DSpace at VNU: New fully portable instrument for the versatile determination of cations and anions by capillary electrophoresis with contactless conductivity detection

2059 Full Paper New Fully Portable Instrument for the Versatile Determination of Cations and Anions by Capillary Electrophoresis with Contactless Conductivity Detection Pavel Kuba´nˇ,a, b Huong Thi Anh Nguyen,a, c Mirek Macka,d, e Paul R Haddad,d Peter C Hausera* a Department of Chemistry, University of Basel, Spitalstrasse 51, 4004 Basel, Switzerland *e-mail: peter.hauser@unibas.ch b Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, Veverˇí 97, 61142 Brno, Czech Republic c Centre for Environmental Technology and Sustainable Development (CETASD), Hanoi University of Science, Nguyen Trai Street 334, Hanoi, Viet Nam d Australian Centre for Research on Separation Science, School of Chemistry, Faculty of Science, Engineering and Technology, University of Tasmania, 7001 Hobart, Tasmania, Australia e Department of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland Received: April 3, 2007 Accepted: May 21, 2007 Abstract A new portable capillary electrophoresis instrument with capacitively coupled contactless conductivity detection was developed and optimized for the sensitive field measurements of ionic compounds in environmental samples It is powered by batteries and the high voltage modules are capable of delivering up to 15 kV at either polarity for more than one working day Inorganic cations and anions, including ions of heavy metals and arsenate, could be determined with detection limits in the range from about 0.2 to mM The instrument was field tested in a remote region of Tasmania and nitrite and ammonium could be determined on-site at concentrations as low as 10 ppb in presence of other common inorganic ions at concentrations which were to orders of magnitude higher Keywords: Capillary electrophoresis, Contactless conductivity detection, Portable instrument, Environmental analyses, Arsenic, Heavy metals, Inorganic ions DOI: 10.1002/elan.200703908 Introduction The development of portable analytical instrumentation is an important trend in analytical research Field analysis is attractive as it minimizes complications with sample storage and transport, enables fast decisions at the sampling site and therefore reduces the overall analysis time Portable instruments are often used in environmental applications for monitoring of water quality, soil contamination and air pollution, in process analysis, but are desirable also for clinical applications, in forensics and in the detection of chemical warfare agents In comparison to conventional bench-top instruments compromises usually have to be made in performance, mainly with regard to sensitivity and precision The most widely used portable instruments are based on electrochemical sensors, for example portable pH-meters, conductometers, ion-selective electrodes and devices for measuring dissolved or atmospheric gases such as oxygen However, field instruments based on more complex analytical techniques have also been described These include photometry [1], voltammetry [2], flow-injection analysis [3] and X-ray fluorescence [4, 5] Moreover, portable instruments based on the separation methods of gas chromatogElectroanalysis 19, 2007, No 19-20, 2059 – 2065 raphy (GC) [6], high-performance liquid-chromatography (HPLC) [7] and ion chromatography (IC) [8, 9] have also been reported Capillary electrophoresis (CE) is well suited for portability as only a separation capillary, a high voltage (HV) power supply and small volumes of buffer solutions are needed to perform the separation High-pressure pumps as required for liquid chromatography are not necessary The most serious challenge in CE is detection and this has always been a critical issue since its introduction in the early 1980s For a portable instrument, the most difficult task is therefore to develop a suitable detection system that can be powered from batteries, can achieve good sensitivity, and is rather universal for the range of analytes with quite different physicochemical properties that can be separated in CE The most commonly used detection modes in bench-top CE are UV/vis absorbance, laser induced fluorescence and mass spectrometry None of these is well suited for small portable instruments because of the power requirements and complexity The simplest detection