Instrument for Sequential Analysis of Silicon and Phosphate in Aqueous Solutions

Abstract

Test the silica and phosphate content of a water sample in a single device. In this test method, a first sample of water is subjected to colorimetric analysis in a reaction chamber to perform a "molybdenum blue" test, in which the silica and phosphate in the sample complex with a first reagent. Then, a second reagent is used to make the phosphate complex optically inert, and a third reagent is used to deepen the color of the silica complex. Thereby, the silica content is calculated. Another sample is subjected to colorimetric analysis without using the second reagent to obtain the combined content of silica and phosphate in the said another sample. The value of the phosphate content of the sample is obtained by subtracting the value of the silica content from the value of the combined content of silica and phosphate. The silica content and phosphate content of the sample are reportable.

Description

Technical Field

[0001] The present invention relates to a single instrument for analyzing the amounts of silica and phosphate present in a water sample and a method of operating the single instrument. Background Art

[0002] In at least some industries, there is a need to provide "ultrapure" water, i.e., water that meets very strict purity standards. In manufacturing applications, the electronics, optics, and pharmaceutical industries require "ultrapure" water. The term "ultrapure" can also be found in the power industry, where the standards for the purity of makeup water used to improve the steam, particularly with respect to the silica content, are very high. In the latter case, the makeup water may need to have a silica content below a very low standard, but the phosphate content of the makeup water must also exceed a predetermined minimum standard to maintain the pH value and prevent corrosion.

[0003] In the known prior art, devices are known for determining the silica content using known and recognized international standard tests. However, such devices cannot be used in the same device to monitor the phosphate content such that a single device can provide the analysis of both silica and phosphate.

[0004] Therefore, an unfulfilled objective of the prior art is to provide a single device and method for analyzing both silica and phosphate. Summary of the Invention

[0005] This and other unfulfilled objectives of the prior art are met by a method and a device having a controller programmed to perform the method. In a method of analyzing the silica and phosphate content of a water sample in a single device, the method includes the following steps:

[0006] Providing a water sample to be analyzed in a reaction chamber of the device;

[0007] Obtaining a value of the silica content of the water sample in the device;

[0008] Storing the obtained value of the silica content in a database communicatively coupled to the device;

[0009] Rinsing and refilling the reaction chamber with additional water samples;

[0010] Obtaining a value of the combined silica and phosphate content of the additional water sample in the device;

[0011] Calculating the phosphate content of the additional water sample by comparing the value of the combined silica and phosphate content with a representative value of the silica content stored in the database.

[0012] In some embodiments, the step of providing a water sample to be analyzed is implemented by a sub-step including the following sub-steps:

[0013] Flush the reaction chamber with the water to be sampled by passing the water flow to be sampled through the reaction chamber;

[0014] Stop the water flow to be sampled from passing through the reaction chamber and retain the water sample in the reaction chamber;

[0015] Cause light from a light source to cross the reaction chamber through the water sample and reach a light detector, measure the current generated in the light detector thereby, and store the current as a baseline value in a database.

[0016] In many embodiments, the step of obtaining a value of the silica content of the water sample is implemented by a sub-step including the following sub-steps:

[0017] Add a first reagent to the water sample, the first reagent being selected to react with silica and phosphate in the water sample to produce a colored silica complex and a colored phosphate complex;

[0018] Cause light from a light source to cross the reaction chamber through the water sample containing the colored silica complex and the colored phosphate complex and reach a light detector, measure the current generated in the light detector thereby, and store the current as a first silica value in a database;

[0019] Add a second reagent to the water sample containing the colored silica complex and the colored phosphate complex, the second reagent being selected to react only with the colored phosphate complex, and the colored phosphate complex being converted into an optically inert phosphate moiety;

[0020] Cause light from a light source to cross the reaction chamber through the water sample containing the colored silica complex and the optically inert phosphate moiety and reach a light detector, measure the current generated in the light detector thereby, and store the current as a second silica value in a database;

[0021] Add a third reagent to the water sample containing the colored silica complex and the optically inert phosphate moiety, the third reagent being selected to react only with the colored silica complex, and the colored silica complex being converted into a colored silica complex with a deeper color;

[0022] Cause light from a light source to cross the reaction chamber through the water sample containing the colored silica complex with a deeper color and the optically inert phosphate moiety and reach a light detector, measure the current generated in the light detector thereby, and store the current as a third silica value in a database;

[0023] In a processor communicating with a database, a value of the silica content in a water sample is calculated based on a relationship between a third silica value and at least one of a baseline value, a first silica value, and a second silica value.

