Justice is Served with XP205 Semi-Microbalance
07/21/2010

The independent Forensic Scientific Service (FND) of the State Police in St. Gallen, Switzerland conducts analytical and forensic tests with the aim of detecting proof of suspected crimes such as the illegal possession of drugs. As samples are generally available in powder form and in rather small quantities, an XP205 semi-microbalance was the customer’s solution to assist in their delicate weighing tasks.

Online PR News – 21-July-2010 – – Handle with Care
A balance in a forensic laboratory has to satisfy high demands as sample material is scarce and the quality of the investigation results depends considerably on the evidence found and the condition of the sample. Drug materials such as heroin, cocaine or amphetamine are often found in very small quantities and the forensic scientific service is forced to examine the sample with great care. Therefore, it was vital to find a balance solution that guarantees the weighing-in of small sample quantities down to 10 mg, avoids influences caused by electrostatic charges on powdery substances and facilitates the error-free positioning of up to 5 different flasks with volumes up to 200 ml.

Small Quantity, Big Impact
”On average, we weigh-in approximately 25 mg of sample, sometimes even smaller amounts down to 10 mg. In this low weighing range, the measurement accuracy of the balance lies within 1% taking a safety factor of 5 into account. Additionally, we need a balance, whose measuring accuracy is traceable and meets the requirements of ISO/IEC17025“, quality manager, Mr. Daniel Eugster, explains.
The XP205 semi-microbalance fulfills this easily with a weighing capacity of 220 g and a readability of 0.01 mg. Performance of the balance was confirmed during installation by issuing a calibration certificate and minimum weight determination (according to DKD; German calibration service). In addition, a service technician from METTLER TOLEDO
maintains and calibrates the balance annually.

Free of Electrostatic Influence
One has to take electrostatic influences into account whilst weighing powdery substances, particularly if the air humidity is less than 45%. Even the sample container itself is usually electrostatically charged, transmitting this charge to the tare vessel with the sample loaded spatula. An electrostatically charged sample influences the weighing cell and generates incorrect results. The solution was simple; METTLER TOLEDO applied an external U-electrode combined with a point electrode. During the weighing process, the technician first holds the sample container under the point electrode to discharge it. Passing the spatula through the U-electrode into the weighing chamber further eliminates electrostatic charges that could adversely affect the measuring result.

Perfect and Secure Positioning
Thanks to the special weighing pan ‘Ergo-Clip Flask’, the positioning of Erlenmeyer flasks on the weighing pan is a straightforward task for the laboratory staff. ”The sample is securely positioned during the weighing process. Therefore we don’t lose time and valuable material“, says crime technician, Ivan Schlatter. “We don’t even need to open a draft shield because of the special ‘MinWeigh Door’ which allows dosing through a small window in the draft shield door directly into the tare container.” Mr. Schlatter adds; “We need reliable and accurate laboratory instruments to obtain precise results with the absolute minimal measurement uncertainty. METTLER TOLEDO is the supplier with extensive experience and has the capacity to offer comprehensive solutions and services.”