Serial Diluter – evolution in sample dilution
In 2014, Inlabtec launched the Serial Diluter TA, the first serial diluter for serial microbiological sample dilution in bags (patented). This was followed by the Serial Diluter SA, which allows the use of pipette straws instead of 1 ml pipette tips. The Serial Diluter UA has been developed and launched due to the customer need to be able to freely use any type of pipette, including filtered pipette tips.
Read more about the individual models and their special features. At the end of the page you will find answers to various questions to find out whether the Serial Diluter would be an advantage for your laboratory.
Serial Diluter UA
Connect the diluent and a 10 ml pipette, insert bags and start diluting! The new Serial Diluter UA with integrated mixer and intelligent process monitoring guarantees reliable and efficient dilution of samples for viable cell counts.
The procedure is 100 % identical to the ISO method – instead of pipetting into a test tube filled with 9 ml of Diluent, pipette into a filled bag. The Serial Diluter UA is available in six or twelve-stage versions.
Videos Serial Diluter UA
Prices and scope of delivery Serial Diluter UA
Specifications Serial Diluter UA
Serial Diluter Demo Request
Serial Diluter TA
With the pioneer model Serial Diluter TA, the sample is placed in the bag together with the tip. The diluent then rinses the sample from the tip followed by a sterile air blast into the bag.
This proven method works reliably with all samples examined in a food control laboratory. The Serial Diluter TA is also available in six or twelve stage versions.
Please note that in contrast to the Serial Diluter UA, no pipette tips with filter can be used for diluting. The reason for this is that the diluent must flow unhindered through the pipette tip.
Videos Serial Diluter TA
Prices and scope of delivery Serial Diluter TA
Specifications Serial Diluter TA
Serial Diluter Demo Request
Serial Diluter SA
The method of operation is the same as with the Serial Diluter TA: Place the sample together with the straw tip into the first bag and attach the dosing arm for automatic dilution – it’s as simple as that! Like the Serial Diluter TA, the Diluent flows through the pipette straw for mixing and diluting.
Videos Serial Diluter SA
Prices and scope of delivery Serial Diluter SA
Specifications Serial Diluter SA
Serial Diluter Demo Request
Questions and answers about Serial Diluters
Here you can find answers to your questions about the Serial Diluter and find out if the solution is useful for your laboratory. If you are interested and need more information, please contact us via contact form. We are happy to be of service.
For which laboratories is the Serial Diluter intended?
The Serial Diluter is designed for users performing dilutions for the plate count method in microbiological testing of food, feed, cosmetica, etc.
What do I save in costs and time using the Serial Diluter?
Cost and time savings by:
– faster dilutions as no manual vortexing and no handling of tubes and caps has to be performed
– eliminating the preparation of test tubes or the expensive pre-filled dilution tubes
– savings of water, electricity, cleaning agents and equipment maintenance costs
– reduced costs for transport, storage and disposal of the consumables
For what sample throughput is the Serial Diluter worth using?
Depending on the costs and the available resources, the use is worthwhile from 100 dilutions per day, i.e. about 30 samples at 3 dilutions each.
The payback time is determined by the previous cost of preparing test tubes or the cost of pre-filled disposable dilution vials. On Our Solution a savings calculator can be found to check whether the purchase of a Serial Diluter is worthwhile for your laboratory under the given circumstances.
Is the instrument also suitable for samples that require only 1 or 2 dilutions?
Yes. In this case, it is recommended to insert, for example, 6 Serial Dilution Bags into the instrument. In that way, 6 samples with one dilution or 3 samples with two dilutions can be processed without having to insert bags separately for each sample.
How fast can I work with the Serial Diluter?
Dilution and mixing of a sample in a Serial Dilution Bag takes place automatically, while the operator changes the pipette tip to be ready for the next dilution step or the inoculation of a Petri dish.
The time required for manual vortexing, as well as the time required for removing and placing the caps on the test tubes for sample addition, is thus saved. Consequently, the time saving per dilution is about 5 – 10 seconds, depending on the usual mixing time of the test tubes and the manual skills of the laboratory technician.
Smaller time savings compared to the traditional test tube method are possible if the work routine with the Serial Diluter is still missing or if the mixing time of the test tubes on the vortexer is only very short.
Note: Vortexing for too short a time increases the risk of inhomogeneous mixtures and inaccurate analysis results, which is prevented by automation with the Serial Diluter, regardless of the user’s experience and working technique.