approach in CE are the electrochemical methods, which mainly consist of electronics and therefore can also be easily translated into the portable format Indeed, electrochemical detection is the only detection scheme that has been implemented in  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2060 portable CE instruments and includes all three different possible variants, namely potentiometry, amperometry and conductometry Potentiometry was first applied to a portable CE system [10], but the construction of the detection cell was difficult, the range of ions that could be detected was incomplete and limits of detection (LOD) at about 10À5 M, were not adequate for many on-site measurements Amperometric detection was applied to the determination of compounds that can easily be oxidized or reduced [11, 12] This resulted in better LODs, however, for amperometry, the cell construction is also difficult and most analytes are not accessible Potential gradient detection (PGD), which can be seen as an indirect conductometric detection method, has been used on portable instruments employing conventional or microchip CE for the determination of DNA fragments [13] and for alkaloids and inorganic cations [14], however, the LODs achieved (from about 10À4 to 10À5 M) also not meet the requirements for the analysis of many samples On the other hand, conductometry can be considered an attractive universal detection method for CE; most inorganic as well as organic cations and anions can be determined The capacitively coupled contactless conductivity detector (C4D) is a highly sensitive tool in CE (see, for example, the following review articles [15 – 17]) A C4D-cell is constructed from two axially positioned tubular electrodes through which the separation capillary is fitted No alignment of the electrodes is necessary and electrode fouling is not possible as these are not in direct contact with the solution [18, 19] Preliminary results obtained with an early, non-optimized and mains powered prototype of a C4D tested on a previous version of a portable CE instrument (which had been designed for potentiometric and amperometric detection) were indeed promising [12] In the current contribution, a new and improved design of a fully portable CE instrument with integrated contactless conductivity detection is presented and characterized, which includes a portable and battery powered data acquisition system connected to a laptop computer for immediate data processing and quantification The C4D was designed for low background noise operation, which ensures low LOD The complete system was tested by field measurements in the remote Tasmanian wilderness Experimental 2.1 Chemicals, Reagents, and Methods All chemicals were of analytical grade Stock solutions of anions (1 mM) were prepared from their corresponding potassium or sodium salts Stock solutions of cations (1 mM) were prepared from their nitrate salts and stock solutions of heavy metal cations (1 mM) were prepared from their chloride or sulfate salts (all chemicals were purchased from Fluka, Buchs, Switzerland or Sigma-Aldrich, Steinheim, Germany) All multi-ion anionic and cationic standard P Kuba´nˇ et al solutions were then freshly prepared from these stock solutions Deionized water obtained from a Milli-Q plus 185 system (Millipore, Bedford, MA, USA) was used for the preparation of the stock, standard and electrolyte solutions Electrolyte solutions were prepared fresh daily from lhistidine (His) (Fluka), 18-crown-6 (Sigma-Aldrich), acetic acid (Biolab, Clayton, Australia) and citric acid (Fluka) Electrolyte solutions were degassed in an ultrasonic bath for and filtered with 0.2 mm syringe filters obtained from Millipore prior to use in the laboratory For field measurements, electrolyte solutions were filtered but no degassing was performed A fused silica capillary (50 mm id and 360 mm o.d.) (Polymicro Technologies, Phoenix, AZ, USA) was used for the separations The capillary was preconditioned with M NaOH for min, deionized water for min, M HCl for min, deionized water for and finally with electrolyte solution for 15 Environmental samples for field measurements were taken and analyzed in the South West Conservation Area, UNESCO World Heritage, Tasmania (Sample 1: water from Lake Pedder; Sample 2: water from Condominium Creek in the Mount Anne Range) Other samples for laboratory measurements were collected