phosphorus, and that which can be made reactive during a digestion step. Molybdate-reactive phosphorus in filtered samples is generally equated to inor-... 

The phosphorus concentration in each operationally defined fraction is typically detected using the phosphomolybdate-blue colorimetric reaction and spectrophoto-metric detection (American Public Health Association, 1995), with or without pre-treatment and/or filtration. The term total phosphorus applies to samples subjected to hydrolysis and/or oxidation pretreatment intended to convert all forms of phosphorus to phosphate (Maher and Woo, 1998 Monaghan and Ruttenberg, 1999). Phosphorus that reacts with molybdate in untreated samples is referred to as reactive phosphorus . Samples may be unfiltered or filtered. When samples are unfiltered, the operationally defined fractions are total... 

Because of the time and labor involved in algal assays, FRP (0.45 or 0.2 pm) has often been used as a surrogate for readily BAP, and TP (which includes the particulate, condensed, and organic phosphorus components) as a measure of potentially BAP. However, a number of studies have shown that neither FRP nor TP correlate well with algal assay-measured BAP. This may be because FRP tends to overestimate the true orthophosphate due to hydrolysis of labile organic and condensed species. Use of ultrafiltration through a low molecular mass filter prior to measurement of reactive phosphorus has been proposed as better estimator of BAP than other available chemical methods. 

Enhanced sensitivity in the determination of reactive phosphorus in seawater has been achieved by extracting PMB from volumes of up to 1000 L onto a synthetic acrylic cation exchange medium (Acrilan) using a 2 L volume of the resin fibers. Filterable unreactive phosphorus was adsorbed to Fe(III) hydroxide coated acryhc fibers in a similar manner [168]. While the extraction efficiency of this technique was >95%, it appears not to have been exploited to gain maximum sensitivity. 

Enameled reactor 4 with inverse cooler 5, an agitator and a jacket is filled with a solution of quinoline in chlorobenzene from agitator 3 and loaded with ammonia chloride and phosphorus pentachloride through a hatch. The synthesis is conducted at 128-130 °C until the quantity of released hydrogen chloride is noticeably reduced. Hydrogen chloride is absorbed with water in packed tower 7. After the process is finished, the reactive mixture is cooled and filtered in nutsch filter 8 to separate muriatic quinoline and the excess of ammonia chloride. Phosphonitrilechloride can also be conducted in tetrachloroethane medium in this case the process is carried out at 135-140 °C. 

Table 1 Specification scheme for phosphorus (P) based on determination of molybdate reactive (R), phosphorus in total (T), filterable (F), and particulate (P) forms O and C designate organic and condensed forms, respectively...

Major differences in size (filterable, particulate) and chemical reactivity (condensed, organic) of phosphorus forms in samples can be used as the basis for speciation, as shown in Table 1. Of these fractions, total phosphorus (TP) and FRP are perhaps the most commonly measured, although it is arguable that the understanding of the aquatic phosphorus cycle is somewhat lopsided because of that bias. For example, wastewater discharge licenses often specify a maximum permissible concentration of TP, and provide an indication of the maximum potentially bioavailable phosphorus discharged. However, FRP, comprising mostly orthophosphate, is a measure of the amount of most readily bioavailable phosphorus. 

Red phosphorus is a term used to describe a variety of different forms, some of which are crystalline and all of which are more or less red in colour [1,3,40]. They show a range of densities from about 2.0 to 2.4 g/cc, and melting points in the range 585-610°C. The stabilities and reactivities of these red forms lie between those of the white and black forms, although they resemble the latter more closely. The vapour pressure of the red is much less than that of the white (Table 4.4). Samples of red phosphorus usually vaporise at about 450°C under atmospheric pressure. Purification of the red variety can be effected by boiling with distilled water followed by filtering and washing with cold [41]. 

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