[0024] In many embodiments, the step of obtaining a value of the combined content of silica and phosphate in the additional water sample is implemented by a sub-step including the following sub-steps:

[0025] Adding a first reagent to the additional water sample to produce a colored silica complex and a colored phosphate complex;

[0026] Passing light from a light source through the reaction chamber through the water sample containing the colored silica complex and the colored phosphate complex to reach a photodetector, measuring the current generated thereby in the photodetector, and storing the current as a first combined value in the database;

[0027] Adding a third reagent to the additional water sample containing the colored silica complex and the colored phosphate complex, the third reagent being selected to react with the colored silica complex and the colored phosphate complex, and the colored silica complex and the colored phosphate complex being converted into a more deeply colored complex;

[0028] Passing light from a light source through the reaction chamber through the additional water sample containing the more deeply colored complex to reach a photodetector, measuring the current generated thereby in the photodetector, and storing the current as a second combined value in the database;

[0029] In a processor communicating with a database, a value of the combined content of silica and phosphate in the additional water sample is calculated based on a relationship between the second combined value and the first combined value.

[0030] In many embodiments, the step of calculating the phosphate content of the additional water sample is implemented by a sub-step including the following sub-steps:

[0031] Determining a representative value of the silica content by using at least one silica content obtained before or after the combined content of silica and phosphate;

[0032] Obtaining the phosphate content by subtracting the representative value of the silica content from the combined content of silica and phosphate.

[0033] In a preferred embodiment, the first reagent is an aqueous solution of ammonium molybdate and an inorganic acid; the second reagent is an aqueous solution of oxalic acid; the third reagent is an aqueous solution of potassium sulfite and 4-(methylamino)phenol hemisulfate.

[0034] In a preferred embodiment, the light source produces monochromatic light having a wavelength of 815 nm.

[0035] In many embodiments, the step of flushing and refilling the reaction chamber with additional water samples is implemented by sub-steps that include the following sub-steps:

[0036] Flush the reaction chamber with the water sample to be sampled by flowing the water sample to be sampled through the reaction chamber;

[0037] Stop the flow of the water sample to be sampled through the reaction chamber and retain the water sample in the reaction chamber;

[0038] Cause light from a light source to cross the reaction chamber through the water sample and reach a light detector, measure the current generated in the light detector thereby, and store the current as a baseline value in a database.

[0039] An apparatus for implementing a method for analyzing the silica and phosphate content of a water sample in a single device, the apparatus comprising:

[0040] An inlet for receiving a flow of a water sample to be tested;

[0041] An outlet for discharging the water sample after testing;

[0042] A flow conduit providing a liquid flow path from the inlet to the outlet;

[0043] A reaction chamber located in the flow conduit, sized to retain a predetermined volume of the water sample, and the reaction chamber comprising:

[0044] A sample inlet in liquid communication with the inlet;

[0045] A sample outlet in liquid communication with the outlet;

[0046] A plurality of reagent inlets;

[0047] A colorimetric device comprising: a window through which light is directed into the volume of the reaction chamber; a reflector for reflecting light incident thereon back into the volume of the reaction chamber; a window through which the reflected light passes and is received by a light detector;

[0048] A valve for controlling the flow into the reaction chamber through the flow conduit;

[0049] A plurality of reagent delivery systems, each reagent delivery system in fluid communication with one of the plurality of reagent inlets;

[0050] A processor in communication with the colorimetric device, the valve, and the plurality of reagent delivery systems, programmed to operate the device according to the method of the present invention.

[0051] Many embodiments of the apparatus will also include: a heater located in the flow conduit between the inlet and the valve for selectively heating the water sample passing therethrough.

[0052] In many embodiments, each reagent delivery system includes a reagent container and a metering pump that is selectively actuated by a processor to provide a predetermined amount of a selected reagent to one of the reagent inlets.