in the Ha Nam provinces and in Ha Noi City (Thanh Tri district), Vietnam (ground water) The samples were used without any pretreatment except for filtration with 0.2 mm syringe filters (Millipore); the samples from Vietnam were diluted : with deionized water 2.2 Apparatus 2.2.1 Portable Capillary Electrophoresis Instrument A sketch of the instrument is given in Figure The main part consists of a box with the dimensions of 310  220  260 mm which is made from poly(methylmethacrylate) (PMMA) plates Two handles are fixed to the side walls so that the instrument can easily be carried The case is divided into two parts One compartment is positioned on the rear of the PMMA box and is used to accommodate the high voltage supply and a 12 V rechargeable battery to power the instrument The battery is of the lead-acid type (NP 3.2-12, Yuasa Battery UK Ltd., Swindon, UK) and has a capacity of 3.2 Ah If the instrument is operated at a site where mains power is available then this may be utilized with an adapter as connectors are provided on the rear These connectors are also used for recharging the battery with a suitable charger connected to the mains A socket for tying the electrical ground of the portable system to an external earth (in a mains socket when available or as a metal rod pushed into the ground for on-site measurements) is also provided An additional aluminum case (70  205  160 mm) mounted on the left side of the PMMA box contains the controls for operating the unit The second compartment is in the front and contains on the left side a sample tray with six positions where electrolyte and sample solutions are placed, a holder for the high voltage (HV) electrode, connectors for switching between Electroanalysis 19, 2007, No 19-20, 2059 – 2065 www.electroanalysis.wiley-vch.de  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2061 Versatile Determination of Cations and Anions Fig Circuit diagram for the instrument Fig Schematic drawing of the portable capillary electrophoresis system 1) control electronics, 2) sample tray, 3) capillary holder, 4) vial holder, 5) detector cell positive and negative HV and a holder for the separation capillary The sample tray is moved by lowering and turning it manually and its height is fixed; samples are injected manually in the electrokinetic or hydrodynamic mode The detection part is positioned on the right and contains an adjustable vial holder, which can be moved up and down in order to match the height of the electrolyte solution to the level of the solution in the sample tray The C4D-cell is mounted on top The cell is connected to the detector electronics via cables fed through a hole in the right wall of the PMMA box The front lid of the box can be opened over its entire width to facilitate manipulations inside Standard high voltage power supplies specified for CE have typical output voltages of 30 kV at 300 mA, a weight of several kilogram and sizeable dimensions This component would be the most expensive and also heaviest part of a purpose made CE-instrument, which is also the main drain for its battery Experience also showed us that for measurements in the outdoors a voltage of 30 kV is not suitable because under conditions of high humidity such high voltages can lead to electrical arcing Furthermore when using conductivity detection, low conductivity buffers are generally employed and capillaries with diameters larger than 50 mm are avoided to minimize Joule heating Therefore the currents drawn from the high voltage power supplies seldom exceed 50 mA when using this mode of detection For this reason it was possible to make a compromise in the specification of the high voltage supply and the two modules (DX150 and the DX150N, EMCO, Sutter Creek, CA, USA) chosen to provide both polarities have maximum output voltages of 15 kV at 100 mA The dimensions of each module are 95  76  25 mm and total weight of both modules is 400 g so that these contribute very little to the size and weight of the whole portable instrument The polarity of the applied separation voltage is set by a switch but also requires manual replugging of the high voltage lead into the appropriate socket A circuit diagram which details the wiring of the high voltage supplies of the portable instrument is shown in Figure Note that for operator safety a microswitch to interrupt the power to the high voltage modules on opening the instrument