Photon counting fibre optic distributed temperature sensing with a CMOS SPAD array.

Time-resolved fibre optic Raman distributed temperature sensing (DTS) measurements experience long measurement times due to a weak backscattered Raman signal inside optical fibres or limited detector count rates. Here, improvements to previous work based on individual detectors are demonstrated using a 512 pixel complementary-metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) line sensor array with integrated (on-chip) timing electronics. Multiplexed single photon counting increases count rate and decreases measurement time for practical applications. This allows temperature to be measured every 0.5 m with 0.7 °C accuracy and a 10 s measurement time using a 13.0 m optical fibre, performance over longer distance is also investigated.

High resolution TCSPC imaging of diffuse light with a one-dimensional SPAD array scanning system.

We report a time-correlated single-photon counting (TCSPC) imaging system based on a line-scanning architecture. The system benefits from the high fill-factor, active area, and large dimension of an advanced CMOS single-photon avalanche diode (SPAD) array line-sensor. A two-dimensional image is constructed using a moving mirror to scan the line-sensor field-of-view (FOV) across the target, to enable the efficient acquisition of a two-dimensional 0.26 Mpixel TCSPC image. We demonstrate the capabilities of the system for TCSPC imaging and locating objects obscured in scattering media - specifically to locate a series of discrete point sources of light along an optical fibre submerged in a highly scattering solution. We demonstrate that by selectively imaging using early arriving photons which have undergone less scattering than later arriving photons, our TCSPC imaging system is able to locate the position of discrete point sources of light than a non-time-resolved imaging system.

Time-resolved spectral-domain optical coherence tomography with CMOS SPAD sensors.

We present a first spectral-domain optical coherence tomography (SD-OCT) system deploying a complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode (SPAD) based, time-resolved line sensor. The sensor with 1024 pixels achieves a sensitivity of 87 dB at an A-scan rate of 1 kHz using a supercontinuum laser source with a repetition rate of 20 MHz, 38 nm bandwidth, and 2 mW power at 850 nm centre wavelength. In the time-resolved mode of the sensor, the system combines low-coherence interferometry (LCI) and massively parallel time-resolved single-photon counting to control the detection of interference spectra on the single-photon level based on the time-of-arrival of photons. For proof of concept demonstration of the combined detection scheme we show the acquisition of time-resolved interference spectra and the reconstruction of OCT images from selected time bins. Then, we exemplify the temporal discrimination feature with 50 ps time resolution and 249 ps timing uncertainty by removing unwanted reflections from along the optical path at a 30 mm distance from the sample. The current limitations of the proposed technique in terms of sensor parameters are analysed and potential improvements are identified for advanced photonic applications.

Direct integration of micro-LEDs and a SPAD detector on a silicon CMOS chip for data communications and time-of-flight ranging.

We present integration of singulated micron-sized light emitting diodes (micro-LEDs) directly onto a silicon CMOS drive chip using a transfer printing method. An 8x8 micro-LED device array with individual control over each pixel is demonstrated with modulation bandwidths up to 50 MHz, limited by the large modulation depth of the driver chip. The 2 kHz frame rate CMOS driver also incorporates a Single Photon Avalanche Diode device thus allowing detection and transmission functionality on a single integrated chip. Visible light communications at data rates up to 1 Mbps, and time-of-flight ranging with cm-scale resolution are demonstrated using this hybrid integrated system.

Time-resolved spectroscopy at 19,000 lines per second using a CMOS SPAD line array enables advanced biophotonics applications.

