Pesticide Analytical Manual Vol. I SECTION 501 Some specialty products exist to facilitate injection and minimize aggravation, and each has found favor with some analysts. For example, syringes with removable needles permit replacement of needles on which"burrs" have formed that destroy septa; removable needles with a"side port point"do not shred the septa as do standard bevel point needles; and syringes with plungers and needles made of a titanium alloy cannot be bent Reagents and gases Reagents associated with GlC include column liquid phases and solid supports gases used for mobile phase and for detector reactions, and certain other reagents relevant to detector operation. Most of these reagents are discussed further in pertinent sections of this chapter; only gases, including filters used to remove contaminants from gas flow, are included in this introductory section Helium, hydrogen, and nitrogen are most commonly used as column carrier gases Purity is always critical to avoid damage to the column, and more stringent purity requirements may be imposed by the detector. Purity specifications of the instru- ment manufacturer should always be followed Helium and hydrogen requirements range from 99.999-999999%o pailable from arity, depend ing on the detector. Even with the highest purity, oxygen traps, chromatography suppliers, are recommended; traps that change color when per meated with oxygen are ideal for alerting the analyst to potential problems Purchase of ultra high purity helium and hydrogen may not be necessary if spe- cially designed purifiers are used. Purifiers are available that permit use of com- purifier gtade gases(99.995%)at a much lower price, justifying the cost of the r.Different purifiers are needed for helium and hydrogen; they are not interchangeable. FDA has had successful experiences with hydrogen purifiers: Model 560, AADCO Instruments, Inc, Clearwater, FL; Model 8372V. Consolidated Technologies. Inc.. West Chester. PA helium purifiers: Product HP, Valco Instrument Co., Houston, TX Model 2-3800, Supelco, Bellefonte, PA Nitrogen is used as a carrier gas only for packed columns(Section 502 B). Either nitrogen or argon/methane (95+5 or 90+10)is also required as a carrier and/or makeup gas for the electron capture detector(Section 503 B). Commercial grades of these gases are acceptable if oxygen and moisture traps are used between the as tank and the chromatograp 501 C RESIDUE METHODOLOGY FOR GLC DETERMINATION Applications of analytical methodology require consideration of many factors to assure compatibility of method steps. The following factors related to extraction and cleanup of food samples profoundly influence accuracy and reliability of glC 501-3Pesticide Analytical Manual Vol. I SECTION 501 501–3 Transmittal No. 94-1 (1/94) Form FDA 2905a (6/92) Some specialty products exist to facilitate injection and minimize aggravation, and each has found favor with some analysts. For example, syringes with removable needles permit replacement of needles on which “burrs” have formed that destroy septa; removable needles with a “side port point” do not shred the septa as do standard bevel point needles; and syringes with plungers and needles made of a titanium alloy cannot be bent. Reagents and Gases Reagents associated with GLC include column liquid phases and solid supports, gases used for mobile phase and for detector reactions, and certain other reagents relevant to detector operation. Most of these reagents are discussed further in pertinent sections of this chapter; only gases, including filters used to remove contaminants from gas flow, are included in this introductory section. Helium, hydrogen, and nitrogen are most commonly used as column carrier gases. Purity is always critical to avoid damage to the column, and more stringent purity requirements may be imposed by the detector. Purity specifications of the instru￾ment manufacturer should always be followed. Helium and hydrogen requirements range from 99.999-99.9999% purity, depend￾ing on the detector. Even with the highest purity, oxygen traps, available from chromatography suppliers, are recommended; traps that change color when per￾meated with oxygen are ideal for alerting the analyst to potential problems. Purchase of ultra high purity helium and hydrogen may not be necessary if spe￾cially designed purifiers are used. Purifiers are available that permit use of com￾mercial grade gases (99.995%) at a much lower price, justifying the cost of the purifier. Different purifiers are needed for helium and hydrogen; they are not interchangeable. FDA has had successful experiences with: hydrogen purifiers: Model 560, AADCO Instruments, Inc., Clearwater, FL; Model 8372V, Consolidated Technologies, Inc., West Chester, PA helium purifiers: Product # HP, Valco Instrument Co., Houston, TX; Model 2-3800, Supelco, Bellefonte, PA Nitrogen is used as a carrier gas only for packed columns (Section 502 B). Either nitrogen or argon/methane (95+5 or 90+10) is also required as a carrier and/or makeup gas for the electron capture detector (Section 503 B). Commercial grades of these gases are acceptable if oxygen and moisture traps are used between the gas tank and the chromatograph. 501 C: RESIDUE METHODOLOGY FOR GLC DETERMINATION Applications of analytical methodology require consideration of many factors to assure compatibility of method steps. The following factors related to extraction and cleanup of food samples profoundly influence accuracy and reliability of GLC determinative steps