Twenty-seven common sense questions were analyzed in the gas chromatography experiment

related topics Liquid phase
chromat spectrum
and gas chromatography technology
gas chromatography common sense question and answer
First, what are the characteristics of gas chromatography?: Gas chromatography is one of the chromatography, that is, the use of gas as a flow phase chromatography, in separation analysis, with the following characteristics: 1, sensitivity: can detect 10-10 grams of substances, can be ultra-pure gas, polymer monolith trace impurities analysis and air trace trace impurity analysis and air trace toxicity analysis.2, high selectivity: can effectively separate the properties of very similar isomer and
isotopes
.3, high efficiency: can be complex parts of the sample separated into a single part.4, fast: general analysis, only a few minutes to complete, conducive to guidance and control of production.5, a wide range of applications: you can analyze low-content gas, liquid, but also can analyze high-content gas, liquid, can not be limited by the content of the parts.6, the required sample amount is small: the general gas sample with a few milliliters, liquid sample with a few microlitres or dozens of microlitres.7, equipment and operation of relatively simple instruments cheap.
the separation principle of gas chromatography?: Gas chromatography is a physical separation method. Using the small differences in the distribution coefficient (solubility) between the different phases of the various parts of the substance under test, when the two phases move relatively, these substances are distributed repeatedly between the two phases, so that the original only small differences in nature have a great effect, and the different compositions are separated.
, what is gas chromatography? What are its classes?
: All the chromatography technology with gas phase as the flow phase, commonly known as gas chromatography.generally can be classified according to the following aspects: 1, by fixed phase aggregation state classification: (1) gas solid chromatography: fixed phase is a solid adsorbent,(2) gas liquid chromatography: fixed phase is a liquid coated on the surface of the body.2, according to the principle of process physicochemistry classification: (1) adsorption chromatography: the use of solid adsorption surface to different parts of the physical adsorption performance differences to achieve separation of the chromatography.(2) distribution chromatography: different distribution coefficients are used in two phases to achieve a separate chromatography. (3) Other: ion exchange chromatography using the principle of ion exchange: electrochromatography established by the electric effect of collomes, thermal chromatography developed by temperature change, etc. 3, classified by fixed phase type: (1) column spectrum: fixed phase installed in
-color column
, fill column, hollow column, capillary column are all of this category. (2) paper chromatography: filter paper as the carrier, (3) film chromatography: fixed phase for powder pressed into a thin desert. 4, according to the principle of dynamic process classification: can be divided into flushing method, subsoic method and head-on method three.
, gas chromatography simple analysis device process is what? : Gas chromatography simple analysis device process is basically composed of four parts: 1, gas source part, 2, sample device, 3, chromatography column, 4, appraizer and recorder.
, gas chromatography, some common terms and basic concepts of interpretation? : 1, Phase, Fixed Phase, and Flow Phase: A uniform part of a system is called phase; 2, chromatography peak: matter through the column into the appraizer, the recorder appears on a curve called chromatography. 3, Baseline: Under the condition of chromatography operation, when no measured part passes through the appraizer, the detector noise recorded by the recorder changes over time and the graph line is called the baseline. 4, peak height and half peak width: the height between the concentration of the chromatography peak and the point at which the time marker is intersected is called the peak height, generally expressed as h. Half the width of the chromatography peak is half the width of the peak, usually expressed as x1/2. 5, peak area: outflow curve (chromatography peak) and baseline composition of the area called peak area, expressed in A. 6, dead time, retention time, and correction retention time: the time from the sample to the extreme value of the noble gas peak is called the dead time, expressed as td. The time it takes from the sample to the highest value of the chromatography peak is called retention time, expressed in tr. The difference between retention time and dead time is called correction retention time. In Vd. 7, dead volume, reserved volume and corrected retained volume: the product of dead time and the average flow rate of the carrier gas is called the dead volume, expressed in Vd, the average flow rate of the carrier air is expressed as Fc, Vd-tdxFc. The product of the retention time and the average flow rate of the carrier air is called the reserved volume, expressed in Vr, Vr-trxFc. 8, Reserved values and relative reserved values: Reserved values are values that represent the time that each group in the sample stays in a column, usually in time or in terms of the volume of gas required to carry the parts with a good column. The ratio of the reserved value of another substance to this standard value is called the relative reserve value. 9, device noise: the degree of instability of the baseline is called noise. 10, the base flow: hydrogen flame chromatography, in the absence of samples, the instrument itself exists the base current (bottom current), referred to as the base current.
, the general choice of air-carrying basis? What are the commonly used carriers of gas chromatography? : As a gas chromatography gas, requires good chemical stability, high purity, cheap and easy to obtain, can be suitable for the use of detectors. Commonly used carriers are hydrogen, nitrogen, argon, helium, carbon dioxide and so on.
, gas why purify? How should it be purified? : The so-called purification, is to remove some
namogenic
in the carrier gas, trace oxygen, moisture and other impurities, in order to improve the purity of the carrier gas. Unreal gas as carrier gas, can lead to column failure, sample changes, hydrogen flame chromatography can lead to increased base flow noise, thermal conductive chromatography can lead to linear deterioration of the appraizer, etc. , so the carrier gas must be purified.
generally use chemical treatment methods to deoxygenate, such as the use of activated copper deoxygenation, the use of molecular sieves, activated carbon and other adsorbents to remove organic impurities, the use of silicone, molecular sieve and other adsorbents dehydration.
methods for samples to be sampled? : Chromatography separation requirements in the shortest possible time, in the form of "plug" into a certain amount of samples, the sample method can be divided into: 1, gas samples: there are four rough sample methods: (1) syringe sample, (2) tube sample, (3) fixed volume sample, (4) gas automatic sample. Generally commonly used syringe samples and gas automatic samples. The advantage of syringe sample is flexible and simple method, but the repetition of the intake is poor. Automatic gas sample is a quantitative valve sample, good repeatability, and can be operated automatically. 2, liquid samples: generally with trace syringes into the sample, the method is simple, the sample is fast. Quantitative automatic samples can also be used, which is repetitive. 3, solid sample: usually with solvent to dissolve the sample, and then use the same method as liquid sample. There are also samples with solid samplers.