A SPAD-based line sensor fabricated in 130 nm CMOS technology capable of acquiring time-resolved fluorescence spectra (TRFS) in 8.3 milliseconds is presented. To the best of our knowledge, this is the fastest time correlated single photon counting (TCSPC) TRFS acquisition reported to date. The line sensor is an upgrade to our prior work and incorporates: i) parallelized interface from sensor to surrounding circuitry enabling high line rate to the PC (19,000 lines/s) and ii) novel time-gating architecture where detected photons in the OFF region are rejected digitally after the output stage of the SPAD. The time-gating architecture was chosen to avoid electrical transients on the SPAD high voltage supplies when gating is achieved by excess bias modulation. The time-gate has an adjustable location and time window width allowing the user to focus on time-events of interest. On-chip integrated center-of-mass (CMM) calculations provide efficient acquisition of photon arrivals and direct lifetime estimation of fluorescence decays. Furthermore, any of the SPC, TCSPC and on-chip CMM modes can be used in conjunction with the time-gating. The higher readout rate and versatile architecture greatly empower the user and will allow widespread applications across many techniques and disciplines. Here we focused on 3 examples of TRFS and time-gated Raman spectroscopy: i) kinetics of chlorophyll A fluorescence from an intact leaf; ii) kinetics of a thrombin biosensor FRET probe from quenched to fluorescence states; iii) ex vivo mouse lung tissue autofluorescence TRFS; iv) time-gated Raman spectroscopy of toluene at 3056 cm-1 peak. To the best of our knowledge, we detect spectrally for the first time the fast rise in fluorescence lifetime of chlorophyll A in a measurement over single fluorescent transient.

pH sensing through a single optical fibre using SERS and CMOS SPAD line arrays.

Full exploitation of fibre Raman probes has been limited by the obstruction of weak Raman signals by background fluorescence of the sample and the intrinsic Raman signal of the delivery fibre. Here we utilised functionalised gold nanoshells (NS) to take advantage of the surface-enhanced Raman spectroscopy (SERS) effect to enhance the pH responsive spectrum of 4-mercaptobenzoic acid (MBA). However, the fibre background is still dominant. Using the photon arrival time-resolving capability of a CMOS single-photon avalanche diode (SPAD) based line sensor, we recover the SERS spectrum without a fibre background in a 10 s measurement. In this manner, pH sensing through a multimode fibre at a low excitation power that is safe for future in vivo applications, with short acquisition times (10 or 60 s), is demonstrated. A measurement precision of ± 0.07 pH units is thus achieved.

Microalgae harvesting using flocculation and dissolved air flotation: Selecting the right vessel for lab-scale experiments.

Flocculation combined with dissolved air flotation (DAF) is a promising technology for harvesting microalgae; therefore, optimisation of flocculant-DAF operating conditions are frequently explored in laboratory experiments. DAF systems have jars of differing volumes, height to diameter ratios, shapes and materials used to manufacture the jars; thus, the harvesting efficiency (η) may differ between these jars. The aim was to systematically compare η between different types of benchtop DAF jars. Evaluation of 30 different types of DAF jars revealed that η was not influenced by the volume of the jars, but was impacted by the height to diameter ratio, with optimal η at a ratio ranging between 1.6 and 2.05. There was no difference in η between cylindrical and cuboid jars, but jars made of hydrophobic (polypropylene) plastic resulted in a lower η. Overall, these results are useful to guide the design of lab-scale DAF microalgae harvesting experiments.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation.

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13-0.75 mg N L-1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15-0.63 mg N L-1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7-14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Understanding variability in algal solid-liquid separation process outcomes by manipulating extracellular protein-carbohydrate interactions.

