Phosphate determination manifold

The sample is inserted simultaneously with the reagents required for a given determination thereafter, it is inserted again but with the reagents required for the second determination. In this way, sequential determinations are performed in the same manifold. This approach was exploited initially in the spectrophotometric determinations of ammonium and phosphate in plant digests [20], which required rather different reaction conditions the ammonium determination was carried out in a highly alkaline medium, whereas the phosphate determination was performed... 

Figure 2.5. Analytical manifolds for the determination of phosphate by flow injection analysis (a) and reverse flow injection (b). The symbols S, M, and A are the seawater, mixed reagent, and the ascorbic acid solutions. The pump injection valve and detector are represented by P, I, and D, respectively. W = waste. From [177]... 

Eberlein and Kattner [194] described an automated method for the determination of orthophosphate and total dissolved phosphorus in the marine environment. Separate aliquots of filtered seawater samples were used for the determination orthophosphate and total dissolved phosphorus in the concentration range 0.01-5 xg/l phosphorus. The digestion mixture for total dissolved phosphorus consisted of sodium hydroxide (1.5 g), potassium peroxidisulfate (5 g) and boric acid (3 g) dissolved in doubly distilled water (100 ml). Seawater samples (50 ml) were mixed with the digestion reagent, heated under pressure at 115-120 °C for 2 h, cooled, and stored before determination in the autoanalyser system. For total phosphorus, extra ascorbic acid was added to the aerosol water of the autoanalyser manifold before the reagents used for the molybdenum blue reaction were added. For measurement of orthophosphate, a phosphate working reagent composed of sulfuric acid, ammonium molyb-... 

The extraction method of Hislop and Cooke (1968), has been outlined in Chapter 4, Phosphate extractants. A blank determination without soil should be carried out. The autoanalysis manifold is shown in Fig. 5.4. Some adjustments to dilution and/or readout sensitivity may be necessary to handle both... 

Figure 1. The manifold (top) for the determination of phosphate hy FIA. Key P, the pump (Gilson Mini Puls) IV, injection valve (Rheodyne Model 50) D, LED photometer (24) with an IR LED (880-nm maximum emission) and R, recorder. Typical results for a series of standards are shown (hottorn).

A reaction need not go to completion before the sample enters the detector in FIA (15-20). The extent of reaction will be the same in all samples and standards if constant flow rates and sample volumes are maintained. Successful FIA systems have been used in which the extent of reaction was less than 10%. However, the extent of reaction is surprisingly high for many reactions with residence times less than 30 s. The reaction used for the determination of phosphate is greater than 90% complete in less than 15 s (13) even though the manual method calls for at least 5 min for full color development (2). This extent of reaction was accomplished by heating a portion of the manifold to 50 °C. Greater than 90% of the nitrate in seawater is reduced to nitrite in a cadmium reductor in less than 2 s (11, 12). The reaction of nitrite to form an azo dye is complete in less than 15 s (15). 

Figure 2. The manifold for the determination of phosphate in seawater (13). All symbols are as in Figure 1. In addition, 3V is a three-way valve (Rheodyne Model 5301) used to switch between samples and standards.

For simultaneous determinations and /or speciation, different separation/ concentration steps can be implemented in the same manifold, as in, e.g., the determination of nitrogen, phosphorus and potassium in fertilisers [314]. The sample was inserted and passed successively through a dialysis unit and a gas diffusion unit to a flow cell for the spectrophotometric determination of phosphate. The dialysed potassium ions and the diffused gaseous ammonia were collected in specific streams and determined by flame photometry and potentiometry, respectively. 

This innovation generally involves modifications to the operation of the sampler and random access reagent selection, and can be implemented in both segmented and unsegmented flow analysers. For unsegmented flow analysis, the spectrophotometric determination of zinc and phosphate in soil extracts [368] is a good example. Zinc was determined only when phosphate was present at concentrations above a threshold level. The number of determinations required was reduced by 30%. Analogously, an expert flow system was proposed for the turbidimetric determination of chloride and sulphate in natural waters [369]. Both methods were implemented in the same manifold, and the need for sulphate determination was dependent on the chloride concentration determined. 

Figure 4.17. Determination of the reaction rate constant for the oxidation of crotonic acid by potassium permanganate, (a) Manifold used (cf. Figs. 4.15c and 4.16). b, c) Absorbancetime response curves actually recorded. The values of the dispersion coefficient Da were obtained by dispersion experiments. All curves in each set of experiments were recorded consecutively from the same starting point (5 ), with an increasing delay time (td - 7, 8, 9, and 10 s, a-d and a -d ) with the stopped-flow period /s = 20 s (additionally, in each series a single run without stop is included), b) KMn04 (C° = 8.54 x lO"" M) in phosphate buffer in absence of crotonic acid, (c) KMn04 (Cli = 8.54 x lO"" M) in phosphate buffer, crotonic acid (C j = 2.10 x lO"" M) in phosphate buffer, stream B. (From Ref 838 by permission of the American Chemical Society).