What sample throughput is possible per Serial Diluter?
The table shows the time needed in minutes for a certain number of dilutions and inoculations of culture media.
Example: The time required for 100 samples with 3 dilutions per sample (total 300 dilutions) and 2 inoculations per dilution (total 600 inoculations) is 140 minutes. Calculation basis: 10 seconds per dilution step, 4 seconds per inoculation, 30 seconds per sample for placing the plates for the inoculations.
Does the Serial Diluter improve the reliability and accuracy of test results?
With the Serial Diluter, the accuracy of the testing results is ensured regardless of sample throughput, time pressure, unplanned work peaks, employee experience, etc. The figure below shows the evaluation of interlaboratory tests with the Serial Diluter in comparison to the test tube method. With the Serial Diluter, all employees of the laboratory achieve z-score values of ± 0.1, i.e. all employees, regardless of their level of experience or individual differences in working technique, delivered almost identical test results.
How is the diluent dispensed?
The Serial Diluter works similar to a pipeting aid. Vacuum aspirates the desired amount of liquid and an excess pressure dispenses the liquid into the Serial Dilution Bag with the sample. The aspirated volume is determined by an optical sensor placed on the side of a 10 ml pipette. Thus, the optical sensor simply replaces the human eye in the determination of the volume making the use of the Serial Diluter even simpler as of a pipeting aid. Pinch valves control the volume flow.
Can I use the Serial Diluter without any training?
Like any new device, it needs a little patience in the beginning to become familiar with it. The installation is comparable to the commissioning of a gravimetric diluter, as is the use. Under Support are training videos available, as well as an extensively illustrated operating manual and a quick start guide.
What kind of materials does the diluent come into contact with?
The diluent comes into contact with silicone, stainless steel, glass or polystyrene (depending on the 10 ml pipette used), polyethylene and polypropylene.
Which directives and ISO standards were taken into account?
Serial dilution with the Serial Diluter complies with the standard method according to ISO 6887-1:2017 and the associated normative reference ISO 7218:2007.
The product is subject to the technical directives: 2006/42/EC, 2004/ 108/EEC. Normen: EN 61010-1:2001, EN 61010-2-081:2002 + A1:2003, EN 61326-1:2006.
How was compliance with the ISO standards verified?
The serial dilution with the Serial Diluter was verified against the standard technique with dilution tubes according to ISO 6887-1 by the Zurich University of Applied Sciences (ZHAW Wädenswil). In addition, the Serial Diluter was tested by ISO 17025 accredited users of the Serial Diluter on the basis of direct comparisons with the test tube technique using various food samples (see test results Campden BRI).
Is there a quality certificate for the Serial Diluter?
The CE-certificate for the Serial Diluter is in the manual.
How is the sterility of the system ensured?
– All parts in contact with liquid can be steam sterilized (tubes, dispensing tip, dilution solution).
– The Serial Diluter can only dispense and cannot aspirate liquid via the dispensing tip.
– During operation, the system is ventilated via sterile filters so that no microorganisms can enter.
– Operation is designed to eliminate contamination of the dispensing tip during normal operation.
A demo video for the Serial Diluter UA shows the comprehensive safety precautions.
Why can I be sure that the dispensing nozzle will not become contaminated during operation?
The risk of contamination of the dispensing nozzle is comparable to the risk of an oncoming vehicle on a busy one-way street. As in a one-way street, the dosing arm moves during a dilution series only in one direction. The dispensing nozzle thus always remains in a sterile zone and never comes into contact with unsterile sample material. That’s how it works:
– To fill a Serial Dilution Bags, the dispensing nozzle has to enter the sterile, empty bag.
– The sample is pipetted into the filled bag through a separate opening. Contact and/or contamination of the dispensing nozzle is thus not possible and the resulting liquid level in the bag cannot touch the dispensing nozzle.
– Mixing does not start until the dispensing nozzle is out of the bag with the sample and already above the next sterile bag. Contamination by the contents of the bag due to mixing is thus excluded.
– Outside the bag, the dispensing tip is protected by a protective sleeve and cannot touch any non-sterile surfaces due to the devise design.
A demo video for the Serial Diluter UA shows the comprehensive safety precautions.
Are there any sterility problems with it?