Coagulation-flocculation followed by sedimentation or dissolved air flotation (DAF) are processes routinely used for separating microalgae from water; however, during algae separation then can exhibit inconsistent separation, high coagulant demand, and high operating cost. To circumvent these problems, previous studies reported the development of a novel DAF process in which bubbles were modified instead of particles. While this process was shown to be sustainable and inexpensive, the problem of inconsistent algal separation across species remained. Recent research has suggested that this could be due to the varying concentration and character of algal-derived proteins and carbohydrates within the extracellular organic matter (EOM) and their associated interactions. This hypothesis is tested in the current study using the novel modified-bubble DAF process, which has been highly susceptible to EOM protein and carbohydrate concentrations and character. Biomolecular additives (commercially available proteins and carbohydrates, and algal-extracted proteins) of widely differing molecular weight (MW) and charge were dosed in varying proportions into samples containing either Chlorella vulgaris CS-42/7, Microcystis aeruginosa CS-564/01, or Microcystis aeruginosa CS-555/1 after removing the intrinsic EOM. These cell-rich suspensions were then subject to flotation using cationic bubbles modified with poly(diallyldimethylammonium chloride) (PDADMAC). When additives were dosed independently, separation increased from <5% to up to 62%. The maximum separation was obtained when the dose was double the respective biopolymer concentration measured in the intrinsic EOM for the equivalent species, and, in the case of protein additives, when MW and charge were >50 kDa, and >0.5 meq·g-1, respectively, irrespective of the species tested. When evaluating steric- and charge-based protein-carbohydrate interactions on cell separation by simultaneously dosing high MW and high charge protein- and carbohydrate-additives, enhanced separation of up to 79% was achieved. It is suggested that enhanced cell separation is achieved due to proteins and carbohydrates bridging with cells and forming protein-carbohydrate-cell suprastructures in the presence of a flocculant, e.g. PDADMAC, and this only occurs when the intrinsic EOM comprises proteins and carbohydrates that have high MW (>25 kDa) and charge (>0.2 meq·g-1), and interactions with each other and with the cell surface.

Demonstrating ultra-filtration and reverse osmosis performance using size exclusion chromatography.

Advanced water treatment plants employing ultrafiltration (UF) and reverse osmosis (RO) membrane processes are frequently implemented for the production of high-quality recycled water. It is important that process performance is able to be quantified and assessed to ensure it is fit for purpose. This research utilizes size exclusion chromatography with organic carbon, organic nitrogen and UV(254) detection to determine the change in both DOC concentration and character through a UF/3 stage-RO pilot plant. It was determined that 97% of the influent DOC was removed on average to produce a water of less than 0.5 mg L(-1) as C. The UF process removed more than half of the biopolymer fraction, equating to 4.5% DOC removal, while the RO process generally removed all DOC except a small proportion of the low MW humics and acids and low MW neutral fraction. While not changing significantly in concentration, the Stage 3 RO permeate typically contained low concentrations of humic fraction, indicating a change in character and therefore a change in rejection mechanism. Overall, it was determined that while TOC monitoring is important in advanced water treatment systems, improved understanding of the character of the TOC present lends greater insight into the assessment of process performance.

Probabilistic analysis of fluorescence signals for monitoring dual reticulation water recycling schemes.

Improved techniques are required for the detection of inadvertent cross-connections between recycled water and potable water systems in dual reticulation schemes. The aim of this research was to assess the potential for fluorescence spectroscopy to be developed as a tool to distinguish recycled water from potable water. Weekly grab samples of recycled and potable water were obtained over 12 weeks from within an Australian dual reticulation site and analysed for fluorescence excitation-emission matrix (EEM), dissolved organic carbon (DOC), electrical conductivity (EC), and pH. Probabilistic techniques including distribution function fitting and Monte Carlo simulation were used to assess the ability to distinguish between recycled water and potable water sample pairs and the reliability of doing so. Fluorescence EEM spectroscopy was determined to be the most effective for the reliable differentiation by monitoring the protein-like fluorescence at peak T(1)--an excitation-emission wavelength pair of λ(ex/em)=300/350 nm. While EC could distinguish between recycled and potable water, it was shown to be less sensitive and less reliable than peak T(1) fluorescence.

Fluorescence monitoring for cross-connection detection in water reuse systems: Australian case studies.

A rapid, highly sensitive method for detection of cross-connections between recycled and potable water in dual reticulation systems is required. The aim of this research was to determine the potential of fluorescence spectroscopy as a monitoring tool at three Australian dual distribution (drinking and recycled water) systems. Weekly grab samples of recycled and potable water were obtained over 12 weeks at each site and analysed for fluorescence excitation-emission matrix (EEM) spectroscopy, UV(254), dissolved organic carbon (DOC), electrical conductivity and pH. Fluorescence EEM spectroscopy was able to differentiate between recycled and potable water at each site by monitoring the protein-like fluorescence at peak T-an excitation-emission wavelength pair of lambda(ex/em) = 300/350 nm. While electrical conductivity was also able to distinguish between recycled and potable water, the differentiation was greatest when using fluorescence. For example, the peak T fluorescence in recycled water was up to 10 times that of potable water in comparison with electrical conductivity that had a maximum 5 times differentiation. Furthermore, by comparing the protein-like fluorescence at peak T and humic-like fluorescence at peak A (lambda(ex/em) = 235/426 nm), the three different recycled water systems were able to be differentiated. Overall, fluorescence shows promise as a monitoring tool for detecting cross-connections.