[0053] In many embodiments, the apparatus further includes a calibration delivery system that includes a calibration fluid container and a metering pump that is selectively actuated by a processor to provide a predetermined amount of a selected calibration fluid to a flow conduit upstream of the valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] The inventive concept will be better understood when reference is made to the accompanying drawings and the detailed description, in which like reference numerals identify like parts, and in which:

[0055] FIG. 1 is a schematic diagram of a flow path provided in a silica analysis device known in the prior art;

[0056] Figure 2 is a schematic top view of the interior of the reaction chamber;

[0057] Figure 3 is a schematic diagram of a flow path provided in an apparatus for analyzing both silica and phosphate according to the inventive concept;

[0058] Figure 4 is a flowchart showing an algorithm programmed into the processor of an apparatus incorporating the inventive concept. DETAILED DESCRIPTION

[0059] APPARATUS

[0060] FIG. 1 shows a schematic diagram of a flow path provided by a prior art silica analysis device 10. A valve 20, preferably a needle valve that allows precise flow control, establishes a flow rate within a sample line 22 that continuously receives a portion of a process fluid that can be analyzed. At least a portion of the process fluid passing through the needle valve 20 always flows towards an outlet 26. A float switch 27 near the outlet 26 and the sample line 22 maintains a pressure differential to provide flow within the analysis device 10. If the entry of the process fluid from the sample line 22 into the inlet of the analysis portion of the device 10 is blocked by a valve 24, all of the process fluid flows to the outlet 26. This flow helps to keep the sample line 22 free of contaminants.

[0061] Valve 24 is preferably a multi-port valve, and even more preferably an automatic valve, which controls the flow of fluid into the analysis section of the device 10. In the first position, the process fluid in the sample line 22 is allowed to enter the analysis feed line 28 of the analysis section. In the second position, fluid from the alternative feed line 30 is allowed to enter the analysis feed line 28. The alternative feed line 30 has an insertion point 32 from which artificial samples, calibration standard samples, etc. can be inserted. As shown here, when valve 24 is a three-way valve, it can shut off all flow in the analysis feed line 28, although this function is not typically used.

[0062] The flow rate through the analysis feed line 28 can be confirmed by a flow meter 34, particularly a volumetric flow meter, located between valve 24 and valve 36. The illustrated embodiment shows the flow meter 34 as a gravity flow meter or a rotameter, in which the upward flow of the liquid operates against the downward gravity to balance a floating element in the flow channel, the flow area of which increases from its bottom to its top. In an alternative embodiment, a flow meter that provides a digital output flow signal can be used. In either case, this flow meter 34 checks the flow rate and provides feedback when adjusting the flow rate through valve 20. Valve 36 is preferably a two-way valve, and more preferably an automatic valve, which provides "on / off" control of the flow of sample fluid into the reaction chamber 40.

[0063] In addition to having sample fluid flow through valve 36, the reaction chamber 40 has several inputs. Three of these inputs 42, 44, and 46 are from reagent sources 52, 54, and 56 via metering pumps 62, 64, and 66. Typically, these metering pumps 62, 64, and 66 will be peristaltic pumps. The reaction chamber 40 also has an outlet 48 for discharging fluid after analysis. Preferably, the reaction chamber 40 is provided with means for agitation, which are depicted in FIG. 1 as a magnetic stirrer motor 70 and a stir bar 72. In a preferred embodiment, the fluid being sampled enters the lower part of the reaction chamber and is discharged through the overflow line 48.

[0064] Figure 2 A top view of the reaction chamber 40 is shown. Since the test conducted therein is a colorimetric test, the reaction chamber 40 has a first window, a reflector 76 on the opposite wall of the chamber, and a second window for a light detector 78, through which light can be directed from a light source 74 into the first window, and the light detector typically has the nature of a photodiode to collect the light that has passed through the chamber and been reflected off the reflector. This colorimetric test will be described in more detail below. When viewed from the side, it should be noted that the first window for the light source 74, the reflector 76, and the second window for the light detector 78 are at the same height, preferably at approximately half the distance between the inlet line and the overflow line 48.

[0065] Figure 3FIG. 0 shows a schematic view of the flow path provided by a silica analyzer 110 that has been modified to provide analysis of both silica and phosphate, i.e., the concept of the present invention. A valve 20, preferably a needle valve that allows precise flow control, establishes a flow rate within a sample line 22 that continuously receives a portion of the process fluid that can be tested. In the depicted embodiment, valve 20 receives an input from a sequencer 21 that can allow selection of the input from multiple streams. As shown in FIG. 1, at least a portion of the process fluid in sample line 22 always flows towards an outlet 26. If there is no flow at the outlet 26, as determined by, for example, a float switch, the operation of the device stops. If the entry of the process fluid from the sample line 22 into the inlet of the analysis section of the device 10 is blocked by valve 24, all of the process fluid flows to the outlet 26. This flow helps keep the sample line 22 free of contaminants.

