Burets

Burets, like measuring pipets, make it possible to deliver any volume up to the maximum capacity of the device. The precision attainable with a buret is substantially greater than the precision with a pipet. A buret consists of a calibrated tube to hold titrant plus a valve arrangement by which the flow of titrant is controlled. This valve is the principal source of difference among burets. The simplest pinchcock valve consists of a close-fitting glass bead inside a short length of rubber tubing that connects the buret and its tip (see Figure 1 a).

Only when the tubing is deformed does liquid flow past the bead. A buret equipped with a glass stopcock for a valve relies on a lubricant between the ground-glass surfaces of stopcock and barrel for a liquid-tight seal. Some solutions, notably bases, cause glass stopcocks to freeze when they are in contact with ground glass for long periods. Therefore, glass stopcocks must be thoroughly cleaned after each use. Most burets made in the last several of decades have Teflon® valves, which are unaffected by most common reagents and require no lubricant (Figure 1 b).

Figure 1  Burets: (a) glass-bead valve,

(b) Teflon valve.

مواضيع ذات صلة

الشكل الوضعي للسكريات الأحادية configuration of monosaccharides

نظام استخلاص الجزئيات البسيطة

اختيار الطور الجديد وعدد مرات الاستخلاص

ميكانيكية الاستخلاص

طبيعة الصنف المستخلص

الاستخلاص بالمذيب

امتصاص الشعاع الكهرومغناطيسي وطيف الامتصاص

الطرق الكيميائية الطيفية في التحليل.

طبيعة الكيمياء التحليلية

التحليل بالحقن الجرياني المتقطع Batch flow injection analysis

الحقن الجرياني متعدد التخفيف Multi-commutation in FIA

التحليل بالحقن المتعاقب Sequential Injection Analysis