Assay

“ Of assays by the dry way.—The assay by the dry way has for its object, to show the nature and proportion of the metals contained in a mineral substance. To make a good assay, however, it is indispensably necessary to know what is the metal associated with it, and even within certain limits, the quantity of the foreign bodies. Only one metal is commonly looked after ”

“ This is based upon the brown coloration produced in very dilute solutions of lead by the action of a solution of sulphuretted hydrogen. The quantity of lead in the 50 c.c. of the assay solution must not much exceed 0.5 milligram, nor be less than 0.01. The sulphuretted hydrogen is used in the form of a solution, and is not bubbled through the assay. The principle of working is the same as previously described. ”

“ Filter off some of the liquor and assay for cyanide, using say 20 c.c. Calculate how much cyanide has been destroyed in the operation. Evaporate 20 c.c. with sulphuric or nitric acid and examine for metal. Test another portion for sulphides, &c.
The student who has mastered the methods of assaying can greatly improve himself by working out such problems as the above. ”

“ The only precaution necessary is always to take the standard weight for the assay answering to the equiv. of the denomination of the per-centage result sought. Thus, in testing a carbonate of potash, we may either wish to determine its per-centage richness in ‘dry carbonate,’ or in ‘pure potassa,’ the latter being usually the case. To obtain the first, we must take 69 gr. for the assay; and to obtain the second, 47 gr. With CAUSTIC ALKALIES, or mixtures containing them, the weight, in grains, taken for the assay, must always correspond to the equiv. ”

“ Using a pipettor with aerosol resistant tips, in an orderly fashion, add 80 μL aliquots of the standards, samples, and controls to the microtiter plate wells in duplicate. NOTE: The ELISA assay is a time dependent matrix. Add reagents in a consistent, uninterrupted manner to avoid variability and a drift effect over the plate. d. In the same order the standards and samples were added to the plate, add 2 drops of enzyme conjugate from the enzyme conjugate bottle. NOTE: If more than 3 rows of wells are to be employed, use a multiwell pipettor. ”

“ The act or process of ascertaining the proportion of a particular metal in an ore or alloy; especially, the determination of the proportion of gold or silver in bullion or coin.
6. The alloy or metal to be assayed.
Ure.
[Assay and essay are radically the same word; but modern usage has appropriated assay chiefly to experiments in metallurgy, and essay to intellectual and bodily efforts. See Essay.]
μ Assay is used adjectively or as the first part of a compound; as, assay balance, assay furnace. ”

“ Precipitation or reduction (or whatever it may be) is now made; the assistant filters the prepared samples, one at a time, whilst the assayer is engaged with the others. The same style of work is continued until the assays are completed. If one should be spoiled, it is better to allow it to stand over for assaying along with the next batch. If one filters slowly or is in any way less forward than the rest, it may lessen the accuracy of the other assays, owing to oxidation, &c., it should, therefore, be put on one side. ”

“ Assaying by acids and other reagents could be done by women. Tests are now imported, but most assayers prefer to make their own tests. Assaying requires patience, a knowledge of metals, and endurance of heat. ”

“ In March, 1904, the reef was visited by P. G. Morgan, who states [7] that a lode 2 ft. wide, which appeared to be a bedded vein enclosed in argillite and greywacke, was showing in the west side of the slip, striking about 322° and dipping to the south-west at 75°. A sample taken by him from the spot yielded on assay only 5 dwt. 16 gr. gold and 1 dwt. 21 gr. silver per ton.
Some time in the early “eighties” a parcel of 10 tons of ore from this lode appears to have been shipped away for treatment, but no records are available as to the results. ”

“ Those of our readers who wish to try the experiments [258] we have described for themselves can obtain all the necessary substances, except the poisons, at any chemists and the quantities required will only be the smallest that can be obtained, in fact any reasonable-minded chemist would probably let a microscopist whom he knew have a few grains of a large number of chemical substances, suitable for this work, at the outlay of a few pence. The chlorides of gold and platinum we fear no one will give away. ”

