Discrete or Continuous Flow Analysis – which is better?


A wide variety of factors affect the choice of analytical instrument. These include target workload (samples/hour), variety of chemistries, methods required, bench space, staff availability etc. In the following article Lalicia Potter, Technical Sales & Support Director at SEAL Analytical, examines one of the common decisions facing laboratory managers.

As the manufacturer of an instrumentation range that includes both discrete analyzers and continuous segmented flow analyzers, SEAL Analytical’s technical support chemists are often asked which is the better technique. Both offer fast, automated, colorimetric analysis of multiple samples, however, the answer depends on the current and future analytical requirements of the laboratory.

Descrete Analyser

Descrete Analyser

SEAL’s discrete analysers employ sample trays and discrete reaction wells in which the colorimetric reaction takes place. In contrast, segmented flow analysers (SFA) employ a continuous flow of samples and reagent, segregated by air bubbles within tubing and mixing coils.

In general terms, discrete analysers are ideal when automation is a priority and/or when many and varied tests are needed on different samples. SFA is ideal when a larger number of samples are to be analysed for a smaller number of chemistries. However, both techniques are flexible, so it is important that expert advice is sought in the choice of analyzer and that the instrument is configured to meet the precise needs of the laboratory.

Discrete Analysers
In order to minimise operator involvement, SEAL’s discrete analyzers are highly automated and simple to set up and run, even overnight. A robotic sampling arm works in conjunction with a stepper motor-driven syringe that is responsible for aspirating, dispensing and mixing accurate and precise quantities of sample and reagent. The SEAL AQ1 and AQ2 discrete analyzers can run seven different chemistries from each sample in the same run – and another seven in another run. These instruments have three separate wash stations including a unique probe washer, so cross-contamination is not a problem. This unique washing feature means that even ammonia (using Phenate), nitrate by cadmium reduction– (using ammonium chloride buffer) and low level phenol can be run together with no issues.

SEAL has also built an auto-dilution feature into the discrete analysers for preparing standards automatically and handling over-range samples. These diluted sample results are automatically bracketed by QC sets.

The reproducibility and detection limits of these discrete analysers have been optimised by ensuring that each sample is read in the same optical glass cuvette with a 10mm path length. The sample is always read in the same position in front of the detector, which eliminates any potential issues with scratching or reaction well variability that can be found with direct-read systems. Since the liquid is moved and not the tray; fewer moving
parts maximises reliability.

Most discrete analysers employ miniaturised components to reduce reagent consumption and waste costs. For example, both the AQ1 and AQ2 analysers use just 20 to 400µl of reagent per sample.

Segmented Flow Autoanalysers
Based on the original tried and tested technology of the Technicon™ /Bran Luebbe™ AutoAnalyzer, today’s SFAs deliver fast, accurate analysis for enormous numbers of samples; the QuAAtro for example can run up to 600 tests per hour. SFA’s are also highly automated and once the analyzer is configured and the reagents and samples are loaded, reliable unattended operation is a major benefit.

Flow Analyser

Flow Analyser

A basic SFA system consists of an autosampler, a peristaltic pump, a chemistry manifold, a detector and AACE data acquisition software. Sample and reagents are pumped continuously through the chemistry manifold and
air bubbles are introduced at precisely defined intervals, forming unique reaction segments which are mixed using glass coils. With SFA, even slow reactions run to completion and the ratio of sample to reagents in the detector reaches a constant maximum value; the steady-state condition.

SFAs have been developed for running a few parameters on a larger number of samples, and the SEAL SFAs are the system of choice for marine and seawater organisations and anyone running very low nutrient waters. The SEAL AutoAnalyzer 3 and QuAAtro deliver high levels of performance and reproducibility, and are also the systems of choice for tobacco, soil and fertiliser testing around the world. These analysers provide maximum sensitivity by ensuring that the reaction always goes to completion, and with a digital true dual-beam detection system with real time referencing, the highest reproducibility and very lowest detection limits are achieved.