is included 2.2.2 Battery Powered Contactless Conductivity Detector and Data Acquisition The excitation sine wave in the new circuitry was generated with a MAX038 integrated circuit oscillator (Maxim Integrated Products Inc., Sunnyvale, CA, USA), which delivers a maximum amplitude of Vpp (peak-to-peak) in a frequency range between about 100 and 1000 kHz The sine wave from this internal oscillator is multiplied from Vpp to 20 Vpp by an operational amplifier (OPA627, Texas Instruments, Dallas, TX, USA) and is applied directly to the excitation electrode of the C4D-cell The resulting current, flowing through the detection cell, is subsequently picked up by another electrode and converted to voltage using an OPA655 (Texas Instruments, MW feedback resistor) operational amplifier located in the cell itself Details on the construction of the detector cell can be found in reference [20] The signal is then rectified, amplified, lowpass filtered and offset using the electronic circuitry described in an earlier publication [21] The detection circuitry, except for the cell itself, is located in a separate shielded aluminum case It is powered by two additional 12 V lead-acid batteries (NP 1.2-12, Yuasa, capacity 1.2 Ah) to provide a split Ỉ 12 V supply Data acquisition was carried out using an e-corder 201 data acquisition system (Product No ED201 with option ED9000 from eDAQ Pty Ltd., Denistone East, NSW, Australia, note that this is a 12 V DC-power variant of a high resolution 16 bit, low noise laboratory grade unit) A separate 12 V lead-acid battery (NP 3.2-12, Yuasa) with a capacity of 3.2 Ah was used as power supply The system was connected through a USB cable to a portable laptop computer for data acquisition with the Chart software (eDAQ) and the acquired data was further processed for quantitative analyses with the Peaks software package (eDAQ) Electroanalysis 19, 2007, No 19-20, 2059 – 2065 www.electroanalysis.wiley-vch.de  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2062 Results and Discussion 3.1 Basic Performance of the Battery Powered Instrument The mains powered C4D employed previously for laboratory based measurements [22] features high voltage excitation for boosting the signal and hence the signal-to-noise ratio This approach was not possible for the field instrument because of its power requirement A comprehensive comparison between the new battery powered detector and the earlier design, as well as a commercially available unit, has been reported previously [23] It was found that a performance in terms of precision and detection limit very similar to the other two detectors could be achieved when evaluating these on a commercial CE-instrument When carrying out preliminary tests with the battery powered detector on the new portable instrument, by elevating the injection end of the capillary to effect hydrodynamic injection rather then pressure driven injection as used on the commercial instrument, similar results were obtained A performance comparable to the combination of a standard contactless conductivity detector with a commercial benchtop instrument is therefore possible with the portable battery powered instrument Note however, that the portable instrument is not thermostatted As several parameters related to injection and separation as well as detection are dependent on temperature it has to be expected that the reproducibility for measurements performed outdoors is not as good as for those carried out in the laboratory where temperature fluctuations are not as pronounced On the other hand, active cooling of capillaries is not needed when using conductivity detection In contrast to optical detection, Joule heating can be minimized by using narrow capillaries, as the sensitivity of conductivity detection shows only little dependence on cell size The separate batteries used for powering the detector and the data acquisition system were chosen to allow an operating time of approximately h for both parts Longer operating times could be achieved by using batteries with higher capacity, however when using a standard notebook computer for the measurements this is the limiting factor; or more sets of notebook batteries are needed to achieve the same operating time as for the other parts of the portable CE-C4D system 3.2 Application Examples 3.2.1 Cations of Heavy Metals A CE-C4D method for determination of several inorganic