With an increasing number of labs upgrading from benchtop spectrophotometers to automatic discrete analysers for their enzymatic testing, it is worth noting that the major difference between the two approaches (apart from speed!) is in the calculation of the sample results.
A discrete analyser calculates a calibration curve from a series of known standard solutions. In order to calculate a sample result, the sample absorbance response is quantified against the calibration curve.
If the calibration curve isn't robust, then the sample results will be innacurate. It's worth looking out for some tell tale signs that can appear in the calibration curve so that you can identify any issues early.
Here are a few examples of things that can go wrong with calibration curves. If you are noticing any of these problems in your calibrations, contact Duane for advice on how to solve the problem.
Many wine labs now have improved quality control systems in place and routinely analyse samples in duplicate and run the same control wine sample each day, plotting the results on control charts. These are great ways to monitor repeatability and reproducibility, two very important quality parameters that indicate how precise a method is. A third parameter of equal importance is trueness, or to put another way, ensuring the result obtained is close to the actual value. Your results might be precise, but if they are not close to the true value, then this is an indication of systematic bias in the method.
One of the best ways to determine trueness is to purchase certified reference materials (CRM’s). Unfortunately this is also the most expensive way to determine trueness, and suitable CRM’s that match your sample matrix and concentration range can be difficult to find.
An alternative way to monitor trueness is to perform routine spike analysis, which is adding a known amount of standard to one of your samples, analysing the spiked and not spiked sample, then calculating the percentage recovery. A practical example for doing this is outlined below:
Test: Malic acid determined by discrete analyser, calibration range 0 – 3g/L
Procedure: Analyse sample (let’s call this result y)
Add 1mL of the top calibration standard (3g/L) to 4mL of sample
(this is the spiked sample)
Analyse this spiked sample (let’s call this result z)
Calculation: % Recovery = z x 100
(0.8 x y) + (0.2 x 3)
Interpretation: For most tests, a recovery of between 95-105% is acceptable.
Depending on the uncertainty of the method, a recovery of between 90-110% may also be accepted.
The level of dissolved carbon dioxide in a wine can greatly effect the taste of the wine, too little and the wine can seem flat and flabby and too much can cause a wine to taste harsh and tannic. Measuring carbon dioxide in the winery can be done a number of ways but the quickest and easiest of these is to use a carbodoseur. The carbodoseur provides fast and easy analysis of dissolved carbon dioxide in wine samples and is able to be used by staff with limited technical training by following the steps below;
It’s winter and it’s cold. But it needn’t be in your lab. Having well maintained heating and cooling systems in your lab is necessary to keep the temperature as close to 20˚C as possible. This not only makes for a comfortable and safer working environment, it can be critical in achieving accurate results.
Here are just a few examples of procedures that could suffer from chilly lab conditions:
Enzymatic Analysis
Enzymes catalyse reactions much better at warmer temperatures. The colder the assay, the longer the incubation times required to complete the reaction.
pH
The pH of buffers and samples are temperature dependent and although correction factors can be applied, for best accuracy it is recommended the buffers and samples should all be analysed at the same temperature. This won’t be the case if the lab is not temperature controlled throughout the day.
Hydrometry
Modern hydrometers are calibrated at 20˚C. If the solution is a lower temperature, then approximate correction factors need to be applied which can introduce greater uncertainty in the result.
Sulfur Dioxide
Even the straightforward aspiration method for determining Free SO2 can be impacted by low temperatures. The colder the sample, the slower the SO2 is aspirated from it. You may not be achieving full recovery without extending your aspiration time.
Reagent Preparation
Most volumetric glassware is calibrated at 20˚C. Volume changes with temperature, so if your solution filled to the line in a 100mL volumetric flask isn’t at 20˚C, then it’s not exactly 100mL.
pH ELECTRODE CARE
Other considerations to ensure greatest accuracy in pH measurements are:
A healthy, properly calibrated, electrode will give you a stable reading fairly quickly (within approximately 10 seconds). Older electrodes may take longer. It will also give you repeatable readings: answers within +/- 0.03pH units for repeated testing of the same sample. Electrodes not performing this well can be cleaned and reconditioned according to the manufacturer’s instructions or with the following procedure:
If the problem is still there, this procedure can be repeated and the electrode left to recover overnight. Alternatively, the bulb can be cleaned with a non-abrasive cream cleanser and a soft cloth, rinsed and returned to storage solution.