Figure 6.3. (a) FIA manifold for spectrophotometric determination of phosphate. The two reagents are premixed in the first coil, whereupon sample is injected (30 ixL). All tubes are 0.5 mm ID. (b) Left record obtained by injecting standards in quadruplicate, containing 5-40 ppm P-PO4 the record to the right shows a scan where the time scale is expanded to show the peak shape when injecting 20 and 40 ppm solutions. Note that it takes only 15 s between sample injection 5 and peak maximum readout / , and another 15 s until the next sample (52) can be injected. Hence, the signal will be below the 1% level before the next readout will be taken, and therefore there is no carryover even at a rate of 120 samples/h. 

Figure 6.9. Readouts for the determination of sulfite in a dilute phosphate buffer solution (0.01 M, pH 6.8) using the manifold system shown in Fig. 6.8. (a) Calibration curve obtained by aspirating thiosulfate standards of 0, 0.25, 0.50, 0.75, 1.00, 1.50, and 2.00 mM prepared in the same buffer solution, b and c) Response signals obtained when monitoring the oxidation of a 1 mM sulfite solution saturated with air, aspirating a sample each minute, to which a catalyst (Cu " ) is added after b) a delay period of 15 min, and (c) at the beginning of the experiment, d) Repetition of the experiment outlined in (b), yet adding 0.01 M EDTA to the sulfite solution at the outset.

Fig.9.2 FI manifold for the spectrophotometric determination of codeine by solvent extraction. P, pump DB. displacement bottle for delivery of chloroform C. carrier, 0.065 M phosphate buffer, pH 6.5 PR, picrate reagent S, sample SG, phase segmentor, EC, extraction coil SP, phase separator, R, restrictor or impediuice coil D, detector, W, waste (233 ] ...

Vitamins, like pharmaceutical substances, can often be determined by UV absorption or electrochemical detection without derivatization. However, vitamins were detennined in a senri-automated manifold by post-column reaction with a coupling reaction with diazotized 5-chloroaniline-2,4-disulphonyl chloride and continuous colorimetric determination of the orange products at 440nm [211]. Post-column derivatization schemes for thiamine and its phosphate esters have also been described [212-214]. 

Some results on using HA in marine chemical investigations are reported. The new modifications of reversed flow-injection manifolds for the determination of dissolved silicate, phosphate, sulfate, sulfide, and manganese(II) in seawater samples and normal flow-injection methods for the determination of total alkalinity, sulfate, and main nutrient-type constituents in interstitial water samples are described. The use of the proposed procedures for obtaining the concentration profiles of some important species in seawater and in interstitial water of marine sediments is shovm. The advantages of FIA techniques for determining the chemical data in a chemical laboratory are demonstrated. 

Phosphate in water may be determined according to a procedure outlined in [9], known as the "molybdenum blue method" It involves the complexation of phosphate with molybdate, with subsequent reduction of the complex with ascorbic acid The result is a complex having an intense blue color The overall reaction rate is limited by the complexation step, with maximum conversion of phosphate to the reduced complex requiring about 10 minutes This analytical procedure has been adapted by many groups for phosphate analysis in flow systems (see, for instance, [2, 10]) In one instance, a system was developed to monitor phosphate concentrations in fermentation broths [11] The flow manifold employed in that application is the model for the phosphate analysis using a stacked system described m this paper... 

FIGURE 1.4 Manifold of a multicommutated flow injection system (MCFA) developed for simultaneous determination of acid phosphatase and alkaline phosphatase activity consisting of substrate/buffer delivery module (a), sample delivery cell module (b), reaction module (c), and detection module (d). V—valves, P—pumps, HC—holding coils, PEDD—paired emitter detector diode, NPP— p-nitrophenyl phosphate, DEA— diethanolamine. (Adapted from Tymecki, L., K. Strzelak, and R. Koncki. 2013. Anal. Chim. Acta 797 57-63.)... 

FIGURE 22.7 A schematic diagram of the SI manifold for enzymatic determination of GSH and GSSG C, carrier (propulsion flow rate of 1.90 mL mim ) - 100 mM phosphate buffer solution (pH 7.0) PP -peristaltic pump SV - solenoid valve HC - holding coil DC - dilution coil S - standard sample RC - reaction coil (fixed in the same water baht) D - spectrophotometric detector W - waste. Chemical conditions DTNB = 3.0 mM DTNB solution GR = 5.0 U/ml enzyme solution (immersed in a water bath thermostatically controlled at 25 °C) NADPH = 1.2 mM NADPH solution. (Adapted from Araujo, A. R. T. S., M. L. M. F. S. Saraiva, and J. L. F. C. Lima. 2008. Talanta 74 1511-1519.)... 

The formation of 2-phenylbenzofuran during the nanosecond laser flash experiment was corroborated by a picosecond study of 8a. A rise time of 2 to 4 ps was determined for the 340 nm transient. A rich fluorescence emission obtained in the nanosecond study was shown to arise from 9 generated during the nanosecond laser excitation pulse. Naphthalene also quenched the formation of 9 at the same rate as the formation of 10, estabhshing that the two primary photoproducts came from the same triplet (i.e., 8a). Thus, for the unsubstituted benzoin phosphates, reaction proceeds exclusively through the triplet manifold... 

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