cations was optimized An electrolyte solution based on histidine and acetic acid was employed and 18-crown-6 was added for baseline separation of ammonium and potassium, while different concentrations of weak complexing agents were examined in order to achieve baseline separation of heavy metal cations a-Hydroxyisobutyric acid and lactic P Kuba´nˇ et al acid [24, 25] had been reported for the separation of several heavy metal cations in CE-C4D, however in our experiments best separation of Mn2ỵ and Fe2ỵ and common inorganic and heavy metal cations was achieved using citric acid Full baseline separation was accomplished in an electrolyte solution containing 11 mM His, 50 mM acetic acid, 1.5 mM 18-crown-6 and 0.1 mM citric acid Analytical parameters of the method were evaluated by consecutive measurements of a standard solution containing mM heavy metal cations and these are summarized in Table Calibration curves were based on five-point calibrations and the linearity was measured in the concentration range from to 200 mM The LOD values were determined as S/N ratio for the most diluted standard solution used for linearity measurements and are also summarized in Table The system was tested by analyzing a sample of potable water obtained from a domestic well in Vietnam The resulting electropherograms of the separation of inorganic and heavy metal cations in a sample from Vietnam (a), spiked sample from Vietnam (b) and standard solution (c) are depicted in Figure 3A An extracted portion of the electropherograms giving detailed information on the determination of heavy metal cations is subsequently shown in Figure 3B Fe2ỵ was spiked to the sample at a concentration of mM, while other heavy metal cation standards were added at a concentration of 2.5 mM The concentration of manganese found in the sample using the standard addition method was 8.0 mM Fe2ỵ was not found in the sample although iron is expected to be present All iron in the sample may have been in the form of Fe3ỵ as it had been exposed to ambient air in transport and storage However, the determination of the oxidized species was beyond the scope of the present investigation For correct speciation of iron, on-site measurements would be mandatory 3.2.2 Arsenic As(V) in the form of the anionic arsenate (H2AsO4À) was determined in an electrolyte solution consisting of dilute acetic acid This was chosen as it enabled separation of arsenate from phosphate, which can be expected to be Table Performance parameters for the determination of heavy metal cations using the portable CE-C4D The relative standard deviation ( RSD ) values of the peak areas were calculated for consecutive injections of standard solutions containing mM of the heavy metal cations The correlation coefficients (r2) were obtained for calibration curves in the range from to 200 mM (5point calibration), and the limits of detection ( LOD ) are the concentrations giving peak heights corresponding to times the baseline noise 2ỵ Mn Cd2ỵ Co2ỵ Zn2ỵ RSD peak area (%) r2 LOD (mM ) 0.82 4.94 5.23 5.26 0.9997 0.9998 0.9996 0.9998 0.3 0.6 0.8 1.0 Electroanalysis 19, 2007, No 19-20, 2059 – 2065 www.electroanalysis.wiley-vch.de  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2063 Versatile Determination of Cations and Anions Fig Determination of As(V) in the form of arsenate in different ground water samples (a – c) from different places in Vietnam Electrolyte solution: 45 mM acetic acid, pH 3.2 Capillary: fused-silica, 50 mm i.d., Ltotal ¼ 75 cm (Leff ¼ 68 cm) Hydrodynamic injection by elevating the capillary end by 20 cm for 60 s Separation voltage: À 15 kV 3.3 On-Site Measurements Fig Determination of metal cations using the portable CEC4D system Electrolyte solution: 11 mM His, 50 mM acetic acid, 1.5 mM 18-crown-6, 0.1 mM citric acid, pH 4.1 Capillary: fusedsilica, 50 mm i.d., Ltotal ¼ 62 cm (Leff ¼ 55 cm) Hydrodynamic injection by elevating the capillary end by 20 cm for 40 s Separation voltage: ỵ 15 kV A) a) sample of well water, b) sample spiked with 2.5 mM Mn2ỵ, Cd2ỵ, Co2ỵ, and Zn2ỵ and mM Fe2ỵ, c) standard solution containing 50 mM NH4ỵ, Kỵ, Ca2ỵ, Naỵ, Mg2ỵ and mM Mn2ỵ, Cd2ỵ, Co2ỵ, and Zn2ỵ B) detailed electropherograms for the time range from 7.8 to 9.8 present in natural water samples A calibration curve was acquired for the range from to 100 mM and a correlation coefficient (r2) of 0.9997 was achieved (based on point