If none of the above helps and you still can’t trust the results, it may just be time to treat yourself to a new electrode!
© Copyright Winechek Pty Ltd. All rights reserved. No part of this publication may be copied or reproduced by any means without the written permission of Winechek Pty Ltd
Download the pH Electrode Care Factsheet
DO YOU KNOW THE QUALITY OF YOUR LIVESTOCK WATER
Water quality guidelines recommended for livestock consumption have been developed by the National Water Quality Management Strategy and are based on the Australian Water Quality Guidelines for Fresh and Marine Waters, November 1992 (ANZECC).
The guidelines cover several water parameters that should be analysed to ensure your water is suitable for its intended use. At Winechek, we have packaged the major parameters into a convenient and cost effective Irrigation Water Test Suite. This suite of tests will give you an overview of the quality of your water and identify any issues that may be affecting water quality.
The Irrigation Water Test Suite is only $99 (+GST) and includes analysis of the following parameters:
pH
The acidity or alkalinity of water should be monitored to ensure it is within a certain range to limit stock digestion issues which can cause animals to reject water, depressing their appetite and reducing production.
Salinity & Electrical Conductivity
High levels of soluble salts in water can result in gastrointestinal symptoms and a reduction in weight gain and milk or egg production. Animals under stress, for example due to pregnancy, lactation or rapid growth are particularly susceptible and high levels may cause upset and in some cases death. However, stock can acclimatise to some extent to water of higher salinity when the level is adjusted over several weeks.
Calcium
High calcium concentrations may cause phosphorus deficiency by interfering with phosphorus absorption in the gastrointestinal tract and calcious formation in the body.
Magnesium
Levels of magnesium in water are closely linked to total dissolved solids and should be look at in conjunction with these results when determining the suitability of water for livestock consumption.
Iron
Iron is essential to animal life and has a low toxicity, being harmful to livestock only if ingested in large amounts. Iron-contaminated water does not contain enough iron to be toxic to livestock. Therefore no guidelines has been established for iron in drinking water for livestock as it poses very low health risk to animals.
Copper
Copper is an essential element in the animal diet and copper deficiency can result in morbidity and in some cases death. The toxic effects of copper depend largely on the type of livestock and the form of copper.
WATER QUALITY GUIDELINE VALUES
| PARAMETER |
VALUE |
COMMENTS |
| pH |
<5.5 6 – 8.5 >9.0 |
Acidosis and reduced feed intake may occur
Recommended range May cause digestive upsets and diarrhoea, lower feed conversion and efficiency and reduced intake of water and feed. |
| Magnesium |
<600mg/L |
Upper limit unless salinity are >15000mg/L, then any level of magnesium is generally unsuitable for all stock. |
| Calcium |
1000mg/L |
Upper limits for stock if dietary phosphorus levels are adequate |
| Copper |
<0.05mg/L <1.0mg/L <5.0mg/L * |
Limit for sheep
Limit for cattle Limit for pigs and poultry No limit set for horses as they have a high tolerance |
| Livestock |
Salinity mg/L |
||
| No adverse effects on animals expected | Animals may have initial reluctance to drink or there may be some scouring but stock should adapt without loss of production | Loss of production and a decline in animal condition and health would be expected. Stock may tolerate these levels for short periods if introduced gradually | |
| Beef Cattle | 0-4000 | 4000-5000 | 5000-10000 |
| Dairy Cattle | 0-2400 | 2400-4000 | 4000-7000 |
| Sheep | 0-4000 | 4000-10000 | 10000-13000 |
| Horses | 0-4000 | 4000-6000 | 6000-7000 |
| Pigs | 0-4000 | 4000-6000 | 6000-8000 |
| Poultry | 0-2000 | 2000-3000 | 3000-4000 |
NOTE: The values in the above table are taken from the Australian and New Zealand Guidelines for Fresh and Marine Water Quality, developed by the Natural Resource Management Ministerial Council (NRMMC) and the Primary Industries Ministerial Council (PIMC).