[0066] As in prior art embodiments, valve 24 is preferably a three-way valve and even more preferably an automated valve that controls the flow of fluid into the analysis section of the device 110. In a first position, the process fluid in the sample line 22 is allowed to enter an analysis feed line 28 of the analysis section. In a second position, fluid from an alternative feed line 130 is allowed to enter the analysis feed line 28. The alternative feed line 130 in this embodiment feeds from an insertion point 32 where artificial samples, calibration standards, etc. can be inserted. Different from prior art embodiments, the fluid from the insertion point 132 does not flow by gravity to valve 24 but is lifted by a pump 68, preferably a peristaltic pump. In a third position of valve 24, all flow through valve 24 to the analysis feed line 28 can be cut off, although as shown in FIG. 1, this is a function that is not typically used.

[0067] Downstream of valve 24, the analysis feed line 28 is shown passing through a heater 138 to condition the fluid if needed before reaching a valve 136. Although not present in prior art devices, the heater 138 provides the valuable advantages of supporting a reduction in the cycle time for performing the analysis and providing a more consistent temperature for performing the analysis. In this case, valve 136 is described as a two-way valve. In a first position, the flow from the analysis feed line 28 is directed to a reaction chamber 40, while in a second position, the valve can be used to vent the reaction chamber 40 to a discharge line 150.

[0068] Since the same basic reactions will occur in reaction chamber 40 of the improved analyzer 110, it can be seen that it has an effective configuration that is the same as the configuration of analyzer 10 of the prior art in FIG. 1. In addition to the input via valve 136, reaction chamber 40 has inputs 42, 44, and 46 from reagent sources 52, 54, and 56 via metering pumps 62, 64, and 66. Preferred metering pumps 62, 64, and 66 are peristaltic pumps, where the pumped reagent is contained within a flexible tube to prevent contamination. Reaction chamber 40 also has an outlet 48 for discharging fluid after analysis. Preferably, reaction chamber 40 is provided with means for agitation, which are depicted in FIG. 1 as magnetic stirrer motor 70 and stir bar 72.

[0069] The top view of reaction chamber 40 of apparatus 110 is the same as the view shown in Figure 2 the same.

[0070] Chemistry

[0071] The basic chemistry of silica analysis that has been used in prior art apparatus is known and is standardized by ASTM International (ASTM-I: ASTM International), an organization that develops and publishes voluntary consensus technical standards such as ASTM D7126, titled "Standard On-line Colorimetric Measurement of Silica". This method is informally referred to as the "molybdenum blue" or "heteropoly blue" method. ASTM-I states that it can be used to determine silica in water in the range of 0.5 ppb to 5000 ppb. ASTM-I also states that this test method covers the determination of soluble silica SiO2 (silica) or silicate in water. Soluble silica compounds are considered molybdate-reactive silica. This test method does not cover the determination of colloidal silica or polymeric silica, which are considered non-molybdate-reactive silica.

[0072] Referring to the prior art apparatus shown in FIG. 1, the reaction chamber 40 is rinsed by flowing the process fluid to be tested through it. After a specified rinse time, the process fluid of the sample is retained in the reaction chamber as a test sample and the flow is stopped.

[0073] At the end of the stabilization period, monochromatic light is projected from light source 74, passes through the first window, across the reaction chamber where the light is reflected from reflector 76 and passes through the test sample again to be received at light detector 78 in the second window. The light received at light detector 78 is measured by light detector 78 in a measurement referred to as Eb or "blank current". The preferred light source 74 is a light-emitting diode (LED) powered by a fixed current drive power supply to ensure consistent light output during all these steps. For the molybdate complex chemicals used here, the preferred wavelength is 815 nm, and thus, all references in describing the preferred method refer to this wavelength. Although other wavelengths (or multiple wavelengths) can be used, it is clearly preferred to use light source 74 that provides 815 nm light.

[0074] Once Eb is established, a 1 ml sample of reagent 1 is added from reagent source 52 to reaction chamber 40 through pump 62. Reagent 1 contains an aqueous solution of ammonium molybdate and an inorganic acid. At this time, the device for stirring the contents in the reaction chamber may or may not be in operation.

[0075] Reagent 1 immediately reacts with the silica and phosphate present in the test sample. A yellow molybdate complex of silica and phosphate is formed. The reaction is allowed to proceed for a predetermined reaction time. During this step, the molybdate complex formed will absorb a small amount of 815 nm light respectively. The current at light detector 78 is monitored, and the current measured at the end of the reaction period is called E2.