calibration) The lower limit of detection, the concentration giving peak heights equivalent to times the baseline noise was determined as 0.2 mM RSD values for peak areas in the concentration range from to 100 mM were found to be between 1.8 and 6.9 % (n ¼ 3) Three Vietnamese ground water samples, known to be contaminated with arsenic, were subsequently analyzed with the portable instrument As(V) was detected in presence of major other anions as is illustrated in Figure The concentrations were determined based on the calibration curve established in the previous procedure and 0.17 Ỉ 0.02 mM, 1.82 Ỉ 0.09 mM, and 0.18 Æ 0.03 mM of As(V) were found in the samples a, b and c respectively (n ¼ 3) For the on-site measurements of inorganic anions and cations, it is desirable that a buffer is employed which is suitable for the determination of ions of either charge as otherwise a lengthy set-up procedure is required between measurements Electrolyte solutions with a relatively low pH-value, between 3.0 and 5.0, were deemed suitable for this purpose The electroosmotic flow is significantly reduced in this pH-range and fast anions can be analyzed in the negative electrophoretic mode while cations can be analyzed in the positive electrophoretic mode using one common electrolyte solution [24, 25] The following anions (ClÀ, NO3À, SO42À, ClO4À, and NO2À) and cations (NH4ỵ, Kỵ, Ca2ỵ, Naỵ and Mg2ỵ) were considered as target analytes and an electrolyte solution based on histidine and acetic acid was optimized in order to achieve baseline separation of all ions Best separation and good sensitivity was achieved for 7.5 mM histidine and 40 mM acetic acid at its natural pHvalue of 4.1 Baseline separation of ammonium and potassium was achieved by addition of mM 18-crown-6, which has only negligible effect on the separation efficiencies for other cations and anions [24] Cations and anions could be separated in this electrolyte solution by simply switching the high voltage module to positive or negative polarity The analytical parameters of the method for on-site determination of inorganic ions were validated and are summarized in Table The detection limits for the inorganic anions and cations are very similar and between about 10À7 and 10À6 M These values are one to three orders of magnitude lower than LOD previously reported for portable CE instruments, employing potentiometric or potential gradient detection [10 – 14] and in the same concentration Electroanalysis 19, 2007, No 19-20, 2059 – 2065 www.electroanalysis.wiley-vch.de  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim 2064 P Kuba´nˇ et al Table Performance parameters for the determination of inorganic anions and cations using the portable CE-C4D The relative standard deviation ( RSD ) values of the peak areas were calculated for consecutive injections of standard solutions containing 50 and 100 mM of anions and cations, respectively The correlation coefficients (r2) were obtained for calibration curves in the range from 0.5 to 100 and to 200 mM for anions and cations (5-point calibration) respectively, and the limits of detection ( LOD ) are the concentrations giving peak heights corresponding to times the baseline noise À Cl NO3À SO42 ClO4 NO2 NH4ỵ Kỵ Ca2ỵ Naỵ Mg2ỵ RSD peak area (%) r2 LOD (mM ) 2.18 2.09 1.16 2.26 1.88 1.20 2.01 2.23 1.95 2.35 0.9997 0.9998 0.9996 0.9999 0.9999 0.9993 0.9998 1.0000 0.9998 0.9999 0.15 0.15 0.1 0.15 0.15 0.3 0.2 0.2 0.4 0.3 Fig Determination of inorganic anions in the field (at Lake Pedder, Tasmania) The sample had been spiked with 0.5 mM ClO4À and mM NO2À Electrolyte solution: 7.5 mM His, 40 mM acetic acid, mM 18-crown-6, pH 4.05 Capillary: fused-silica, 50 mm i.d., Ltotal ¼ 62 cm (Leff ¼ 55 cm) Hydrodynamic injection by elevating the capillary end by 20 cm for 60 s Separation voltage: À 15 kV Fig Determination of inorganic cations in the field (at Lake Pedder, Tasmania) Electrolyte solution: 7.5 mM His, 40 mM acetic acid, mM 18-crown-6, pH 4.05 Capillary: fused-silica, 50 mm i.d., Ltotal ¼ 62 cm (Leff ¼ 55 cm) Hydrodynamic injection by elevating the capillary end by 20 cm for 20 s Separation voltage: ỵ 15 kV range as LOD for amperometric detection [11, 12] Note, however, that amperometry is not suitable for the comprehensive determination of inorganic species as only a few inorganic ions can be detected by this means The analysis of real samples was carried out