Problems with sterility caused by the use can be excluded due to the comprehensive safety precautions (see question above). The sterile, contamination-free commissioning is comparable with the easy setup of a gravimetrical diluter and also does not represent a contamination risk : Training video.
If the system is not sterile, it can be assumed that the diluent or the tubing set with the dispensing nozzle have not been completely autoclaved. This error can occur regardless of the Serial Diluter. For reliable sterilization of the tubing set and dispensing nozzle, sterilization pouches with a paper layer should be used to ensure complete penetration of steam.
An error during commissioning is also possible. During installation, care must be taken to ensure that the dispensing nozzle does not touch any non-sterile surfaces. With a little experience in handling the Serial Diluter, this is absolutely no problem.
How can I test whether the components used were sterile and the determined bacterial counts are correct?
You cannot test sterility in rapid time. If you are skeptical about the Serial Diluter, we recommend performing a sterility check before and after starting work. For this purpose, an aliquot of the first and last 9 ml diluent dispensed is plated out on a culture medium and incubated for the sterility control. This will allow you to confirm that maintaining system sterility is not a problem.
Are the sterile filters used hydrophobic or hydrophilic and are they autoclavable?
The PTFE (Teflon) filters used are hydrophobic and autoclavable. Difference between hydrophobic and hydrophylic filters: Trainings video
Attention: Do not install hydrophilic filters on bottles with diluent or on the Serial Diluter.
How does the environment benefit from the use of the Serial Diluter?
Serial Dilution Bags reduce plastic waste by a factor of 10-30 compared to conventional consumables.
Approximately 250 mg of polyethylene (PE) is required for the production of a Serial Dilution Bag. In contrast, a prefilled disposable container consumes between 2.5 – 7.5 g of plastic, depending on the design. One kilogram of polyethlyene is sufficient for 4’000 dilutions in Serial Dilution Bags; with conventional consumables, it is only sufficient for 130 to max. 400 dilutions.
The energy consumption for transport is also lower by factors: 250 mg per serial dilution bag vs. 11.5 – 16 g per plastic container filled with 9 ml diluent.
We believe that it makes no sense to send dilution vials filled with saline/peptone water around the world. Usually the diluent is already prepared in larger quantities in bottles for the primary dilutions in blenders/ stomacher and it’s easy and cheap to increase the prepared quantity by 30 % for the serial dilutions.
The energy consumption for the production of the Serial Dilution Bags is also moderate compared to the rinsing of test tubes: The energy consumption of one rinsing machine cycle corresponds approximately to the consumption for the production of 400 Serial Dilution Bags. Taking into account the energy required for filling and autoclaving the dilution vials, the energy required for bag use is not significantly higher, if at all.
Can Serial Dilution Bags be recycled?
The used Serial Dilution Bags can basically be recycled with other polyethylen waste (PE). In this case, the health risks due to the potential contamination of the bags must be taken into account and appropriate precautions must be taken.
We believe that eliminating plastic waste is a better strategy to help the environment. This principle was the driver for the development of the Serial Diluter.
What maintenance and service is required for the Serial Diluter?
There is no need for regular maintenance and service. The instrument itself detects e.g. clogged filters, leaks, etc. and reports these to the user. Maintenance is limited to changing the easily accessible filters and adhesion grippers. If something is still wrong, a trained sales and service partner is available.
How is the service of the products ensured?
Inlabtec products are sold through authorised distributors, who can perform all service work. The Serial Diluter is based on very solid, proven technology, which keeps service work to an absolute minimum.
How reliable works the opening of the Serial Dilution Bags? Is there wear and tear?
A microstructured silicone is used to open the Serial Dilution Bags wear-free. If the adhesive force would decrease due to dirt, the adhesion gripper can be cleaned with water, 70 % ethanol, etc. and is then functional again. If cleaning does not bring any improvement and the service life of 6 – 12 months has been reached, the gripper can be removed and a new self-adhesive gripper can be attached: Trainings video.
Are there components that need to be replaced regularly?
According to the filter manufacturer, the sterile filters of the bottles containing the diluting solution should be replaced after eight autoclaving cycles. The sterile filter on the unit should be changed every 6 – 9 months.
How do I clean the Serial Diluter?
The device surfaces can be cleaned with a commercially available cleaner/soapy water and disinfected with 70 % ethanol.
The liquid-conducting parts are removed from the Serial Diluter after use, cleaned and rinsed with water and then autoclaved for sterilization. Important: Rinse the dispensing tip well to prevent corrosion caused by salt residues during autoclaving.