Detailed algal extracellular carbohydrate-protein characterisation lends insight into algal solid-liquid separation process outcomes.

The effectiveness of algal solid-liquid separation processes has been impacted by the strong influence of algal extracellular organic matter (EOM), where the composition of proteins and carbohydrates and their associated interactions have been implicated. However, despite this, no studies have analysed the detailed protein and carbohydrate composition in EOM in relation to their impacts on separation. Hence, the aim of this study was to explore the relationship between the variety of carbohydrates and proteins present in the EOM of select algal and cyanobacterial samples and the associated separation performance to better understand the influence of specific biopolymers. The protein and carbohydrate composition of the EOM of three species - Microcystis aeruginosa CS-555/1, Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-564/01, previously observed to result in variable treatment performance were investigated. The carbohydrates were analysed via high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) while the proteins were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) combined with liquid chromatography-mass spectrometry (LC-MS). Ten unique monosaccharides were identified; of these, the greatest proportion of charged uronic acid carbohydrates were present in the EOM of M. aeruginosa CS-564/01. The protein profiling revealed that M. aeruginosa CS-564/01 had a greater proportion and concentration of proteins >75 kDa when compared to M. aeruginosa CS-555/1 or C. vulgaris CS-42/7. It was determined that three serine- and two threonine-based proteins, detected in greater concentrations in M. aeruginosa CS-564/01 than CS-555/1, could covalently interact with carbohydrates (OHenderson et al., 2010a, 2010b-linked glycosylation). These proteins have the ability to form numerous localised networks with carbohydrates and cells in the presence of coagulant molecules, thereby providing a good hypothesis to explain the excellent treatment performance observed for M. aeruginosa CS-564/01 previously. It is proposed that the uronic acids in M. aeruginosa CS-564/01 could interact with proteins via glycosylation, explaining why the coagulant demand for this strain remained low despite the high charged carbohydrate concentration. Overall, it is proposed that process performance could be impacted by: (a) physicochemical characteristics and (b) carbohydrate-protein interactions.

Formation of algal-derived nitrogenous disinfection by-products during chlorination and chloramination.

Algal cells and algal organic matter (AOM) are a source of high dissolved organic carbon (DOC) and nitrogen (DON) concentrations. This poses a possible health risk due to their potential to form disinfection by-products (DBPs), some of which may be of health concern, after disinfection. While several studies have focussed on the formation of carbonaceous DBPs from AOM, only a few studies have focussed on the formation of nitrogen containing N-DBPs from AOM. Hence, the main aim of this study was to thoroughly investigate the N-DBP formation potential of the AOM from a species of cyanobacteria commonly found in natural waters, Microcystis aeruginosa. Three haloacetonitriles, two halonitromethanes, two haloacetamides, and eight N-nitrosamines were analysed by gas chromatography-mass spectrometry after chlorination and chloramination of the extracted AOM. To provide further insight into the influence of changing DON character on N-DBP formation potential, the AOM from three other species, Chlorella vulgaris, Dolichospermum circinale and Cylindrospermopsis raciborskii, were also tested. Dichloroacetonitrile (DCAN) was the DBP formed in the highest concentrations for both chlorination and chloramination of bulk AOM from all the species. Furthermore, during chlorination and chloramination, the high molecular weight fraction (>1 kDa) of AOM from M. aeruginosa had a greater DCAN formation potential (normalised to DOC or DON) than the AOM in the low molecular weight fraction (<1 kDa) of M. aeruginosa, regardless of growth stage. N-Nitrosamine formation from the bulk AOM of all species occurred only after chloramination. The molar concentration of N-nitrosodimethylamine (NDMA) was lower than the other N-nitrosamines detected. However, NDMA formation increased with culture age for all four species, in contrast to most other N-nitrosamines whose formation remained consistent or decreased with culture age. Overall, algal growth could result in elevated concentrations of N-DBPs due to the increasing concentrations of high molecular weight algal DON in the AOM. It is suggested that the AOM comprises precursors containing long C-chain amine (R1-NH-R2) or cyclic N-containing amine structures. Comparisons to previously measured N-DBP concentrations in drinking water suggest that the AOM from the algae and cyanobacteria examined in this study are not likely to be a major source of precursors for either DCAN or NDMA in real waters. However, AOM may present a major precursor source for other N-nitrosamines.