in the South West Conservation Area of the remote Tasmanian wilderness, which belongs to the UNESCO World Heritage list Only trace concentrations of inorganic pollutants are expected to be found in this area and therefore only highly sensitive instruments can be used for their determination No sample storage and transport issues arise for portable CE-C4D system, which enables precise determination of persistent (perchlorate) as well as non-persistent (nitrite) inorganic pollutants The results for the determination of inorganic ions in two real samples (#1: Lake Pedder and #2: side branch of Condominium Creek that joins Lake Pedder in the valley) are summarized in Table Nitrite was determined in one of the samples, while perchlorate was not found in either of the samples investigated The determination of the inorganic cations at lake Pedder is illustrated by the electropherogram of Figure and an electropherogram for the anions is shown in Figure Note, that the sample had been spiked with 0.5 mM of perchlorate and mM of nitrite to illustrate the possibility of the determination of these potential pollutants at this level Conclusions The entire system, including capillary electrophoresis instrument, detection and data acquisition is powered by batteries and can be carried into the field by one person as the dimensions of the equipment not exceed the size of a regular outdoor rucksack Its performance in terms of Table Concentrations (in mM ) of selected inorganic ions in natural water samples determined on-site ND: not detected Lake Pedder Condominium Creek Cl NO3 SO42 ClO4 NO2 NH4ỵ Kỵ Ca2ỵ Naỵ Mg2ỵ 380 357 2.4 0.9 15.8 8.6 ND ND 0.2 ND 0.5 1.4 4.8 1.1 25.2 4.9 160 154.2 79.4 41.2 Electroanalysis 19, 2007, No 19-20, 2059 – 2065 www.electroanalysis.wiley-vch.de  2007 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Versatile Determination of Cations and Anions sensitivity was found to be comparable to conventional bench-top instrumentation In field work direct sunlight onto the portable system should be avoided during operation as this could lead to an increased temperature in the injection and separation compartment as no thermostatting is available Conductivity detection is versatile, and while generally good detection limits can be achieved, please note that these are not sufficient for all trace level environmental analysis However, it is possible for instance to determine perchlorate at a level below the current EPA guideline for drinking water (24.5 ppb) [26] Acknowledgements This work was supported by the Swiss National Science Foundation (Grant Nos 200020-105176/1 and 200020113335/1) and a grant from the Science, Engineering and Technology Unit, Department of Prime Minister and Cabinet, Federal Government of Australia The authors would also like to thank Boris Schlensky (eDAQ) for his help and donation of a prototype of the portable data acquisition system and John Davis (University of Tasmania) for helpful discussions on the noise reduction of the portable C4D PK thanks ACROSS for funding his stay in Tasmania References [1] K B Thurbide, T C Hayward, Anal Chim Acta 2004, 519, 121 [2] L Novotny, T Navra´til, Chem Listy 1996, 90, 121 [3] P W Alexander, L T DiBenedetto, T Dimitrakopoulos, D B Hibbert, J C Ngila, M Sequira, D Shiels, Talanta 1996, 43, 915 2065 [4] X D Hou, Y H He, B T Jones, Appl Spectrosc Rev 2004, 39, [5] P J Potts, A T Ellis, P Kregsamer, C Streli, C Vanhoof, M West, P Wobrauschek, J Anal At Spectrom 2005, 20, 1124 [6] F J Santos, M T Galceran, TrAC 2002, 21, 672 [7] M A Nelson, A Gates, M Dodlinger, D S Hage, Anal Chem 2004, 76, 805 [8] C B Boring, P K Dasgupta, A Sjogren, J Chromatogr A 1998, 804, 45 [9] O P Kalyakina, A M Dolgonosov, J Anal Chem 2003, 58, 951 [10] T 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Table Performance parameters for the determination of inorganic anions and cations using the portable CE-C4D The relative standard deviation ( RSD ) values of the peak areas were calculated for consecutive... one of the samples, while perchlorate was not found in either of the samples investigated The determination of the inorganic cations at lake Pedder is illustrated by the electropherogram of Figure... Table Performance parameters for the determination of heavy metal cations using the portable CE-C4D The relative standard deviation ( RSD ) values of the peak areas were calculated for consecutive