[0076] At this time, a 1 ml sample of reagent 2 is added from reagent source 54 to reaction chamber 40 through pump 64. As previously described, the device for stirring may or may not be in operation. Reagent 2 is an aqueous solution of oxalic acid, which reacts with any phosphate-molybdate complex present in the reaction chamber, thereby decomposing the phosphate-molybdate complex into an optically inactive moiety, particularly a moiety that does not absorb light at 815 nm. Oxalic acid does not significantly affect the silica-molybdate complex present. After allowing the reaction to proceed for a predetermined reaction time, the current at light detector 78 is measured again. The value obtained is designated as E3, which should be greater than E2 because the phosphate-molybdate complex will no longer absorb.

[0077] At this time, a sample of Reagent 3 is added to the reaction chamber 40 from the reagent source 56 through the pump 66. Reagent 3 is an aqueous solution of potassium disulfite and 4-(methylamino)phenol hemisulfate salt. The stirring device may or may not be in operation. The reaction of the silica-molybdate complex with Reagent 3 produces a new complex with a deeper blue color, so the amount of light at 815 nm absorbed is greatly increased, thereby reducing the amount of light received at the photodetector 78. After a predetermined reaction time, the current is measured at the photodetector 78. This measurement result is called E4.

[0078] Beer's law is a well-known chemical principle. According to Beer's law:

[0079] A = -log(Ef / Ei) = εbc

[0080] where A is the absorbance, Ei is the initial current, Ef is the final current, ε is the molar extinction coefficient, b is the optical path length of the optical sample, and c is the concentration of the optically active substance.

[0081] Rearranging the equation and solving for c, where c is the measurement result of interest, it can be seen that:

[0082] c = -log(Ef / Ei) / εb.

[0083] Among these quantities, two currents have been measured, and the product εb is a constant predetermined from the calibration of the device and stored in the memory of the processor of the operating device. Although the equation is accurate at lower concentrations, some correction may be required for the deviation from the ideal Beer's law at higher concentrations. This is the basic working chemical process of the prior art silica analyzer. To complete the cycle, it is necessary to rinse the reaction chamber 40 with the process fluid and re-establish Eb. From start to finish, the prior art requires about 20 minutes for one cycle.

[0084] The above steps describe the measurement of silica in water, but since the phosphate has been removed by adding Reagent 2, the phosphate cannot be measured.

[0085] However, under the concept of the present invention, the phosphate in the test fluid can also be selectively measured. To implement the concept of the present invention, the above process is used to determine the silica content of the process fluid. This process ends with a rinsed reaction chamber, ready for a new Eb determination.

[0086] Then, a 1 ml sample of Reagent 1 is added from the reagent source 52 to the reaction chamber 40 by means of a pump 62. At this time, the device for stirring the contents of the reaction chamber may or may not be in operation.

[0087] As in the silica determination, Reagent 1 immediately reacts with the silica and phosphate present in the test sample. A yellow molybdate complex is formed. The reaction is allowed to proceed, but if the heater 138 provides temperature control, the predetermined reaction time can be reduced. During this step, the molybdate complex formed will absorb a small amount of 815 nm light respectively. The current at the photodetector 78 is monitored, and the current measured at the end of the reaction period is referred to as E2.

[0088] At this time, the step of injecting Reagent 2 to decompose the phosphomolybdate complex and render the phosphate optically inert is not performed. Since the predetermined reaction time for this step in the silica analysis is shorter than that of other steps, omitting this step will not significantly shorten the total processing time.

[0089] Now, the reaction chamber 40 contains a process fluid having a silica molybdate complex and a phosphate molybdate complex. Adding a sample of Reagent 3 from the reagent source 56 to the reaction chamber 40 by means of a pump 66 will produce a deeper blue color, so the amount of 815 nm light absorbed will increase significantly, thereby reducing the amount received at the photodetector 78. Since the blue color is now attributable to both the silica complex and the phosphate complex of molybdate, the amount of 815 nm light at the photodetector 78 is even more reduced than in the silica determination. This measurement result is referred to as E4.

[0090] Once this E4 value is obtained, Beer's law is applied again using the Eb value determined at the start of the phosphate determination cycle. The resulting concentration c is the concentration of silica plus phosphate. When comparing the absorbance of this test with the absorbance of at least one "silica only" test, the phosphate content can be determined by difference.

[0091] Helpfully, in a typical power plant water system, the acceptable level of silica will be very low, while the aim is to maintain a consistent positive level of phosphate to maintain the pH value and prevent corrosion. For this reason, the concentration of silica plus phosphate in this application will be generally close to the determination of "phosphate only".

[0092] Algorithm

[0093] Other aspects of the concept of the present invention are shown in Figure 4 to be implemented by appropriate programming of an algorithm 210 for a processor that operates the device 110 as described herein.