, briefly describe the effect of column length, column diameter, column temperature, carrier air flow rate, fixed phase, sample and other operating conditions on separation in gas chromatography analysis. : Operating conditions have a great impact on chromatography separation. 1, column length, column diameter: Generally speaking, column tube growth, can improve separation capacity, short fractions distillate faster; The average inner diameter of the column tube used for analysis is 3-6 mm and the column length is 1-4 m. 2, column temperature: is an important operating variable, directly affect the separation efficiency and analysis speed. The column temperature is selected according to the boiling point range of the mixture, the ratio of the fixed liquid and the sensitivity of the appraizer. Improving the column temperature can shorten the analysis time, and reducing the column temperature can increase the selectivity of the column, which is conducive to the separation of components and the improvement of the stability of the column column, and the extension of the column life.
generally use the column temperature equal to or higher than the average boiling point of the sample is more appropriate, for volatile samples with low column temperature, not easy to volatile samples using high column temperature. 3, carrier air flow rate: carrier air flow rate is one of the important reasons to determine the separation of chromatography. Generally speaking, the flow rate is high chromatography peak narrow, the other is wider, but the flow rate is too high or too low on the separation have a negative impact. Flow rate requirements to be smooth, the commonly used flow rate range of 10-100 liters per minute. 4, fixed phase: fixed phase is composed of a solid adsorbent or a burden coated with a fixed liquid.
(1) solid adsorbent or weight: generally 40-60, 60-80, 80-100. When using columns of the same length, the separation efficiency of fine particles is better than that of coarseness.
(2) fixed liquid content: fixed liquid content on the separation efficiency of a large impact, it and the weight ratio of the burden is generally used 15%-25%. Too large a scale is detrimental to separation, and too small a scale can cause the chromatography peak to drag its tail. 5, into the sample: generally speaking fast, the amount of sample is small, the temperature of the sample is high and its separation effect is good. For the liquid sample, the speed should be fast, the vaporization temperature should be higher than the boiling point value of the high boiling point part in the sample, a vaporization, to ensure that the chromatography peak shape will not spread wide, so that the column effect is high. When the sample is within a certain limit, the half-peak width of the chromatography peak is unchanged.
too much sample will cause the column to overload. Generally, the length of the column is increased fourfold and the amount of samples licensed is doubled. For conventional analysis, the liquid sample is 1-20 microlitres and the gas sample is 0, 1-5 ml.
, chromatography column tube material should be selected according to what principles? What material is the commonly used column tube made of? : for the column tube material, should be selected according to the following requirements: 1, should be fixed phase, sample, gas can not carry chemical reactions. 2, to be easy to process molding. 3, the inner wall of the tube should be smooth, cross-section should be evenly circular. General column tube shape is U-shaped or spiral, mostly made of copper, stainless steel, glass and other materials.
the new column tube (copper or stainless steel tube) should be treated before it can be used? : The new column tube should be washed with thin acid or alkali (1:1 sodium hydrochloric acid or sodium hydroxide) to remove dirt such as oil, and then rinsed with tap water, then rinsed with distilled water to neutral, and then blown and dried with clean air, can be used.
, what is a burden? What are the requirements for the body? : The burden is a porous chemically inert solid that is used to support the fixing fluid in the gas chromatography. There are the following requirements for the burden: 1, the surface area is larger, generally should be between 0, 5-2 meters / g; 2, with chemical inertness and thermal stability; 3, there is a certain mechanical strength, so that the staining and filling process does not cause crushing; 4, there is an appropriate pore structure, which is good for the rapid mass transmission between the two phases; 5, can be made into uniform spratly particles, is good for gas phase penetration and filling uniformity; 6, has a very good immersion, easy to fix the uniform distribution of liquid. It is difficult to fully meet the above requirements of the burden, people in practice can only find out the performance of relatively good burden.
13, the burden is divided into several categories? What are its characteristics? : Usually divided into diatom soil and non-diatom soil two major categories, each category has a variety of small categories. 1, diatom soil type: (1) white: small surface area, loose, brittle, small adsorption properties, after appropriate treatment, can be analyzed strong polarity parts; (2) Red: has a larger surface area and better mechanical strength, but the adsorption is greater. 2, non-diatom soil type: (1) fluorine body: surface inert, can be used to analyze high polarity and corrosive substances, but the column is not easy, column efficiency is lower. (2) glass microsphere: the surface area is small, with it as a burden column temperature can be greatly reduced, and separation is complete and fast. However, staining is difficult and the column effect is low. (3) porous high-polymer ball: high mechanical strength, good thermal stability, low adsorption, corrosion resistance, high separation efficiency, is a new type of color spectrometry fixed phase with excellent performance. (4) carbon molecular sieve: neutral, large surface area, high strength, long life, in the micro-analysis has incomparable advantages. (5) activated carbon: can be used as a fixed phase alone. (6) sand: mainly used to separate metals.
, what kinds of burdens are commonly used? What kind? : 101 burden: for white diatom burden; 102 burden: for white diatom burden; celite545