Mask-less ultraviolet photolithography based on CMOS-driven micro-pixel light emitting diodes.

We report on an approach to ultraviolet (UV) photolithography and direct writing where both the exposure pattern and dose are determined by a complementary metal oxide semiconductor (CMOS) controlled micro-pixellated light emitting diode array. The 370 nm UV light from a demonstrator 8 x 8 gallium nitride micro-pixel LED is projected onto photoresist covered substrates using two back-to-back microscope objectives, allowing controlled demagnification. In the present setup, the system is capable of delivering up to 8.8 W/cm2 per imaged pixel in circular spots of diameter approximately 8 microm. We show example structures written in positive as well as in negative photoresist.

Fluorescence as a potential monitoring tool for recycled water systems: a review.

A rapid, highly sensitive and selective detector is urgently required to detect contamination events in recycled water systems - for example, cross-connection events in dual reticulation pipes that recycle advanced treated sewage effluent - as existing technologies, including total organic carbon and conductivity monitoring, cannot always provide the sensitivity required. Fluorescence spectroscopy has been suggested as a potential monitoring tool given its high sensitivity and selectivity. A review of recent literature demonstrates that by monitoring the fluorescence of dissolved organic matter (DOM), the ratios of humic-like (Peak C) and protein-like (Peak T) fluorescence peaks can be used to identify trace sewage contamination in river waters and estuaries, a situation analogous to contamination detection in recycled water systems. Additionally, strong correlations have been shown between Peak T and biochemical oxygen demand (BOD) in rivers, which is indicative of water impacted by microbial activity and therefore of sewage impacted systems. Hence, this review concludes that the sensitive detection of contamination events in recycled water systems may be achieved by monitoring Peak T and/or Peak C fluorescence. However, in such systems, effluent is treated to a high standard resulting in much lower DOM concentrations and the impact of these advanced treatment processes on Peaks T and C fluorescence is largely unknown and requires investigation. This review has highlighted that further work is also required to determine (a) the stability and distinctiveness of recycled water fluorescence in relation to the treatment processes utilised, (b) the impact of matrix effects, particularly the impact of oxidation, (c) calibration issues for online monitoring, and (d) the advanced data analytical techniques required, if any, to improve detection of contamination events.

Distinguishing Stage 1 and 2 reverse osmosis permeates using fluorescence spectroscopy.

Fluorescence excitation-emission matrix (EEM) spectroscopy was used to distinguish between two stages of reverse osmosis (RO) permeates as the first step towards investigating the potential application of fluorescence as a monitoring tool for membrane performance. The signal response of several fluorescence peaks present in Stage 1 and Stage 2 RO permeates of an advanced water treatment plant were compared. The humic-like fluorescence region was found to have the largest percentage difference between stages and therefore was the most appropriate for enabling differentiation. Increases in humic-like fluorescence did not correlate with increases in conductivity or dissolved organic carbon measurements. This suggests that fluorescence is a more selective and sensitive method for monitoring the organic composition of RO permeates than established methods. Fluorescence is therefore a promising tool for improved water quality monitoring of RO permeates.

The impact of cell morphology and algal organic matter on algal floc properties.