[0094] Algorithm 210 begins with the initialization step 212 of apparatus 110. In this step, the state of the system is verified, including items such as verification of the process fluid, verification of the availability of system reagents, etc.

[0095] Once the system is initialized, the processor queries its storage unit at step 214 to determine if apparatus 110 needs to be calibrated. The need for calibration is indicated by exceeding a predetermined calibration threshold. The calibration threshold at step 214 can be based on one or more of a variety of factors, for example, for illustrative purposes, the amount of time elapsed since the last calibration, the number of analyses performed since the last calibration, or the presence of error messages from previously performed analyses. If calibration is not required, path 312 leads to step 216.

[0096] If calibration is required, path 314 leads to calibration step 218, which must be performed before any further operation of the apparatus. Calibration can be performed in a variety of ways, but the preferred ways include the analysis of known standards. After performing calibration step 218, the data from the calibration is stored in the storage unit, and path 316 leads to step 216.

[0097] At step 216, the processor queries its storage unit to determine if the user has stored an analysis sequence. Since apparatus 110 can perform the analysis of silica (“S”) and the combined analysis of silica and phosphate (“C”), the analysis sequence can be represented as a series of “S” and “C” values. The first value in the sequence should always be “S”, and consecutive “S” values may occur, but consecutive “C” values render the sequence invalid. For example, the sequence “SCSCSC” is a valid sequence, but the phosphate may be tested more frequently than desired. The sequence “SSSCSSSCSSSC” is a valid sequence. Some sequences, such as “CSSCSS” (initial “C” value) or “SCCSSSC” (consecutive “C” values) may be feasible but may be determined to be invalid under the programmed algorithm. If a valid sequence is stored in the memory, path 318 leads to step 220.

[0098] If no sequence or an invalid sequence is stored, path 320 leads to step 222. At this point, the user is required to input a sequence by entering a sequence of “S” and / or “C” values or by selecting a predetermined sequence from among a plurality of such predetermined sequences stored in the memory. After the sequence is input, path 320 returns to step 216, where the validity of the input sequence is verified and then path 318 leads to step 220.

[0099] Using an appropriate sequence, operation begins at step 220. The reaction chamber 40 is flushed for a predetermined flushing time, typically a few minutes. At the end of the flushing time, the flow of process fluid to the reaction chamber is stopped, thereby retaining the sample in the reaction chamber. Light at 815 nm from the light source 74 is detected at the photodetector 78, and as the absorbance level at the photodetector 78 stabilizes, a baseline absorbance E is established. b And its value is stored in the memory. Path 321 leads the process to step 223.

[0100] At step 223, the reactant pump 62 injects a sample of reagent 1 from the reagent bottle 52 into the sample and causes ammonium molybdate to react in an acidified aqueous medium. This reaction results in the formation of yellow molybdate complexes of silica and phosphate in the sample. When a nominal predetermined reaction time is programmed into the processor, the temperature of the sample can be considered in reducing the reaction time. The molybdate complexes of silica and phosphate will cause some absorption of the 815 nm light during this step. Preferably, the current at the photodetector 78 is monitored throughout the step, and in some cases, the rate of change of the measured current at the photodetector 78 can be used to determine that one or more than one reactions are effectively completed. The absorbance at the end of step 223 is stored in the memory as E2, and path 322 leads to step 224.

[0101] At Figure 4 In the depicted algorithm 210, step 224 is an inquiry as to whether the analysis starting from step 216 is "S" or "C" in sequence. It should be recognized that this inquiry may have been made before step 223, but the information is not needed until that point because the information may lead to differences in processing. If the analysis is "S", path 326 leads to step 226. If the analysis is "C", path 330 bypasses step 226 and leads directly to step 228.

[0102] In step 226, according to a signal from the processor, a sample of reagent 2 (an aqueous solution of oxalic acid) is added to the reaction chamber 40 through the pump 64 from the reagent source 54. Oxalic acid reacts with any phosphate-molybdate complexes present in the reaction chamber, thereby decomposing the phosphate-molybdate complexes into optically inert moieties, particularly moieties that do not absorb light at 815 nm. Oxalic acid does not significantly affect the silica-molybdate complexes present. After allowing the reaction to proceed for a predetermined reaction time, the current at the photodetector 78 is measured again. The obtained current value is designated as E3, which should be greater than E2 because the presence of phosphate does not cause light absorption. In an optional part of step 226, the comparison of E3 with Eb can be used as an indication of an error in the test, thereby generating at least one error message. At the end of step 226, path 328 leads to step 228.