“ Given an unlimited quantity of a substance for testing purposes it is not always easy to determine its composition. With very small quantities, perhaps less than a tea-spoon full in all, the difficulties of the analyst are increased tenfold and without the assistance of the microscope his efforts would be unavailing, he deals in drops and every drop is precious. Sad to relate this form of testing, known to science as micro-chemical analysis, has been practised to a far greater extent on the continent than in this country. ”

“ Blood Agar, Human.—
1. Melt a tube of sterile agar and pour it into a sterile plate; let it set. [Pg 251]
2. Collect a few drops of human blood, under all aseptic conditions, in a sterile capillary teat pipette.
3. Raise the cover of the Petri dish very slightly, insert the extremity of the capillary pipette, and deposit the blood on the centre of the agar surface. Close the dish.
4. Charge a platinum loop with a small quantity of the inoculum. Raise the cover of the plate, introduce the loop, mix its contents with the drop of blood, remove the loop, close the dish and sterilise the loop. ”

“ The confusion of the bacteriological laboratory was ecstasy to him—the students in shirt-sleeves, filtering nutrient gelatine, their fingers gummed from the crinkly gelatine leaves; or heating media in an autoclave like a silver howitzer. ”

“ Calibrate the spectrometer according to manufacturer's recommendations. NOTE: Typically, an acid blank and 10 μg/mL multielement solutions are used. Analyze a standard for every ten samples. Check measurement recoveries for all elements of interest with at least three spiked, unexposed samples or with reference materials of known elemental composition. These quality control samples should constitute 15 to 20% of all samples analyzed. NOTE: For blood or tissue spikes, split a control sample and spike one fraction. ”

“ Correct all samples for this measurement recovery. This is especially important for blood samples because routine interelement corrections will not adequately compensate for the high levels of iron present, which has numerous spectral emission wavelengths.
MEASUREMENT: 12. 13.
Set the spectrometer to conditions specified by the manufacturer. Analyze standards and samples. NOTE: If the values for the samples are above the range of the standards, dilute the sample solutions with 10% H 2SO 4, reanalyze, and apply the appropriate dilution factor in calculations. ”

“ Yet there are some simple tests which serve to point out certain forms of adulteration and can be employed by the careful housewife with the reagents in her medicine closet and the apparatus in her kitchen. The number may be greatly extended by the purchase of a very few articles that may be procured for a few cents at any drug store. In applying these tests, one general rule must always be kept carefully in mind. Every one, whether layman or chemist, must familiarize himself with a reaction before drawing any conclusions from it. ”

“ The blood of animals is analogous in its office to the sap of plants, but differs greatly from it under the microscope. In sap there seem to be no microscopic characters, except that when a branch is cut, as in the vine, the flowing sap may contain certain substances formed in the wounded cells, such as chlorophyll, starch, and raphides; but the blood is known to be an exceedingly complex substance both in a microscopic and a chemical point of view. ”

“ Even then the microscope tells whether the stain is blood.
Our detective mixes the particle of blood-stained wood, or earth, or dust, or cloth fibres, with water and caustic potash, and filters it. Then he takes a drop of the liquid and places it in the useful watch-glass. Into this he puts some glacial acetic acid and a crystal of ordinary table salt. He heats the mixture and lets it cool. And, if it is blood, he gets peculiar crystals visible under the microscope. These, by the way, differ to some extent in different animals. ”

“ Calibrate daily with at least six working standards over the range 0.01 to 3 mg analyte per sample. a. Add known amounts of calibration stock solution, or a dilution thereof, in n-hexane to 95% ethanol in 10-mL volumetric flasks and dilute to the mark. b. Analyze together with samples and blanks (steps 11 and 12) . c. Prepare calibration graph (peak area or height vs. mg analyte) . Determine desorption efficiency (DE) at least once for each lot of silica gel used for sampling in the calibration range. ”

“ Maintain standardization by analyzing a standard after every 5 samples. 11. Run a spiked control or pooled sample from exposed workers or commercial control every 10 samples or at least 3 per study. NOTE: Blood or urine lead background levels must be determined before spiked controls are prepared. ”