In summary, when choosing the most appropriate analytical technique, it is important to consider both the current and likely future needs of the laboratory. However, one of the reasons behind the large numbers of SEAL instruments in laboratories around the globe, is that each analyzer has been configured to meet the individual needs of its laboratory. So, it is good practice to contact SEAL’s technical support team at an early stage because if the question is: “Which technique is better,” the answer is: “It depends…”

Caffiene concentration


Measuring caffiene concentration in decaff coffee!

The Reason
While it may mystify those of us that need strong coffee to get through the workday, some people actually drink decaf (decaffeinated coffee), whether for health reasons (high blood pressure, hypertension, sleep difficulties), pregnancy cautions, or personal preference. In lieu of more firm legal standards, decaf is supposed to have its caffeine content reduced by no less than 97.5% of the source coffee (USDA guideline). Accurate validation of the caffeine levels in decaffeinated coffee bean batches would reduce sensitive consumers’ health risks by preventing the wildly inconsistent caffeine levels among available “decaf” blends (as documented by the Journal of Analytical Toxicology –  McCusker, Rachel R., Brian Fuehrlein, Bruce A. Goldberger, Mark S. Gold, and Edward J. Cone. “Caffeine Content of Decaffeinated Coffee.” Journal of Analytical Toxicology 30.8 (2006): 611-13.). Moreover, producers can use real-time caffeine monitoring to conclude the decaffeination cycle as soon as the specified caffeine threshold is achieved, thus wasting no more caffeine solvent or production time than absolutely necessary.

An online analysis solution would provide continuous, live caffeine measurement in an automated fashion. The High-Performance Liquid Chromatography currently used in some caffeine applications is quite costly to own and maintain while delivering slow response.

The Method
While certain selective solvents are extremely effective at removing caffeine from coffee beans, many of these chemicals have been classified as carcinogenic or toxic. Though less powerful, the supercritical CO2 extraction method is a harmless decaffeination process common in large-scale operations. Supercritical CO2 fluid is a hybrid gaseous/liquid resource maintained by exceeding the critical temperature (31 °C) and pressure (73 atm) of CO2; for the supercritical CO2 to act as an effective solvent for caffeine molecules, it actually has to be kept at more extreme conditions (around 94°C and 225 atm). These conditions are expensive to maintain, and the 10-hour process cycle is time-consuming; the caffeine extract is sold off to pharmaceutical and soft drink companies, but this only partially alleviates process cost.

With real-time caffeine monitoring at ±1 ppm accuracy, the OMA-300 Process Analyzer allows decaf coffee producers to automatically end an extraction cycle when the specified caffeine maximum is reached. Doing away with the preset 10-hour cycle, this method banishes both overprocessing (which wastes production resources) and underprocessing (which upsets customers). While highly suitable for monitoring the 0-1,000 ppm caffeine range established by international standards as “legally” decaf, the OMA-300’s UV-VIS spectrophotometer has a true detection limit of 2 ppm caffeine, thus theoretically capable of validating a cup of perfect decaf.


NI Week ’09


Who’s listening?

This is the second day of the annual NI Week 2009. This is National Instruments 15th annual customer and technology conference, opens August 4 in Austin (TX US), for three days of interactive technical sessions, targeted summits, hands-on workshops, and exhibitions on the latest developments for design, control, automation, manufacturing, and test.
We usually seek reports on these events and put links to these reports on the Read-out Signpost events page (right-hand column). The last such event was the Honeywell User Group, rather wonderfully shortened to HUG. We have put in links to the INTECH and Automation.com reports on HUG (and will link to others if and when we become aware of them!

In out daily perusal of twitter we spotted that a number of people were sending 140 character messages from the event. These ranged from the intriguing “OH would you like a bite of my meat”,
through the understandable “SWEET! I won a LAVA mug at the #niweek LAVA BBQ!!!”,
the effusive “Relaxing after a great first day of #NIWeek. Can’t wait to see what is in store for tomorrow! Its the most wonderful time of the year! ;)”,
the practical “learning about software eng tools in 16B”
and the unexpected “Mention NiWeek Conference and get 20% off! Click here for directions. http://ow.ly/iXso Here for reservations http://ow.ly/9G2v” (This from a local restauraunt – good marketing there!).

As we look at the twitters (do a search for #NIweek) and the entries come thick and fast. “25 entries since you started this search. Click refresh to see them!”