Physical floc properties were systematically investigated by analysing the structure of algal and cyanobacterial flocs produced by five species (green algae (Chlorella vulgaris) and cyanobacteria (Microcystis aeruginosa (strain CS-564), Microcystis aeruginosa (strain CS-555/01), Dolichospermum circinale and Cylindrospermopsis raciborskii) using aluminium sulphate (alum) at different doses and pH values. The properties of spherical, compact flocs were determined using a laser diffraction instrument and a new in situ image analysis technique was validated to analyse the structure of more complex flocs. The incorporation of algal-derived organic matter (AOM) into the flocs was inferred by evaluating the dissolved organic matter concentration character before and after flocculation using liquid chromatography with organic carbon detection (LC-OCD). D. circinale, C. raciborskii, and M. aeruginosa (CS-564) produced large flocs (2-9 mm), while M. aeruginosa (CS-555) and C. vulgaris produced smaller flocs (<2 mm). While differences in physical floc properties were observed to result from changes in coagulation mechanism, the cell morphology and the AOM composition were the most influential factors. Examination of floc properties can give a rapid insight at the plant for trouble shooting, particularly through the use of the in situ techniques and provide a mechanism by which floc properties can be tailored to downstream processes.

Enhanced real-time cyanobacterial fluorescence monitoring through chlorophyll-a interference compensation corrections.

In situ fluorometers can be used as a real-time cyanobacteria detection tool to maintain safe drinking and recreational water standards. However, previous studies into fluorometers have established issues arising mainly from measurement inaccuracies due to green algae interference. Therefore, this study focusses on developing correction factors from a systematic study on the impact of green algae as an interference source. This study brings a novel technique where the chlorophyll-a (Chl-a) and phycocyanin measurements are used to correct the fluorometer output for interference bias; four fluorometers were tested against three key cyanobacterial species and the relationship between phycocyanin output, green algae and cyanobacteria concentrations were investigated. Good correlation (R2 > 0.9, p-value < 0.05) was found between the fluorometer phycocyanin output and increasing green algae concentration. The optimal correction method was selected for each of the fluorometer and cyanobacteria species pairs by validating against data from the investigation of green algae as an interference source. The correction factors determined in this study reduced the measurement error for almost all the fluorometers and species tested by 21%-99% depending on the species and fluorometer, compared to previous published correction factors in which the measurement error was reduced by approximately 11%-81%. Field validation of the correction factors showed reduction in fluorometer measurement error at sites in which cyanobacterial blooms were dominated by a single species.

An evaluation of measurement techniques for algal-derived organic nitrogen.

Algal-derived organic matter (AOM) from algal blooms in water supply systems contains dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) among other constituents. The DON and DOC are disinfection by-product (DBP) precursor compounds, and must be well characterised to facilitate effective removal, thus minimising DBP formation during disinfection. While DOC character has been studied extensively, DON analysis suffers from inaccuracies due to sample pre-treatment and instrument sensitivities. A liquid chromatography method that combines size exclusion chromatography with highly sensitive organic carbon and nitrogen detectors (LC-OCND) has been widely adopted for DOC analysis; however, its potential for application for DON charactersation has been suggested as a viable alternative to existing DON characterisation techniquesnot been assessed despite its potential. Hence, the aim was to compare the effectiveness of conventional total dissolved N-dissolved inorganic N (TN-DIN), and LC-OCND methods for analysing DON in AOM. A suite of N-containing model compounds representative of DON and AOM extracted from Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-555/1 were used to evaluate the techniques. The DON of both model compounds and AOM was first analysed using the conventional method and, then, via LC-OCND. It was observed that LC-OCND had a better precision for DON when TN contained more DIN. LC-OCND provided direct quantitative measurements for bulk and fractionated DON and DIN, with little interference caused by DIN. Additionally, LC-OCND provided information on MW distribution and protein content of the AOM. For example, LC-OCND results showed that M. aeruginosa AOM contained more HMW material than C. vulgaris AOM. However, as LC-OCND uses UV oxidation, it could not completely oxidise complex aromatic structures, and thus had a lower recovery for HMW model compounds and algal DON in comparison to the conventional method that used high temperature catalytic oxidation. Overall, it is advised that a combination of LC-OCND and TN analysis be used to provide a more detailed characterisation of N-containing AOM and other similar HMW aquatic NOM samples.