[0103] At step 228, path 328 and path 330 converge. In this step, a sample of reagent 3 is injected into reaction chamber 40 from reagent source 56 by pump 66. Reagent 3 is an aqueous solution of potassium sulfite and 4-(methylamino)phenol hemisulfate, which produces a deep blue color by reacting with the silica molybdate complex and (if the test sample has not undergone step 226) the phosphate molybdate complex. The blue color strongly absorbs light at 815 nm, so the amount of light received at photodetector 78 is reduced. This measured absorbance is referred to as E4. At the end of step 228, path 332 leads to step 230, which is again an inquiry as to whether the analysis being performed is "S" or "C". If the analysis is "S", path 334 leads to step 232. If the analysis is "C", path 336 leads to step 234.

[0104] At step 232, the silica concentration is calculated using the Beer's law relationship described above. In a preferred embodiment of the inventive concept, the silica concentration calculated from a predetermined number of the latest "S" analyses is retained in memory, and the latest concentration replaces the oldest concentration in the stored values. This data can be used for a variety of purposes, including the calculation of the phosphate content in a "C" analysis or the trend of the silica concentration over time.

[0105] At step 234, the combined concentration of silica and phosphate is calculated using the Beer's law relationship described above. To obtain the phosphate concentration, the silica concentration needs to be subtracted from the combined concentration. There are various options as to how this can be programmed into an algorithm. In one embodiment, the silica concentration from the previous silica analysis is used. In another embodiment, the combined concentration is stored, and the silica concentration used is the average of the silica analyses that occurred before and after the combined analysis. In yet another embodiment, based on a predetermined number of silica analyses that occurred before and / or after the combined analysis, a statistical calculated value, such as the average of the silica concentrations, is used to determine the phosphate concentration.

[0106] In either case of an "S" analysis or a "C" analysis, the corresponding path 338 or 340 returns to step 214, and the system is ready for another analysis.

[0107] In a preferred algorithm for operating the device, at least the latest current values Eb (or E1), E2, E3, and E4 are stored in memory, and even more preferably, several of the latest values of each of them are stored. It is also preferred to store temperature values, which include at least the temperature in heater 138, the temperature of the walls of reaction chamber 40, and the ambient temperature. Since it is known that temperature affects calculations involving Beer's law, the latter two values can be used to estimate the temperature of the sample fluid. The current values, particularly Eb and E3, are known to be useful for detecting and troubleshooting diagnostic errors.

Claims

1. A method for analyzing the silica and phosphate contents in a water sample in a single device, the method comprising the following steps: Providing a water sample to be analyzed in a reaction chamber of the device; Obtaining a value of the silica content of the water sample in the device; Storing the obtained value of the silica content in a database communicating with the device; Rinsing and refilling the reaction chamber with another water sample; Obtaining a value of the combined content of silica and phosphate of the said another water sample in the device; Calculating and reporting the phosphate content of the said another water sample by comparing the value of the combined content of silica and phosphate with a representative value of the silica content stored in the database; Wherein, the step of obtaining a value of the silica content of the water sample is implemented by a sub-step comprising the following sub-steps: Adding a first reagent to the water sample, the first reagent being selected to react with silica and phosphate in the water sample to produce a colored silica complex and a colored phosphate complex; Causing light from a light source to cross the reaction chamber through the water sample containing the colored silica complex and the colored phosphate complex and reach a light detector, measuring the current generated thereby in the light detector, and storing the current as a first silica value in the database; Adding a second reagent to the water sample containing the colored silica complex and the colored phosphate complex, the second reagent being selected to react only with the colored phosphate complex, and the colored phosphate complex being converted into an optically inert phosphate moiety; Causing light from a light source to cross the reaction chamber through the water sample containing the colored silica complex and the optically inert phosphate moiety and reach a light detector, measuring the current generated thereby in the light detector, and storing the current as a second silica value in the database; Adding a third reagent to the water sample containing the colored silica complex and the optically inert phosphate moiety, the third reagent being selected to react only with the colored silica complex, and the colored silica complex being converted into a colored silica complex with a deeper color; Causing light from a light source to cross the reaction chamber through the water sample containing the colored silica complex with a deeper color and the optically inert phosphate moiety and reach a light detector, measuring the current generated thereby in the light detector, and storing the current as a third silica value in the database; In a processor communicating with the database, calculating a value of the silica content in the water sample according to the relationship between the third silica value and at least one of the first silica value and the second silica value; Wherein, the step of obtaining a value of the combined content of silica and phosphate in the said another water sample is implemented by a sub-step comprising the following sub-steps: Adding a first reagent to the said another water sample to produce a colored silica complex and a colored phosphate complex; Causing light from a light source to cross the reaction chamber through the water sample containing the colored silica complex and the colored phosphate complex and reach a light detector, measuring the current generated thereby in the light detector, and storing the current as a first combined value in the database; A third reagent is added to the additional water sample containing the colored silica complex and the colored phosphate complex, the third reagent being selected to react with the colored silica complex and the colored phosphate complex, and the colored silica complex and the colored phosphate complex being converted into a more deeply colored complex; Light from a light source is passed through the reaction chamber through the additional water sample containing the more deeply colored complex to a light detector, the current generated thereby in the light detector is measured, and the current is stored as a second combined value in a database; In a processor in communication with the database, a value of the combined content of silica and phosphate in the additional water sample is calculated based on the relationship between the second combined value and the first combined value, and wherein the step of calculating and reporting the phosphate content of the additional water sample is implemented by a sub-step comprising the following sub-steps: A representative value of the silica content is determined by using at least one silica content obtained before or after the combined content of silica and phosphate; The phosphate content is obtained by subtracting the representative value of the silica content from the combined content of silica and phosphate.