So if your not there then this is a flavour of what is happening!

OK so that’s a flavour. But what is the message from the first day?

Well who better to set the tone than Dr James Truchard, founder of National Instruments in his opening remarks. I think that Gary Mintchell of the American publication Automation World encapsulates it well “NI execs – financial engineers would benefit from real engineers, understand the constraints of your model.”

It is very interesting how this simple 140 character messaging system is enabling this correspondant in this beautiful corner of Ireland’s west coast can get something of the experience of these events.

But I can’t help asking myself the question, “If the audience are busy twittering who’s actually listening to what’s been said?”

Laboratory efficiency


TOC analyser improves lab efficiency

Leading instrumentation company HACH LANGE is helping a number of key customers save valuable time and costs with its new IL550 TOC-TN analyser.

TOC analysis is vitally important in applications ranging from power generation, wastewater, drinking water, surface water and ultrapure water, to agricultural soils, contaminated land and food. These analysers therefore offer a range of options designed to meet every need.

A typical analysis for total organic carbon (TOC) measures both the total carbon present as well as the inorganic carbon. This method has traditionally been the preferred analytical technique to measure water quality during the purification process.

COD (Chemical Oxygen Demand) is the total measurement of all chemicals in the water that can be oxidised. BOD (Biochemical Oxygen Demand) is a longer method designed to measure the amount of material (or organic carbons) that bacteria can oxidise.
Although closely related to both BOD and COD analysis, TOC is important in its own right because it is the sole analytical method able to quantify only those species that contain carbon. For this reason TOC is a parameter that is required by regulations in many industries, for example, as a waste acceptance criterion of hazardous waste TOC analysis is now compulsory. It also provides a number of key benefits over BOD and COD including a significantly improved analysis speed and higher accuracy.

The IL550 can also be used for the determination of dissolved organic carbon (DOC) as well as total organic carbon (TOC) in sewage, river, landfill leachates, effluents and groundwater samples. Subsequently, it has proved to be an important addition for HACH LANGE customers including Britin’s Environment Agency’s National Laboratory Services (NLS), South West Water and laboratory testing services company Chemtest.

At the NLS, much of the analytical work is for regulatory purposes, so it is vitally important that fast, accurate, reliable results are produced. Richard Yates, Inorganic Analysis Team Leader at the NLS, said: “The high calibration range of the IL550 reduces the number of over-range repeat analyses we have to perform, thereby saving valuable lab time and improving the sampling process. In addition, the instrument is very easy to use and meets our required limit of detection.”

Tracy Churchill, Senior Assistant Scientist for South West Water, also praised the benefits of the IL500. She explained: “The IL 550 software is very user-friendly, making it easy to train analysts. Additionally, and most importantly, because the analyser has a ‘stand-by’ mode we are able to leave the instrument on at a reduced temperature, which prolongs the life of the catalyst. As a result of these features we have significantly reduced downtime and maintenance costs, because previously we had to replace the catalyst on a fairly regular basis. We are delighted with the TOC-TN analyser and the results it is producing.”

The IL550 has also helped Chemtest save significant time and costs over the past year. Laboratory manager Darrell Hall said: “We have found the IL550 more reliable than the previous methods we used for TOC analysis on water and leachates samples and in general it has made the lab analysis process much more efficient.”

A key feature of the IL550 is particle tolerance in liquids. The autosampler needle has a large internal diameter and the sample is injected directly via the pneumatic port into the furnace – this eliminates blockages, cross-contamination or leaks because there is no septum or valve. This also removes the need to filter waste water samples because the IL550 measures the TOC of both liquid and solid particulates in a sample. Samples are also stirred prior to injection to ensure homogeneity.

With the IL550, digestion takes place at up to 950 Deg C and the solids module is able to increase the temperature to an unrivalled 1300 Deg C. The UV version is equipped with a high-energy UV lamp, which offers the advantage of direct contact with the sample.
In summary, Matthew Dillon, lab sales manager at HACH LANGE says, “The key feature of the IL550, that sets it apart from other instruments, is its ability to provide highly accurate results for a wide range of sample types and we are delighted that so many of our customers have benefitted from the efficiencies that the instrument delivers.”