They should not be used as a sole determination of the suitability of irrigation water. Other factors such as soil characteristics, climate, plant species and irrigation management must also be considered.
© Winechek Pty Ltd. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without the prior written permission of the publisher.
Download the Livestock Water factsheet as a PDF
By now, you may have heard that Winechek Laboratories have their very own range of Discrete Analysers - the easiest way to automatically perform all your enzymatic testing needs.
Our two units, The ChemWell and the Chemwell-T are manufactured in the USA. ChemWell technology is trusted across the globe, and is found in many types of laboratories, including medical ones.
Users of the ChemWells here in Australia receive a comprehensive installation visit that includes two full days of staff training and instrument setup. From then on you also receive technical support so you are equipped with the necessary knowledge to take full advantage of the features offered in each unit.
The Winechek range of Discrete Analyser Test Kits is designed so that you receive the best results, without compromising on quality and efficiency. We have visited the manufacturer for training with their skilled technicians and chemists and we have fine-tuned our kits to give the best performance possible.
Whether you want to check your wine has finished MLF, the level of glucose and fructose, or to calculate your YAN value on juice, our Discrete Analyser Test Kits are the perfect complement to our ChemWell range to save you time and money during the impending vintage period.
Need more info? Contact us directly
You use them every day for your enzymatic analysis and probably don’t think too much about them. But the quality and correct use of your disposable cuvettes are critically important for ensuring accurate enzymatic or colorimetric results.
We use high quality disposable cuvettes in our NATA accredited labs, for analysis as well as for validation of our Test Kits. These are the same cuvettes available on our website store for you to purchase.
A few things to consider when next using cuvettes:
• Watch out for scratches or small etches on plastic cuvettes, these can affect your absorbance readings.
• Glass and plastic cuvettes are suitable for use in the visible wavelength range. Quartz cuvettes should be used for measurements in the UV range.
• Cuvettes have two opaque surfaces for handling purposes. Avoid touching the optical windows, but if they do become dirty, then wipe with a soft cloth or lens tissue. Do not wipe with paper tissues as they are abrasive and may leave fibre residue and brightening agents on the optical windows.
• Tap out any air bubbles caught in the solution in the cuvette prior to taking an absorbance reading.
• It is not recommended to wash and reuse plastic disposable cuvettes.
For Measurement Uncertainty (MU) data for accredited method results please contact us on 1300 302 242
Use the Free Winechek EasyTest Sample System to send your samples to your nearest laboratory. This system has been designed to make sending test samples simple, while protecting your sample integrity.
The Winechek EasyTest Sample Kit includes:
- 50mL sample vials
- Pre-printed test selection labels
- Pre-printed Reply Paid Address labels
How to use your Winechek Easy Test Sample System:
- Fill the sample vial, close the lid firmly and check for leaks. If leaks occur, some adhesive tape around the top can help.
- For a number of different tests on one sample, more than one vial may be required. Sample size is noted in each test. For some testing it may be necessary to send a full bottle.
- Fermenting Samples: The sample vials are rated to 2 bar pressure. To ensure your sample’s integrity, do not send wine that is fermenting! If necessary, add SO2 to stop the fermentation.
- Write sample details onto pre-printed test selection label, tick the test/s required, and stick to vial.
- If you do not have enough labels, or need more space, you can include a note with your samples, or email us: info@winechek.com
- Pack samples securely – padded envelopes or foam boxes are recommended.
- If sending more than one package, tape them together to ensure they arrive together.
- Australia Post have requested that customers do not send glass containers unless in a foam pack. If a breakage does occur then Australia Post will hold the sender liable for damage to any other postal items.