2. The method according to claim 1, wherein The step of providing a water sample to be analyzed is implemented by a sub-step comprising the following sub-steps: The reaction chamber is rinsed with the water to be sampled by flowing the water to be sampled through the reaction chamber; The flow of the water to be sampled through the reaction chamber is stopped, and the water sample is retained in the reaction chamber; Light from a light source is passed through the reaction chamber through the water sample to a light detector, the current generated thereby in the light detector is measured, and the current is stored as a baseline value in a database.

3. The method according to claim 1, wherein: The first reagent is an aqueous solution of ammonium molybdate and an inorganic acid; The second reagent is an aqueous solution of oxalic acid; The third reagent is an aqueous solution of potassium sulfite and 4-methylaminophenol hemisulfate.

4. The method according to claim 1, wherein The light source generates monochromatic light having a wavelength of 815 nm.

5. The method according to claim 1, wherein The step of rinsing and refilling the reaction chamber with the additional water sample is implemented by a sub-step comprising the following sub-steps: The reaction chamber is rinsed with the water to be sampled by flowing the water to be sampled through the reaction chamber; The flow of the water to be sampled through the reaction chamber is stopped, and the water sample is retained in the reaction chamber; Light from a light source is passed through the reaction chamber through the water sample to a light detector, the current generated thereby in the light detector is measured, and the current is stored as a baseline value in a database.

6. An apparatus for analyzing the silica and phosphate content of a water sample, the apparatus comprising: An inlet for receiving a flow of a water sample to be tested; An outlet for discharging the water sample after testing; A flow conduit providing a liquid flow path from the inlet to the outlet; A reaction chamber located in the flow conduit, sized to retain a predetermined volume of the water sample, and the reaction chamber comprising: A sample inlet in liquid communication with the inlet; A sample outlet in liquid communication with the outlet; A plurality of reagent inlets; A colorimetric device comprising: a window through which light from a light source is passed and directed into the volume of the reaction chamber; a reflector for reflecting the light incident thereon back into the volume of the reaction chamber; a window through which the reflected light is passed and received by a light detector; A valve for controlling the flow into a reaction chamber through a flow conduit; A plurality of reagent feeding systems, each reagent feeding system being in fluid communication with one of the plurality of reagent inlets; A processor in communication with a colorimetric device, the valve, and the plurality of reagent feeding systems, programmed to operate the device according to the method of claim 1.

7. The apparatus according to claim 6, the apparatus further comprising: A heater located in the flow conduit between the inlet and the valve for heating the water sample passing therethrough.

8. The apparatus according to claim 6, wherein: Each reagent feeding system includes a reagent container and a metering pump actuated by the processor to provide a predetermined amount of a selected reagent to one of the reagent inlets.

9. The apparatus according to claim 6, the apparatus further comprising: A calibration feeding system including a calibration fluid container and a metering pump actuated by the processor to provide a predetermined amount of a selected calibration fluid to the flow conduit upstream of the valve.

10. The apparatus according to claim 7, the apparatus further comprising: A calibration feeding system including a calibration fluid container and a metering pump actuated by the processor to provide a predetermined amount of a selected calibration fluid to the flow conduit upstream of the heater through an additional valve in the flow conduit between the inlet and the heater.

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