How long is the warranty period of the Serial Diluter?
The warranty period for all device components is two years. Details can be found in our AGB (General Terms and Conditions).
What is the difference between accuracy and precision?
Accuracy indicates how close the average actual value, i.e. the mean value, is to the target value. The deviation is also called systematic error. The precision indicates how close the individual measured values are to each other. The statistical measure of precision is the standard deviation, often called random error.
How accurate can be dispensed with the Serial Diluter?
The volume determining element in the Serial Diluter is a pipette in combination with an optical sensor. Since the Serial Diluter dispenses exactly the volume that is aspirated into the pipette and indicated by the meniscus position of the liquid column, the accuracy of the dispensed volume depends on the accuracy of the scale / graduation of the pipette used. The inaccuracy of the volume indication of serological pipettes made of plastic is approximately ± 2 %, for graduated pipettes made of glass ± 0.5 % for class AS and ± 1 % for class B.
Which serological pipettes and graduated pipettes can be used with the Serial Diluter?
All 10 ml serological pipettes and graduated pipettes in the standard version can be used. Other pipette sizes are possible as long as the outer diameter of the pipette is between 8 – 15 mm and the length between 150 – 350 mm.
Under which conditions should the dispensed volume be checked and calibrated?
The accuracy of plastic serological pipettes should be checked before using a new pipette type or a new lot (lot number). A simple check can determine the systematic deviation of the pipette scale (pipette scale calibration) and accurately determine the correct sensor position for the desired volume.This calibration is valid for all pipettes with the same lot number, which speeds up and simplifies the correct volume setting when installing the pipette. Instructions for performing the calibration are also available under Support.
How can I be sure that the set volume was actually dispensed?
The volume can be checked visually before dispensing by reading the meniscus in the pipette. The sensor monitoring of the aspirated liquid ensures that dispensing of the liquid is only released when the correct volume is available in the pipette. Deviations caused by air bubbles, an empty bottle, etc. are detected immediately and reported to the user via the display. The internal pressure sensor monitors the dispensing and ensures complete delivery of the dilution solution completed by an heard air blast.
How do I check the volume dispensed by the Serial Diluter?
Volume testing of the dispensed liquid is most easily done with a measuring cylinder or with a balance, as is often done in the laboratory to check volume measuring devices:
Dispensed liquid = weight of filled bag – weight of empty bag
The Serial Diluter manual contains detailed instructions for checking and the corresponding Excel template can be downloaded.
Can I leave the Serial Diluter operational overnight and continue working the next day?
The Serial Diluter can be left operational until the connected diluent is used up. Since the dispensing nozzle is shielded from the outside by the protective sleeve, the risk of contamination via the laboratory air is very low.
As an additional precautionary measure, the dosing tip can be parked in 70 % ethanol when not in use for a longer period of time, e.g. over the weekend. For details please refer to the operating instructions.
Can the system be operated in the sterile bench and UV-sterilized overnight?
The Serial Diluter can be operated in a sterial bench, laminar flow, etc. and the device is UV-resistant for regular surface sterilisation.
What are alternatives to a Serial Diluter?
Test tubes prepared by the laboratory
Advantage: established standard method, every laboratory technician knows the procedure
Disadvantage: time-consuming preparation, manual skill and good workplace organization required for efficient work and correct cell counts.
Ready made disposable dilution vials, dilution blanks, cups, etc.
Advantage: Immediately available, no preparation required.
Disadvantage: Significant costs for procurement, transport, storage and disposal, high environmental impact, not all diluents available, carrying out dilutions is not simplified and accelerated (exception: Dilucup together with Dilushaker)
Advantage: up to 105 CFU/ ml and plate, well suited for beverages, milk, etc.
Disadvantage: Sensitive to clogging by particles in the sample, high requirement for flatness of culture media, no cast plates possible, no dry film media possible (Petrifilm, Compact Dry, etc.), special counting procedure of colonies on the plates, regular maintenance and servicing necessary.
Tempo MPN System
Advantage: Fully automated system for microbial count, ideal for very high throughput and uniform sample type.
Disadvantage: less accurate than standard method, no visual control possible, high operating and acquisition costs, high validation effort per sample type, high environmental impact, significant maintenance and service costs.
More information on how to use our products can be found in Support.