“ The microscope required for bacteriological studies should be perfect in all its parts. With regard to the choice of an instrument, it is very much a matter of price, since the most perfect is usually the most costly; I shall therefore proceed to give a typical example of the instrument in use in a bacteriological laboratory. The microscope should possess the following qualifications, all of which are absolutely necessary for the study of such minute objects as bacteria and other micro-organisms. ”

“ Tea is difficult to prepare for microscopic examination and most of the tests call for expert knowledge, not only in the management of the microscope but of the plant itself. The structure of the leaves can be made out clearly in specimens which have been soaked for a time in water, but this is of little interest to the ordinary microscopist. One very pretty test may, however, easily be performed. We all know that it is not good to drink tea which has been standing for a long time. ”

“ Transfer the entire quantity of blood collected from the rabbit's heart to a small Erlenmeyer flask containing a number of sterile glass beads and 5 c.c. concentrated sod. citrate solution. (See page 378.)
10. Agitate thoroughly and set aside for a couple of hours.
11. Melt up several tubes of nutrient agar (see page 167) and cool to 42° C.
12. With a sterile 10 c.c. graduated pipette transfer 1 c.c. citrated blood from the Erlenmeyer flask to each tube of liquefied agar. Rotate the tube between the hands in order to diffuse the citrated blood evenly throughout the agar. ”

“ Results will vary from instrument to instrument, and from time to time on the same instrument. c. Plot nL EtO vs. peak height or area. This plot should be a straight line. d. Periodically throughout the day, check calibration by repeating some of these injections of standards. Ideally, each sample would be bracketed, before and after, with injections of standards, although this is seldom practical. 3. Check the sampling equipment to prevent contamination. a. Use different syringes for sampling and for standard preparation. Identify each syringe with a unique number. ”

“ In practice all the different ingredients must be accurately tested, standardized and used in exact quantities, and tests must also be run as controls with a known normal blood of an animal of the same species as the one examined and with a known positive blood. ”

“ Supposing it is judged that a sheet of tissue under some one negative ought to be exposed to light corresponding to a given number of thicknesses, chloride of silver paper is placed alongside the negative beneath the actinometer and allowed to remain there until it takes a visible tint beneath a number of thicknesses equivalent to the strength of the negative. ”

“ In medico-legal researches there is seldom any considerable quantity of the material to work upon. Hence the greatest care must be taken from the commencement not to waste the substance in useless tests, but to study well at the outset what—by the method of extraction used, the microscopic appearance, the reaction to litmus paper, and the solubility in different menstrua—it is likely to be. ”

“ A biological monitoring analytical result is a determination of the level of the biomarker in the biological matrix from which the sample was taken, at the time it was taken. Extrapolation from that datum to insight on the exposure of the worker requires knowledge of how the human body responds to the agent. ”

“ In this test, a round paper disc, which has been impregnated with a specific antibiotic, is placed in contact with sample cultures, or isolates, of a patient's virus, grown in a special culture medium (agar) from a specimen of the patient's fluid (blood, spinal fluid, sputum, urine, etc.) ”

“ When we carry out certain experiments in a laboratory and try to study, for instance, the interaction of two substances upon each other, we choose the most favourable conditions possible, and take particular precautions against the presence of any other substances than those essential to the reaction. It is a well-known fact that the slightest contamination may influence the reaction to a very great extent. ”

“ Every instrument of precision used in the laboratory should be a standard of its kind, the best which could be made; otherwise the work of the institution might fall short of the high character intended for it. So also with the chemicals: only the best should be tolerated. ”

“ When substances other than the analytes are suspected to be present in the blood, record their identities to determine possible interferences [2] .
OTHER METHODS: None are known that can determine these constituents simultaneously. Other methods require extraction or distillation for concentration of trace amounts of these chemicals in blood. ”

“ If renewable electrodes are used, clean the glassy carbo n electrode and de posit a fresh m ercury film prior to conducting analyses. 12. Transfer sample aliquot (1 to 5 mL) to analytical cell, and dilute with 10% HNO 3, if necessary. NOT E: High concentrations of lead may require analysis of diluted analyte solutions. 13. Add supporting electrolyte and oxygen scavenger to sample cell. ”